DS31256+ [MAXIM]
256-Channel, High-Throughput HDLC Controller;
| 型号： | DS31256+ |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 256-Channel, High-Throughput HDLC Controller 电信 电信集成电路 |
| 文件： | 总183页 (文件大小：1218K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
DEMO KIT AVAILABLE
DS31256
256-Channel, High-Throughput
www.maxim-ic.com
GENERAL DESCRIPTION
FEATURES
The DS31256 Envoy is a 256-channel HDLC ꢀ 256 Independent, Bidirectional HDLC
controller that can handle up to 60 T1 or 64 E1
Channels
data streams or two T3 data streams. Each of the ꢀ Up to 132Mbps Full-Duplex Throughput
16 physical ports can handle one, two, or four ꢀ Supports Up to 60 T1 or 64 E1 Data Streams
T1 or E1 data streams. The DS31256 is ꢀ 16 Physical Ports (16 Tx and 16 Rx) That
composed of the following blocks: Layer 1,
HDLC processing, FIFO, DMA, PCI bus, and
local bus.
Can Be Independently Configured for
Channelized or Unchannelized Operation
ꢀ Three Fast (52Mbps) Ports; Other Ports
Capable of Speeds Up to 10Mbps
(Unchannelized)
There are 16 HDLC engines (one for each port)
that are each capable of operating at speeds up ꢀ Channelized Ports Can Each Handle One,
to 8.192Mbps in channelized mode and up to
10Mbps in unchannelized mode. The DS31256 ꢀ Per-Channel DS0 Loopbacks in Both
Envoy also has three fast HDLC engines that Directions
Two, or Four T1 or E1 Lines
only reside on Ports 0, 1, and 2. They are ꢀ Over-Subscription at the Port Level
capable of operating at speeds up to 52Mbps.
ꢀ Transparent Mode Supported
ꢀ On-Board Bit Error-Rate Tester (BERT)
with Automatic Error Insertion Capability
ꢀ BERT Function Can Be Assigned to Any
HDLC Channel or Any Port
APPLICATIONS
Channelized and Clear-Channel
(Unchannelized) T1/E1 and T3/E3
Routers with Multilink PPP Support
High-Density Frame-Relay Access
xDSL Access Multiplexers (DSLAMs)
Triple HSSI
ꢀ Large 16kB FIFO in Both Receive and
Transmit Directions
ꢀ Efficient Scatter/Gather DMA Maximizes
Memory Efficiency
ꢀ Receive Data Packets are Time-Stamped
ꢀ Transmit Packet Priority Setting
ꢀ V.54 Loopback Code Detector
ꢀ Local Bus Allows for PCI Bridging or Local
Access
High-Density V.35
SONET/SDH EOC/ECC Termination
ORDERING INFORMATION
PART
DS31256
DS31256+
TEMP RANGE PIN-PACKAGE
ꢀ Intel or Motorola Bus Signals Supported
ꢀ Backward Compatibility with DS3134
ꢀ 33MHz 32-Bit PCI (V2.1) Interface
ꢀ 3.3V Low-Power CMOS with 5V Tolerant
I/O
0°C to +70°C
256 PBGA
0°C to +70°C
256 PBGA
+Denotes lead-free/RoHS-compliant package.
ꢀ JTAG Support IEEE 1149.1
ꢀ 256-Pin Plastic BGA (27mm x 27mm)
Features continued on page 6.
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata.
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DS31256 256-Channel, High-Throughput HDLC Controller
TABLE OF CONTENTS
1.
2.
3.
MAIN FEATURES............................................................................................................6
DETAILED DESCRIPTION..............................................................................................7
SIGNAL DESCRIPTION ................................................................................................13
OVERVIEW/SIGNAL LIST.............................................................................................................13
SERIAL PORT INTERFACE SIGNAL DESCRIPTION..........................................................................18
LOCAL BUS SIGNAL DESCRIPTION ..............................................................................................19
JTAG SIGNAL DESCRIPTION ......................................................................................................22
PCI BUS SIGNAL DESCRIPTION ..................................................................................................22
PCI EXTENSION SIGNALS...........................................................................................................25
SUPPLY AND TEST SIGNAL DESCRIPTION....................................................................................25
MEMORY MAP ..............................................................................................................26
INTRODUCTION ..........................................................................................................................26
GENERAL CONFIGURATION REGISTERS (0XX).............................................................................26
RECEIVE PORT REGISTERS (1XX)...............................................................................................27
TRANSMIT PORT REGISTERS (2XX).............................................................................................27
CHANNELIZED PORT REGISTERS (3XX).......................................................................................28
HDLC REGISTERS (4XX)............................................................................................................29
BERT REGISTERS (5XX)............................................................................................................29
RECEIVE DMA REGISTERS (7XX) ...............................................................................................29
TRANSMIT DMA REGISTERS (8XX) .............................................................................................30
FIFO REGISTERS (9XX) .............................................................................................................30
PCI CONFIGURATION REGISTERS FOR FUNCTION 0 (PIDSEL/AXX).............................................31
PCI CONFIGURATION REGISTERS FOR FUNCTION 1 (PIDSEL/BXX).............................................31
GENERAL DEVICE CONFIGURATION AND STATUS/INTERRUPT...........................32
MASTER RESET AND ID REGISTER DESCRIPTION........................................................................32
MASTER CONFIGURATION REGISTER DESCRIPTION ....................................................................32
STATUS AND INTERRUPT ............................................................................................................34
3.1
3.2
3.3
3.4
3.5
3.6
3.7
4.
4.1
4.2
4.3
4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11
4.12
5.
6.
5.1
5.2
5.3
5.3.1
5.3.2
General Description of Operation ....................................................................................................... 34
Status and Interrupt Register Description........................................................................................... 37
TEST REGISTER DESCRIPTION ...................................................................................................43
5.4
LAYER 1........................................................................................................................44
GENERAL DESCRIPTION.............................................................................................................44
PORT REGISTER DESCRIPTIONS.................................................................................................48
LAYER 1 CONFIGURATION REGISTER DESCRIPTION ....................................................................51
RECEIVE V.54 DETECTOR..........................................................................................................56
BERT .......................................................................................................................................60
BERT REGISTER DESCRIPTION .................................................................................................61
HDLC .............................................................................................................................67
GENERAL DESCRIPTION.............................................................................................................67
HDLC REGISTER DESCRIPTION .................................................................................................69
FIFO...............................................................................................................................74
GENERAL DESCRIPTION AND EXAMPLE.......................................................................................74
6.1
6.2
6.3
6.4
6.5
6.6
7.
8.
7.1
7.2
8.1
8.1.1
Receive High Watermark .................................................................................................................... 76
Transmit Low Watermark.................................................................................................................... 76
FIFO REGISTER DESCRIPTION ...................................................................................................76
8.1.2
8.2
9.
DMA...............................................................................................................................83
INTRODUCTION ..........................................................................................................................83
RECEIVE SIDE ...........................................................................................................................85
9.1
9.2
9.2.1
Overview ............................................................................................................................................. 85
Packet Descriptors.............................................................................................................................. 90
Free Queue......................................................................................................................................... 92
Done Queue........................................................................................................................................ 97
9.2.2
9.2.3
9.2.4
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DS31256 256-Channel, High-Throughput HDLC Controller
9.2.5
DMA Channel Configuration RAM .................................................................................................... 102
TRANSMIT SIDE .......................................................................................................................105
Overview ........................................................................................................................................... 105
Packet Descriptors............................................................................................................................ 114
Pending Queue ................................................................................................................................. 116
Done Queue...................................................................................................................................... 120
DMA Configuration RAM................................................................................................................... 125
9.3
9.3.1
9.3.2
9.3.3
9.3.4
9.3.5
10.
PCI BUS.......................................................................................................................130
10.1
GENERAL DESCRIPTION OF OPERATION ...................................................................................130
10.1.1 PCI Read Cycle................................................................................................................................. 131
10.1.2 PCI Write Cycle................................................................................................................................. 132
10.1.3 PCI Bus Arbitration............................................................................................................................ 133
10.1.4 PCI Initiator Abort.............................................................................................................................. 133
10.1.5 PCI Target Retry ............................................................................................................................... 134
10.1.6 PCI Target Disconnect...................................................................................................................... 134
10.1.7 PCI Target Abort ............................................................................................................................... 135
10.1.8 PCI Fast Back-to-Back...................................................................................................................... 136
10.2
PCI CONFIGURATION REGISTER DESCRIPTION .........................................................................137
10.2.1 Command Bits (PCMD0)................................................................................................................... 138
10.2.2 Status Bits (PCMD0)......................................................................................................................... 139
10.2.3 Command Bits (PCMD1)................................................................................................................... 143
10.2.4 Status Bits (PCMD1)......................................................................................................................... 144
11.
LOCAL BUS ................................................................................................................147
11.1
GENERAL DESCRIPTION...........................................................................................................147
11.1.1 PCI Bridge Mode............................................................................................................................... 149
11.1.2 Configuration Mode........................................................................................................................... 151
11.2
11.3
LOCAL BUS BRIDGE MODE CONTROL REGISTER DESCRIPTION..................................................153
EXAMPLES OF BUS TIMING FOR LOCAL BUS PCI BRIDGE MODE OPERATION .............................155
JTAG............................................................................................................................163
JTAG DESCRIPTION ................................................................................................................163
TAP CONTROLLER STATE MACHINE DESCRIPTION ...................................................................164
INSTRUCTION REGISTER AND INSTRUCTIONS ............................................................................166
TEST REGISTERS.....................................................................................................................167
AC CHARACTERISTICS.............................................................................................168
REVISION HISTORY ...................................................................................................176
PACKAGE INFORMATION.........................................................................................177
256-PIN PBGA (27MM X 27MM) ...............................................................................................177
THERMAL CHARACTERISTICS.................................................................................178
APPLICATIONS...........................................................................................................179
16 PORT T1 OR E1 WITH 256 HDLC CHANNEL SUPPORT.........................................................180
DUAL T3 WITH 256 HDLC CHANNEL SUPPORT ........................................................................181
SINGLE T3 WITH 512 HDLC CHANNEL SUPPORT......................................................................182
SINGLE T3 WITH 672 HDLC CHANNEL SUPPORT......................................................................183
12.
12.1
12.2
12.3
12.4
13.
14.
15.
15.1
16.
17.
17.1
17.2
17.3
17.4
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DS31256 256-Channel, High-Throughput HDLC Controller
LIST OF FIGURES
Figure 2-1. Block Diagram.......................................................................................................................10
Figure 5-1. Status Register Block Diagram for SM and SV54.................................................................36
Figure 6-1. Layer 1 Block Diagram..........................................................................................................46
Figure 6-2. Port Timing (Channelized and Unchannelized Applications) ................................................47
Figure 6-3. Layer 1 Register Set .............................................................................................................51
Figure 6-4. Port RAM Indirect Access .....................................................................................................53
Figure 6-5. Receive V.54 Host Algorithm ................................................................................................58
Figure 6-6. Receive V.54 State Machine.................................................................................................59
Figure 6-7. BERT Mux Diagram ..............................................................................................................60
Figure 6-8. BERT Register Set................................................................................................................61
Figure 8-1. FIFO Example.......................................................................................................................75
Figure 9-1. Receive DMA Operation........................................................................................................88
Figure 9-2. Receive DMA Memory Organization.....................................................................................89
Figure 9-3. Receive Descriptor Example.................................................................................................90
Figure 9-4. Receive Packet Descriptors..................................................................................................91
Figure 9-5. Receive Free-Queue Descriptor............................................................................................92
Figure 9-6. Receive Free-Queue Structure .............................................................................................94
Figure 9-7. Receive Done-Queue Descriptor ..........................................................................................97
Figure 9-8. Receive Done-Queue Structure............................................................................................99
Figure 9-9. Receive DMA Configuration RAM.......................................................................................102
Figure 9-10. Transmit DMA Operation...................................................................................................108
Figure 9-11. Transmit DMA Memory Organization................................................................................109
Figure 9-12. Transmit DMA Packet Handling ........................................................................................110
Figure 9-13. Transmit DMA Priority Packet Handling............................................................................111
Figure 9-14. Transmit DMA Error Recovery Algorithm..........................................................................113
Figure 9-15. Transmit Descriptor Example............................................................................................114
Figure 9-16. Transmit Packet Descriptors.............................................................................................115
Figure 9-17. Transmit Pending-Queue Descriptor.................................................................................116
Figure 9-18. Transmit Pending-Queue Structure...................................................................................118
Figure 9-19. Transmit Done-Queue Descriptor .....................................................................................120
Figure 9-20. Transmit Done-Queue Structure .......................................................................................122
Figure 9-21. Transmit DMA Configuration RAM....................................................................................125
Figure 10-1. PCI Configuration Memory Map........................................................................................130
Figure 10-2. PCI Bus Read ...................................................................................................................131
Figure 10-3. PCI Bus Write....................................................................................................................132
Figure 10-4. PCI Bus Arbitration Signaling Protocol..............................................................................133
Figure 10-5. PCI Initiator Abort..............................................................................................................133
Figure 10-6. PCI Target Retry ...............................................................................................................134
Figure 10-7. PCI Target Disconnect......................................................................................................134
Figure 10-8. PCI Target Abort ...............................................................................................................135
Figure 10-9. PCI Fast Back-To-Back.....................................................................................................136
Figure 11-1. Bridge Mode......................................................................................................................148
Figure 11-2. Bridge Mode with Arbitration Enabled...............................................................................148
Figure 11-3. Configuration Mode...........................................................................................................149
Figure 11-4. Local Bus Access Flowchart .............................................................................................152
Figure 11-5. 8-Bit Read Cycle ...............................................................................................................155
Figure 11-6. 16-Bit Write Cycle..............................................................................................................156
Figure 11-7. 8-Bit Read Cycle ...............................................................................................................157
Figure 11-8. 16-Bit Write (Only Upper 8 Bits Active) Cycle ...................................................................158
Figure 11-9. 8-Bit Read Cycle ...............................................................................................................159
Figure 11-10. 8-Bit Write Cycle..............................................................................................................160
Figure 11-11. 16-Bit Read Cycle ...........................................................................................................161
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 11-12. 8-Bit Write Cycle..............................................................................................................162
Figure 12-1. Block Diagram...................................................................................................................163
Figure 12-2. TAP Controller State Machine...........................................................................................164
Figure 13-1. Layer 1 Port AC Timing Diagram ......................................................................................169
Figure 13-2. Local Bus Bridge Mode (LMS = 0) AC Timing Diagram....................................................170
Figure 13-3. Local Bus Configuration Mode (LMS = 1) AC Timing Diagrams.......................................172
Figure 13-4. Local Bus Configuration Mode (LMS = 1) AC Timing Diagrams (continued)....................173
Figure 13-5. PCI Bus Interface AC Timing Diagram..............................................................................174
Figure 13-6. JTAG Test Port Interface AC Timing Diagram ..................................................................175
Figure 16-1. 27mm x 27mm PBGA with 256 Balls, 2oz Planes, +70°C Ambient, Under Natural
Convection at 3.0W.........................................................................................................................178
Figure 17-1. Application Drawing Key ...................................................................................................179
Figure 17-2. Single T1/E1 Line Connection...........................................................................................179
Figure 17-3. Quad T1/E1 Connection....................................................................................................180
Figure 17-4. 16-Port T1 Application.......................................................................................................180
Figure 17-5. Dual T3 Application...........................................................................................................181
Figure 17-6. T3 Application (512 HDLC Channels) ...............................................................................182
Figure 17-7. T3 Application (672 HDLC Channels) ...............................................................................183
LIST OF TABLES
Table 1-A. Data Sheet Definitions .............................................................................................................7
Table 2-A. Restrictions ............................................................................................................................11
Table 2-B. Initialization Steps..................................................................................................................12
Table 2-C. Indirect Registers...................................................................................................................12
Table 3-A. Signal Description..................................................................................................................13
Table 3-B. RS Sampled Edge .................................................................................................................18
Table 3-C. TS Sampled Edge..................................................................................................................19
Table 4-A. Memory Map Organization.....................................................................................................26
Table 6-A. Channelized Port Modes........................................................................................................44
Table 6-B. Receive V.54 Search Routine................................................................................................57
Table 7-A. Receive HDLC Packet Processing Outcomes .......................................................................67
Table 7-B. Receive HDLC Functions.......................................................................................................68
Table 7-C. Transmit HDLC Functions .....................................................................................................68
Table 8-A. FIFO Priority Algorithm Select ...............................................................................................74
Table 9-A. DMA Registers to be Configured by the Host on Power-Up ..................................................84
Table 9-B. Receive DMA Main Operational Areas ..................................................................................86
Table 9-C. Receive Descriptor Address Storage.....................................................................................90
Table 9-D. Receive Free-Queue Read/Write Pointer Absolute Address Calculation ..............................93
Table 9-E. Receive Free-Queue Internal Address Storage.....................................................................93
Table 9-F. Receive Done-Queue Internal Address Storage....................................................................98
Table 9-G. Transmit DMA Main Operational Areas...............................................................................106
Table 9-H. Done-Queue Error-Status Conditions..................................................................................112
Table 9-I. Transmit Descriptor Address Storage ...................................................................................114
Table 9-J. Transmit Pending-Queue Internal Address Storage.............................................................117
Table 9-K. Transmit Done-Queue Internal Address Storage.................................................................121
Table 11-A. Local Bus Signals ..............................................................................................................147
Table 11-B. Local Bus 8-Bit Width Address, LBHE Setting...................................................................150
Table 11-C. Local Bus 16-Bit Width Address, LD, LBHE Setting ..........................................................150
Table 12-A. Instruction Codes...............................................................................................................166
Table 16-A. Thermal Properties, Natural Convection............................................................................178
Table 16-B. Thermal Properties vs. Airflow...........................................................................................178
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DS31256 256-Channel, High-Throughput HDLC Controller
1. MAIN FEATURES
ꢀ
ꢀ
ꢀ
Layer 1
ꢀ
DMA
Can simultaneously support up to 60 T1 or 64 E1
data streams, or two T3 data streams
16 independent physical ports capable of speeds
up to 10MHz; three ports are also capable of
speeds up to 52MHz
Efficient scatter-gather DMA minimizes system
memory utilization
Programmable small and large buffer sizes up to
8188 Bytes and algorithm select
Descriptor bursting to conserve PCI bus
bandwidth
Each port can be independently configured for
either channelized or unchannelized
operation
Identical receive and transmit descriptors
minimize host processing in store-and-
forward
Each physical channelized port can handle one,
two, or four T1 or E1 data streams
Supports N x 64kbps and N x 56kbps
On-board V.54 loopback detector
On-board BERT generation and detection
Per DS0 channel loopback in both directions
Unchannelized loopbacks in both directions
HDLC
Automatic channel disabling and enabling on
transmit errors
Receive packets are timestamped
Transmit packet priority setting
PCI Bus
ꢀ
ꢀ
32-bit, 33MHz
Version 2.1 Compliant
256 independent channels
Contains extension signals that allow adoption to
custom buses
Up to 132Mbps throughput in both the receive
and transmit directions
Can burst up to 256 32-bit words to maximize
bus efficiency
Transparent mode
Three fast HDLC controllers capable of
operating up to 52 MHz
Local Bus
Can be bridged from the PCI bus to simplify
system design, or a configuration bus
Can arbitrate for the bus when in bridge mode
Configurable as 8 or 16 bits wide
Supports a 1MB address space when in bridge
mode
Automatic flag detection and generation
Shared opening and closing flag
Interfame fill
Zero stuffing and destuffing
CRC16/32 checking and generation
Abort detection and generation
CRC error and long/short frame error detection
Invert clock
Supports Intel and Motorola bus timing
JTAG Test Access
3.3V low-power CMOS with 5V tolerant I/Os
256-pin plastic BGA package (27mm x 27mm)
ꢀ
ꢀ
ꢀ
Invert data
FIFO
Large 16kB receive and 16kB transmit buffers
maximize PCI bus efficiency
Small block size of 16 Bytes allows maximum
flexibility
Programmable low and high watermarks
Programmable HDLC channel priority setting
Governing Specifications
The DS31256 fully meets the following specifications:
•
ANSI (American National Standards Institute) T1.403-1995 Network-to-Customer Installation DS1 Metallic
Interface March 21, 1995
•
•
•
PCI Local Bus Specification V2.1 June 1, 1995
ITU Q.921 March 1993
ISO Standard 3309-1979 Data Communications–HDLC Procedures–Frame Structure
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DS31256 256-Channel, High-Throughput HDLC Controller
Table 1-A. Data Sheet Definitions
The following terms are used throughout this data sheet.
Note: The DS31256’s ports are numbered 0 to 255; the HDLC channels are numbered 1 to 256. HDLC Channel 1 is always associated with
Port 0, HDLC Channel 2 with Port 1, and so on.
TERM
BERT
DEFINITION
Bit Error-Rate Tester
Descriptor
Dword
DMA
FIFO
A message passed back and forth between the DMA and the host
Double word; a 32-bit data entity
Direct Memory Access
First In, First Out. A temporary memory storage scheme.
High-Level Data-Link Control
The main controller that resides on the PCI Bus.
Not assigned
HDLC
Host
n/a
V.54
A pseudorandom pattern that controls loopbacks (see ANSI T1.403)
2. DETAILED DESCRIPTION
This data sheet is broken into sections detailing each of the DS31256’s blocks. See Figure 2-1 for a block
diagram.
The Layer 1 block handles the physical input and output of serial data to and from the DS31256. The
DS31256 can handle up to 60 T1 or 64 E1 data streams or two T3 data streams simultaneously. Each of
the 16 physical ports can handle up to two or four T1 or E1 data streams. Section 17 details a few
common applications for the DS31256. The Layer 1 block prepares the incoming data for the HDLC
block and grooms data from the HDLC block for transmission. The block can perform both channelized
and unchannelized loopbacks as well as search for V.54 loop patterns. It is in the Layer 1 block that the
host enables HDLC channels and assigns them to a particular port and/or DS0 channel(s). The host
assigns HDLC channels through the R[n]CFG[j] and T[n]CFG[j] registers, which are described in
Section 6.3. The Layer 1 block interfaces directly to the BERT block. The BERT block can generate and
detect both pseudorandom and repeating bit patterns, and is used to test and stress data communication
links.
The HDLC block consists of two types of HDLC controllers. There are 16 slow HDLC engines (one for
each port) that are capable of operating at speeds up to 8.192Mbps in channelized mode and up to
10Mbps in unchannelized mode. There are also three fast HDLC engines, which only reside on Ports 0,
1, and 2 and they are capable of operating at speeds up to 52Mbps. Via the RP[n]CR and TP[n]CR
registers in the Layer 1 block, the host configures Ports 0, 1, and 2 to use either the slow or the fast
HDLC engine. The HDLC engines perform all of the Layer 2 processing, including zero stuffing and
destuffing, flag generation and detection, CRC generation and checking, abort generation and checking.
In the receive path, the following process occurs. The HDLC engines collect the incoming data into
32-bit dwords and then signal the FIFO that the engine has data to transfer to the FIFO. The 16 ports are
priority decoded (Port 0 gets the highest priority) for the transfer of data from the HDLC Engines to the
FIFO Block. Please note that in a channelized application, a single port may contain up to 128 HDLC
channels and since HDLC channel numbers can be assigned randomly, the HDLC channel number has
no bearing on the priority of this data transfer. This situation is of no real concern however since the
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DS31256 256-Channel, High-Throughput HDLC Controller
DS31256 has been designed to handle up to 132Mbps in both the receive and transmit directions without
any potential loss of data due to priority conflicts in the transfer of data from the HDLC engines to the
FIFO and vice versa.
The FIFO transfers data from the HDLC engines into the FIFO and checks to see if the FIFO has filled to
beyond the programmable high watermark. If it has, then the FIFO signals to the DMA that data is ready
to be burst read from the FIFO to the PCI Bus. The FIFO block controls the DMA block and it tells the
DMA when to transfer data from the FIFO to the PCI Bus. Since the DS31256 can handle multiple
HDLC channels, it is quite possible that at any one time, several HDLC channels will need to have data
transferred from the FIFO to the PCI Bus. The FIFO determines which HDLC channel the DMA will
handle next via a Host configurable algorithm, which allows the selection to be either round robin or
priority, decoded (with HDLC Channel 1 getting the highest priority). Depending on the application, the
selection of this algorithm can be quite important. The DS31256 cannot control when it will be granted
PCI Bus access and if bus access is restricted, then the host may wish to prioritize which HDLC channels
get top priority access to the PCI Bus when it is granted to the DS31256.
When the DMA transfers data from the FIFO to the PCI Bus, it burst reads all available data in the FIFO
(even if the FIFO contains multiple HDLC packets) and tries to empty the FIFO. If an incoming HDLC
packet is not large enough to fill the FIFO to the high watermark, then the FIFO will not wait for more
data to enter the FIFO, it will signal the DMA that an end-of-frame (EOF) was detected and that data is
ready to be transferred from the FIFO to the PCI Bus by the DMA.
In the transmit path, a very similar process occurs. As soon as a HDLC channel is enabled, the HDLC
(Layer 2) engines begin requesting data from the FIFO. Like the receive side, the 16 ports are priority
decoded with Port 0 generally getting the highest priority. Hence, if multiple ports are requesting packet
data, the FIFO will first satisfy the requirements on all the enabled HDLC channels in the lower
numbered ports before moving on to the higher numbered ports. Again there is no potential loss of data
as long as the transmit throughput maximum of 132Mbps is not exceeded. When the FIFO detects that a
HDLC engine needs data, it then transfers the data from the FIFO to the HDLC engines in 32-bit chunks.
If the FIFO detects that the FIFO is below the low watermark, it then checks with the DMA to see if
there is any data available for that HDLC Channel. The DMA will know if any data is available because
the Host on the PCI Bus will have informed it of such via the pending-queue descriptor. When the DMA
detects that data is available, it informs the FIFO and then the FIFO decides which HDLC channel gets
the highest priority to the DMA to transfer data from the PCI Bus into the FIFO. Again, since the
DS31256 can handle multiple HDLC channels, it is quite possible that at any one time, several HDLC
channels will need the DMA to burst data from the PCI Bus into the FIFO. The FIFO determines which
HDLC channel the DMA will handle next via a host configurable algorithm, which allows the selection
to be either round robin or priority, decoded (with HDLC Channel 1 generally getting the highest
priority).
When the DMA begins burst writing data into the FIFO, it will try to completely fill the FIFO with
HDLC packet data even if it that means writing multiple packets. Once the FIFO detects that the DMA
has filled it to beyond the low watermark (or an EOF is reached), the FIFO will begin transferring 32-bit
dwords to the HDLC engine.
One of the unique attributes of the DS31256 is the structure of the DMA. The DMA has been optimized
to maintain maximum flexibility yet reduce the number of bus cycles required to transfer packet data.
The DMA uses a flexible scatter/gather technique, which allows that packet data to be place anywhere
within the 32-bit address space. The user has the option on the receive side of two different buffer sizes
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DS31256 256-Channel, High-Throughput HDLC Controller
which are called “large” and “small” but that can be set to any size up to 8188 bytes. The user has the
option to store the incoming data either, only in the large buffers, only in the small buffers, or fill a small
buffer first and then fill large buffers as needed. The varying buffer storage options allow the user to
make the best use of the available memory and to be able to balance the tradeoff between latency and bus
utilization.
The DMA uses a set of descriptors to know where to store the incoming HDLC packet data and where to
obtain HDLC packet data that is ready to be transmitted. The descriptors are fixed size messages that are
handed back and forth from the DMA to the host. Since this descriptor transfer utilizes bus cycles, the
DMA has been structured to minimize the number of transfers required. For example on the receive side,
the DMA obtains descriptors from the host to know where in the 32-bit address space to place the
incoming packet data. These descriptors are known as free-queue descriptors. When the DMA reads
these descriptors off of the PCI Bus, they contain all the information that the DMA needs to know where
to store the incoming data. Unlike other existing scatter/gather DMA architectures, the DS31256 DMA
does not need to use any more bus cycles to determine where to place the data. Other DMA architectures
tend to use pointers, which require them to go back onto the bus to obtain more information and hence
use more bus cycles.
Another technique that the DMA uses to maximize bus utilization is the ability to burst read and write
the descriptors. The device can be enabled to read and write the descriptors in bursts of 8 or 16 instead of
one at a time. Since there is fixed overhead associated with each bus transaction, the ability to burst read
and write descriptors allows the device to share the bus overhead among 8 or 16 descriptor transactions
which reduces the total number of bus cycles needed.
The DMA can also burst up to 256 dwords (1024 bytes) onto the PCI Bus. This helps to minimize bus
cycles by allowing the device to burst large amounts of data in a smaller number of bus transactions that
reduces bus cycles by reducing the amount of fixed overhead that is placed on the bus.
The Local Bus block has two modes of operation. It can be used as either a bridge from the PCI Bus in
which case it is a bus master or it can be used as a configuration bus in which case it is a bus slave. The
bridge mode allows the host on the PCI Bus to access the local bus. The DS31256 maps data from the
PCI Bus to the local bus. In the configuration mode, the local bus is used only to control and monitor the
DS31256 while the HDLC packet data will still be transferred to the host through the PCI Bus.
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 2-1. Block Diagram
RECEIVE DIRECTION
TRANSMIT DIRECTION
PCLK
RC0
RD0
RS0
TC0
TD0
TS0
PRST
PAD[31:0]
PCBE[3:0]
PPAR
PFRAME
PIRDY
HDLC
FIFO
Block
DMA
PCI
PTRDY
PSTOP
PIDSEL
PDEVSEL
PREQ
PGNT
PPERR
PSERR
RC1
RD1
RS1
TC1
TD1
TS1
Block
Block
Block
(Sec. 10)
(Sec. 8)
(Sec. 7)
(Sec. 9)
Layer
One
RC2
RD2
RS2
TC2
TD2
TS2
Block
PXAS
PXDS
PXBLAST
(Sec. 6)
LA[19:0]
LD[15:0]
LWR (LR/W)
LRD (LDS)
LIM
RC15
RD15
RS15
TC15
TD15
TS15
Local
Bus
LINT
Block
LRDY
BERT
Sec. 6.5)
LMS
(Sec. 11)
LCS
Dallas Semiconductor
LHOLD (LBR)
LHLDA (LBG)
LBGACK
LCLK
DS31256
JTRST
JTAG
JTDI
Test
LBHE
JTMS
JTCLK
JTDO
Access
(Sec. 12)
Pin Names in ( )
are active when
the device is in
the MOT mode
(i.e., LIM = 1)
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DS31256 256-Channel, High-Throughput HDLC Controller
Restrictions
In creating the overall system architecture, the user must balance the port, throughput, and HDLC
channel restrictions of the DS31256. Table 2-A lists all of the upper-bound maximum restrictions.
Table 2-A. Restrictions
ITEM
RESTRICTION
Port
Maximum of 16 channelized and unchannelized physical ports
Ports 0 to 2: Maximum data rate of 52Mbps
Unchannelized
Channelized
Ports 3 to 15: Maximum data rate of 10Mbps
Channelized and with byte interleave interfaces: 60 T1/64 E1 links
Maximum receive: 132Mbps
Throughput
Maximum transmit: 132Mbps
Maximum of 256 channels:
If the fast HDLC engine on Port 0 is being used, then it must be
HDLC Channel 1*
HDLC
If the fast HDLC engine on Port 1 is being used, then it must be
HDLC Channel 2*
If the fast HDLC engine on Port 2 is being used, then it must be
HDLC Channel 3*
*The 256 HDLC channels within the device are numbered 1 to 256.
Internal Device Configuration Registers
All internal device configuration registers (with the exception of the PCI configuration registers, which
are 32-bit registers) are 16 bits wide and are not byte addressable. When the host on the PCI bus accesses
these registers, the particular combination of byte enables (i.e., PCBE signals) is not important, but at
least one of the byte enables must be asserted for a transaction to occur. All registers are read/write,
unless otherwise noted. Not assigned (n/a) bits should be set to 0 when written to allow for future
upgrades. These bits should be treated as having no meaning and could be either 0 or 1 when read.
Initialization
On a system reset (which can be invoked by either hardware action through the PRST signal or software
action through the RST control bit in the master reset and ID register), all of the internal device
configuration registers are set to 0 (0000h). The local bus bridge mode control register (LBBMC) is not
affected by a software-invoked system reset; it is forced to all zeros only by a hardware reset. The
internal registers that are accessed indirectly (these are listed as “indirect registers” in the data sheet and
consist of the channelized port registers in the Layer 1 block, the DMA configuration RAMs, the HDLC
configuration registers, and the FIFO registers) are not affected by a system reset, so they must be
configured on power-up by the host to a proper state. Table 2-B lists the steps required to initialize the
DS31256.
Note: After device power-up and reset, it takes 0.625ms to get a port up and operating, therefore, the
ports must wait a minimum of 0.625ms before packet data can be processed.
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DS31256 256-Channel, High-Throughput HDLC Controller
Table 2-B. Initialization Steps
INITIALIZATION STEP
COMMENTS
Achieved by asserting the PIDSEL signal.
It is recommended that all of the indirect registers be set to
0000h (Table 2-C).
1) Initialize the PCI configuration registers
2) Initialize all indirect registers
3) Configure the device for operation
4) Enable the HDLC channels
5) Load the DMA descriptors
6) Enable the DMAs
Program all necessary registers, which include the Layer 1,
HDLC, FIFO, and DMA registers.
Done through the RCHEN and TCHEN bits in the
R[n]CFG[j] and T[n]CFG[j] registers.
Indicate to the DMA where packet data can be written and
where pending data (if any) resides.
Done through the RDE and TDE control bits in the master
configuration (MC) register.
Done through the channel-enable bit in the receive and
transmit configuration RAM.
7) Enable DMA for each HDLC channel
8) Enable data transmission
Set TFDA1 bit in TPnCR registers.
Table 2-C. Indirect Registers
REGISTER
NAME
CP0RD to CP15RD
NUMBER OF INDIRECT REGISTERS
6144 (16 Ports x 128 DS0 Channels x 3
Registers for each DS0 Channel)
256 (one for each HDLC Channel)
256 (one for each HDLC Channel)
1536 (one for each HDLC Channel)
3072 (one for each HDLC Channel)
256 (one for each HDLC Channel)
1024 (one for each FIFO Block)
256 (one for each HDLC Channel)
256 (one for each HDLC Channel)
1024 (one for each FIFO Block)
256 (one for each HDLC Channel)
Channelized Port
Receive HDLC Channel Definition
Transmit HDLC Channel Definition
Receive DMA Configuration
Transmit DMA Configuration
Receive FIFO Staring Block Pointer
Receive FIFO Block Pointer
RHCD
THCD
RDMAC
TDMAC
RFSBP
RFBP
Receive FIFO High Watermark
Transmit FIFO Staring Block Pointer
Transmit FIFO Block Pointer
RFHWM
TFSBP
TFBP
Transmit FIFO Low Watermark
TFLWM
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DS31256 256-Channel, High-Throughput HDLC Controller
3. SIGNAL DESCRIPTION
3.1 Overview/Signal List
This section describes the input and output signals on the DS31256. Signal names follow a convention
that is shown in the Signal Naming Convention table below. Table 3-A lists all the signals, their signal
type, description, and pin location.
Signal Naming Convention
FIRST LETTER
SIGNAL CATEGORY
SECTION
R
T
L
J
Receive Serial Port
Transmit Serial Port
Local Bus
JTAG Test Port
PCI Bus
3.2
3.2
3.3
3.4
3.5
P
Table 3-A. Signal Description
PIN
NAME
TYPE
FUNCTION
V19
U18
T17
W20
U19
G20
G19
F20
G18
F19
E20
G17
F18
E19
D20
E18
D19
C20
E17
D18
C19
B20
C18
B19
A20
L20
H20
J20
JTCLK
JTDI
JTDO
JTMS
JTRST
LA0
I
JTAG IEEE 1149.1 Test Serial Clock
JTAG IEEE 1149.1 Test Serial Data Input
JTAG IEEE 1149.1 Test Serial Data Output
JTAG IEEE 1149.1 Test Mode Select
JTAG IEEE 1149.1 Test Reset
Local Bus Address Bit 0, LSB
Local Bus Address Bit 1
I
O
I
I
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
O
LA1
LA2
Local Bus Address Bit 2
LA3
Local Bus Address Bit 3
LA4
Local Bus Address Bit 4
LA5
Local Bus Address Bit 5
LA6
Local Bus Address Bit 6
LA7
Local Bus Address Bit 7
LA8
Local Bus Address Bit 8
LA9
Local Bus Address Bit 9
LA10
LA11
LA12
LA13
LA14
LA15
LA16
LA17
LA18
LA19
LBGACK
LBHE
LCLK
LCS
Local Bus Address Bit 10
Local Bus Address Bit 11
Local Bus Address Bit 12
Local Bus Address Bit 13
Local Bus Address Bit 14
Local Bus Address Bit 15
Local Bus Address Bit 16
Local Bus Address Bit 17
Local Bus Address Bit 18
Local Bus Address Bit 19, MSB
Local Bus Grant Acknowledge
Local Bus Byte High Enable
Local Bus Clock
O
O
K19
V20
U20
T18
T19
I
Local Bus Chip Select
LD0
I/O
I/O
I/O
I/O
Local Bus Data Bit 0, LSB
Local Bus Data Bit 1
LD1
LD2
Local Bus Data Bit 2
LD3
Local Bus Data Bit 3
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DS31256 256-Channel, High-Throughput HDLC Controller
PIN
NAME
TYPE
FUNCTION
T20
R18
P17
R19
R20
P18
P19
P20
N18
N19
N20
M17
L18
L19
M18
K20
M19
H18
LD4
LD5
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I
Local Bus Data Bit 4
Local Bus Data Bit 5
LD6
Local Bus Data Bit 6
LD7
Local Bus Data Bit 7
LD8
Local Bus Data Bit 8
LD9
Local Bus Data Bit 9
LD10
Local Bus Data Bit 10
LD11
Local Bus Data Bit 11
LD12
Local Bus Data Bit 12
LD13
Local Bus Data Bit 13
LD14
Local Bus Data Bit 14
LD15
Local Bus Data Bit 15, MSB
Local Bus Hold Acknowledge (Local Bus Grant)
Local Bus Hold (Local Bus Request)
Local Bus Intel/Motorola Bus Select
Local Bus Interrupt
LHLDA (LBG)
LHOLD (LBR)
LIM
O
I
LINT
LMS
I/O
I
Local Bus Mode Select
I/O
I
Local Bus Read Enable (Local Bus Data Strobe)
Local Bus PCI Bridge Ready
Local Bus Write Enable (Local Bus Read/Write Select)
LRD (LDS)
LRDY
K18
H19
I/O
LWR (LR/W)
A2, A8, A11, A19,
B2, B18, J18, J19,
K1–K3, L1–L3,
N.C.
—
No Connect. Do not connect any signal to this pin.
M20, U14, W2, W9,
Y1, Y19
V17
U16
Y18
W17
V16
Y17
W16
V15
W15
V14
Y15
W14
Y14
V13
W13
Y13
V9
PAD0
PAD1
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
PCI Multiplexed Address and Data Bit 0
PCI Multiplexed Address and Data Bit 1
PCI Multiplexed Address and Data Bit 2
PCI Multiplexed Address and Data Bit 3
PCI Multiplexed Address and Data Bit 4
PCI Multiplexed Address and Data Bit 5
PCI Multiplexed Address and Data Bit 6
PCI Multiplexed Address and Data Bit 7
PCI Multiplexed Address and Data Bit 8
PCI Multiplexed Address and Data Bit 9
PCI Multiplexed Address and Data Bit 10
PCI Multiplexed Address and Data Bit 11
PCI Multiplexed Address and Data Bit 12
PCI Multiplexed Address and Data Bit 13
PCI Multiplexed Address and Data Bit 14
PCI Multiplexed Address and Data Bit 15
PCI Multiplexed Address and Data Bit 16
PCI Multiplexed Address and Data Bit 17
PCI Multiplexed Address and Data Bit 18
PCI Multiplexed Address and Data Bit 19
PCI Multiplexed Address and Data Bit 20
PCI Multiplexed Address and Data Bit 21
PCI Multiplexed Address and Data Bit 22
PCI Multiplexed Address and Data Bit 23
PCI Multiplexed Address and Data Bit 24
PCI Multiplexed Address and Data Bit 25
PCI Multiplexed Address and Data Bit 26
PAD2
PAD3
PAD4
PAD5
PAD6
PAD7
PAD8
PAD9
PAD10
PAD11
PAD12
PAD13
PAD14
PAD15
PAD16
PAD17
PAD18
PAD19
PAD20
PAD21
PAD22
PAD23
PAD24
PAD25
PAD26
U9
Y8
W8
V8
Y7
W7
V7
U7
V6
Y5
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DS31256 256-Channel, High-Throughput HDLC Controller
PIN
NAME
TYPE
FUNCTION
W5
V5
PAD27
PAD28
PAD29
PAD30
PAD31
PCBE0
PCBE1
PCBE2
PCBE3
PCLK
PDEVSEL
PFRAME
PGNT
PIDSEL
PINT
I/O
PCI Multiplexed Address and Data Bit 27
PCI Multiplexed Address and Data Bit 28
PCI Multiplexed Address and Data Bit 29
PCI Multiplexed Address and Data Bit 30
PCI Multiplexed Address and Data Bit 31
PCI Bus Command/Byte Enable Bit 0
PCI Bus Command/Byte Enable Bit 1
PCI Bus Command/Byte Enable Bit 2
PCI Bus Command/Byte Enable Bit 3
PCI and System Clock. A 25MHz to 33MHz clock is applied here.
PCI Device Select
I/O
Y4
I/O
Y3
U5
Y16
V12
Y9
W6
Y2
Y11
W10
W4
Y6
W18
V10
W12
V11
V4
I/O
I/O
I/O
I/O
I/O
I/O
I
I/O
I/O
PCI Cycle Frame
I
I
PCI Bus Grant
PCI Initialization Device Select
PCI Interrupt
O
I/O
I/O
I/O
O
I
PIRDY
PPAR
PPERR
PREQ
PRST
PSERR
PSTOP
PTRDY
PXAS
PXBLAST
PXDS
RC0
PCI Initiator Ready
PCI Bus Parity
PCI Parity Error
PCI Bus Request
W3
Y12
W11
Y10
V18
Y20
W19
B1
PCI Reset
O
I/O
I/O
O
O
O
I
PCI System Error
PCI Stop
PCI Target Ready
PCI Extension Signal: Address Strobe
PCI Extension Signal: Burst Last
PCI Extension Signal: Data Strobe
Receive Serial Clock for Port 0
Receive Serial Clock for Port 1
Receive Serial Clock for Port 2
Receive Serial Clock for Port 3
Receive Serial Clock for Port 4
Receive Serial Clock for Port 5
Receive Serial Clock for Port 6
Receive Serial Clock for Port 7
Receive Serial Clock for Port 8
Receive Serial Clock for Port 9
Receive Serial Clock for Port 10
Receive Serial Clock for Port 11
Receive Serial Clock for Port 12
Receive Serial Clock for Port 13
Receive Serial Clock for Port 14
Receive Serial Clock for Port 15
Receive Serial Data for Port 0
Receive Serial Data for Port 1
Receive Serial Data for Port 2
Receive Serial Data for Port 3
Receive Serial Data for Port 4
Receive Serial Data for Port 5
Receive Serial Data for Port 6
Receive Serial Data for Port 7
Receive Serial Data for Port 8
Receive Serial Data for Port 9
D1
RC1
I
F2
RC2
I
H2
RC3
I
M1
P1
RC4
I
RC5
I
P4
RC6
I
V1
RC7
I
B17
B16
C14
D12
A10
B8
RC8
I
RC9
I
RC10
RC11
RC12
RC13
RC14
RC15
RD0
I
I
I
I
B6
I
C5
I
D2
I
E2
RD1
I
G3
RD2
I
J4
RD3
I
M3
R1
RD4
I
RD5
I
T2
RD6
I
U3
RD7
I
D16
C15
RD8
I
RD9
I
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DS31256 256-Channel, High-Throughput HDLC Controller
PIN
NAME
TYPE
FUNCTION
A14
B12
C10
A7
D7
A3
C2
RD10
RD11
RD12
RD13
RD14
RD15
RS0
I
I
Receive Serial Data for Port 10
Receive Serial Data for Port 11
Receive Serial Data for Port 12
Receive Serial Data for Port 13
Receive Serial Data for Port 14
Receive Serial Data for Port 15
Receive Serial Sync for Port 0
Receive Serial Sync for Port 1
Receive Serial Sync for Port 2
Receive Serial Sync for Port 3
Receive Serial Sync for Port 4
Receive Serial Sync for Port 5
Receive Serial Sync for Port 6
Receive Serial Sync for Port 7
Receive Serial Sync for Port 8
Receive Serial Sync for Port 9
Receive Serial Sync for Port 10
Receive Serial Sync for Port 11
Receive Serial Sync for Port 12
Receive Serial Sync for Port 13
Receive Serial Sync for Port 14
Receive Serial Sync for Port 15
Transmit Serial Clock for Port 0
Transmit Serial Clock for Port 1
Transmit Serial Clock for Port 2
Transmit Serial Clock for Port 3
Transmit Serial Clock for Port 4
Transmit Serial Clock for Port 5
Transmit Serial Clock for Port 6
Transmit Serial Clock for Port 7
Transmit Serial Clock for Port 8
Transmit Serial Clock for Port 9
Transmit Serial Clock for Port 10
Transmit Serial Clock for Port 11
Transmit Serial Clock for Port 12
Transmit Serial Clock for Port 13
Transmit Serial Clock for Port 14
Transmit Serial Clock for Port 15
Transmit Serial Data for Port 0
Transmit Serial Data for Port 1
Transmit Serial Data for Port 2
Transmit Serial Data for Port 3
Transmit Serial Data for Port 4
Transmit Serial Data for Port 5
Transmit Serial Data for Port 6
Transmit Serial Data for Port 7
Transmit Serial Data for Port 8
Transmit Serial Data for Port 9
Transmit Serial Data for Port 10
Transmit Serial Data for Port 11
Transmit Serial Data for Port 12
Transmit Serial Data for Port 13
I
I
I
I
I
E3
RS1
I
F1
RS2
I
H1
M2
P2
RS3
I
RS4
I
RS5
I
R3
T4
RS6
I
RS7
I
C17
A16
B14
C12
B10
C8
RS8
I
RS9
I
RS10
RS11
RS12
RS13
RS14
RS15
TC0
I
I
I
I
A5
B4
I
I
D3
E1
I
TC1
I
G2
J3
TC2
I
TC3
I
N1
P3
TC4
I
TC5
I
U1
V2
A18
D14
C13
A12
A9
B7
TC6
I
TC7
I
TC8
I
TC9
I
TC10
TC11
TC12
TC13
TC14
TC15
TD0
TD1
TD2
TD3
TD4
TD5
TD6
TD7
TD8
TD9
TD10
TD11
TD12
TD13
I
I
I
I
C6
D5
C1
G4
H3
J1
N3
T1
I
I
O
O
O
O
O
O
O
O
O
O
O
O
O
O
U2
V3
C16
A15
A13
C11
C9
C7
16 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
PIN
NAME
TYPE
FUNCTION
A4
TD14
TD15
TEST
TS0
O
O
I
Transmit Serial Data for Port 14
Transmit Serial Data for Port 15
Test. Factory tests signal; leave open circuited
Transmit Serial Sync for Port 0
Transmit Serial Sync for Port 1
Transmit Serial Sync for Port 2
Transmit Serial Sync for Port 3
Transmit Serial Sync for Port 4
Transmit Serial Sync for Port 5
Transmit Serial Sync for Port 6
Transmit Serial Sync for Port 7
Transmit Serial Sync for Port 8
Transmit Serial Sync for Port 9
Transmit Serial Sync for Port 10
Transmit Serial Sync for Port 11
Transmit Serial Sync for Port 12
Transmit Serial Sync for Port 13
Transmit Serial Sync for Port 14
Transmit Serial Sync for Port 15
B3
C3
E4
I
F3
TS1
I
G1
TS2
I
J2
TS3
I
N2
TS4
I
R2
TS5
I
T3
TS6
I
W1
TS7
I
A17
TS8
I
B15
B13
TS9
I
TS10
TS11
TS12
TS13
TS14
TS15
I
B11
I
B9
I
A6
I
B5
I
C4
I
D6, D10, D11, D15,
F4, F17, K4, K17,
L4, L17, R4, R17,
U6, U10, U11, U15
A1, D4, D8, D9,
D13, D17, H4, H17,
J17, M4, N4, N17,
U4, U8, U12, U13,
U17
VDD
—
—
Positive Supply. 3.3V (±10%)
VSS
Ground Reference
17 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
3.2 Serial Port Interface Signal Description
Signal Name:
RC0 to RC15
Receive Serial Clock
Input
Signal Description:
Signal Type:
Data can be clocked into the device either on rising edges (normal clock mode) or falling edges (inverted clock
mode) of RC. This is programmable on a per port basis. RC0–RC2 can operate at speeds up to 52MHz.
RC3–RC15 can operate at speeds up to 10MHz. Unused signals should be wired low.
Signal Name:
RD0 to RD15
Receive Serial Data
Input
Signal Description:
Signal Type:
Can be sampled either on the rising edge of RC (normal clock mode) or the falling edge of RC (inverted clock
mode). Unused signals should be wired low.
Signal Name:
RS0 to RS15
Signal Description:
Signal Type:
Receive Serial Data Synchronization Pulse
Input
This is a one-RC clock-wide synchronization pulse that can be applied to the DS31256 to force byte/frame
alignment. The applied sync-signal pulse can be either active high (normal sync mode) or active low (inverted
sync mode). The RS signal can be sampled either on the falling edge or on rising edge of RC (Table 3-B). The
applied sync pulse can be during the first RC clock period of a 193/256/512/1024-bit frame or it can be applied
1/2, 1, or 2 RC clocks early. This input sync signal resets a counter that rolls over at a count of either 193 (T1
mode) or 256 (E1 mode) or 512 (4.096MHz mode) or 1024 (8.192MHz mode) RC clocks. It is acceptable to pulse
the RS signal once to establish byte boundaries and allow the DS31256 to track the byte/frame boundaries by
counting RC clocks. If the incoming data does not require alignment to byte/frame boundaries, this signal should
be wired low.
Table 3-B. RS Sampled Edge
SIGNAL
NORMAL RC CLOCK MODE
INVERTED RC CLOCK MODE
0 RC Clock Early Mode
1/2 RC Clock Early Mode
1 RC Clock Early Mode
2 RC Clock Early Mode
Falling Edge
Rising Edge
Falling Edge
Falling Edge
Rising Edge
Falling Edge
Rising Edge
Rising Edge
Signal Name:
TC0 to TC15
Signal Description:
Signal Type:
Transmit Serial Clock
Input
Data can be clocked out of the device either on rising edges (normal clock mode) or falling edges (inverted clock
mode) of TC. This is programmable on a per port basis. TC0 and TC1 can operate at speeds up to 52MHz. TC2–
TC15 can operate at speeds up to 10MHz. Unused signals should be wired low.
Signal Name:
TD0 to TD15
Transmit Serial Data
Output
Signal Description:
Signal Type:
This can be updated either on the rising edge of TC (normal clock mode) or the falling edge of TC (inverted clock
mode). Data can be forced high.
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DS31256 256-Channel, High-Throughput HDLC Controller
Signal Name:
TS0 to TS15
Signal Description:
Signal Type:
Transmit Serial Data Synchronization Pulse
Input
This is a one-TC clock-wide synchronization pulse that can be applied to the DS31256 to force byte/frame
alignment. The applied sync signal pulse can be either active high (normal sync mode) or active low (inverted
sync mode). The TS signal can be sampled either on the falling edge or on rising edge of TC (Table 3-C). The
applied sync pulse can be during the first TC clock period of a 193/256/512/1024-bit frame or it can be applied
1/2, 1, or 2 TC clocks early. This input sync signal resets a counter that rolls over at a count of either 193 (T1
mode) or 256 (E1 mode) or 512 (4.096MHz mode) or 1024 (8.192MHz mode) TC clocks. It is acceptable to pulse
the TS signal once to establish byte boundaries and allow the DS31256 to track the byte/frame boundaries by
counting TC clocks. If the incoming data does not require alignment to byte/frame boundaries, this signal should
be wired low.
Table 3-C. TS Sampled Edge
SIGNAL
NORMAL TC CLOCK MODE
INVERTED TC CLOCK MODE
0 TC Clock Early Mode
1/2 TC Clock Early Mode
1 TC Clock Early Mode
2 TC Clock Early Mode
Falling Edge
Rising Edge
Falling Edge
Falling Edge
Rising Edge
Falling Edge
Rising Edge
Rising Edge
3.3 Local Bus Signal Description
Signal Name:
LMS
Signal Description:
Signal Type:
Local Bus Mode Select
Input
This signal should be connected low when the device operates with no local bus access or if the local bus is used
as a bridge from the PCI bus. This signal should be connected high if the local bus is to be used by an external host
to configure the device.
0 = local bus is in the PCI bridge mode (master)
1 = local bus is in the configuration mode (slave)
Signal Name:
LIM
Signal Description:
Signal Type:
Local Bus Intel/Motorola Bus Select
Input
The signal determines whether the local bus operates in the Intel mode (LIM = 0) or the Motorola mode
(LIM = 1). The signal names in parentheses are operational when the device is in the Motorola mode.
0 = local bus is in the Intel mode
1 = local bus is in the Motorola mode
Signal Name:
LD0 to LD15
Signal Description:
Signal Type:
Local Bus Nonmultiplexed Data Bus
Input/Output (tri-state capable)
In PCI bridge mode (LMS = 0), data from/to the PCI bus can be transferred to/from these signals. When writing
data to the local bus, these signals are outputs and updated on the rising edge of LCLK. When reading data from
the local bus, these signals are inputs, which are sampled on the rising edge of LCLK. Depending on the assertion
of the PCI byte enables (PCBE0 to PCBE3) and the local bus-width (LBW) control bit in the local bus bridge
mode control register (LBBMC), this data bus uses all 16 bits (LD[15:0]) or just the lower 8 bits (LD[7:0]) or the
upper 8 bits (LD[15:8]). If the upper LD bits (LD[15:8]) are used, then the local bus high-enable signal (LBHE) is
asserted during the bus transaction. If the local bus is not currently involved in a bus transaction, all 16 signals are
tri-stated. When reading data from the local bus, these signals are outputs that are updated on the rising edge of
LCLK. When writing data to the local bus, these signals become inputs, which are sampled on the rising edge of
LCLK. In configuration mode (LMS = 1), the external host configures the device and obtains real-time status
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information about the device through these signals. Only the 16-bit bus width is allowed (i.e., byte addressing is
not available).
Signal Name:
LA0 to LA19
Signal Description:
Signal Type:
Local Bus Nonmultiplexed Address Bus
Input/Output (tri-state capable)
In the PCI bridge mode (LMS = 0), these signals are outputs that are asserted on the rising edge of LCLK to
indicate which address to be written to or read from. These signals are tri-stated when the local bus is not currently
involved in a bus transaction and driven when a bus transaction is active. In configuration mode
(LMS = 1), these signals are inputs and only the bottom 16 (LA[15:0]) are active. The upper four (LA[19:16]) are
ignored and should be connected low.
Signal Name:
LWR (LR/W)
Signal Description:
Signal Type:
Local Bus Write Enable (Local Bus Read/Write Select)
Input/Output (tri-state capable)
In the PCI bridge mode (LMS = 0), this output signal is asserted on the rising edge of LCLK. In Intel mode
(LIM = 0), it is asserted when data is to be written to the local bus. In Motorola mode (LIM = 1), this signal
determines whether a read or write is to occur. If bus arbitration is enabled through the LARBE control bit in the
LBBMC register, this signal is tri-stated when the local bus is not currently involved in a bus transaction and
driven when a bus transaction is active. When bus arbitration is disabled, this signal is always driven. In Intel
mode (LIM = 0), it determines when data is to be written to the device. In Motorola mode (LIM = 1), this signal
determines whether a read or write is to occur.
Signal Name:
LRD (LDS)
Signal Description:
Signal Type:
Local Bus Read Enable (Local Bus Data Strobe)
Input/Output (tri-state capable)
In the PCI bridge mode (LMS = 0), this active-low output signal is asserted on the rising edge of LCLK. In Intel
mode (LIM = 0), it is asserted when data is to be read from the local bus. In Motorola mode (LIM = 1), the rising
edge is used to write data into the slave device. If bus arbitration is enabled through the LARBE control bit in the
LBBMC register, this signal is tri-stated when the local bus is not currently involved in a bus transaction and
driven when a bus transaction is active. When bus arbitration is disabled, this signal is always driven. In Intel
mode (LIM = 0), it determines when data is to be read from the device. In Motorola mode (LIM = 1), the rising
edge writes data into the device.
Signal Name:
LINT
Signal Description:
Signal Type:
Local Bus Interrupt
Input/Output (open drain)
In the PCI bridge mode (LMS = 0), this active-low signal is an input that is sampled on the rising edge of LCLK.
If asserted and unmasked, this signal causes an interrupt at the PCI bus through the PINTA signal. If not used in
PCI bridge mode, this signal should be connected high. In configuration mode (LMS = 1), this signal is an open-
drain output that is forced low if one or more unmasked interrupt sources within the device is active. The signal
remains low until either the interrupt is serviced or masked.
Signal Name:
LRDY
Signal Description:
Signal Type:
Local Bus PCI Bridge Ready (PCI Bridge Mode Only)
Input
This active-low signal is sampled on the rising edge of LCLK to determine when a bus transaction is complete.
This signal is only examined when a bus transaction is taking place. This signal is ignored when the local bus is in
configuration mode (LMS = 1) and should be connected high.
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Signal Name:
LHLDA (LBG)
Signal Description:
Signal Type:
Local Bus Hold Acknowledge (Local Bus Grant) (PCI Bridge Mode Only)
Input
This input signal is sampled on the rising edge of LCLK to determine when the device has been granted access to
the bus. In Intel mode (LIM = 0), this is an active-high signal; in Motorola mode (LIM = 1) this is an active-low
signal. This signal is ignored and should be connected high when the local bus is in configuration mode
(LMS = 1). Also, in PCI bridge mode (LMS = 0), this signal should be wired deasserted when the local bus
arbitration is disabled through the LBBMC register.
Signal Name:
LHOLD (LBR)
Signal Description:
Signal Type:
Local Bus Hold (Local Bus Request) (PCI Bridge Mode Only)
Output
This signal is asserted when the DS31256 is attempting to control the local bus. In Intel mode (LIM = 0), this
signal is an active-high signal; in Motorola mode (LIM = 1) this signal is an active-low signal. It is deasserted
concurrently with LBGACK. This signal is tri-stated when the local bus is in configuration mode (LMS = 1) and
also in PCI bridge mode (LMS = 0) when the local bus arbitration is disabled through the LBBMC register.
Signal Name:
LBGACK
Signal Description:
Signal Type:
Local Bus Grant Acknowledge (PCI Bridge Mode Only)
Output (tri-state capable)
This active-low signal is asserted when the local bus hold-acknowledge/bus grant signal (LHLDA/LBG) has been
detected and continues its assertion for a programmable (32 to 1,048,576) number of LCLKs, based on the local
bus arbitration timer setting in the LBBMC register. This signal is tri-stated when the local bus is in configuration
mode (LMS = 1).
Signal Name:
LBHE
Signal Description:
Signal Type:
Local Bus Byte-High Enable (PCI Bridge Mode Only)
Output (tri-state capable)
This active-low output signal is asserted when all 16 bits of the data bus (LD[15:0]) are active. It remains high if
only the lower 8 bits (LD[7:0)] are active. If bus arbitration is enabled through the LARBE control bit in the
LBBMC register, this signal is tri-stated when the local bus is not currently involved in a bus transaction and
driven when a bus transaction is active. When bus arbitration is disabled, this signal is always driven. This signal
remains in tri-state when the local bus is not involved in a bus transaction and is in configuration mode
(LMS = 1).
Signal Name:
LCLK
Signal Description:
Signal Type:
Local Bus Clock (PCI Bridge Mode Only)
Output (tri-state capable)
This signal outputs a buffered version of the clock applied at the PCLK input. All local bus signals are generated
and sampled from this clock. This output is tri-stated when the local bus is in configuration mode (LMS = 1). It
can be disabled in the PCI bridge mode through the LBBMC register.
Signal Name:
LCS
Signal Description:
Signal Type:
Local Bus Chip Select (Configuration Mode Only)
Input
This active-low signal must be asserted for the device to accept a read or write command from an external host.
This signal is ignored in the PCI bridge mode (LMS = 0) and should be connected high.
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3.4 JTAG Signal Description
Signal Name:
JTCLK
Signal Description:
Signal Type:
JTAG IEEE 1149.1 Test Serial Clock
Input
This signal is used to shift data into JTDI on the rising edge and out of JTDO on the falling edge. If unused, this
signal should be pulled high.
Signal Name:
JTDI
Signal Description:
Signal Type:
JTAG IEEE 1149.1 Test Serial-Data Input
Input (with internal 10kΩ pullup)
Test instructions and data are clocked into this signal on the rising edge of JTCLK. If unused, this signal should be
pulled high. This signal has an internal pullup.
Signal Name:
JTDO
Signal Description:
Signal Type:
JTAG IEEE 1149.1 Test Serial-Data Output
Output
Test instructions are clocked out of this signal on the falling edge of JTCLK. If unused, this signal should be left
open circuited.
Signal Name:
JTRST
Signal Description:
Signal Type:
JTAG IEEE 1149.1 Test Reset
Input (with internal 10kΩ pullup)
This signal is used to asynchronously reset the test access port controller. At power-up, JTRST must be set low
and then high. This action sets the device into the boundary scan bypass mode, allowing normal device operation.
If boundary scan is not used, this signal should be held low. This signal has an internal pullup.
Signal Name:
JTMS
Signal Description:
Signal Type:
JTAG IEEE 1149.1 Test Mode Select
Input (with internal 10kΩ pullup)
This signal is sampled on the rising edge of JTCLK and is used to place the test port into the various defined IEEE
1149.1 states. If unused, this signal should be pulled high. This signal has an internal pullup.
3.5 PCI Bus Signal Description
Signal Name:
PCLK
Signal Description:
Signal Type:
PCI and System Clock
Input (Schmitt triggered)
This clock input provides timing for the PCI bus and the device’s internal logic. A 25MHz to 33MHz clock with a
nominal 50% duty cycle should be applied here.
Signal Name:
PRST
Signal Description:
Signal Type:
PCI Reset
Input
This active-low input is used to force an asynchronous reset to both the PCI bus and the device’s internal logic.
When forced low, this input forces all the internal logic of the device into its default state, forces the PCI outputs
into tri-state, and forces the TD[15:0] output port-data signals high.
Signal Name:
PAD0 to PAD31
Signal Description:
Signal Type:
PCI Address and Data Multiplexed Bus
Input/Output (tri-state capable)
Both address and data information are multiplexed onto these signals. Each bus transaction consists of an address
phase followed by one or more data phases. Data can be either read or written in bursts. The address is transferred
during the first clock cycle of a bus transaction. When the Little Endian format is selected, PAD[31:24] is the
MSB of the DWORD; when Big Endian is selected, PAD[7:0] contains the MSB. When the device is an initiator,
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these signals are always outputs during the address phase. They remain outputs for the data phase(s) in a write
transaction and become inputs for a read transaction. When the device is a target, these signals are always inputs
during the address phase. They remain inputs for the data phase(s) in a read transaction and become outputs for a
write transaction. When the device is not involved in a bus transaction, these signals remain tri-stated. These
signals are always updated and sampled on the rising edge of PCLK.
Signal Name:
PCBE0/PCBE1/PCBE2/PCBE3
PCI Bus Command and Byte Enable
Input/Output (tri-state capable)
Signal Description:
Signal Type:
Bus command and byte enables are multiplexed onto the same PCI signals. During an address phase, these signals
define the bus command. During the data phase, these signals are used as byte enables. During data phases,
PCBE0 refers to the PAD[7:0] and PCBE3 refers to PAD[31:24]. When this signal is high, the associated byte is
invalid; when low, the associated byte is valid. When the device is an initiator, this signal is an output and is
updated on the rising edge of PCLK. When the device is a target, this signal is an input and is sampled on the
rising edge of PCLK. When the device is not involved in a bus transaction, these signals are tri-stated.
Signal Name:
PPAR
Signal Description:
Signal Type:
PCI Bus Parity
Input/Output (tri-state capable)
This signal provides information on even parity across both the PAD address/data bus and the PCBE bus
command/byte enable bus. When the device is an initiator, this signal is an output for writes and an input for reads.
It is updated on the rising edge of PCLK. When the device is a target, this signal is an input for writes and an
output for reads. It is sampled on the rising edge of PCLK. When the device is not involved in a bus transaction,
PPAR is tri-stated.
Signal Name:
PFRAME
Signal Description:
Signal Type:
PCI Cycle Frame
Input/Output (tri-state capable)
This active-low signal is created by the bus initiator and is used to indicate the beginning and duration of a bus
transaction. PFRAME is asserted by the initiator during the first clock cycle of a bus transaction and remains
asserted until the last data phase of a bus transaction. When the device is an initiator, this signal is an output and is
updated on the rising edge of PCLK. When the device is a target, this signal is an input and is sampled on the
rising edge of PCLK. When the device is not involved in a bus transaction, PFRAME is tri-stated.
Signal Name:
PIRDY
Signal Description:
Signal Type:
PCI Initiator Ready
Input/Output (tri-state capable)
The initiator creates this active-low signal to signal the target that it is ready to send/accept or to continue
sending/accepting data. This signal handshakes with the PTRDY signal during a bus transaction to control the rate
at which data transfers across the bus. During a bus transaction, PIRDY is deasserted when the initiator cannot
temporarily accept or send data, and a wait state is invoked. When the device is an initiator, this signal is an output
and is updated on the rising edge of PCLK. When the device is a target, this signal is an input and is sampled on
the rising edge of PCLK. When the device is not involved in a bus transaction, PIRDY is tri-stated.
Signal Name:
PTRDY
Signal Description:
Signal Type:
PCI Target Ready
Input/Output (tri-state capable)
The target creates this active-low signal to signal the initiator that it is ready to send/accept or to continue
sending/accepting data. This signal handshakes with the PIRDY signal during a bus transaction to control the rate
at which data transfers across the bus. During a bus transaction, PTRDY is deasserted when the target cannot
temporarily accept or send data, and a wait state is invoked. When the device is a target, this signal is an output
and is updated on the rising edge of PCLK. When the device is an initiator, this signal is an input and is sampled
on the rising edge of PCLK. When the device is not involved in a bus transaction, PTRDY is tri-stated.
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Signal Name:
PSTOP
Signal Description:
Signal Type:
PCI Stop
Input/Output (tri-state capable)
The target creates this active-low signal to signal the initiator to stop the current bus transaction. When the device
is a target, this signal is an output and is updated on the rising edge of PCLK. When the device is an initiator, this
signal is an input and is sampled on the rising edge of PCLK. When the device is not involved in a bus transaction,
PSTOP is tri-stated.
Signal Name:
PIDSEL
Signal Description:
Signal Type:
PCI Initialization Device Select
Input
This input signal is used as a chip select during configuration read and write transactions. This signal is disabled
when the local bus is set in configuration mode (LMS = 1). When PIDSEL is set high during the address phase
of a bus transaction and the bus command signals (PCBE0 to PCBE3) indicate a register read or write, the device
allows access to the PCI configuration registers, and the PDEVSEL signal is asserted during the PCLK cycle.
PIDSEL is sampled on the rising edge of PCLK.
Signal Name:
PDEVSEL
Signal Description:
Signal Type:
PCI Device Select
Input/Output (tri-state capable)
The target creates this active-low signal when it has decoded the address sent to it by the initiator as its own to
indicate that the address is valid. If the device is an initiator and does not see this signal asserted within six PCLK
cycles, the bus transaction is aborted and the PCI host is alerted. When the device is a target, this signal is an
output and is updated on the rising edge of PCLK. When the device is an initiator, this signal is an input and is
sampled on the rising edge of PCLK. When the device is not involved in a bus transaction, PDEVSEL is tri-stated.
Signal Name:
PREQ
Signal Description:
Signal Type:
PCI Bus Request
Output (tri-state capable)
The initiator asserts this active-low signal to request that the PCI bus arbiter allow it access to the bus. PREQ is
updated on the rising edge of PCLK.
Signal Name:
PGNT
Signal Description:
Signal Type:
PCI Bus Grant
Input
The PCI bus arbiter asserts this active-low signal to indicate to the PCI requesting agent that access to the PCI bus
has been granted. The device samples PGNT on the rising edge of PCLK and, if detected, initiates a bus
transaction when it has sensed that the PFRAME signal has been deasserted.
Signal Name:
PPERR
Signal Description:
Signal Type:
PCI Parity Error
Input/Output (tri-state capable)
This active-low signal reports parity errors. PPERR can be enabled and disabled through the PCI configuration
registers. This signal is updated on the rising edge of PCLK.
Signal Name:
PSERR
Signal Description:
Signal Type:
PCI System Error
Output (open drain)
This active-low signal reports any parity errors that occur during the address phase. PSERR can be enabled and
disabled through the PCI configuration registers. This signal is updated on the rising edge of PCLK.
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Signal Name:
PINTA
Signal Description:
Signal Type:
PCI Interrupt
Output (open drain)
This active-low (open drain) signal is asserted low asynchronously when the device is requesting attention from
the device driver. PINTA is deasserted when the device-interrupting source has been serviced or masked. This
signal is updated on the rising edge of PCLK.
3.6 PCI Extension Signals
These signals are not part of the normal PCI bus signal set. There are additional signals that are asserted when the
DS31256 is an initiator on the PCI bus to help users interpret the normal PCI bus signal set and connect them to a
non-PCI environment like an Intel i960-type bus.
Signal Name:
PXAS
Signal Description:
Signal Type:
PCI Extension Address Strobe
Output
This active-low signal is asserted low on the same clock edge as PFRAME and is deasserted after one clock
period. This signal is only asserted when the device is an initiator. This signal is an output and is updated on the
rising edge of PCLK.
Signal Name:
PXDS
Signal Description:
Signal Type:
PCI Extension Data Strobe
Output
This active-low signal is asserted when the PCI bus either contains valid data to be read from the device or can
accept valid data that is written into the device. This signal is only asserted when the device is an initiator. This
signal is an output and is updated on the rising edge of PCLK.
Signal Name:
PXBLAST
Signal Description:
Signal Type:
PCI Extension Burst Last
Output
This active-low signal is asserted on the same clock edge as PFRAME is deasserted and is deasserted on the same
clock edge as PIRDY is deasserted. This signal is only asserted when the device is an initiator. This signal is an
output and is updated on the rising edge of PCLK.
3.7 Supply and Test Signal Description
Signal Name:
TEST
Signal Description:
Signal Type:
Factory Test Input
Input (with internal 10kΩ pullup)
This input should be left open-circuited by the user.
Signal Name:
VDD
Signal Description:
Signal Type:
Positive Supply
n/a
3.3V (±10%). All VDD signals should be connected together.
Signal Name:
VSS
Signal Description:
Signal Type:
Ground Reference
n/a
All VSS signals should be connected to the local ground plane.
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4. MEMORY MAP
4.1 Introduction
All addresses within the memory map are on dword boundaries, even though all internal device
configuration registers are only one word (16 bits) wide. The memory map consumes an address range of
4kB (12 bits). When the PCI bus is the host (i.e., the local bus is in bridge mode), the actual 32-bit PCI
bus addresses of the internal device configuration registers are obtained by adding the DC base address
value in the PCI device-configuration memory-base address register (Section 10.2) to the offset listed in
Sections 4.1 to 4.10. When an external host is configuring the device through the local bus (i.e., the local
bus is in the configuration mode), the offset is 0h and the host on the local bus uses the 16-bit addresses
listed in Sections 4.2 to 4.10.
Table 4-A. Memory Map Organization
PCI HOST [OFFSET
FROM DC BASE]
(0x000)
LOCAL BUS HOST
(16-BIT ADDRESS)
(00xx)
REGISTER
SECTION
General Configuration Registers
Receive Port Registers
4.2
4.3
(0x1xx)
(01xx)
Transmit Port Registers
(0x2xx)
(02xx)
4.4
Channelized Port Registers
HDLC Registers
(0x3xx)
(03xx)
4.6
(0x4xx)
(04xx)
4.6
BERT Registers
(0x5xx)
(05xx)
4.7
Receive DMA Registers
Transmit DMA Registers
FIFO Registers
PCI Configuration Registers for Function 0
PCI Configuration Registers for Function 1
(0x7xx)
(07xx)
4.8
(0x8xx)
(08xx)
4.9
(0x9xx)
(09xx)
4.10
4.11
4.12
(PIDSEL)
(PIDSEL)
(0Axx)
(0Bxx)
4.2 General Configuration Registers (0xx)
OFFSET/
NAME
REGISTER
SECTION
ADDRESS
0000
MRID
MC
Master Reset and ID Register
Master Configuration
5.1
5.2
0010
0020
SM
Master Status Register
5.3.2
5.3.2
5.3.2
5.3.2
5.3.2
5.3.2
11.2
5.4
0024
ISM
Interrupt Mask Register for SM
Status Register for DMA
Interrupt Mask Register for SDMA
Status Register for V.54 Loopback Detector
Interrupt Mask Register for SV.54
Local Bus Bridge Mode Control Register
Test Register
0028
SDMA
ISDMA
SV54
ISV54
LBBMC
TEST
002C
0030
0034
0040
0050
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4.3 Receive Port Registers (1xx)
OFFSET/
NAME
REGISTER
Receive Port 0 Control Register
SECTION
ADDRESS
0100
0104
0108
010C
0110
0114
0118
011C
0120
0124
0128
012C
0130
0134
0138
013C
RP0CR
RP1CR
RP2CR
RP3CR
RP4CR
RP5CR
RP6CR
RP7CR
RP8CR
RP9CR
RP10CR
RP11CR
RP12CR
RP13CR
RP14CR
RP15CR
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
Receive Port 1 Control Register
Receive Port 2 Control Register
Receive Port 3 Control Register
Receive Port 4 Control Register
Receive Port 5 Control Register
Receive Port 6 Control Register
Receive Port 7 Control Register
Receive Port 8 Control Register
Receive Port 9 Control Register
Receive Port 10 Control Register
Receive Port 11 Control Register
Receive Port 12 Control Register
Receive Port 13 Control Register
Receive Port 14 Control Register
Receive Port 15 Control Register
4.4 Transmit Port Registers (2xx)
OFFSET/
NAME
REGISTER
SECTION
ADDRESS
0200
0204
0208
020C
0210
0214
0218
021C
0220
0224
0228
022C
0230
0234
0238
023C
TP0CR
TP1CR
TP2CR
TP3CR
TP4CR
TP5CR
TP6CR
TP7CR
TP8CR
TP9CR
TP10CR
TP11CR
TP12CR
TP13CR
TP14CR
TP15CR
Transmit Port 0 Control Register
Transmit Port 1 Control Register
Transmit Port 2 Control Register
Transmit Port 3 Control Register
Transmit Port 4 Control Register
Transmit Port 5 Control Register
Transmit Port 6 Control Register
Transmit Port 7 Control Register
Transmit Port 8 Control Register
Transmit Port 9 Control Register
Transmit Port 10 Control Register
Transmit Port 11 Control Register
Transmit Port 12 Control Register
Transmit Port 13 Control Register
Transmit Port 14 Control Register
Transmit Port 15 Control Register
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
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4.5 Channelized Port Registers (3xx)
OFFSET/
NAME
REGISTER
SECTION
ADDRESS
0300
0304
0308
030C
0310
0314
0318
031C
0320
0324
0328
032C
0330
0334
0338
033C
0340
0344
0348
034C
0350
0354
0358
035C
0360
0364
0368
036C
0370
0374
0378
037C
CP0RDIS
CP0RD
Channelized Port 0 Register Data Indirect Select
Channelized Port 0 Register Data
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
6.3
CP1RDIS
CP1RD
Channelized Port 1 Register Data Indirect Select
Channelized Port 1 Register Data
CP2RDIS
CP2RD
Channelized Port 2 Register Data Indirect Select
Channelized Port 2 Register Data
CP3RDIS
CP3RD
Channelized Port 3 Register Data Indirect Select
Channelized Port 3 Register Data
CP4RDIS
CP4RD
Channelized Port 4 Register Data Indirect Select
Channelized Port 4 Register Data
CP5RDIS
CP5RD
Channelized Port 5 Register Data Indirect Select
Channelized Port 5 Register Data
CP6RDIS
CP6RD
Channelized Port 6 Register Data Indirect Select
Channelized Port 6 Register Data
CP7RDIS
CP7RD
Channelized Port 7 Register Data Indirect Select
Channelized Port 7 Register Data
CP8RDIS
CP8RD
Channelized Port 8 Register Data Indirect Select
Channelized Port 8 Register Data
CP9RDIS
CP9RD
Channelized Port 9 Register Data Indirect Select
Channelized Port 9 Register Data.
CP10RDIS
CP10RD
CP11RDIS
CP11RD
CP12RDIS
CP12RD
CP13RDIS
CP13RD
CP14RDIS
CP14RD
CP15RDIS
CP15RD
Channelized Port 10 Register Data Indirect Select.
Channelized Port 10 Register Data.
Channelized Port 11 Register Data Indirect Select.
Channelized Port 11 Register Data
Channelized Port 12 Register Data Indirect Select
Channelized Port 12 Register Data
Channelized Port 13 Register Data Indirect Select
Channelized Port 13 Register Data
Channelized Port 14 Register Data Indirect Select
Channelized Port 14 Register Data
Channelized Port 15 Register Data Indirect Select
Channelized Port 15 Register Data
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4.6 HDLC Registers (4xx)
OFFSET/
NAME
REGISTER
SECTION
ADDRESS
0400
0404
0410
0480
0484
RHCDIS
RHCD
Receive HDLC Channel Definition Indirect Select
Receive HDLC Channel Definition
Receive HDLC maximum Packet Length. One per device.
Transmit HDLC Channel Definition Indirect Select
Transmit HDLC Channel Definition
7.2
7.2
7.2
7.2
7.2
RHPL
THCDIS
THCD
4.7 BERT Registers (5xx)
OFFSET/
NAME
REGISTER
SECTION
ADDRESS
0500
0504
0508
050C
0510
0514
0518
051C
BERTC0
BERTC1
BERT Control 0
6.6
6.6
6.6
6.6
6.6
6.6
6.6
6.6
BERT Control 1
BERTRP0
BERTRP1
BERTBC0
BERTBC1
BERTEC0
BERTEC1
BERT Repetitive Pattern Set 0 (lower word)
BERT Repetitive Pattern Set 1 (upper word)
BERT Bit Counter 0 (lower word)
BERT Bit Counter 1 (upper word)
BERT Error Counter 0 (lower word)
BERT Error Counter 1 (upper word)
4.8 Receive DMA Registers (7xx)
OFFSET/
NAME
REGISTER
SECTION
ADDRESS
0700
0704
0708
070C
0710
0714
0718
071C
0730
0734
0738
073C
0740
0744
0750
0754
0770
0774
0780
0790
0794
RFQBA0
RFQBA1
RFQEA
Receive Free-Queue Base Address 0 (lower word)
Receive Free-Queue Base Address 1 (upper word)
Receive Free-Queue End Address
9.2.3
9.2.3
9.2.3
9.2.3
9.2.3
9.2.3
9.2.3
9.2.3
9.2.4
9.2.4
9.2.4
9.2.4
9.2.4
9.2.4
9.2.2
9.2.2
9.3.5
9.3.5
9.2.3/9.2.4
9.2.1
9.2.1
RFQSBSA
RFQLBWP
RFQSBWP
RFQLBRP
RFQSBRP
RDQBA0
RDQBA1
RDQEA
Receive Free-Queue Small Buffer Start Address
Receive Free-Queue Large Buffer Host Write Pointer
Receive Free-Queue Small Buffer Host Write Pointer
Receive Free-Queue Large Buffer DMA Read Pointer
Receive Free-Queue Small Buffer DMA Read Pointer
Receive Done-Queue Base Address 0 (lower word)
Receive Done-Queue Base Address 1 (upper word)
Receive Done-Queue End Address
RDQRP
Receive Done-Queue Host Read Pointer
Receive Done-Queue DMA Write Pointer
Receive Done-Queue FIFO Flush Timer
Receive Descriptor Base Address 0 (lower word)
Receive Descriptor Base Address 1 (upper word)
Receive DMA Configuration Indirect Select
Receive DMA Configuration
RDQWP
RDQFFT
RDBA0
RDBA1
RDMACIS
RDMAC
RDMAQ
RLBS
Receive DMA Queues Control
Receive Large Buffer Size
RSBS
Receive Small Buffer Size
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4.9 Transmit DMA Registers (8xx)
OFFSET/
NAME
REGISTER
SECTION
ADDRESS
0800
0804
0808
080C
0810
0830
0834
0838
083C
0840
0844
0850
0854
0870
0874
0880
TPQBA0
TPQBA1
TPQEA
TPQWP
TPQRP
Transmit Pending-Queue Base Address 0 (lower word)
Transmit Pending-Queue Base Address 1 (upper word)
Transmit Pending-Queue End Address
9.3.3
9.3.3
9.3.3
Transmit Pending-Queue Host Write Pointer
Transmit Pending-Queue DMA Read Pointer
Transmit Done-Queue Base Address 0 (lower word)
Transmit Done-Queue Base Address 1 (upper word)
Transmit Done-Queue End Address
9.3.3
9.3.3
TDQBA0
TDQBA1
TDQEA
TDQRP
9.3.4
9.3.4
9.3.4
Transmit Done-Queue Host Read Pointer
Transmit Done-Queue DMA Write Pointer
Transmit Done-Queue FIFO Flush Timer
Transmit Descriptor Base Address 0 (lower word)
Transmit Descriptor Base Address 1 (upper word)
Transmit DMA Configuration Indirect Select
Transmit DMA Configuration
9.3.4
TDQWP
TDQFFT
TDBA0
9.3.4
9.3.4
9.3.2
TDBA1
9.3.2
TDMACIS
TDMAC
TDMAQ
9.3.5
9.3.5
Transmit DMA Queues Control
9.3.3/9.3.4
4.10FIFO Registers (9xx)
OFFSET/
NAME
REGISTER
SECTION
ADDRESS
0900
0904
0910
0914
0920
0924
0980
0984
0990
0994
09A0
09A4
RFSBPIS
RFSBP
RFBPIS
RFBP
Receive FIFO Starting Block Pointer Indirect Select
Receive FIFO Starting Block Pointer
Receive FIFO Block Pointer Indirect Select
Receive FIFO Block Pointer
8.2
8.2
8.2
8.2
8.2
8.2
8.2
8.2
8.2
8.2
8.2
8.2
RFHWMIS Receive FIFO High-Watermark Indirect Select
RFHWM
TFSBPIS
TFSBP
TFBPIS
TFBP
TFLWMIS
TFLWM
Receive FIFO High Watermark
Transmit FIFO Starting Block Pointer Indirect Select
Transmit FIFO Starting Block Pointer
Transmit FIFO Block Pointer Indirect Select
Transmit FIFO Block Pointer
Transmit FIFO Low-Watermark Indirect Select
Transmit FIFO Low Watermark
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DS31256 256-Channel, High-Throughput HDLC Controller
4.11PCI Configuration Registers for Function 0 (PIDSEL/Axx)
OFFSET/
ADDRESS
0x000/0A00
0x004/0A04
0x008/0A08
0x00C/0A0C
0x010/0A10
0x03C/0A3C
NAME
REGISTER
SECTION
PVID0
PCMD0
PRCC0
PLTH0
PDCM
PINTL0
PCI Vendor ID/Device ID 0
10.2
10.2
10.2
10.2
10.2
10.2
PCI Command Status 0
PCI Revision ID/Class Code 0
PCI Cache Line Size/Latency Timer/Header Type 0
PCI Device Configuration Memory Base Address
PCI Interrupt Line and Pin/Min Grant/Max Latency 0
4.12PCI Configuration Registers for Function 1 (PIDSEL/Bxx)
OFFSET/
NAME
REGISTER
SECTION
ADDRESS
0x100/0B00
0x104/0B04
0x108/0B08
0x10C/0B0C
0x110/0B10
0x13C/0B3C
PVID1
PCMD1
PRCC1
PLTH1
PLBM
PCI Vendor ID/Device ID 1
10.2
10.2
10.2
10.2
10.2
10.2
PCI Command Status 1
PCI Revision ID/Class Code 1
PCI Cache Line Size/Latency Timer/Header Type 1
PCI Device Local Base Memory Base Address
PCI Interrupt Line and Pin/Min Grant/Max Latency 1
PINTL1
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5. GENERAL DEVICE CONFIGURATION AND STATUS/INTERRUPT
5.1 Master Reset and ID Register Description
The master reset and ID (MRID) register can be used to globally reset the device. When the RST bit is
set to 1, all the internal registers (except the PCI configuration registers) are placed into their default
state, which is 0000h. The host must set the RST bit back to 0 before the device can be programmed for
normal operation. The RST bit does not force the PCI outputs to tri-state as does the hardware reset,
which is invoked by the PRST pin. A reset invoked by the PRST pin forces the RST bit to 0 as well as
the rest of the internal configuration registers. See Section 2 for more details about device initialization.
The upper byte of the MRID register is read-only and it can be read by the host to determine the chip
revision. Contact the factory for specifics on the meaning of the value read from the ID0 to ID7 bits.
Register Name:
MRID
Register Description: Master Reset and ID Register
Register Address:
0000h
Bit #
Name
Default
7
n/a
0
6
n/a
0
5
n/a
0
4
n/a
0
3
n/a
0
2
n/a
0
1
n/a
0
0
RST
0
Bit #
Name
Default
15
ID7
0
14
ID6
0
13
ID5
0
12
ID4
0
11
ID3
0
10
ID2
0
9
ID1
0
8
ID0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Master Software Reset (RST)
0 = normal operation
1 = force all internal registers (except LBBMC) to their default value of 0000h
Bits 8 to 15/Chip Revision ID Bit 0 to 7 (ID0 to ID7). Read-only. Contact the factory for details on the meaning
of the ID bits.
5.2 Master Configuration Register Description
The master configuration (MC) register is used by the host to enable the receive and transmit DMAs as
well as to control their PCI bus bursting attributes and select which port the BERT is dedicated to.
Register Name:
MC
Register Description: Master Configuration Register
Register Address:
0010h
Bit #
Name
Default
7
6
5
TDT1
0
4
TDT0
0
3
TDE
0
2
RDT1
0
1
DT0
0
0
RDE
0
BPS0
0
PBO
0
Bit #
Name
Default
15
TFPC1
0
14
TFPC0
0
13
RFPC1
0
12
RFPC0
0
11
BPS4
0
10
BPS3
0
9
BPS2
0
8
BPS1
0
Note: Bits that are underlined are read-only; all other bits are read-write.
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DS31256 256-Channel, High-Throughput HDLC Controller
Bit 0/Receive DMA Enable (RDE). This bit is used to enable the receive DMA. When it is set to 0, the receive
DMA does not pass any data from the receive FIFO to the PCI bus, even if one or more HDLC channels is
enabled. On device initialization, the host should fully configure the receive DMA before enabling it through this
bit.
0 = receive DMA is disabled
1 = receive DMA is enabled
Bit 1/Receive DMA Throttle Select Bit 0 (RDT0); Bit 2/Receive DMA Throttle Select Bit 1 (RDT1). These
two bits select the maximum burst length that the receive DMA is allowed on the PCI bus. The DMA can be
restricted to a maximum burst length of just 32 dwords (128 Bytes) or it can be incrementally adjusted up to 256
dwords (1024 Bytes). The host selects the optimal length based on a number of factors, including the system
environment for the PCI bus, the number of HDLC channels being used, and the trade-off between channel latency
and bus efficiency.
00 = burst length maximum is 32 dwords
01 = burst length maximum is 64 dwords
10 = burst length maximum is 128 dwords
11 = burst length maximum is 256 dwords
Bit 3/Transmit DMA Enable (TDE). This bit is used to enable the transmit DMA. When it is set to 0, the
transmit DMA does not pass any data from the PCI bus to the transmit FIFO, even if one or more HDLC channels
is enabled. On device initialization, the host should fully configure the transmit DMA before enabling it through
this bit.
0 = transmit DMA is disabled
1 = transmit DMA is enabled
Bit 4/Transmit DMA Throttle Select Bit 0 (TDT0); Bit 5/Transmit DMA Throttle Select Bit 1 (TDT1). These
two bits select the maximum burst length the transmit DMA is allowed on the PCI bus. The DMA can be restricted
to a maximum burst length of just 32 dwords (128 Bytes) or it can be incrementally adjusted up to 256 dwords
(1024 Bytes). The host selects the optimal length based on a number of factors, including the system environment
for the PCI bus, the number of HDLC channels being used, and the trade-off between channel latency and bus
efficiency.
00 = burst length maximum is 32 dwords
01 = burst length maximum is 64 dwords
10 = burst length maximum is 128 dwords
11 = burst length maximum is 256 dwords
Bit 6/PCI Bus Orientation (PBO). This bit selects whether HDLC packet data on the PCI bus operates in either
Little Endian or Big Endian format. Little Endian byte ordering places the least significant byte at the lowest
address, while Big Endian places the least significant byte at the highest address. This bit setting only affects
HDLC data on the PCI bus. All other PCI bus transactions to the internal device configuration registers, PCI
configuration registers, and local bus are always in Little Endian format.
0 = HDLC packet data on the PCI bus is in Little Endian format
1 = HDLC packet data on the PCI bus is in Big Endian format
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DS31256 256-Channel, High-Throughput HDLC Controller
Bits 7 to 11/BERT Port Select Bits 0 to 4 (BPS0 to BPS4). These bits select which port has the dedicated
resources of the BERT.
00000 = Port 0
00001 = Port 1
00010 = Port 2
00011 = Port 3
00100 = Port 4
00101 = Port 5
00110 = Port 6
00111 = Port 7
01000 = Port 8
01001 = Port 9
01010 = Port 10
01011 = Port 11
01100 = Port 12
01101 = Port 13
01110 = Port 14
01111 = Port 15
10000 = Port 0 (high speed)
10001 = Port 1 (high speed)
10010 = Port 2 (high speed)
10011 = n/a
11000 = n/a
11001 = n/a
11010 = n/a
11011 = n/a
11100 = n/a
11101 = n/a
11110 = n/a
11111 = n/a
10100 = n/a
10101 = n/a
10110 = n/a
10111 = n/a
Bit 12/Receive FIFO Priority Control Bit 0 (RFPC0); Bit 13/Receive FIFO Priority Control Bit 1 (RFPC1).
These bits select the algorithm the FIFO uses to determine which HDLC channel gets the highest priority to the
DMA to transfer data from the FIFO to the PCI bus. In the priority decoded scheme, the lower the HDLC channel
numbers, generally the higher the priority. In schemes ’10 and ’11, the upper priority decode channels have
priority over the lower priority decode channels.
00 = all HDLC channels are serviced round robin
01 = HDLC channels 1 to 3 are priority decoded; other HDLC channels are round robin
10 = HDLC channels 16 to 1 are priority decoded; HDLC channels 17-up are round robin
11 = HDLC channels 64 to 1 are priority decoded; HDLC channels 65-up are round robin
Bit 14/Transmit FIFO Priority Control Bit 0 (TFPC0); Bit 15/Transmit FIFO Priority Control Bit 1
(TFPC1). These two bits select the algorithm the FIFO uses to determine which HDLC channel gets the highest
priority to the DMA to transfer data from the PCI bus to the FIFO. In the schemes ’01 and ‘11m upper priority
decode channels have priority over the lower priority decode channels.
00 = all HDLC channels are serviced round robin
01 = HDLC channels 1 to 3 are priority decoded; other HDLC channels are round robin
10 = HDLC channels 16 to 1 are priority decoded; other HDLC channels 17-up re round robin
11 = HDLC channels 64 to 1 are priority decoded; other HDLC channels 65-up are round robin
5.3 Status and Interrupt
5.3.1 General Description of Operation
There are three status registers in the device: status master (SM), status for the receive V.54 loopback
detector (SV54), and status for DMA (SDMA). These registers report events in real-time by setting a bit
within the register to 1. All bits that have been set within the register are cleared when the register is
read, and the bit is not set again until the event has occurred again. Each bit can generate an interrupt at
the PCI bus through the PINTA output signal pin, and, if the local bus is in the configuration mode, then
an interrupt also be created at the LINT output signal pin. Each status register has an associated interrupt
mask register, which can allow/deny interrupts from being generated on a bit-by-bit basis. All status
registers remain active even if the associated interrupt is disabled.
SM Register
The status master (SM) register reports events that occur at the port interface, at the BERT receiver, at
the PCI bus, and at the local bus. See Figure 5-1 for details.
The port interface reports change-of-frame alignment (COFA) events. If the software detects that one of
these bits is set, the software must begin polling the RP[n]CR or TP[n]CR registers of each active port (a
maximum of 16 reads) to determine which port or ports has incurred a COFA. Also, the host can
allow/deny the COFA indications to be passed to the SRCOFA and STCOFA status bits through the
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DS31256 256-Channel, High-Throughput HDLC Controller
interrupt enable for the receive COFA (IERC) and interrupt enable for the transmit COFA (IETC)
control bits in the RP[n]CR and TP[n]CR registers, respectively.
The BERT receiver reports three events: a change in the receive synchronizer status, a bit error being
detected, and if either the bit counter or the error counter overflows. Each of these events can be masked
within the BERT function through the BERT control register (BERTC0). If the software detects that the
BERT has reported an event, the software must read the BERT status register (BERTEC0) to determine
which event(s) has occurred.
The SM register also reports events as they occur in the PCI bus and the local bus. There are no control
bits to stop these events from being reported in the SM register. When the local bus is operated in the
PCI bridge mode, SM reports any interrupts detected through the local bus LINT input signal pin and if
any timing errors occur because the external timing signal LRDY. When the local bus is operated in the
configuration mode, the LBINT and LBE bits are meaningless and should be ignored.
SV54 Register
The status for receive V.54 detector (SV54) register reports if the V.54 loopback detector has either
timed out in its search for the V.54 loop-up pattern or if the detector has found and verified the loop-
up/down pattern. There is a separate status bit (SLBP) for each port. When set, the host must read the
VTO and VLB status bits in the RP[n]CR register of the corresponding port to find the exact state of the
V.54 detector. When the V.54 detector experiences a timeout in its search for the loop-up code
(VTO = 1), then the SLBP status bit is continuously set until the V.54 detector is reset by the host,
toggling the VRST bit in RP[n]CR register. There are no control bits to stop these events from being
reported in the SV54 register. See Figure 5-1 for details on the status bits and Section 6 for details on the
operation of the V.54 loopback detector.
SDMA Register
The status DMA (SDMA) register reports events pertaining to the receive and transmit DMA blocks as
well as the receive HDLC controller and FIFO. The SDMA reports when the DMA reads from either the
receive free queue or transmit pending queue or writes to the receive or transmit done queues. Also
reported are error conditions that might occur in the access of one of these queues. The SDMA reports if
any of the HDLC channels experiences an FIFO overflow/underflow condition and if the receive HDLC
controller encounters a CRC error, abort signal, or octet length problem on any of the HDLC channels.
The host can determine which specific HDLC channel incurred an FIFO overflow/underflow, CRC error,
octet length error, or abort by reading the status bits as reported in done queues, which are created by the
DMA. There are no control bits to stop these events from being reported in the SDMA register.
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 5-1. Status Register Block Diagram for SM and SV54
Transmit
BERT
Receive
Port I/F # 0
Port I/F # 0
BERTEC0 Bit 1 (BECO)
OR
BERTEC0 Bit 2 (BBCO)
BERTC0 Bit 13 (IEOF)
TCOFA
TP0CR
Bit #14
RCOFA
RP0CR
Bit #14
Change in BERTEC0 Bit 0 (SYNC)
BERTC0 Bit 15 (IESYNC)
BERTEC0 Bit 3 (BED)
BERTC0 Bit 14 (IEBED)
#1
#2
#3
#1
#2
#3
OR
#13
#14
#15
#13
#14
#15
int_bd
OR
OR
SM: Status Master Register
ST
SR
PPERR PSERR
SBERT
LBINT
LBE
n/a
n/a
COFA COFA
SV54: Status for V54 Detector
SLBP13
SLBP15
SLBP14
SLBP5 SLBP4 SLBP3 SLBP2 SLBP1 SLBP0
Change in
V.54 Detector
(SLBP)
Change in
Change in
V.54 Detector
(SLBP)
Change in
V.54 Detector
(SLBP)
V.54 Detector
(SLBP)
Port #1
Port #0
Port #14
Port #15
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DS31256 256-Channel, High-Throughput HDLC Controller
5.3.2 Status and Interrupt Register Description
Register Name:
SM
Register Description: Status Master Register
Register Address:
0020h
Bit #
Name
Default
7
n/a
0
6
5
n/a
0
4
PPERR
0
3
PSERR
0
2
SBERT
0
1
0
n/a
STCOFA SRCOFA
0
0
0
Bit #
Name
Default
15
LBINT
0
14
LBE
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
n/a
0
8
n/a
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Status Bit for Change-of-Frame Alignment (SRCOFA). This status bit is set to 1 if one or more of the
receive ports has experienced a COFA event. The host must read the RCOFA bit in the receive port control
registers (RP[n]CR) of each active port to determine which port or ports has seen the COFA. The SRCOFA bit is
cleared when read and is not set again until the one or more receive ports has experienced another COFA. If
enabled through the SRCOFA bit in the interrupt mask for SM (ISM), the setting of this bit causes a hardware
interrupt at the PCI bus through the PINTA signal pin and also at the LINT if the local bus is in configuration
mode.
Bit 1/Status Bit for Transmit Change-of-Frame Alignment (STCOFA). This status bit is set to 1 if one or more
of the transmit ports has experienced a COFA event. The host must read the TCOFA bit in the transmit port
control registers (TP[n]CR) of each active port to determine which port or ports has seen the COFA. The STCOFA
bit is cleared when read and is not set again until one or more transmit ports has experienced another COFA. If
enabled through the STCOFA bit in the ISM, the setting of this bit causes a hardware interrupt at the PCI bus
through the PINTA signal pin and also at the LINT if the local bus is in configuration mode.
Bit 2/Status Bit for Change of State in BERT (SBERT). This status bit is set to 1 if there is a major change of
state in the BERT receiver. A major change of state is defined as either a change in the receive synchronization
(i.e., the BERT has gone into or out of receive synchronization), a bit error has been detected, or an overflow has
occurred in either the bit counter or the error counter. The host must read the status bits of the BERT in the BERT
status register (BERTEC0) to determine the change of state. The SBERT bit is cleared when read and is not set
again until the BERT has experienced another change of state. If enabled through the SBERT bit in the ISM, the
setting of this bit causees a hardware interrupt at the PCI bus through the PINTA signal pin and also at the LINT if
the local bus is in configuration mode.
Bit 3/Status Bit for PCI System Error (PSERR). This status bit is a software version of the PCI bus hardware
pin PSERR. It is set to 1 if the PCI bus detects an address parity error or other PCI bus error. The PSERR bit is
cleared when read and is not set again until another PCI bus error has occurred. If enabled through the PSERR bit
in the ISM, the setting of this bit causes a hardware interrupt at the PCI bus through the PINTA signal pin and also
at the LINT if the local bus is in configuration mode. This status bit is also reported in the control/status register in
the PCI configuration registers (Section 10).
Bit 4/Status Bit for PCI System Error (PPERR). This status bit is a software version of the PCI bus hardware
pin PPERR. It is set to 1 if the PCI bus detects parity errors on the PAD and PCBE buses as experienced or
reported by a target. The PPERR bit is cleared when read and is not set again until another parity error has been
detected. If enabled through the PPERR bit in the interrupt mask for SM (ISM), the setting of this bit causes a
hardware interrupt at the PCI bus through the PINTA signal pin and also at the LINT if the local bus is in
configuration mode. This status bit is also reported in the control/status register in the PCI configuration registers
(Section 10).
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DS31256 256-Channel, High-Throughput HDLC Controller
Bit 14/Status Bit for Local Bus Error (LBE). This status bit applies to the local bus when it is operated in PCI
bridge mode. It is set to 1 when the local bus LRDY signal is not detected within nine LCLK periods. This
indicates to the host that an aborted local bus access has occurred. If enabled through the LBE bit in the interrupt
mask for SM (ISM), the setting of this bit causes a hardware interrupt at the PCI bus through the PINTA signal pin
and also at the LINT if the local bus is in configuration mode. The LBE bit is meaningless when the local bus is
operated in the configuration mode and should be ignored.
Bit 15/Status Bit for Local Bus Interrupt (LBINT). This status bit is set to 1 if the local bus LINT signal has
been detected as asserted. This status bit is only valid when the local bus is operated in PCI bridge mode. The
LBINT bit is cleared when read and is not set again until the LINT signal pin once again has been detected as
asserted. If enabled through the LBINT bit in the interrupt mask for SM (ISM), the setting of this bit causes a
hardware interrupt at the PCI bus through the PINTA signal pin. The LBINT bit is meaningless when the local bus
is operated in the configuration mode and should be ignored.
Register Name:
ISM
Register Description: Interrupt Mask Register for SM
Register Address:
0024h
Bit #
Name
Default
7
n/a
0
6
n/a
0
5
n/a
0
4
PPERR
0
3
PSERR
0
2
SBERT
0
1
0
STCOFA SRCOFA
0
0
Bit #
Name
Default
15
LBINT
0
14
LBE
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
n/a
0
8
n/a
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Status Bit for Receive Change-of-Frame Alignment (SRCOFA)
0 = interrupt masked
1 = interrupt unmasked
Bit 1/Status Bit for Transmit Change-of-Frame Alignment (STCOFA)
0 = interrupt masked
1 = interrupt unmasked
Bit 2/Status Bit for Change of State in BERT (SBERT)
0 = interrupt masked
1 = interrupt unmasked
Bit 3/Status Bit for PCI System Error (PSERR)
0 = interrupt masked
1 = interrupt unmasked
Bit 4/Status Bit for PCI System Error (PPERR)
0 = interrupt masked
1 = interrupt unmasked
Bit 14/Status Bit for Local Bus Error (LBE)
0 = interrupt masked
1 = interrupt unmasked
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DS31256 256-Channel, High-Throughput HDLC Controller
Bit 15/Status Bit for Local Bus Interrupt (LBINT)
0 = interrupt masked
1 = interrupt unmasked
Register Name:
SV54
Register Description: Status Register for the Receive V.54 Detector
Register Address:
0030h
Bit #
Name
Default
7
6
5
SLBP5
0
4
SLBP4
0
3
SLBP3
0
2
SLBP2
0
1
SLBP1
0
0
SLBP0
0
SLBP7
0
SLBP6
0
Bit #
Name
Default
15
SLBP15
0
14
SLBP14
0
13
SLBP13
0
12
SLBP12
0
11
SLBP11
0
10
SLBP10
0
9
SLBP9
0
8
SLBP8
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 15/Status Bits for Change of State in Receive V.54 Loopback Detector (SLBP0 to SLBP15). These
status bits are set to 1 when the V.54 loopback detector within the port has either timed out in its search for the
loop-up pattern or it has detected and validated the loop-up or loop-down pattern. There is one status bit per port.
The host must read the VTO and VLB status bits in RP[n]CR register of the corresponding port to determine the
exact status of the V.54 detector. If the V.54 detector has timed out in its search for the loop-up code (VTO = 1),
then SLBP is continuously set until the host resets the V.54 detector by toggling the VRST bit in RP[n]CR. If
enabled through the SLBP[n] bit in the interrupt mask for SV54 (ISV54), the setting of these bits causes a
hardware interrupt at the PCI bus through the PINTA signal pin and also at the LINT if the local bus is in
configuration mode. See Section 6 for specific details about the operation of the V.54 loopback detector.
Register Name:
ISV54
Register Description: Interrupt Mask Register for SV54
Register Address:
0034h
Bit #
Name
Default
7
6
5
SLBP5
0
4
SLBP4
0
3
SLBP3
0
2
SLBP2
0
1
SLBP1
0
0
SLBP0
0
SLBP7
0
SLBP6
0
Bit #
Name
Default
15
SLBP15
0
14
SLBP14
0
13
SLBP13
0
12
SLBP12
0
11
SLBP11
0
10
SLBP10
0
9
SLBP9
0
8
SLBP8
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 15/Status Bit for Change of State in Receive V.54 Loopback Detector (SLBP0 to SLBP15)
0 = interrupt masked
1 = interrupt unmasked
39 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
SDMA
Register Description: Status Register for DMA
Register Address:
0028h
Bit #
Name
Default
7
6
RLBR
0
5
ROVFL
0
4
RLENC
0
3
RABRT
0
2
RCRCE
0
1
n/a
0
0
n/a
0
RLBRE
0
Bit #
15
TDQWE
0
14
TDQW
0
13
TPQR
0
12
TUDFL
0
11
RDQWE
0
10
RDQW
0
9
RSBRE
0
8
RSBR
0
Name
Default
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 2/Status Bit for Receive HDLC CRC Error (RCRCE). This status bit is set to 1 if any of the receive HDLC
channels experiences a CRC checksum error. The RCRCE bit is cleared when read and is not set again until
another CRC checksum error has occurred. If enabled through the RCRCE bit in the interrupt mask for SDMA
(ISDMA), the setting of this bit causes a hardware interrupt at the PCI bus through the PINTA signal pin and also
at the LINT if the local bus is in configuration mode.
Bit 3/Status Bit for Receive HDLC Abort Detected (RABRT). This status bit is set to 1 if any of the receive
HDLC channels detects an abort. The RABRT bit is cleared when read and is not set again until another abort has
been detected. If enabled through the RABRT bit in the interrupt mask for SDMA (ISDMA), the setting of this bit
causes a hardware interrupt at the PCI bus through the PINTA signal pin and also at the LINT if the local bus is in
configuration mode.
Bit 4/Status Bit for Receive HDLC Length Check (RLENC). This status bit is set to 1 if any of the HDLC
channels:
•
•
•
exceeds the octet length count (if so enabled to check for octet length)
receives an HDLC packet that does not meet the minimum length criteria of either 4 or 6 bytes
experiences a nonintegral number of octets between opening and closing flags
The RLENC bit is cleared when read and is not set again until another length violation has occurred. If enabled
through the RLENC bit in the interrupt mask for SDMA (ISDMA), the setting of this bit causes a hardware
interrupt at the PCI bus through the PINTA signal pin and also at the LINT if the local bus is in configuration
mode.
Bit 5/Status Bit for Receive FIFO Overflow (ROVFL). This status bit is set to 1 if any of the HDLC channels
experiences an overflow in the receive FIFO. The ROVFL bit is cleared when read and is not set again until
another overflow has occurred. If enabled through the ROVFL bit in the interrupt mask for SDMA (ISDMA), the
setting of this bit causes a hardware interrupt at the PCI bus through the PINTA signal pin and also at the LINT if
the local bus is in configuration mode.
Bit 6/Status Bit for Receive DMA Large Buffer Read (RLBR). This status bit is set to 1 each time the receive
DMA completes a single read or a burst read of the large buffer free queue. The RLBR bit is cleared when read
and is not be set again until another read of the large buffer free queue has occurred. If enabled through the RLBR
bit in the interrupt mask for SDMA (ISDMA), the setting of this bit causes a hardware interrupt at the PCI bus
through the PINTA signal pin and also at the LINT if the local bus is in configuration mode.
Bit 7/Status Bit for Receive DMA Large Buffer Read Error (RLBRE). This status bit is set to 1 each time the
receive DMA tries to read the large buffer free queue and it is empty. The RLBRE bit is cleared when read and is
not set again until another read of the large buffer free queue detects that it is empty. If enabled through the
RLBRE bit in the interrupt mask for SDMA (ISDMA), the setting of this bit causes a hardware interrupt at the PCI
bus through the PINTA signal pin and also at the LINT if the local bus is in configuration mode.
40 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Bit 8/Status Bit for Receive DMA Small Buffer Read (RSBR). This status bit is set to 1 each time the receive
DMA completes a single read or a burst read of the small buffer free queue. The RSBR bit is cleared when read
and is not set again until another read of the small buffer free queue has occurred. If enabled through the RSBR bit
in the interrupt mask for SDMA (ISDMA), the setting of this bit causes a hardware interrupt at the PCI bus
through the PINTA signal pin and also at the LINT if the local bus is in configuration mode.
Bit 9/Status Bit for Receive DMA Small Buffer Read Error (RSBRE). This status bit is set to 1 each time the
receive DMA tries to read the small buffer free queue and it is empty. The RSBRE bit is cleared when read and is
not set again until another read of the small buffer free queue detects that it is empty. If enabled through the
RSBRE bit in the interrupt mask for SDMA (ISDMA), the setting of this bit causes a hardware interrupt at the PCI
bus through the PINTA signal pin and also at the LINT if the local bus is in configuration mode.
Bit 10/Status Bit for Receive DMA Done-Queue Write (RDQW). This status bit is set to 1 when the receive
DMA writes to the done queue. Based of the setting of the receive done-queue threshold setting (RDQT0 to
RDQT2) bits in the receive DMA queues-control (RDMAQ) register, this bit is set either after each write or after a
programmable number of writes from 2 to 128 (Section 9.2.4). The RDQW bit is cleared when read and is not set
again until another write to the done queue has occurred. If enabled through the RDQW bit in the interrupt mask
for SDMA (ISDMA), the setting of this bit causes a hardware interrupt at the PCI bus through the PINTA signal
pin and also at the LINT if the local bus is in configuration mode.
Bit 11/Status Bit for Receive DMA Done-Queue Write Error (RDQWE). This status bit is set to 1 each time
the receive DMA tries to write to the done queue and it is full. The RDQWE bit is cleared when read and is not set
again until another write to the done queue detects that it is full. If enabled through the RDQWE bit in the interrupt
mask for SDMA (ISDMA), the setting of this bit causes a hardware interrupt at the PCI bus through the PINTA
signal pin and also at the LINT if the local bus is in configuration mode.
Bit 12/Status Bit for Transmit FIFO Underflow (TUDFL). This status bit is set to 1 if any of the HDLC
channels experiences an underflow in the transmit FIFO. The TUDFL bit is cleared when read and is not set again
until another underflow has occurred. If enabled through the TUDFL bit in the interrupt mask for SDMA
(ISDMA), the setting of this bit causes a hardware interrupt at the PCI bus through the PINTA signal pin and also
at the LINT if the local bus is in configuration mode.
Bit 13/Status Bit for Transmit DMA Pending-Queue Read (TPQR). This status bit is set to 1 each time the
transmit DMA reads the pending queue. The TPQR bit is cleared when read and is not set again until another read
of the pending queue has occurred. If enabled through the TPQR bit in the interrupt mask for SDMA (ISDMA),
the setting of this bit causes a hardware interrupt at the PCI bus through the PINTA signal pin and also at the LINT
if the local bus is in configuration mode.
Bit 14/Status Bit for Transmit DMA Done-Queue Write (TDQW). This status bit is set to 1 when the transmit
DMA writes to the done queue. Based on the setting of the transmit done-queue threshold setting (TDQT0 to
TDQT2) bits in the transmit DMA queues-control (TDMAQ) register, this bit is set either after each write or after
a programmable number of writes from 2 to 128 (Section 9.2.4). The TDQW bit is cleared when read and is not set
again until another write to the done queue has occurred. If enabled through the TDQW bit in the interrupt mask
for SDMA (ISDMA), the setting of this bit causes a hardware interrupt at the PCI bus through the PINTA signal
pin and also at the LINT if the local bus is in configuration mode.
Bit 15/Status Bit for Transmit DMA Done-Queue Write Error (TDQWE). This status bit is set to 1 each time
the transmit DMA tries to write to the done queue and it is full. The TDQWE bit is cleared when read and is not
set again until another write to the done queue detects that it is full. If enabled through the TDQWE bit in the
interrupt mask for SDMA (ISDMA), the setting of this bit causes a hardware interrupt at the PCI bus through the
PINTA signal pin and also at the LINT if the local bus is in configuration mode.
41 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
ISDMA
Register Description: Interrupt Mask Register for SDMA
Register Address:
002Ch
Bit #
Name
Default
7
6
5
ROVFL
0
4
RLENC
0
3
RABRT
0
2
RCRCE
0
1
n/a
0
0
n/a
0
RLBRE
0
RLBR
0
Bit #
Name
Default
15
TDQWE
0
14
TDQW
0
13
TPQR
0
12
TUDFL
0
11
RDQWE
0
10
RDQW
0
9
RSBRE
0
8
RSBR
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 2/Status Bit for Receive HDLC CRC Error (RCRCE)
0 = interrupt masked
1 = interrupt unmasked
Bit 3/Status Bit for Receive HDLC Abort Detected (RABRT)
0 = interrupt masked
1 = interrupt unmasked
Bit 4/Status Bit for Receive HDLC Length Check (RLENC)
0 = interrupt masked
1 = interrupt unmasked
Bit 5/Status Bit for Receive FIFO Overflow (ROVFL)
0 = interrupt masked
1 = interrupt unmasked
Bit 6/Status Bit for Receive DMA Large Buffer Read (RLBR)
0 = interrupt masked
1 = interrupt unmasked
Bit 7/Status Bit for Receive DMA Large Buffer Read Error (RLBRE)
0 = interrupt masked
1 = interrupt unmasked
Bit 8/Status Bit for Receive DMA Small Buffer Read (RSBR)
0 = interrupt masked
1 = interrupt unmasked
Bit 9/Status Bit for Receive DMA Small Buffer Read Error (RSBRE)
0 = interrupt masked
1 = interrupt unmasked
Bit 10/Status Bit for Receive DMA Done-Queue Write (RDQW)
0 = interrupt masked
1 = interrupt unmasked
Bit 11/Status Bit for Receive DMA Done-Queue Write Error (RDQWE)
0 = interrupt masked
1 = interrupt unmasked
Bit 12/Status Bit for Transmit FIFO Underflow (TUDFL)
0 = interrupt masked
1 = interrupt unmasked
42 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Bit 13/Status Bit for Transmit DMA Pending-Queue Read (TPQR)
0 = interrupt masked
1 = interrupt unmasked
Bit 14/Status Bit for Transmit DMA Done-Queue Write (TDQW)
0 = interrupt masked
1 = interrupt unmasked
Bit 15/Status Bit for Transmit DMA Done-Queue Write Error (TDQWE)
0 = interrupt masked
1 = interrupt unmasked
5.4 Test Register Description
Register Name:
TEST
Register Description: Test Register
Register Address:
0050h
Bit #
Name
Default
7
n/a
0
6
n/a
0
5
n/a
0
4
n/a
0
3
n/a
0
2
n/a
0
1
n/a
0
0
FT
0
Bit #
Name
Default
15
n/a
0
14
n/a
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
n/a
0
8
n/a
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Factory Test (FT). This bit is used by the factory to place the DS31256 into the test mode. For normal
device operation, this bit should be set to 0 whenever this register is written to. Setting this bit places the RAMs
into a low-power standby mode.
Bit 1 to 15/Device Internal Test Bits. Bits 1 to 15 are for internal (Dallas Semiconductor) test use only, not user
test-mode controls. Values of these bits should always be 0. If any of these bits are set to 1 the device does not
function properly.
43 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
6. LAYER 1
6.1 General Description
Figure 6-1 shows the Layer 1 block. Each of the DS31256’s 16 Layer 1 ports can be configured to
support either a channelized application or an unchannelized application. Users can mix the applications
on the ports as needed. Some or all of the ports can be channelized, while the others can be configured as
unchannelized. A channelized application is defined as one that requires an 8kHz synchronization pulse
to subdivide the serial data stream into a set of 8-bit DS0 channels (also called time slots), which are
time division multiplexed (TDM) one after another. Ports running a channelized application require an
8kHz pulse at the RS and TS signals. An unchannelized application is defined as a synchronous clock
and data interface. No synchronization pulse is required and the RS and TS signals are forced low in this
application. Section 17 contains examples of some various configurations.
In channelized applications, the Layer 1 ports can be configured to operate in one of four modes, as
shown in Table 6-A. Each port is capable of handling one, two, or four T1/E1 data streams. When more
than one T1/E1 data stream is applied to the port, the individual T1/E1 data streams must be TDM into a
single data stream at either a 4.096MHz or 8.192MHz data rate. Since the DS31256 can map any HDLC
channel to any DS0 channel, it can support any form (byte interleaved, frame interleaved, etc.) of TDM
that the application may require. On a DS0-by-DS0 basis, the DS31256 can be configured to process all
8 bits (64kbps), the seven most significant bits (56kbps), or no data.
Table 6-A. Channelized Port Modes
MODE
FUNCTION
T1 (1.544MHz) N x 64kbps or N x 56kbps; where N = 1 to 24 (one T1 data stream)
E1 (2.048MHz) N x 64kbps or N x 56kbps; where N = 1 to 32 (one T1 or E1 data stream)
4.096MHz
8.192MHz
N x 64kbps or N x 56kbps; where N = 1 to 64 (two T1 or E1 data streams)
N x 64kbps or N x 56kbps; where N = 1 to 128 (four T1 or E1 data streams)
Each port in the Layer 1 block is connected to a slow HDLC engine. The slow HDLC engine can handle
channelized applications at speeds up to 8.192Mbps and unchannelized applications at speeds of up to
10Mbps. Ports 0 and 1 have the added capability of fast HDLC engines that can only handle
unchannelized applications but at speeds of up to 52MHz.
Each port has an associated receive port control register (RP[n]CR, where n = 0 to 15) and a transmit
port control register (TP[n]CR where n = 0 to 15). These control registers are defined in detail in
Section 6.2. They control all the circuitry in the Layer 1 block with the exception of the Layer 1 state
machine, which is shown in the center of the block diagram (Figure 6-1).
Each port contains a Layer 1 state machine that connects directly to the slow HDLC engine. It prepares
the raw incoming data for the slow HDLC engine and grooms the outgoing data. The Layer 1 state
machine performs a number of tasks that include the following:
ꢀ Assigning the HDLC channel number to the incoming and outgoing data
ꢀ Channelized local and network loopbacks
ꢀ Channelized selection of 64kbps, 56kbps, or no data
ꢀ Channelized transmits DS0 channel fill of all ones
ꢀ Routing data to and from the BERT function
ꢀ Routing data to the V.54 loop pattern detector
44 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
The DS31256 has a set of three registers per DS0 channel for each port that determine how each DS0
channel is configured. These three registers are defined in Section 6.3. If the fast (52Mbps) HDLC
engine is enabled on port 0, then HDLC channel 1 is assigned to it. Likewise, HDLC channel 2 is
assigned to the fast HDLC engine on port 1 if it is enabled, and HDLC channel 2 is assigned to the fast
HDLC engine on port 2 if it is enabled.
The DS31256 contains an on-board full-featured BERT capable of generating and detecting both
pseudorandom and repeating serial bit patterns. The BERT function is a shared resource among the 16
ports on the DS31256 and can only be assigned to one port at a time. It can be used in both channelized
and unchannelized applications and at speeds up to 52MHz. In channelized applications, data can be
routed to and from any combination of DS0 channels that are being used on the port. The details on the
BERT function are covered in Section 6.5.
The Layer 1 block also contains a V.54 detector. Each of the 16 ports contains a V.54 loop pattern
detector on the receive side. The device can search for the V.54 loop-up and loop-down patterns in both
channelized and unchannelized applications at speeds up to 10MHz. In channelized applications, the
device can be configured to search for the patterns in any combination of DS0 channels. Section 6.4
describes all of the details on the V.54 detector.
45 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 6-1. Layer 1 Block Diagram
1 of 16
V.54
Detector
Layer 1
State Machine
RC
Local
Loop-
Back
(LLB)
Invert
Clock /
Data /
Sync
Over-
Sample
with
RS
RD
Receive
PCLK
SLOW
HDLC
To /
PORT
RAM
(see
Sec.
5.3)
Channel- Channel-
ized
ized
From
FIFO
Block
Local
Loop-
Back
(CLLB)
Network
Loop-
Back
(One
per
LLB
UNLB
Port)
(CNLB)
TC
TS
Over-
Sample
with
Invert
Clock /
Data /
Sync
Transmit
Un-
Channel-
ized
PCLK
Force
TD
All
Network
Loopback
(UNLB)
Ones
BERT/
Fast
Ports 0 & 1 Only
Ports
0, 1, 2
Only
HDLC
Mux
FAST
HDLC
l1_bd
BERT Mux
(Figure 6-7)
46 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 6-2. Port Timing (Channelized and Unchannelized Applications)
RC[n] / TC[n]
Normal Mode
RC[n] / TC[n]
Inverted Mode
Bit 191 or 254
or 510 or 1022
Bit 192 or 255
or 511 or 1023
Bit 0
Bit 1
Last Bit of
the Frame
First Bit of
the Frame
RD[n]
TD[n]
RS[n] / TS[n]
0 Clock Early &
Not Inverted
RS[n] / TS[n]
1/2 Clock Early &
Inverted
RS[n] / TS[n]
1 Clock Early &
Not Inverted
RS[n] / TS[n]
2 Clocks Early &
Not Inverted
tdm_tim
47 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
6.2 Port Register Descriptions
Receive-Side Control Bits (one each for all 16 ports)
Register Name:
Register Description: Receive Port [n] Control Register
Register Address: See the Register Map in Section 4.
RP[n]CR, where n = 0 to 15 for each port
Bit #
Name
Default
7
RSS1
0
6
RSS0
0
5
RSD1
0
4
RSD0
0
3
VRST
0
2
RISE
0
1
RIDE
0
0
RICE
0
Bit #
Name
Default
15
RCOFA
0
14
IERC
0
13
VLB
0
12
VTO
0
11
n/a
0
10
LLB
0
9
RUEN
0
8
RP[i]HS
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Invert Clock Enable (RICE)
0 = do not invert clock (normal mode)
1 = invert clock (inverted clock mode)
Bit 1/Invert Data Enable (RIDE)
0 = do not invert data (normal mode)
1 = invert data (inverted data mode)
Bit 2/Invert Sync Enable (RISE)
0 = do not invert sync pulse (normal mode)
1 = invert sync pulse (inverted sync pulse mode)
Bit 3/V.54 Detector Reset (VRST). Toggling this bit from 0 to 1 and then back to 0 causes the internal V.54
detector to be reset and begin searching for the V.54 loop-up pattern. See Section 6.4 for more details.
Bit 4/Sync Delay Bit 0 (RSD0); Bit 5/Sync Delay Bit 1 (RSD1). These two bits define the format of the sync
signal that is applied to the RS[n] input. These bits are ignored if the port has been configured to operate in an
unchannelized fashion (RUEN = 1).
00 = sync pulse is 0 clocks early
01 = sync pulse is 1/2 clock early
10 = sync pulse is 1 clock early
11 = sync pulse is 2 clocks early
Bit 6/Sync Select Bit 0 (RSS0); Bit 7/Sync Select Bit 1 (RSS1). These two bits select the mode in which each
port is to be operated. Each port can be configured to accept 24, 32, 64, or 128 DS0 channels at an 8kHz rate.
These bits are ignored if the port has been configured to operate in an unchannelized fashion (RUEN = 1).
00 = T1 Mode (24 DS0 channels and 193 RC clocks between RS sync signals)
01 = E1 Mode (32 DS0 channels and 256 RC clocks between RS sync signals)
10 = 4.096MHz Mode (64 DS0 channels and 512 RC clocks between RS sync signals)
11 = 8.192MHz Mode (128 DS0 channels and 1024 RC clocks between RS sync signals)
48 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Bit 8/Port 0 High-Speed Mode (RP0 (1, 2) HS). If enabled, the port 0 (1 or 2) Layer 1 state machine logic is
defeated, and RC0 (1, 2) and RD0 (1, 2) are routed to some dedicated high-speed HDLC processing logic. Only
present in RP0CR, RP1CR, and RP2CR. Bit 8 is not assigned in ports 3 through 15.
0 = disabled
1 = enabled
Bit 9/Unchannelized Enable (RUEN). When enabled, this bit forces the port to operate in an unchannelized
fashion. When disabled, the port operates in a channelized mode.
0 = channelized mode
1 = unchannelized mode
Bit 10/Local Loopback Enable (LLB). This loopback routes transmit data back to the receive port. It can be used
in both channelized and unchannelized port operating modes, even on ports 0, 1, and 2 operating at speeds up to
52MHz (Figure 6-1). In channelized applications, a per-channel loopback can be realized by using the channelized
local loopback (CLLB) function. See Section 6.3 for details on CLLB.
0 = loopback disabled
1 = loopback enabled
Bit 12/V.54 Time Out (VTO). This read-only bit reports the real-time status of the V.54 detector. It is set to 1
when the V.54 detector has finished searching for the V.54 loop-up pattern and has not detected it. This indicates
to the host that the V.54 detector can now be used to search for the V.54 loop-up pattern on other HDLC channels,
and the host can initiate this by configuring the RV54 bits in the RP[n]CR register and then toggling the VRST
control bit. See Section 6.4 for more details about how the V.54 detector operates.
Bit 13/V.54 Loopback (VLB). This read-only bit reports the real-time status of the V.54 detector. It is set to 1
when the V.54 detector has verified that a V.54 loop-up pattern has been seen. When set, it remains set until either
the V.54 loop-down pattern is seen or the V.54 detector is reset by the host (i.e., by toggling VRST). See
Section 6.4 for more details on how the V.54 detector operates.
Bit 14/Interrupt Enable for RCOFA (IERC)
0 = interrupt masked
1 = interrupt enabled
Bit 15/COFA Status Bit (RCOFA). This latched read-only status bit sets if a COFA is detected. The COFA is
detected by sensing that a sync pulse has occurred during a clock period that was not the first bit of the
193/256/512/1024-bit frame. This bit resets when read and does not set again until another COFA has occurred.
Transmit-Side Control Bits (one each for all 16 ports)
Register Name:
Register Description: Transmit Port [n] Control Register
Register Address: See the Register Map in Section 4.
TP[n]CR, where n = 0 to 15 for each port
Bit #
Name
Default
7
TSS1
0
6
TSS0
0
5
TSD1
0
4
TSD0
0
3
TFDA1
0
2
TISE
0
1
TIDE
0
0
TICE
0
Bit #
Name
Default
15
TCOFA
0
14
IETC
0
13
n/a
0
12
n/a
0
11
TUBS
0
10
UNLB
0
9
TUEN
0
8
TP[i]HS
0
Note: Bits that are underlined are read-only; all other bits are read-write.
49 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Bit 0/Invert Clock Enable (TICE)
0 = do not invert clock (normal mode)
1 = invert clock (inverted mode)
Bit 1/Invert Data Enable (TIDE)
0 = do not invert data (normal mode)
1 = invert data (inverted mode)
Bit 2/Invert Sync Enable (TISE)
0 = do not invert sync (normal mode)
1 = invert sync pulse (inverted mode)
Bit 3/Force Data All Ones (TFDA1)
0 = force all data at TD to be 1
1 = allow data to be transmitted normally
Bit 4/Sync Delay Bit 0 (TSD0); Bit 5/Sync Delay Bit 1 (TSD1). These bits define the format of the sync signal
that is applied to the TS[n] input. These bits are ignored if the port has been configured to operate in an
unchannelized fashion (TUEN = 1).
00 = sync pulse is 0 clocks early
01 = sync pulse is 1/2 clock early
10 = sync pulse is 1 clock early
11 = sync pulse is 2 clocks early
Bit 6/Sync Select Bit 0 (TSS0); Bit 7/Sync Select Bit 1 (TSS1). These bits select the mode in which each port
operates. Each port can be configured to accept 24, 32, 64, or 128 DS0 channels at an 8kHz rate. These bits are
ignored if the port has been configured to operate in an unchannelized fashion (TUEN = 1).
00 = T1 Mode (24 DS0 channels and 193 RC clocks between TS sync signals)
01 = E1 Mode (32 DS0 channels and 256 RC clocks between TS sync signals)
10 = 4.096MHz Mode (64 DS0 channels and 512 RC clocks between TS sync signals)
11 = 8.192MHz Mode (128 DS0 channels and 1024 RC clocks between TS sync signals)
Bit 8/Port 0 High-Speed Mode (TP0 (1, 2) HS). If enabled, the port 0 (1 or 2) Layer 1 state machine logic is
defeated and TC0 (1, 2) and TD0 (1, 2) are routed to some dedicated high-speed HDLC processing logic. Only
present in TP0CR, TP1CR, and TP2CR. Bit 8 is not assigned in ports 3 through 15.
0 = disabled
1 = enabled
Bit 9/Unchannelized Enable (TUEN). When enabled, this bit forces the port to operate in an unchannelized
fashion. When disabled, the port operates in a channelized mode. This bit overrides the transmit channel-enable
(TCHEN) bit in the transmit Layer 1 configuration (T[n]CFG[j]) registers, which are described in Section 6.3.
0 = channelized mode
1 = unchannelized mode
Bit 10/Unchannelized Network Loopback Enable (UNLB). See Figure 6-1 for details. This loopback cannot be
used for ports 0 and 1 when they are operating at speeds greater than 10MHz.
0 = loopback disabled
1 = loopback enabled
Bit 11/Unchannelized BERT Select (TUBS). This bit is ignored if TUEN = 0. This bit overrides the transmit
BERT (TBERT) bit in the transmit layer 1 configuration (T[n]CFG[j]) registers, which are described in
Section 6.3.
0 = source transmit data from the HDLC controller
1 = source transmit data from the BERT block
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DS31256 256-Channel, High-Throughput HDLC Controller
Bit 14/Interrupt Enable for TCOFA (IETC)
0 = interrupt masked
1 = interrupt enabled
Bit 15/COFA Status Bit (TCOFA). This latched read-only status bit is set if a COFA is detected. A COFA is
detected by sensing that a sync pulse has occurred during a clock period that was not the first bit of the
193/256/512/1024-bit frame. This bit is reset when read and is not set again until another COFA has occurred.
6.3 Layer 1 Configuration Register Description
There are three configuration registers for each DS0 channel on each port (Figure 6-3). As shown in
Figure 6-1, each of the 16 ports contains a PORT RAM, which controls the Layer 1 state machine. These
384 registers (three registers x 128 DS0 channels per port) comprise the PORT RAM for each port,
controlling and providing access to the Layer 1 state machine. The registers are accessed indirectly
through the channelized port register data (CP[n]RD) register. The host must first write to the
channelized port register data-indirect select (CP[n]RDIS) register to choose which DS0 channel and
channelized PORT RAM it wishes to configure or read. On power-up, the host must write to all the used
R[n]CFG[j] and T[n]CFG[j] locations to make sure they are set into a known state.
Figure 6-3. Layer 1 Register Set
C[n]DAT[j]: Channelized DS0 Data
RDATA(8): Receive DS0 Data
LSB
MSB
TDATA(8): Transmit DS0 Data
R[n]CFG[j]: Receive Configuration
LSB
RCH#(8): Receive HDLC Channel Number
n/a RV54 n/a CLLB
MSB
RCHEN RBERT
n/a
R56
T[n]CFG[j]: Transmit Configuration
TCH#(8): Transmit HDLC Channel Number
LSB
MSB
TCHEN
TBERT
n/a
n/a
CNLB
n/a
TFAO
T56
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
Register Description: Channelized Port [n] Register Data Indirect Select
Register Address: See the Register Map in Section 4.
CP[n]RDIS, where n = 0 to 15 for each port
Bit #
Name
Default
7
n/a
0
6
CHID6
0
5
CHID5
0
4
CHID4
0
3
CHID3
0
2
CHID2
0
1
CHID1
0
0
CHID0
0
Bit #
Name
Default
15
IAB
0
14
IARW
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
CPRS1
0
8
CPRS0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 6/DS0 Channel ID (CHID0 to CHID6). The number of DS0 channels used depends on whether the port
has been configured for an unchannelized application or for a channelized application. If set for a channelized
application, the number of DS0 channels depends on whether the port has been configured in the T1, E1,
4.096MHz, or 8.192MHz mode.
0000000 (00h) = DS0 channel number 0
1111111 (7Fh) = DS0 channel number 127
DS0 CHANNELS
PORT MODE
AVAILABLE
Unchannelized (RUEN/TUEN = 1)
0
Channelized T1 (RUEN/TUEN = 0 and RSS0/TSS0 = 0 and RSS1/TSS1 = 0)
Channelized E1 (RUEN/TUEN = 0 and RSS0/TSS0 = 1 and RSS1/TSS1 = 0)
Channelized 4.096MHz (RUEN/TUEN = 0 and RSS0/TSS0 = 0 and RSS1/TSS1 = 1)
Channelized 8.192MHz (RUEN/TUEN = 0 and RSS0/TSS0 = 1 and RSS1/TSS1 = 1)
0 to 23
0 to 31
0 to 63
0 to 127
Bit 8/Channelized PORT RAM Select Bit 0 (CPRS0); Bit 9/Channelized PORT RAM Select Bit 1 (CPRS1)
00 = channelized DS0 data (C[n]DAT[j])
01 = receive configuration (R[n]CFG[j])
10 = transmit configuration (T[n]CFG[j])
11 = illegal selection
Bit 14/Indirect Access Read/Write (IARW). When the host wishes to read data from the internal channelized
PORT RAM, this bit should be written to 1 by the host. This causes the device to begin obtaining data from the
DS0 channel location indicated by the CHID bits and the data from the PORT RAM indicated by the CPRS0 and
CPRS1 bits. During the read access, the IAB bit is set to 1. Once the data is ready to be read from the CP[n]RD
register, the IAB bit is set to 0. When the host wishes to write data to the internal channelized PORT RAM, the
host should write this bit to 0. This causes the device to take the data that is currently present in the CP[n]RD
register and write it to the PORT RAM indicated by the CPRS0 and CPRS1 bits and the DS0 channel indicated by
the CHID bits. When the device has completed the write, the IAB is set to 0.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit is set to 1 until data is ready to be read. It is set to 0 when the data is ready to
be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the write
operation has completed.
52 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
Register Description: Channelized Port [n] Register Data
Register Address: See the Register Map in Section 4.
CP[n]RD, where n = 0 to 15 for each port
Bit #
Name
Default
7
6
CHD6
0
5
CHD5
0
4
CHD4
0
3
CHD3
0
2
CHD2
0
1
CHD1
0
0
CHD0
0
CHD7
0
Bit #
Name
Default
15
CHD15
0
14
CHD14
0
13
CHD13
0
12
CHD12
0
11
CHD11
0
10
CHD10
0
9
CHD9
0
8
CHD8
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 15/DS0 Channel Data (CHD0 to CHD15). This is the 16-bit data that is to either be written into or read
from the PORT RAM, specified by the CP[n]RDIS register.
Figure 6-4. Port RAM Indirect Access
CP[n]RDIS
CP[n]RD
Port RAM (one each for all 16 ports; n = 0 to 15)
C[n]DAT0
C[n]DAT1
C[n]DAT2
C[n]DAT3
C[n]DAT4
...
R[n]CFG0
R[n]CFG1
R[n]CFG2
R[n]CFG3
R[n]CFG4
...
T[n]CFG0
T[n]CFG1
T[n]CFG2
T[n]CFG3
T[n]CFG4
...
C[n]DAT126
C[n]DAT127
R[n]CFG126
R[n]CFG127
T[n]CFG126
T[n]CFG127
Register Name:
Register Description: Channelized Layer 1 DS0 Data Register
Register Address: Indirect Access through CP[n]RD
C[n]DAT[j], where n = 0 to 15 for each port and j = 0 to 127 for each DS0
Bit #
7
6
5
4
3
2
1
9
0
8
Name
Default
RDATA(8): Receive DS0 Data
Bit #
Name
Default
15
14
13
12
11
10
TDATA(8): Transmit DS0 Data
Note: Bits that are underlined are read-only; all other bits are read-write.
Note: In normal device operation, the host must never write to the C[n]DAT[j] registers.
Bits 0 to 7/Receive DS0 Data (RDATA). This register holds the most current DS0 byte received. It is used by the
transmit-side Layer 1 state machine when channelized network loopback (CNLB) is enabled.
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DS31256 256-Channel, High-Throughput HDLC Controller
Bits 8 to 15/Transmit DS0 Data (TDATA). This register holds the most current DS0 byte transmitted. It is used
by the receive-side Layer 1 state machine when channelized local loopback (CLLB) is enabled.
Register Name:
Register Description: Receive Layer 1 Configuration Register
Register Address: Indirect Access through CP[n]RD
R[n]CFG[j] where n = 0 to 15 for each port and j = 0 to 127 for each DS0
Bit #
Name
Default
7
6
5
4
3
2
1
0
RCH#(8): Receive HDLC Channel Number
Bit #
Name
Default
15
RCHEN
14
RBERT
13
n/a
12
RV54
11
n/a
10
CLLB
9
n/a
8
R56
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 7/Receive Channel Number (RCH#). The CPU loads the number of the HDLC channels associated
with this particular DS0 channel. If the port is running in an unchannelized mode (RUEN = 1), the HDLC channel
number only needs to be loaded into R[n]CFG0. If the fast (52Mbps) HDLC engine is enabled on port 0, HDLC
channel 1 is assigned to it and, likewise, HDLC channel 2 is assigned to the fast HDLC engine on port 2, if it is
enabled. Therefore, these HDLC channel numbers should not be used if the fast HDLC engines are enabled.
00000000 (00h) = HDLC channel number 1 (also used for the fast HDLC engine on port 0)
00000001 (01h) = HDLC channel number 2 (also used for the fast HDLC engine on port 1)
00000010 (02h) = HDLC channel number 3 (also used for the fast HDLC engine on port 2)
00000011 (03h) = HDLC channel number 4
11111111 (FFh) = HDLC channel number 256
Bit 8/Receive 56kbps (R56). If the port is running a channelized application, this bit determines whether the LSB
of each DS0 should be processed or not. If this bit is set, the LSB of each DS0 channel is not routed to the HDLC
controller (or the BERT, if it has been enabled through the RBERT bit). This bit does not affect the operation of
the V.54 detector. It always searches on all 8 bits in the DS0.
0 = 64kbps (use all 8 bits in the DS0)
1 = 56kbps (use only the first 7 bits received in the DS0)
Bit 10/Channelized Local Loopback Enable (CLLB). Enabling this loopback forces the transmit data to replace
the receive data. This bit must be set for each and every DS0 channel that is to be looped back. In order for the
loopback to become active, the DS0 channel must be enabled (RCHEN = 1) and the DS0 channel must be set into
the 64kbps mode (R56 = 0).
0 = loopback disabled
1 = loopback enabled
Bit 12/Receive V.54 Enable (RV54E). If this bit is cleared, this DS0 channel is not examined to check if the V.54
loop pattern is present. If set, the DS0 is examined for the V.54 loop pattern. When searching for the V.54 pattern
within a DS0 channel, all 8 bits of the DS0 channel are examined, regardless of how the DS0 channel is
configured (i.e., 64k or 56k).
0 = do not examine this DS0 channel for the V.54 loop pattern
1 = examine this DS0 channel for the V.54 loop pattern
Bit 14/Route Data Into BERT (RBERT). Setting this bit routes the DS0 data into the BERT function. If the DS0
channel has been configured for 56kbps operation (R56 = 1), the LSB of each DS0 channel is not routed to the
BERT block. In order for the data to make it to the BERT block, the host must also configure the BERT for the
proper port through the master control register (Section 5).
0 = do not route data to BERT
1 = route data to BERT
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DS31256 256-Channel, High-Throughput HDLC Controller
Bit 15/Receive DS0 Channel Enable (RCHEN). This bit must be set for each active DS0 channel in a
channelized application. In a channelized application, although a DS0 channel is deactivated, the channel can still
be set up to route data to the V.54 detector and/or the BERT block. In addition, although a DS0 channel is active,
the loopback function (CLLB = 1) overrides this activation and routes transmit data back to the HDLC controller
instead of the data coming in through the RD pin. In an unchannelized mode (RUEN = 1), only the RCHEN bit in
R[n]CFG0 needs to be configured.
0 = deactivated DS0 channel
1 = active DS0 channel
Register Name:
Register Description: Transmit Layer 1 Configuration Register
Register Address: Indirect Access through CP[n]RD
T[n]CFG[j], where n = 0 to 15 for each port and j = 0 to 127 for each DS0
Bit #
Name
Default
7
6
5
4
3
2
1
0
TCH#(8): Transmit HDLC Channel Number
Bit #
Name
Default
15
TCHEN
14
TBERT
13
n/a
12
n/a
11
CNLB
10
n/a
9
8
T56
TFAO
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 7/Transmit Channel Number (TCH#). The CPU loads the number of the HDLC channels associated
with this particular DS0 channel. If the port is running in an unchannelized mode (TUEN = 1), the HDLC channel
number only needs to be loaded into T[n]CFG0. If the fast (52Mbps) HDLC engine is enabled on port 0, HDLC
channel 1 is assigned to it and, likewise, HDLC channel 2 is assigned to the fast HDLC engine on port 2, if it is
enabled. Therefore, these HDLC channel numbers should not be used if the fast HDLC engines are enabled.
00000000 (00h) = HDLC channel number 1 (also used for the fast HDLC engine on port 0)
00000001 (01h) = HDLC channel number 2 (also used for the fast HDLC engine on port 1)
00000010 (02h) = HDLC channel number 3 (also used for the fast HDLC engine on port 2)
00000011 (03h) = HDLC channel number 4
11111111 (FFh) = HDLC channel number 256
Bit 8/Transmit 56kbps (T56). If the port is running a channelized application, this bit determines whether or not
the LSB of each DS0 should be processed. If this bit is set, the LSB of each DS0 channel is not routed from the
HDLC controller (or the BERT, if it has been enabled through the RBERT bit), and the LSB bit position is forced
to 1.
0 = 64kbps (use all 8 bits in the DS0)
1 = 56kbps (use only the first 7 bits transmitted in the DS0; force the LSB to 1)
Bit 9/Transmit Force All Ones (TFAO). If this bit is set, then eight 1s are placed into the DS0 channel for
transmission instead of the data that is being sourced from the HDLC controller. If this bit is cleared, the data from
the HDLC controller is transmitted. This bit is useful in instances when CLLB is being activated to keep the
looped back data from being sent out onto the network. This bit overrides TCHEN.
0 = transmit data from the HDLC controller
1 = force transmit data to all 1s
Bit 11/Channelized Network Loopback Enable (CNLB). Enabling this loopback forces the receive data to
replace the transmit data. This bit must be set for each and every DS0 channel that is to be looped back. This bit
overrides TBERT, TFAO, and TCHEN.
0 = loopback disabled
1 = loopback enabled
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DS31256 256-Channel, High-Throughput HDLC Controller
Bit 14/Route Data from BERT (TBERT). Setting this bit routes DS0 data to the TD pin from the BERT block
instead of from the HDLC controller. If the DS0 channel has been configured for 56kbps operation (T56 = 1), the
LSB of each DS0 channel is not routed from the BERT block but instead is forced to 1. In order for the data to
make it from the BERT block, the host must also configure the BERT for the proper port through the master
control register (Section 5). This bit overrides TFAO and TCHEN.
0 = do not route data from BERT
1 = route data from BERT (override the data from the HDLC controller)
Bit 15/Transmit DS0 Channel Enable (TCHEN). This bit must be set for each active DS0 channel in a
channelized application. In a channelized application, although a DS0 channel is deactivated, the channel can still
be set up to route data from the BERT block. In addition, although a DS0 channel is active, the loopback function
(CNLB = 1) overrides this activation and routes receive data to the TD pin instead of from the HDLC. In an
unchannelized mode (TUEN = 1), only the TCHEN bit in T[n]CFG0 needs to be configured.
0 = deactivated DS0 channel
1 = active DS0 channel
6.4 Receive V.54 Detector
Each port within the device contains a V.54 loop pattern detector. V.54 is a pseudorandom pattern that is
sent for at least 2 seconds, followed immediately by an all-ones pattern for at least 2 seconds if the
channel is to be placed into loopback. The exact pattern and sequence is defined in Annex B of ANSI
T1.403-1995.
When a port is configured for unchannelized operation (RUEN = 1), all data entering the port through
RD is routed to the V.54 detector. If the host wishes not to use the V.54 detector, the SLBP status bits in
the status V.54 (SV54) register should be ignored, and their corresponding interrupt mask bits in ISV54
should be set to 0 to keep from disturbing the host. Details about the status and interrupt bits can be
found in Section 5.
When the port is configured for channelized operation (RUEN = 0), it is the host’s responsibility to
determine which DS0 channels should be searched for the V.54 pattern. In channelized applications, it
may be that there are multiple HDLC channels the host wishes to look in for the V.54 pattern. If this is
true, then the host performs the routine shown in Table 6-B. A flow chart of the same routine is shown in
Figure 6-5.
56 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Table 6-B. Receive V.54 Search Routine
STEP
DIRECTION
FUNCTION
By configuring the RV54 bit in the R[n]CFG[j] register, the host
determines in which DS0 channels the V.54 search is to take place. If
this search sequence does not detect the V.54 pattern, the host can pick
some new DS0 channels and try again.
1
Set up the channel search
Once the DS0 channels have been set, the host toggles the VRST bit in
the RP[n]CR register and begins monitoring the SLBP status bit.
2
3
Toggle VRST
Wait for SLBP
The SLBP status bit reports any change of state in the V.54 search
process. It can also generate a hardware interrupt (Section 5). When
SLBP is set, the host knows that something significant has occurred and
that it should read the VLB and VTO real-time status bits in the
RP[n]CR register.
If VTO = 1, the V.54 pattern did not appear in this set of channels and
the host can reconfigure the search in other DS0 channels and move
back to Step #1.
If VLB = 1, the V.54 loop-up pattern has been detected and the channel
should be placed into loopback. A loopback can be invoked by the host
by configuring the CNLB bit in the T[n]CFG[j] register for each DS0
channel that needs to be placed into loopback. Move back to Step #3.
If VLB = 0, if the DS0 channels are already in loopback, the host
monitors VLB to know when the loop-down pattern has been detected
and when to take the channels out of loopback. The DS0 channels are
taken out of loopback by again configuring the CNLB bits. Move on to
Step #1.
4
Read VTO and VLB
57 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 6-5. Receive V.54 Host Algorithm
ALGORITHM
NOTES
DS0 channels can be configured to search
Set Up the
DS0 Channel
Search
for the V.54 loop pattern via the Receive
Layer 1 Configuration Register (Section 6.3)
VRST is a control bit that is in the Receive
Port Control Register (Section 6.2)
Toggle VRST
SLBP is a status bit that is reported
in the SV54 register (Section 5.3)
Wait for
SLBP = 1
Yes
VTO is a status bit that is in the Receive
Port Control Register (Section 6.2)
VTO = 1?
No
Place DS0
Channels into
Loopback
DS0 channels can be placed into loopback
via the Receive Layer 1 Configuration Register
(Section 6.3)
SLBP is a status bit that is reported
in the SV54 register (Section 5.3)
Wait for
SLBP = 1
Take DS0
DS0 channels can be taken out of loopback
via the Receive Layer 1 Configuration Register
Channels out
of Loopback
(Section 6.3)
v54host
58 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 6-6. Receive V.54 State Machine
VRST = 1
VLB = 0
VTO = 0
SLBP = 0
CLK
Data
Time Out (VTO)
Loopback (VLB);
both in RP[n]CR
V.54 State
Machine
VRST (in RP[n]CR)
SYSCLK
Change of
State in Status
(SLBP); in SV54
Search for
Loop Up
Sysclk is used only to time
a 4 second timer. It is run into
a 2E27 counter which provides
a 4.03 second time out with a
33MHz clock and a 5.37 second
time out with a 25MHz clock
Pattern for
32 VCLKs
Sync = 0
Sync = 1
Reset 4 second timer;
wait for Loss of Sync or
All 1s (64 in a Row)
or for the 4 second
timer to expire
All Ones
Sync = 0 or
SLBP = 1
4 Second Timer
Has Expired
Sync = 0
Search for
Loop Down
Pattern
VLB = 1
Sync = 1
Sync = 0
wait for Loss of Sync or
All 1s (64 in a Row)
All Ones
VLB = 0
v54sm
VTO = 1
SLBP = 1
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DS31256 256-Channel, High-Throughput HDLC Controller
6.5 BERT
The BERT block is capable of generating and detecting the following patterns:
ꢀ The pseudorandom patterns 2E7, 2E11, 2E15, and QRSS
ꢀ A repetitive pattern from 1 to 32 bits in length
ꢀ Alternating (16-bit) words that flip every 1 to 256 words
The BERT receiver has a 32-bit bit counter and a 24-bit error counter. It can generate interrupts upon
detecting a bit error, a change in synchronization, or if an overflow occurs in the bit and error counters.
See Section 5 for details on status bits and interrupts from the BERT block. To activate the BERT block,
the host must configure the BERT mux (Figure 6-7). In channelized applications, the host must also
configure the Layer 1 state machine to send/obtain data to/from the BERT block through the Layer 1
configuration registers (Section 6.3).
Figure 6-7. BERT Mux Diagram
Port 0 (slow)
Port 1 (slow)
Port 2 (slow)
Port 3 (slow)
Port 4 (slow)
BERT
Mux
SBERT STATUS
BIT IN SM
BERT
Port 5 (slow)
BLOCK
Port 13 (slow)
Port 14 (slow)
Port 15 (slow)
Port 0 (fast)
INTERNAL CONTROL AND
CONFIGURATION BUS
Port 1 (fast)
Port 2 (fast)
BERT SELECT (5)
IN THE MASTER CONFIGURATION REGISTER
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DS31256 256-Channel, High-Throughput HDLC Controller
6.6 BERT Register Description
Figure 6-8. BERT Register Set
BERTC0: BERT Control 0
LSB
n/a
MSB
IESYNC
TINV
RINV
PS2
n/a
PS1
PS0
LC
RESYNC
IEBED
IEOF
RPL3
RPL2
RPL1
RPL0
BERTC1: BERT Control 1
EIB2 EIB1
MSB
LSB
TC
EIB0
SBE
n/a
n/a
n/a
Alternating Word Count
BERTRP0: BERT Repetitive Pattern Set 0 (lower word)
LSB
LSB
LSB
LSB
BERT Repetitive Pattern Set (lower byte)
MSB
BERT Repetitive Pattern Set
BERTRP1: BERT Repetitive Pattern Set 1 (upper word)
BERT Repetitive Pattern Set
MSB
BERT Repetitive Pattern Set (upper byte)
BERTBC0: BERT Bit Counter 0 (lower word)
BERT 32-Bit Bit Counter (lower byte)
MSB
BERT 32-Bit Bit Counter
BERTBC1: BERT Bit Counter 0 (upper word)
BERT 32-Bit Bit Counter
MSB
BERT 32-Bit Bit Counter (upper byte)
BERTEC0: BERT Error Counter 0/Status
LSB
SYNC
n/a
MSB
RA1
RA0
RLOS
BED
BBCO
BECO
BERT 24-Bit Error Counter (lower byte)
BERTEC1: BERT Error Counter 1 (upper word)
BERT 24-Bit Error Counter
LSB
MSB
BERT 24-Bit Error Counter (upper byte)
61 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
BERTC0
Register Description: BERT Control Register 0
Register Address:
0500h
Bit #
Name
Default
7
n/a
0
6
5
RINV
0
4
PS2
0
3
PS1
0
2
PS0
0
1
LC
0
0
RESYNC
0
TINV
0
Bit #
15
IESYNC
0
14
IEBED
0
13
IEOF
0
12
n/a
0
11
RPL3
0
10
RPL2
0
9
RPL1
0
8
RPL0
0
Name
Default
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Force Resynchronization (RESYNC). A low-to-high transition forces the receive BERT synchronizer to
resynchronize to the incoming data stream. This bit should be toggled from low to high whenever the host wishes
to acquire synchronization on a new pattern. It must be cleared and set again for a subsequent resynchronization.
Note: Bits 2, 3, and 4 must be set, minimum of 64 system clock cycles, before toggling the resync bit (bit 0).
Bit 1/Load Bit and Error Counters (LC). A low-to-high transition latches the current bit and error counts into
the host accessible registers BERTBC and BERTEC and clears the internal count. This bit should be toggled from
low to high whenever the host wishes to begin a new acquisition period. Must be cleared and set again for
subsequent loads.
Bit 2/Pattern Select Bit 0 (PS0); Bit 3/Pattern Select Bit 1 (PS1); Bit 4/Pattern Select Bit 2 (PS2)
000 = pseudorandom pattern 2E7 - 1
001 = pseudorandom pattern 2E11 - 1
010 = pseudorandom pattern 2E15 - 1
011 = pseudorandom pattern QRSS (2E20 - 1 with a 1 forced, if the next 14 positions are 0)
100 = repetitive pattern
101 = alternating word pattern
110 = illegal state
111 = illegal state
Bit 5/Receive Invert Data Enable (RINV)
0 = do not invert the incoming data stream
1 = invert the incoming data stream
Bit 6/Transmit Invert Data Enable (TINV)
0 = do not invert the outgoing data stream
1 = invert the outgoing data stream
Bit 8/Repetitive Pattern Length Bit 0 (RPL0); Bit 9/Repetitive Pattern Length Bit 1 (RPL1);
Bit 10/Repetitive Pattern Length Bit 2 (RPL2); Bit 11/Repetitive Pattern Length Bit 3 (RPL3). RPL0 is the
LSB and RPL3 is the MSB of a nibble that describes the how long the repetitive pattern is. The valid range is 17
(0000) to 32 (1111). These bits are ignored if the receive BERT is programmed for a pseudorandom pattern. To
create repetitive patterns less than 17 bits in length, the user must set the length to an integer number of the desired
length that is less than or equal to 32. For example, to create a 6-bit pattern, the user can set the length to 18 (0001)
or 24 (0111) or 30 (1101).
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DS31256 256-Channel, High-Throughput HDLC Controller
Repetitive Pattern Length Map
Length
17 Bits
21 Bits
25 Bits
29 Bits
Code
0000
0100
1000
1100
Length
18 Bits
22 Bits
26 Bits
30 Bits
Code
0001
0101
1001
1101
Length
19 Bits
23 Bits
27 Bits
31 Bits
Code
0010
0110
1010
1101
Length
20 Bits
24 Bits
28 Bits
32 Bits
Code
0011
0111
1011
1111
Bit 13/Interrupt Enable for Counter Overflow (IEOF). Allows the receive BERT to cause an interrupt if either
the bit counter or the error counter overflows.
0 = interrupt masked
1 = interrupt enabled
Bit 14/Interrupt Enable for Bit Error Detected (IEBED). Allows the receive BERT to cause an interrupt if a bit
error is detected.
0 = interrupt masked
1 = interrupt enabled
Bit 15/Interrupt Enable for Change-of-Synchronization Status (IESYNC). Allows the receive BERT to cause
an interrupt if there is a change of state in the synchronization status (i.e., the receive BERT either goes into or out
of synchronization).
0 = interrupt masked
1 = interrupt enabled
Register Name:
BERTC1
Register Description: BERT Control Register 1
Register Address:
0504h
Bit #
Name
Default
7
EIB2
0
6
EIB1
0
5
EIB0
0
4
SBE
0
3
n/a
0
2
n/a
0
1
n/a
0
0
TC
0
Bit #
Name
Default
15
14
13
12
11
10
0
9
0
8
0
Alternating Word Count
0
0
0
0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Transmit Pattern Load (TC). A low-to-high transition loads the pattern generator with repetitive or
pseudorandom pattern that is to be generated. This bit should be toggled from low to high whenever the host
wishes to load a new pattern. Must be cleared and set again for subsequent loads.
Bit 4/Single Bit-Error Insert (SBE). A low-to-high transition creates a single bit error. Must be cleared and set
again for a subsequent bit error to be inserted.
Bit 5/Error Insert Bit 0 (EIB0); Bit 6/Error Insert Bit 1 (EIB1); Bit 7/Error Insert Bit 2 (EIB2).
Automatically inserts bit errors at the prescribed rate into the generated data pattern. Useful for verifying error
detection operation.
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DS31256 256-Channel, High-Throughput HDLC Controller
Error Rate Inserted
EIB2
EIB1
EIB0
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
No errors automatically inserted
10E-1
10E-2
10E-3
10E-4
10E-5
10E-6
10E-7
Bits 8 to 15/Alternating Word Count Rate. When the BERT is programmed in the alternating word mode, the
words repeat for the count loaded into this register, then flip to the other word and again repeat for the number of
times loaded into this register. The valid count range is from 05h to FFh.
Register Name:
BERTBRP0
Register Description: BERT Repetitive Pattern Set 0
Register Address:
Register Name:
0508h
BERTBRP1
Register Description: BERT Repetitive Pattern Set 1
Register Address:
050Ch
BERTRP0: BERT Repetitive Pattern Set 0 (lower word)
Bit #
Name
Default
7
6
5
4
3
2
1
0
BERT Repetitive Pattern Set (lower byte)
0
15
0
0
14
0
0
13
0
0
0
0
10
0
0
9
0
0
8
0
Bit #
Name
Default
12
11
BERT Repetitive Pattern Set
0
0
BERTRP1: BERT Repetitive Pattern Set 1 (upper word)
Bit #
Name
Default
23
22
21
20
19
18
0
17
0
16
0
BERT Repetitive Pattern Set
0
0
0
0
0
31
30
29
28
27
26
25
24
Bit #
Name
BERT Repetitive Pattern Set (upper byte)
0
Default
0
0
0
0
0
0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 31/BERT Repetitive Pattern Set (BERTRP0 and BERTRP1). These registers must be properly loaded
for the BERT to properly generate and synchronize to either a repetitive pattern, a pseudorandom pattern, or an
alternating word pattern. For a repetitive pattern that is less than 32 bits, the pattern should be repeated so that all
32 bits are used to describe the pattern. For example, if the pattern was the repeating 5-bit pattern …01101…
(where the right-most bit is sent first and received first), then PBRP0 should be loaded with xB5AD and PBRP1
should be loaded with x5AD6. For a pseudorandom pattern, both registers should be loaded with all ones (i.e.,
xFFFF). For an alternating word pattern, one word should be placed into PBRP0 and the other word should be
placed into PBRP1. For example, if the DDS stress pattern “7E” is to be described, the user would place x0000 in
PBRP0 and x7E7E in PBRP1 and the alternating word counter would be set to 50 (decimal) to allow 100 Bytes of
00h followed by 100 Bytes of 7Eh to be sent and received.
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
BERTBC0
Register Description: BERT 32-Bit Bit Counter (lower word)
Register Address:
Register Name:
0510h
BERTBC1
Register Description: BERT 32-Bit Bit Counter (upper word)
Register Address:
0514h
BERTBC0: BERT Bit Counter 0 (lower word)
Bit #
Name
Default
7
6
5
4
3
2
1
0
BERT 32-Bit Bit Counter (lower byte)
0
15
0
0
14
0
0
13
0
0
0
0
10
0
0
9
0
0
8
0
Bit #
Name
Default
12
11
BERT 32-Bit Bit Counter
0
0
BERTBC1: BERT Bit Counter 0 (upper word)
Bit #
Name
Default
23
22
21
20
19
18
17
16
BERT 32-Bit Bit Counter
0
31
0
0
30
0
0
0
0
0
0
25
0
0
24
0
Bit #
Name
Default
29
28
27
26
BERT 32-Bit Bit Counter (upper byte)
0
0
0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 31/BERT 32-Bit Bit Counter (BERTBC0 and BERTBC1). This 32-bit counter increments for each
data bit (i.e., clock) received. This counter is not disabled when the receive BERT loses synchronization. This
counter is loaded with the current bit count value when the LC control bit in the BERTC0 register is toggled from
low (0) to high (1). When full, this counter saturates and sets the BBCO status bit.
Register Name:
BERTEC0
Register Description: BERT 24-Bit Error Counter (lower) and Status Information
Register Address:
0518h
Bit #
7
6
5
RA0
0
4
RLOS
0
3
BED
0
2
BBCO
0
1
BECO
0
0
SYNC
0
Name
Default
n/a
0
RA1
0
14
0
Bit #
Name
Default
15
13
12
11
10
9
0
8
0
BERT 24-Bit Error Counter (lower byte)
0
0
0
0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Real-Time Synchronization Status (SYNC). Real-time status of the synchronizer (this bit is not latched). Is
set when the incoming pattern matches for 32 consecutive bit positions. Is cleared when six or more bits out of 64
are received in error.
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DS31256 256-Channel, High-Throughput HDLC Controller
Bit 1/BERT Error Counter Overflow (BECO). A latched bit that is set when the 24-bit BERT error counter
(BEC) overflows. Cleared when read and is not set again until another overflow occurs.
Bit 2/BERT Bit Counter Overflow (BBCO). A latched bit that is set when the 32-bit BERT bit counter (BBC)
overflows. Cleared when read and is not set again until another overflow occurs.
Bit 3/Bit Error Detected (BED). A latched bit that is set when a bit error is detected. The receive BERT must be
in synchronization for it to detect bit errors. Cleared when read.
Bit 4/Receive Loss of Synchronization (RLOS). A latched bit that is set whenever the receive BERT begins
searching for a pattern. Once synchronization is achieved, this bit remains set until read.
Bit 5/Receive All Zeros (RA0). A latched bit that is set when 31 consecutive 0s are received. Allowed to be
cleared once a 1 is received.
Bit 6/Receive All Ones (RA1). A latched bit that is set when 31 consecutive 1s are received. Allowed to be
cleared once 0 is received.
Bits 8 to 15/BERT 24-Bit Error Counter (BEC). Lower word of the 24-bit error counter. See the BERTEC1
register description for details.
Register Name:
BERTEC1
Register Description: BERT 24-Bit Error Counter (upper)
Register Address:
051Ch
Bit #
Name
Default
7
6
5
4
3
2
1
0
BERT 24-Bit Error Counter
0
15
0
0
14
0
0
0
0
0
0
9
0
0
8
0
Bit #
Name
Default
13
12
11
10
BERT 24-Bit Error Counter (upper byte)
0
0
0
0
Note: Bits that are underlined are read-only; all other bits are read-write. default value for all bits is 0.
Bits 0 to 15/BERT 24-Bit Error Counter (BEC). Upper two words of the 24-bit error counter. This 24-bit
counter increments for each data bit received in error. This counter is not disabled when the receive BERT loses
synchronization. This counter is loaded with the current bit count value when the LC control bit in the BERTC0
register is toggled from low (0) to high (1). When full, this counter saturates and sets the BECO status bit.
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DS31256 256-Channel, High-Throughput HDLC Controller
7. HDLC
7.1 General Description
The DS31256 contains two different types of HDLC controllers. Each port has a slow HDLC engine
(type #1) associated with it that can operate in either a channelized mode up to 8.192Mbps or an
unchannelized mode at rates up to 10Mbps. Ports 0 and 1 also have an additional fast HDLC engine
(type #2) that can operate in only an unchannelized fashion up to 52Mbps. Through the Layer 1 registers
(Section 6.2), the host determines which type of HDLC controller is used on a port and if the HDLC
controller is to be operated in either a channelized or unchannelized mode. If the HDLC controller is to
be operated in the channelized mode, then the Layer 1 registers (Section 6.3) also determine which
HDLC channels are associated with which DS0 channels. If the fast HDLC engine is enabled on port 0,
HDLC channel 1 is assigned to it and, likewise, HDLC channel 2 is assigned to the fast HDLC engine on
port 1 if it is enabled.
The HDLC controllers can handle all required normal real-time tasks. Table 7-B lists all the functions
supported by the receive HDLC and Table 7-C lists all the functions supported by the transmit HDLC.
Each of the 256 HDLC channels within the DS31256 are configured by the host through the receive
HDLC channel definition (RHCD) and transmit channel definition (THCD) registers. There is a separate
RHCD and THCD register for each HDLC channel. The host can access the RHCD and THCD registers
indirectly through the RHCDIS indirect select and THCDIS indirect select registers. See Section 7.2 for
details.
On the receive side, one of the outcomes shown in Table 7-A occurs when the HDLC block is processing
a packet. For each packet, one of these outcomes is reported in the receive done-queue descriptor
(Section 9.2.4). On the transmit side, when the HDLC block is processing a packet, an error in the PCI
block (parity or target abort) or transmit FIFO underflow causes the HDLC block to send an abort
sequence (eight 1s in a row) followed continuously by the selected interfill (either 7Eh or FFh) until the
HDLC channel is reset by the transmit DMA block (Section 9.3.1). This same sequence of events will
occur even if the transmit HDLC channel is being operated in the transparent mode. In the transparent
mode, when the FIFO empties the device sends either 7Eh or FFh.
If any of the 256 receive HDLC channels detects an abort sequence, an FCS checksum error, or if the
packet length was incorrect, then the appropriate status bit in SDMA is set. If enabled, the setting of any
of these statuses can cause a hardware interrupt to occur. See Section 5.3.2 for details about the operation
of these status bits.
Table 7-A. Receive HDLC Packet Processing Outcomes
OUTCOME
EOF/Normal Packet
EOF/Bad FCS
CRITERIA
Integral number of packets > min and < max is received and CRC is okay
Integral number of packets > min and < max is received and CRC is bad
Seven or more 1s in a row detected
Abort Detected
EOF/Too Few Bytes
Too Many Bytes
EOF/Bad # of Bits
FIFO Overflow
Fewer than 4 or 6 Bytes received
Greater than the packet maximum is received (if detection enabled)
Not an integral number of bytes received
Tried to write a byte into an already full FIFO
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DS31256 256-Channel, High-Throughput HDLC Controller
Table 7-B. Receive HDLC Functions
FUNCTION
DESCRIPTION
Zero Destuff
This operation is disabled if the channel is set to transparent mode.
Flag Detection and
Byte Alignment
Okay to have two packets separated by only one flag or by two flags sharing a 0.
This operation is disabled if the channel is set to transparent mode.
The minimum check is for 4 Bytes with CRC-16 and 6 Bytes with CRC-32 (packets
with less than the minimum lengths are not passed to the PCI bus).
The maximum check is programmable up to 65,536 Bytes through the RHPL register.
The maximum check can be disabled through the ROLD control bit in the RHCD
register.
Octet Length Check
The minimum and maximum counts include the FCS.
An error is also reported if a noninteger number of octets occur between flags.
Can be either set to CRC-16 or CRC-32 or none.
CRC Check
The CRC can be passed through to the PCI bus or not.
The CRC check is disabled if the channel is set to transparent mode.
Abort Detection
Invert Data
Checks for seven or more 1s in a row.
All data (including the flags and FCS) is inverted before HDLC processing.
Also available in the transparent mode.
The first bit received becomes either the LSB (normal mode) or the MSB (telecom
Bit Flip
mode) of the byte stored in the FIFO.
Also available in the transparent mode.
If enabled, flag detection, zero destuffing, abort detection, length checking, and FCS
checking are disabled.
Transparent Mode
Data is passed to the PCI bus on octet (i.e., byte) boundaries in channelized operation.
Table 7-C. Transmit HDLC Functions
Only used between opening and closing flags.
Is disabled between a closing flag and an opening flag and for sending aborts and/or
interfill data.
Zero Stuffing
Disabled if the channel is set to the transparent mode.
Interfill Selection
Flag Generation
Can be either 7Eh or FFh.
A programmable number of flags (1 to 16) can be set between packets.
Disabled if the channel is set to the transparent mode.
Can be either CRC-16 or CRC-32 or none.
CRC Generation
Invert Data
Disabled if the channel is set to transparent mode.
All data (including the flags and FCS) is inverted after processing.
Also available in the transparent mode.
The LSB (normal mode) of the byte from the FIFO becomes the first bit sent or the
MSB (telecom mode) becomes the first bit sent.
Bit Flip
Also available in the transparent mode.
If enabled, flag generation, zero stuffing, and FCS generation is disabled.
Transparent Mode
Invert FCS
Passes bytes from the PCI Bus to Layer 1 on octet (byte) boundaries.
When enabled, it inverts all of the bits in the FCS (useful for HDLC testing).
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DS31256 256-Channel, High-Throughput HDLC Controller
7.2 HDLC Register Description
Register Name:
RHCDIS
Register Description: Receive HDLC Channel Definition Indirect Select
Register Address:
0400h
Bit #
Name
Default
7
6
5
HCID5
0
4
HCID4
0
3
HCID3
0
2
HCID2
0
1
HCID1
0
0
HCID0
0
HCID7
0
HCID6
0
Bit #
Name
Default
15
IAB
0
14
IARW
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
n/a
0
8
n/a
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 7/HDLC Channel ID (HCID0 to HCID7)
00000000 (00h) = HDLC channel number 1 (also used for the fast HDLC engine on port 0)
00000001 (01h) = HDLC channel number 2 (also used for the fast HDLC engine on port 1)
00000010 (02h) = HDLC channel number 3 (also used for the fast HDLC engine on port 2)
00000011 (03h) = HDLC channel number 4
11111111 (FFh) = HDLC channel number 256
Bit 14/Indirect Access Read/Write (IARW). When the host wishes to read data from the internal receive HDLC
definition RAM, the host should write this bit to 1. This causes the device to begin obtaining the data from the
channel location indicated by the HCID bits. During the read access, the IAB bit is set to 1. Once the data is ready
to be read from the RHCD register, the IAB bit is set to 0. When the host wishes to write data to the internal
receive HDLC definition RAM, the host should write this bit to 0. This causes the device to take the data that is
currently present in the RHCD register and write it to the channel location indicated by the HCID bits. When the
device completes the write, the IAB is set to 0.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit sets to 1 until the data is ready to be read. It is set to 0 when the data is ready
to be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the write
operation completes.
Register Name:
RHCD
Register Description: Receive HDLC Channel Definition
Register Address:
0404h
Bit #
Name
Default
7
RABTD
0
6
RCS
0
5
RBF
0
4
RID
0
3
RCRC1
0
2
RCRC0
0
1
ROLD
0
0
RTRANS
0
Bit #
Name
Default
15
n/a
0
14
n/a
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
n/a
0
8
RZDD
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Receive Transparent Enable (RTRANS). When this bit is set low, the HDLC controller performs flag
delineation, zero destuffing, abort detection, octet length checking (if enabled through ROLD), and FCS checking
(if enabled through RCRC0/1). When this bit is set high, the HDLC controller does not perform flag delineation,
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DS31256 256-Channel, High-Throughput HDLC Controller
zero destuffing, and abort detection, octet length checking, or FCS checking. When in transparent mode, the
device must not be configured to write done-queue descriptors only at the end of a packet, if it is desired that done-
queue descriptors be written; there is not an end of packet on the receive side in transparent mode by definition.
Please note that an end of packet does not occur on the receive side while in transparent mode.
0 = transparent mode disabled
1 = transparent mode enabled
Bit 1/Receive Octet Length-Detection Enable (ROLD). When this bit is set low, the HDLC engine does not
check to see if the octet length of the received packets exceeds the count loaded into the receive HDLC packet
length (RHPL) register. When this bit is set high, the HDLC engine checks to see if the octet length of the received
packets exceeds the count loaded into the RHPL register. When an incoming packet exceeds the maximum length,
the packet is aborted and the remainder is discarded. This bit is ignored if the HDLC channel is set to transparent
mode (RTRANS = 1).
0 = octet length detection disabled
1 = octet length detection enabled
Bits 2, 3/Receive CRC Selection (RCRC0/RCRC1). These two bits are ignored if the HDLC channel is set into
transparent mode (RTRANS = 1).
RCRC1
RCRC0
ACTION
No CRC verification performed
16-bit CRC (CCITT/ITU Q.921)
32-bit CRC
0
0
1
1
0
1
0
1
Illegal state
Bit 4/Receive Invert Data Enable (RID). When this bit is set low, the incoming HDLC packets are not inverted
before processing. When this bit is set high, the HDLC engine inverts all the data (flags, information fields, and
FCS) before processing the data. The data is not reinverted before passing to the FIFO.
0 = do not invert data
1 = invert all data (including flags and FCS)
Bit 5/Receive Bit Flip (RBF). When this bit is set low, the HDLC engine places the first HDLC bit received in the
lowest bit position of the PCI bus bytes (i.e., PAD[0], PAD[8], PAD[16], PAD[24]). When this bit is set high, the
HDLC controller places the first HDLC bit received in the highest bit position of the PCI bus bytes (i.e., PAD[7],
PAD[15], PAD[23], PAD[31]).
0 = the first HDLC bit received is placed in the lowest bit position of the bytes on the PCI bus
1 = the first HDLC bit received is placed in the highest bit position of the bytes on the PCI bus
Bit 6/Receive CRC Strip Enable (RCS). When this bit is set high, the FCS is not transferred through to the PCI
bus. When this bit is set low, the HDLC engine includes the 2-Byte FCS (16-bit) or 4-Byte FCS (32-bit) in the
data that it transfers to the PCI bus. This bit is ignored if the HDLC channel is set into transparent mode
(RTRANS = 1).
0 = send FCS to the PCI bus
1 = do not send the FCS to the PCI bus
Bit 7/Receive Abort Disable (RABTD). When this bit is set low, the HDLC engine examines the incoming data
stream for the abort sequence, which is seven or more consecutive 1s. When this bit is set high, the incoming data
stream is not examined for the abort sequence, and, if an incoming abort sequence is received, no action is taken.
This bit is ignored when the HDLC controller is configured in the transparent mode (RTRANS = 1).
Bit 8/Receive Zero Destuffing Disable (RZDD). When this bit is set low, the HDLC engine zero destuffs the
incoming data stream. When this bit is set high, the HDLC engine does not zero destuff the incoming data stream.
This bit is ignored when the HDLC engine is configured in the transparent mode (RTRANS = 1).
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
RHPL
Register Description: Receive HDLC Maximum Packet Length
Register Address:
0410h
Bit #
Name
Default
7
RHPL7
0
6
RHPL6
0
5
RHPL5
0
4
RHPL4
0
3
RHPL3
0
2
RHPL2
0
1
RHPL1
0
0
RHPL0
0
Bit #
Name
Default
15
14
13
12
11
10
9
RHPL9
0
8
RHPL8
0
RHPL15 RHPL14 RHPL13 RHPL12 RHPL11 RHPL10
0
0
0
0
0
0
Note: Bits that are underlined are read-only; all other bits are read-write. This is a globe control; only one per device, not one for each
individual HDLC channel.
Bits 0 to 15/Receive HDLC Packet Length (RHPL0 to RHPL15). If the receive length-detection enable bit is
set to 1, the HDLC engine checks the number of received octets in a packet to see if they exceed the count in this
register. If the length is exceeded, the packet is aborted and the remainder is discarded. The definition of “octet
length” is everything between the opening and closing flags, which includes the address field, control field,
information field, and FCS.
Register Name:
THCDIS
Register Description: Transmit HDLC Channel Definition Indirect Select
Register Address:
0480h
Bit #
Name
Default
7
6
5
HCID5
0
4
HCID4
0
3
HCID3
0
2
HCID2
0
1
HCID1
0
0
HCID0
0
HCID7
0
HCID6
0
Bit #
Name
Default
15
IAB
0
14
IARW
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
n/a
0
8
n/a
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 7/HDLC Channel ID (HCID0 to HCID7)
00000000 (00h) = HDLC channel number 1 (also used for the fast HDLC engine on port 0)
00000001 (01h) = HDLC channel number 2 (also used for the fast HDLC engine on port 1)
00000010 (02h) = HDLC channel number 3 (also used for the fast HDLC engine on port 2)
00000011 (03h) = HDLC channel number 4
11111111 (FFh) = HDLC channel number 256
Bit 14/Indirect Access Read/Write (IARW). When the host wishes to read data from the internal transmit HDLC
definition RAM, this bit should be written to 1 by the host. This causes the device to begin obtaining the data from
the channel location indicated by the HCID bits. During the read access, the IAB bit is set to 1. Once the data is
ready to be read from the THCD register, the IAB bit is set to 0. When the host wishes to write data to the internal
transmit HDLC definition RAM, this bit should be written to 0 by the host. This causes the device to take the data
that is currently present in the THCD register and write it to the channel location indicated by the HCID bits.
When the device completes the write, the IAB is set to 0.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit is set to 1 until the data is ready to be read. It is set to 0 when the data is
ready to be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the
write operation is complete.
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
THCD
Register Description: Transmit HDLC Channel Definition
Register Address:
0484h
Bit #
Name
Default
7
6
5
TBF
4
TID
3
2
1
0
TABTE
TCFCS
TCRC1
TCRC0
TIFS
TTRANS
Bit #
Name
Default
15
n/a
14
n/a
13
n/a
12
TZSD
11
TFG3
10
TFG2
9
8
TFG1
TFG0
Note: Bits that are underlined are read only, all other bits are read-write.
Bit 0/Transmit Transparent Enable (TTRANS). When this bit is set low, the HDLC engine generates flags and
the FCS (if enabled through TCRC0/1) and performs zero stuffing. When this bit is set high, the HDLC engine
does not generate flags or the FCS and does not perform zero stuffing.
0 = transparent mode disabled
1 = transparent mode enabled
Bit 1/Transmit Interfill Select (TIFS)
0 = the interfill byte is 7Eh (01111110)
1 = the interfill byte is FFh (11111111)
Bits 2, 3/Transmit CRC Selection (TCRC0/TCRC1). These bits are ignored if the HDLC channel is set to
transparent mode (TTRANS = 1).
TCRC1 TCRC0
ACTION
No CRC is generated
16-bit CRC (CCITT/ITU Q.921)
32-bit CRC
0
0
1
1
0
1
0
1
Illegal state
Bit 4/Transmit Invert Data Enable (TID). When this bit is set low, the outgoing HDLC packets are not inverted
after being generated. When this bit is set high, the HDLC engine inverts all the data (flags, information fields, and
FCS) after the packet has been generated.
0 = do not invert data
1 = invert all data (including flags and FCS)
Bit 5/Transmit Bit Flip (TBF). When this bit is set low, the HDLC engine obtains the first HDLC bit to be
transmitted from the lowest bit position of the PCI bus bytes (i.e., PAD[0], PAD[8], PAD[16], PAD[24]). When
this bit is set high, the HDLC engine obtains the first HDLC bit to be transmitted from the highest bit position of
the PCI bus bytes (i.e., PAD[7], PAD[15], PAD[23], PAD[31]).
0 = the first HDLC bit transmitted is obtained from the lowest bit position of the bytes on the PCI bus
1 = the first HDLC bit transmitted is obtained from the highest bit position of the bytes on the PCI bus
Bit 6/Transmit Corrupt FCS (TCFCS). When this bit is set low, the HDLC engine allows the frame checksum
sequence (FCS) to be transmitted as generated. When this bit is set high, the HDLC engine inverts all the bits of
the FCS before transmission occurs. This is useful in debugging and testing HDLC channels at the system level.
0 = generate FCS normally
1 = invert all FCS bits
Bit 7/Transmit Abort Enable (TABTE). When this bit is set low, the HDLC engine performs normally, only
sending an abort sequence (eight 1s in a row) when an error occurs in the PCI block or the FIFO underflows.
When this bit is set high, the HDLC engine continuously transmits an all-ones pattern (i.e., an abort sequence).
This bit is still active when the HDLC engine is configured in the transparent mode (TTRANS = 1).
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DS31256 256-Channel, High-Throughput HDLC Controller
Bits 8 to 11/Transmit Flag Generation Bits 0 to 3 (TFG0/TFG1/TFG2/TFG3). These four bits determine how
many flags and interfill bytes are sent between consecutive packets.
TFG3
TFG2
TFG1
TFG0
ACTION
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Share closing and opening flag
Closing flag/no interfill bytes/opening flag
Closing flag/1 interfill byte/opening flag
Closing flag/2 interfill bytes/opening flag
Closing flag/3 interfill bytes/opening flag
Closing flag/4 interfill bytes/opening flag
Closing flag/5 interfill bytes/opening flag
Closing flag/6 interfill bytes/opening flag
Closing flag/7 interfill bytes/opening flag
Closing flag/8 interfill bytes/opening flag
Closing flag/9 interfill bytes/opening flag
Closing flag/10 interfill bytes/opening flag
Closing flag/11 interfill bytes/opening flag
Closing flag/12 interfill bytes/opening flag
Closing flag/13 interfill bytes/opening flag
Closing flag/14 interfill bytes/opening flag
Bit 12/Transmit Zero Stuffing Disable (TZSD). When this bit is set low, the HDLC engine performs zero
stuffing on the outgoing data stream. When this bit is set high, the outgoing data stream is not zero stuffed. This
bit is ignored when the HDLC engine is configured in the transparent mode (TTRANS = 1).
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DS31256 256-Channel, High-Throughput HDLC Controller
8. FIFO
8.1 General Description and Example
The DS31256 contains one 16kB FIFO for the receive path and another 16kB FIFO for the transmit path.
Both of these FIFOs are organized into blocks. Since a block is defined as 4 dwords (16 Bytes), each
FIFO is made up of 1024 blocks. Figure 8-1 shows an FIFO example.
The FIFO contains a state machine that is constantly polling the 16 ports to determine if any data is ready
for transfer to/from the FIFO from/to the HDLC engines. The 16 ports are priority decoded with port 0
getting the highest priority and port 15 getting the lowest priority. Therefore, all the enabled HDLC
channels on the lower numbered ports are serviced before the higher numbered ports. As long as the
maximum throughput rate of 132Mbps is not exceeded, the DS31256 ensures there is enough bandwidth
in this transfer to prevent any data loss between the HDLC engines and the FIFO.
The FIFO also controls which HDLC channel the DMA should service to read data out of the FIFO on
the receive side and to write data into the FIFO on the transmit side. Which channel gets the highest
priority from the FIFO is configurable through some control bits in the master configuration register
(Section 5.2). There are two control bits for the receive side (RFPC0 and RFPC1) and two control bits
for the transmit side (TFPC0 and TFPC1) that determine the priority algorithm as shown in Table 8-A.
Table 8-A. FIFO Priority Algorithm Select
HDLC CHANNELS THAT ARE
HDLC CHANNELS THAT ARE SERVICED
OPTION
PRIORITY DECODED
ROUND ROBIN
1 to 256
1
2
3
4
None
1 to 3
16 to 1
64 to 1
4 to 256
17 to 256
65 to 256
To maintain maximum flexibility for channel reconfiguration, each block within the FIFO can be
assigned to any of the 256 HDLC channels. Also, blocks are link-listed together to form a chain whereby
each block points to the next block in the chain. The minimum size of the link-listed chain is 4 blocks
(64 Bytes) and the maximum is the full size of the FIFO, which is 1024 blocks.
To assign a set of blocks to a particular HDLC channel, the host must configure the starting block pointer
and the block pointer RAM. The starting block pointer assigns a particular HDLC channel to a set of
link-listed blocks by pointing to one of the blocks within the chain (it does not matter which block in the
chain is pointed to). The block pointer RAM must be configured for each block that is being used within
the FIFO. The block pointer RAM indicates the next block in the link-listed chain.
Figure 8-1 shows an example of how to configure the starting block pointer and the block pointer RAM.
In this example, only three HDLC channels are being used (channels 2, 6, and 16). The device knows
that channel 2 has been assigned to the eight link-listed blocks of 112, 118, 119, 120, 121, 122, 125, and
126 because a block pointer of 125 has been programmed into the channel 2 position of the starting
block pointer. The block pointer RAM tells the device how to link the eight blocks together to form a
circular chain.
The host must set the watermarks for the receive and transmit paths. The receive path has a high
watermark and the transmit path has a low watermark.
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 8-1. FIFO Example
HDLC
Starting Block
Pointer
1024 Block FIFO
Block Pointer
RAM
Channel
Number
(1 Block = 4 dwords)
CH 1
not used
Block Pointer 125
not used
not used
not used
not used
not used
Block 4
Block 5
Block 3
Block 2
not used
Block 0
Block 1
Block 2
Block 3
Block 4
Block 5
Block 6
Block 0
Block 1
Block 2
Block 3
Block 4
Block 5
Block 6
CH 2
CH 3
Channel 16
Channel 16
Channel 16
Channel 16
not used
CH 4
not used
CH 5
not used
CH 6
Block Pointer 113
not used
CH 7
CH 8
not used
CH 9
not used
CH 10
CH 11
CH 12
CH 13
CH 14
CH 15
CH 16
CH 17
CH 18
CH 19
CH 20
CH 21
not used
Block 112
Block 113
Block 114
Block 115
Block 116
Block 117
Block 118
Block 119
Block 120
Block 121
Block 122
Block 123
Block 124
Block 125
Block 126
Block 127
Channel 2
Channel 6
Channel 6
not used
Block 112
Block 113
Block 114
Block 115
Block 116
Block 117
Block 118
Block 119
Block 120
Block 121
Block 122
Block 123
Block 124
Block 125
Block 126
Block 127
Block 118
Block 114
Block 113
not used
not used
not used
Block 119
Block 120
Block 121
Block 122
Block 125
not used
not used
Block 126
Block 112
not used
not used
not used
not used
not used
not used
not used
not used
Block Pointer 5
not used
Channel 2
Channel 2
Channel 2
Channel 2
Channel 2
not used
not used
not used
not used
not used
not used
Channel 2
Channel 2
not used
not used
not used
CH 255
CH 256
Block 1022
Block 1023
not used
not used
Block 1022
Block 1023
not used
not used
fifobd.drw
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DS31256 256-Channel, High-Throughput HDLC Controller
8.1.1 Receive High Watermark
The high watermark tells the device how many blocks the HDLC engines should write into the receive
FIFO before the DMA sends data to the PCI bus, or rather, how full the FIFO should get before it should
be emptied by the DMA. When the DMA begins reading the data from the FIFO, it reads all available
data and tries to completely empty the FIFO even if one or more EOFs (end of frames) are detected. For
example, if four blocks were link-listed together and the host programmed the high watermark to three
blocks, then the DMA would read the data out of the FIFO and transfer it to the PCI bus after the HDLC
controller had written three complete blocks in succession into the FIFO and still had one block left to
fill. The DMA would not read the data out of the FIFO again until another three complete blocks had
been written into the FIFO in succession by the HDLC engine or until an EOF was detected. In this
example of four blocks being link-listed together, the high watermark could also be set to 1 or 2, but no
other values would be allowed. If an incoming packet does not fill the FIFO enough to reach the high
watermark before an EOF is detected, the DMA still requests that the data be sent to the PCI bus; it does
not wait for additional data to be written into the FIFO by the HDLC engines.
8.1.2 Transmit Low Watermark
The low watermark tells the device how many blocks should be left in the FIFO before the DMA should
begin getting more data from the PCI bus, or rather, how empty the FIFO should get before it should be
filled again by the DMA. When the DMA begins reading the data from the PCI bus, it reads all available
data and tries to completely fill the FIFO even if one or more EOFs (HDLC packets) are detected. For
example, if five blocks were link-listed together and the host programmed the low watermark to two
blocks, then the DMA would read the data from the PCI bus and transfer it to the FIFO after the HDLC
engine has read three complete blocks in succession from the FIFO and, therefore, still had two blocks
left before the FIFO was empty. The DMA would not read the data from the PCI bus again until another
three complete blocks had been read from the FIFO in succession by the HDLC engines. In this example
of five blocks being link-listed together, the low watermark could also be set to any value from 1 to 3
(inclusive) but no other values would be allowed. In other words, the tranmist low watermark can be set
to a value of 1 to N - 2, where N = number of blocks linked together. When a new packet is written into a
completely empty FIFO by the DMA, the HDLC engines wait until the FIFO fills beyond the low
watermark or until an EOF is seen before reading the data out of the FIFO.
8.2 FIFO Register Description
Register Name:
RFSBPIS
Register Description: Receive FIFO Starting Block Pointer Indirect Select
Register Address:
0900h
Bit #
Name
Default
7
HCID7
0
6
HCID6
0
5
HCID5
0
4
HCID4
0
3
HCID3
0
2
HCID2
0
1
HCID1
0
0
HCID0
0
Bit #
Name
Default
15
IAB
0
14
IARW
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
n/a
0
8
n/a
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 7/HDLC Channel ID (HCID0 to HCID7)
00000000 (00h) = HDLC channel number 1
11111111 (FFh) = HDLC channel number 256
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DS31256 256-Channel, High-Throughput HDLC Controller
Bit 14/Indirect Access Read/Write (IARW). When the host wishes to write data to set the internal receive
starting block pointer, the host should write this bit to 0. This causes the device to take data that is currently
presetn in the RFSBP register and write it to the channel location indicated by the HCID bits. When the device
completes the write, the IAB is set to 0.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit is set to 1 until the data is ready to be read. It is set to 0 when the data is
ready to be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the
write operation completes.
Register Name:
RFSBP
Register Description: Receive FIFO Starting Block Pointer
Register Address:
0904h
Bit #
Name
Default
7
6
5
4
3
2
1
0
RSBP7
RSBP6
RSBP5
RSBP4
RSBP3
RSBP2
RSBP1
RSBP0
Bit #
Name
Default
15
n/a
14
n/a
13
n/a
12
n/a
11
n/a
10
n/a
9
8
RSBP9
RSBP8
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 9/Starting Block Pointer (RSBP0 to RSBP9). These bits determine which of the 1024 blocks within the
receive FIFO the host wants the device to configure as the starting block for a particular HDLC channel. Any of
the blocks within a chain of blocks for an HDLC channel can be configured as the starting block. When these bits
are read, they report the current block pointer being used to write data into the receive FIFO from the HDLC Layer
2 engines.
0000000000 (000h) = use block 0 as the starting block
0111111111 (1FFh) = use block 511 as the starting block
1111111111 (3FFh) = use block 1023 as the starting block
Register Name:
RFBPIS
Register Description: Receive FIFO Block Pointer Indirect Select
Register Address:
0910h
Bit #
Name
Default
7
6
5
4
3
2
1
0
BLKID0
0
BLKID7 BLKID6 BLKID5 BLKID4 BLKID3 BLKID2 BLKID1
0
0
0
0
0
0
0
Bit #
Name
Default
15
IAB
0
14
IARW
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
BLKID9
0
8
BLKID8
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 9/Block ID (BLKID0 to BLKID9)
0000000000 (000h) = block number 0
0111111111 (1FFh) = block number 511
1111111111 (3FFh) = block number 1023
Bit 14/Indirect Access Read/Write (IARW). When the host wishes to read data from the internal receive block
pointer RAM, the host should write this bit to 1. This causes the device to begin obtaining the data from the block
location indicated by the BLKID bits. During the read access, the IAB bit is set to 1. Once the data is ready to be
read from the RFBP register, the IAB bit is set to 0. When the host wishes to write data to the internal receive
77 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
block pointer RAM, the host should write this bit to 0. This causes the device to take the data that is currently
present in the RFBP register and write it to the channel location indicated by the BLKID bits. When the device
completes the write, the IAB is set to 0.
Note: The RFSBP is write-only memory. Once this register has been written to and the operation has started, the
DS31256 internal state machine changes the value in this memory.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit is set to 1 until the data is ready to be read. It is set to 0 when the data is
ready to be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the
write operation completes.
Register Name:
RFBP
Register Description: Receive FIFO Block Pointer
Register Address:
0914h
Bit #
Name
Default
7
6
5
4
3
2
1
0
RBP7
RBP6
RBP5
RBP4
RBP3
RBP2
RBP1
RBP0
Bit #
Name
Default
15
n/a
14
n/a
13
n/a
12
n/a
11
n/a
10
n/a
9
8
RBP9
RBP8
Note: Bits that are underlined are read only, all other bits are read-write.
Bits 0 to 9/Block Pointer (RBP0 to RBP9). These bits indicate which of the 10242 blocks is the next block in the
link-list chain. A block is not allowed to point to itself.
0000000000 (000h) = block 0 is the next linked block
0111111111 (1FFh) = block 511 is the next linked block
1111111111 (3FFh) = block 1023 is the next linked block
Register Name:
RFHWMIS
Register Description: Receive FIFO High-Watermark Indirect Select
Register Address:
0920h
Bit #
Name
Default
7
HCID7
0
6
HCID6
0
5
HCID5
0
4
HCID4
0
3
HCID3
0
2
HCID2
0
1
HCID1
0
0
HCID0
0
Bit #
Name
Default
15
IAB
14
IARW
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
n/a
0
8
n/a
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 7/HDLC Channel ID (HCID0 to HCID7)
00000000 (00h) = HDLC channel number 1
11111111 (FFh) = HDLC channel number 256
Bit 14/Indirect Access Read/Write (IARW). When the host wishes to read data from the internal receive high-
watermark RAM, this bit should be written to 1 by the host. This causes the device to begin obtaining the data
from the channel location indicated by the HCID bits. During the read access, the IAB bit is set to 1. Once the data
is ready to be read from the RFHWM register, the IAB bit is set to 0. When the host wishes to write data to the
internal receive high-watermark RAM, this bit should be written to 0 by the host. This causes the device to take
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DS31256 256-Channel, High-Throughput HDLC Controller
the data that is currently present in the RFHWM register and write it to the channel location indicated by the HCID
bits. When the device has completed the write, the IAB is set to 0.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit is set to 1 until the data is ready to be read. It is set to 0 when the data is
ready to be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the
write operation has completed.
Register Name:
RFHWM
Register Description: Receive FIFO High Watermark
Register Address:
0924h
Bit #
7
6
5
4
3
2
1
0
Name
RHWM7 RHWM6
RHWM5
RHWM4
RHWM3
RHWM2
RHWM1
RHWM0
Default
Bit #
Name
Default
15
n/a
14
n/a
13
n/a
12
n/a
11
n/a
10
n/a
9
8
RHWM9
RHWM8
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 9/High Watermark (RHWM0 to RHWM9). These bits indicate the setting of the receive high-
watermark. The high-watermark setting is the number of successive blocks that the HDLC controller writes to the
FIFO before the DMA sends the data to the PCI bus. The high-watermark setting must be between (inclusive) one
block and one less than the number of blocks in the link-list chain for the particular channel involved. For
example, if four blocks are linked together, the high watermark can be set to either 1, 2, or 3. In other words, the
high watermark can be set to a value of 1 to N - 1, where N = number of block linked together. Any other numbers
are illegal.
0000000000 (000h) = invalid setting
0000000001 (001h) = high watermark is 1 block
0000000010 (002h) = high watermark is 2 blocks
0111111111 (1FFh) = high watermark is 511 blocks
1111111111 (3FFh) = high watermark is 1023 blocks
Register Name:
TFSBPIS
Register Description: Transmit FIFO Starting Block Pointer Indirect Select
Register Address:
0980h
Bit #
7
6
5
HCID5
0
4
HCID4
0
3
HCID3
0
2
HCID2
0
1
HCID1
0
0
HCID0
0
Name
HCID7
0
HCID6
0
Default
Bit #
Name
Default
15
IAB
0
14
IARW
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
n/a
0
8
n/a
0
Note: Bits that are underlined are read-only; all other bits are read-write.
79 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Bits 0 to 7/HDLC Channel ID (HCID0 to HCID7)
00000000 (00h) = HDLC channel number 1
11111111 (FFh) = HDLC channel number 256
Bit 14/Indirect Access Read/Write (IARW). When the host wishes to write data to the internal transmit starting
block pointer RAM, this bit should be written to 1 by the host. This causes the device to take the data that is in the
TFSBP register and write it to the channel location indicated by the HCID bits. When the device has completed the
write, the IAB is set to 0.
Note: The TFSBP register is write-only memory. Once this register has been written to and the operation has
started, the DS31256 internal state machine changes the value in this memory.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit is set to 1 until the data is ready to be read. It is set to 0 when the data is
ready to be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the
write operation has completed.
Register Name:
TFSBP
Register Description: Transmit FIFO Starting Block Pointer
Register Address:
0984h
Bit #
Name
Default
7
6
5
4
3
2
1
0
TSBP7
TSBP6
TSBP5
TSBP4
TSBP3
TSBP2
TSBP1
TSBP0
Bit #
Name
Default
15
n/a
14
n/a
13
n/a
12
n/a
11
n/a
10
n/a
9
8
TSBP9
TSBP8
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 9/Starting Block Pointer (TSBP0 to TSBP9). These bits determine which of the 1024 blocks within the
transmit FIFO the host wants the device to configure as the starting block for a particular HDLC channel. Any of
the blocks within a chain of blocks for an HDLC channel can be configured as the starting block. When these bits
are read, they report the current block pointer being used to read data from the transmit FIFO by the HDLC Layer
2 engines.
0000000000 (000h) = use block 0 as the starting block
0111111111 (1FFh) = use block 511 as the starting block
1111111111 (3FFh) = use block 1023 as the starting block
Register Name:
TFBPIS
Register Description: Transmit FIFO Block Pointer Indirect Select
Register Address:
0990h
Bit #
Name
Default
7
6
5
4
3
2
1
0
BLKID7 BLKID6 BLKID5 BLKID4 BLKID3 BLKID2 BLKID1 BLKID0
0
0
0
0
0
0
0
0
Bit #
Name
Default
15
IAB
0
14
IARW
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
8
BLKID9 BLKID8
0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
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DS31256 256-Channel, High-Throughput HDLC Controller
Bits 0 to 9/Block ID (BLKID0 to BLKID9)
00000000000 (000h) = block number 0
01111111111 (1FFh) = block number 511
1111111111 (3FFh) = block number 1023
Bit 14/Indirect Access Read/Write (IARW). When the host wishes to read data from the internal transmit block
pointer RAM, this bit should be written to 1 by the host. This causes the device to begin obtaining the data from
the block location indicated by the BLKID bits. During the read access, the IAB bit is set to 1. Once the data is
ready to be read from the TFBP register, the IAB bit is set to 0. When the host wishes to write data to the internal
transmit block pointer RAM, this bit should be written to 0 by the host. This causes the device to take the data that
is currently present in the TFBP register and write it to the channel location indicated by the BLKID bits. When
the device has completed the write, the IAB is set to 0.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit is set to 1 until the data is ready to be read. It is set to 0 when the data is
ready to be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the
write operation has completed.
Register Name:
TFBP
Register Description: Transmit FIFO Block Pointer
Register Address:
0994h
Bit #
Name
Default
7
6
5
4
3
2
1
0
TBP7
TBP6
TBP5
TBP4
TBP3
TBP2
TBP1
TBP0
Bit #
Name
Default
15
n/a
14
n/a
13
n/a
12
n/a
11
n/a
10
n/a
9
8
TBP9
TBP8
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 9/Block Pointer (TBP0 to TBP9). These bits indicate which of the 1024 blocks is the next block in the
link list chain. A block is not allowed to point to itself.
0000000000 (000h) = block 0 is the next linked block
0111111111 (1FFh) = block 511 is the next linked block
1111111111 (3FFh) = block 1023 is the next linked block
Register Name:
TFLWMIS
Register Description: Transmit FIFO Low-Watermark Indirect Select
Register Address:
09A0h
Bit #
Name
Default
7
HCID7
0
6
HCID6
0
5
HCID5
0
4
HCID4
0
3
HCID3
0
2
HCID2
0
1
HCID1
0
0
HCID0
0
Bit #
Name
Default
15
IAB
0
14
IARW
0
13
n/a
0
12
n/a
0
11
n/a
0
10
n/a
0
9
n/a
0
8
n/a
0
Note: Bits that are underlined are read-only, all other bits are read-write.
Bits 0 to 7/HDLC Channel ID (HCID0 to HCID7)
00000000 (00h) = HDLC channel number 1
11111111 (FFh) = HDLC channel number 256
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DS31256 256-Channel, High-Throughput HDLC Controller
Bit 14/Indirect Access Read/Write (IARW). When the host wishes to read data from the internal transmit low-
watermark RAM, this bit should be written to 1 by the host. This causes the device to begin obtaining the data
from the channel location indicated by the HCID bits. During the read access, the IAB bit is set to 1. Once the data
is ready to be read from the TFLWM register, the IAB bit is set to 0. When the host wishes to write data to the
internal transmit low-watermark RAM, this bit should be written to 0 by the host. This causes the device to take
the data that is currently present in the TFLWM register and write it to the channel location indicated by the HCID
bits. When the device has completed the write, the IAB is set to 0.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit is set to 1 until the data is ready to be read. It is set to 0 when the data is
ready to be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the
write operation has completed.
Register Name:
TFLWM
Register Description: Transmit FIFO Low Watermark
Register Address:
09A4h
Bit #
Name
Default
7
6
5
4
3
2
1
0
TLWM7 TLWM6 TLWM5 TLWM4 TLWM3 TLWM2 TLWM1 TLWM0
Bit #
Name
Default
15
n/a
14
n/a
13
n/a
12
n/a
11
n/a
10
n/a
9
8
TLWM9 TLWM8
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 9/Low Watermark (TLWM0 to TLWM9). These bits indicate the setting of the transmit low
watermark. The low watermark setting is the number of blocks left in the transmit FIFO before the DMA gets
more data from the PCI bus. The low-watermark setting must be between (inclusive) one block and one less than
the number of blocks in the link-list chain for the particular channel involved. For example, if five blocks are
linked together, the low watermark can be set to 1, 2, or 3. In other words, the low watermark can be set at a value
of 1 to N - 2, where N = number of block linked together. Any other numbers are illegal.
0000000000 (000h) = invalid setting
0000000001 (001h) = low watermark is 1 block
0000000010 (002h) = low watermark is 2 blocks
0111111111 (1FFh) = low watermark is 511 blocks
1111111111 (3FFh) = low watermark is 1023 blocks
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DS31256 256-Channel, High-Throughput HDLC Controller
9. DMA
9.1 Introduction
The DMA block (Figure 2-1) handles the transfer of packet data from the FIFO block to the PCI block
and vice versa. Throughout this section, the terms host and descriptor are used. Host is defined as the
CPU or intelligent controller that sits on the PCI bus and instructs the device about how to handle the
incoming and outgoing packet data. Descriptor is defined as a preformatted message that is passed from
the host to the DMA block or vice versa to indicate where packet data should be placed or obtained from.
On power-up, the DMA is disabled because the RDE and TDE control bits in the master configuration
register (Section 5) are set to 0. The host must configure the DMA by writing to all of the registers listed
in Table 9-A (which includes all 256 channel locations in the receive and transmit configuration RAMs),
then enable the DMA by setting to the RDE and TDE control bits to 1.
The structure of the DMA is such that the receive- and transmit-side descriptor-address spaces can be
shared, even among multiple chips on the same bus. Through the master control register, the host
determines how long the DMA is allowed to burst onto the PCI bus. The default value is 32 dwords (128
Bytes) but, through the DT0 and DT1 control bits, the host can enable the receive or transmit DMAs to
burst either 64 dwords (256 Bytes), 128 dwords (512 Bytes), or 256 dwords (1024 Bytes).
The receive and transmit packet descriptors have almost identical structures (Sections 9.2.2 and 9.3.2),
which provide a minimal amount of host intervention in store-and-forward applications. In other words,
the receive descriptors created by the receive DMA can be used directly by the transmit DMA. The
receive and transmit portions of the DMA are completely independent and are discussed separately.
The DS31256 has no restrictions on the transmit side, but has the following restrictions on the location
and size of receive buffers in host memory:
• All receive buffers must start on a DWORD aligned address.
• All receive buffers must have a size in bytes that is a multiple of 4.
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DS31256 256-Channel, High-Throughput HDLC Controller
Table 9-A. DMA Registers to be Configured by the Host on Power-Up
ADDRESS
NAME
REGISTER
SECTION
0700
0704
0708
070C
0710
0714
0718
071C
0730
0734
0738
073C
0740
0744
0750
0754
0770
0774
0780
0790
0794
0800
0804
0808
080C
0810
0830
0834
0838
083C
0840
0844
0850
0854
0870
0874
0880
RFQBA0
RFQBA1
RFQEA
Receive Free-Queue Base Address 0 (lower word)
Receive Free-Queue Base Address 1 (upper word)
Receive Free-Queue End Address
9.2.3
9.2.3
9.2.3
9.2.3
9.2.3
9.2.3
9.2.3
9.2.3
9.2.4
9.2.4
9.2.4
9.2.4
9.2.4
9.2.4
9.2.2
9.2.2
9.2.5
9.2.5
9.2.3, 9.2.4
9.2.1
9.2.1
9.3.3
9.3.3
9.3.3
9.3.3
9.3.3
9.3.4
9.3.4
9.3.4
9.3.4
9.3.4
9.3.4
9.3.2
9.3.2
9.3.5
9.3.5
9.3.3, 9.3.4
RFQSBSA
RFQLBWP
RFQSBWP
RFQLBRP
RFQSBRP
RDQBA0
RDQBA1
RDQEA
RDQRP
Receive Free-Queue Small Buffer Start Address
Receive Free-Queue Large Buffer Host Write Pointer
Receive Free-Queue Small Buffer Host Write Pointer
Receive Free-Queue Large Buffer DMA Read Pointer
Receive Free-Queue Small Buffer DMA Read Pointer
Receive Done-Queue Base Address 0 (lower word)
Receive Done-Queue Base Address 1 (upper word)
Receive Done-Queue End Address
Receive Done-Queue Host Read Pointer
RDQWP
RDQFFT
RDBA0
Receive Done-Queue DMA Write Pointer
Receive Done-Queue FIFO Flush Timer
Receive Descriptor Base Address 0 (lower word)
Receive Descriptor Base Address 1 (upper word)
Receive DMA Configuration Indirect Select
RDBA1
RDMACIS
RDMAC
RDMAQ
RLBS
Receive DMA Configuration (all 256 channels)
Receive DMA Queues Control
Receive Large Buffer Size
RSBS
Receive Small Buffer Size
TPQBA0
TPQBA1
TPQEA
Transmit Pending-Queue Base Address 0 (lower word)
Transmit Pending-Queue Base Address 1 (upper word)
Transmit Pending-Queue End Address
TPQWP
TPQRP
Transmit Pending-Queue Host Write Pointer
Transmit Pending-Queue DMA Read Pointer
Transmit Done-Queue Base Address 0 (lower word)
Transmit Done-Queue Base Address 1 (upper word)
Transmit Done-Queue End Address
TDQBA0
TDQBA1
TDQEA
TDQRP
Transmit Done-Queue Host Read Pointer
Transmit Done-Queue DMA Write Pointer
Transmit Done-Queue FIFO Flush Timer
Transmit Descriptor Base Address 0 (lower word)
Transmit Descriptor Base Address 1 (upper word)
Transmit DMA Configuration Indirect Select
Transmit DMA Configuration (all 256 channels)
Transmit Queues FIFO Control
TDQWP
TDQFFT
TDBA0
TDBA1
TDMACIS
TDMAC
TDMAQ
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DS31256 256-Channel, High-Throughput HDLC Controller
9.2 Receive Side
9.2.1 Overview
The receive DMA uses a scatter-gather technique to write packet data into main memory. The host keeps
track of and decides where the DMA should place the incoming packet data. There are a set of
descriptors that get handed back and forth between the DMA and the host. Through these descriptors, the
host can inform the DMA where to place the packet data and the DMA can tell the host when the data is
ready to be processed.
The operation of the receive DMA has three main areas, as shown in Figure 9-1, Figure 9-2, and
Table 9-B. The host writes to the free-queue descriptors informing the DMA where it can place the
incoming packet data. Associated with each free data buffer location is a free packet descriptor where the
DMA can write information to inform the host about the attributes of the packet data (i.e., status
information, number of bytes, etc.) that it outputs. To accommodate the various needs of packet data, the
host can quantize the free data buffer space into two different buffer sizes. The host sets the size of the
buffers through the receive large buffer size (RLBS) and the receive small buffer size (RSBS) registers.
Register Name:
RLBS
Register Description: Receive Large Buffer Size Select
Register Address:
0790h
Bit #
Name
Default
7
LBS7
0
6
LBS6
0
5
LBS5
0
4
LBS4
0
3
LBS3
0
2
LBS2
0
1
LBS1
0
0
LBS0
0
Bit #
Name
Default
15
n/a
0
14
n/a
0
13
n/a
0
12
LBS12
0
11
LBS11
0
10
LBS10
0
9
LBS9
0
8
LBS8
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 12/Large Buffer Select Bit (LBS0 to LBS12)
0000000000000 (0000h) = buffer size is 0 Bytes
1111111111100 (1FFCh) = buffer size is 8188 Bytes
Register Name:
RSBS
Register Description: Receive Small Buffer Size Select
Register Address:
0794h
Bit #
Name
Default
7
SBS7
0
6
SBS6
0
5
SBS5
0
4
SBS4
0
3
SBS3
0
2
SBS2
0
1
SBS1
0
0
SBS0
0
Bit #
Name
Default
15
n/a
0
14
n/a
0
13
n/a
0
12
SBS12
0
11
SBS11
0
10
SBS10
0
9
SBS9
0
8
SBS8
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 12/Small Buffer Select Bit (SBS0 to SBS12)
0000000000000 (0000h) = buffer size is 0 Bytes
1111111111100 (1FFCh) = buffer size is 8188 Bytes
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DS31256 256-Channel, High-Throughput HDLC Controller
On an HDLC-channel basis in the receive DMA configuration RAM, the host instructs the DMA how to
use the large and small buffers for the incoming packet data on that particular HDLC channel. The host
has three options: (1) only use large buffers, (2) only use small buffers, or (3) first fill a small buffer,
then, if the incoming packet requires more buffer space, use one or more large buffers for the remainder
of the packet. The host selects the option through the size field in the receive configuration RAM
(Section 9.2.5). Large buffers are best used for data-intensive, time-insensitive packets like graphics
files, whereas small buffers are best used for time-sensitive information like real-time voice.
Table 9-B. Receive DMA Main Operational Areas
DESCRIPTORS
FUNCTION
SECTION
9.2.2
A dedicated area of memory that describes the location and attributes of
the packet data.
Packet
A dedicated area of memory that the host writes to inform the DMA
where to store incoming packet data.
Free Queue
Done Queue
9.2.3
A dedicated area of memory that the DMA writes to inform the host
that the packet data is ready for processing.
9.2.4
The done-queue descriptors contain information that the DMA wishes to pass to the host. Through the
done-queue descriptors, the DMA informs the host about the incoming packet data and where to find the
packet descriptors that it has written into main memory. Each completed descriptor contains the starting
address of the data buffer where the packet data is stored.
If enabled, the DMA can burst read the free-queue descriptors and burst write the done-queue
descriptors. This helps minimize PCI bus accesses, freeing the PCI bus up to do more time critical
functions. See Sections 9.2.3 and 9.2.4 for more details about this feature.
Receive DMA Actions
A typical scenario for the receive DMA is as follows:
1) The receive DMA gets a request from the receive FIFO that it has packet data that needs to be sent to
the PCI bus.
2) The receive DMA determines whether the incoming packet data should be stored in a large buffer or
a small buffer.
3) The receive DMA then reads a free-queue descriptor (either by reading a single descriptor or a burst
of descriptors), indicating where, in main memory, there exists some free data buffer space and
where the associated free packet descriptor resides.
4) The receive DMA starts storing packet data in the previously free buffer data space by writing it out
through the PCI bus.
5) When the receive DMA realizes that the current data buffer is filled (by knowing the buffer size it
can calculate this), it then reads another free-queue descriptor to find another free data buffer and
packet descriptor location.
6) The receive DMA then writes the previous packet descriptor and creates a linked list by placing the
current descriptor in the next descriptor pointer field; it then starts filling the new buffer location.
Figure 9-1 provides an example of packet descriptors being link listed together (see channel 2).
7) This continues until the entire packet data is stored.
8) The receive DMA either waits until a packet has been completely received or until a programmable
number (from 1 to 7) of data buffers have been filled before writing the done-queue descriptor, which
indicates to the host that packet data is ready for processing.
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DS31256 256-Channel, High-Throughput HDLC Controller
Host Actions
The host typically handles the receive DMA as follows:
1) The host is always trying to make free data buffer space available and therefore tries to fill the free-
queue descriptor.
2) The host either polls, or is interrupted, when some incoming packet data is ready for processing.
3) The host then reads the done-queue descriptor circular queue to find out which channel has data
available, what the status is, and where the receive packet descriptor is located.
4) The host then reads the receive packet descriptor and begins processing the data.
5) The host then reads the next descriptor pointer in the link-listed chain and continues this process
until either a number (from 1 to 7) of descriptors have been processed or an end of packet has been
reached.
6) The host then checks the done-queue descriptor circular queue to see if any more data buffers are
ready for processing.
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 9-1. Receive DMA Operation
Free Queue Descriptors
(circular queue)
Free Data Buffer Address
00h
unused
Free Desc. Ptr.
Free Data Buffer Address
unused Free Desc. Ptr.
Free Data Buffer Address
unused Free Desc. Ptr.
08h
10h
Open Descriptor Space
Available for Use by the DMA
Free Data Buffer
(up to 8188 bytes)
Open Descriptor Space
Available for Use by the DMA
Free Data Buffer
(up to 8188 bytes)
Free Packet Descriptors & Data Buffers
Used Packet Descriptors & Data Buffers
Done Queue Descriptors
(circular queue)
Data Buffer Address
Status # Bytes Next Desc. Ptr.
Timestamp CH #2
Unused
First Filled
Status CH #5
Status CH #2
Status CH #9
Status CH #
Desc. Ptr.
Desc. Ptr.
Desc. Ptr.
Desc. Ptr.
EOF
EOF
EOF
EOF
00h
Data Buffer
for Channel 2
04h
08h
0Ch
Data Buffer Address
Single Filled
Data Buffer
for Channel 5
Status # Bytes Next Desc. Ptr.
Timestamp
CH #5
Data Buffer Address
Second Filled
Data Buffer
Status # Bytes Next Desc. Ptr.
Timestamp
CH #2
for Channel 2
Data Buffer Address
Last Filled
Status # Bytes Next Desc. Ptr.
Timestamp
CH #2
Data Buffer
for Channel 2
Data Buffer Address
dmarbd
Single Filled
Data Buffer
for Channel 9
Status # Bytes Next Desc. Ptr.
Timestamp
CH #9
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 9-2. Receive DMA Memory Organization
Main Off-Board Memory
(32-Bit Address Space)
Internal Registers
Free Data Buffer Space
Used Data Buffer Space
Free-Queue Base Address (32)
Receive Free-Queue Descriptors:
Contains 32-Bit Addresses for Free Data
Buffers and their Associated
Free-Queue Large Buffer Host Write Pointer (16)
Free-Queue Large Buffer DMA Read Pointer (16)
Free-Queue Small Buffer Start Address (16)
Free-Queue Small Buffer Host Write Pointer (16)
Free-Queue Small Buffer DMA Read Pointer (16)
Free-Queue End Address (16)
Free Packet Descriptors
Up to 64k Dual dwords
Free-Queue Descriptors Allowed
Done-Queue Base Address (32)
Done-Queue DMA Write Pointer (16)
Done-Queue Host Read Pointer (16)
Receive Done-Queue Descriptors:
Contains Index Pointers to
Used Packet Descriptors
Upto64kdwordsDone-Queue
Descriptors Allowed
Done-Queue End Address (16)
Descriptor Base Address (32)
Receive Packet Descriptors:
Contains 32-Bit Addresses
to Free Buffer as well as
Status/Control Information and
Links to Other Packet Descriptors
Up to 64k Quad dwords
Descriptors Allowed
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DS31256 256-Channel, High-Throughput HDLC Controller
9.2.2 Packet Descriptors
A contiguous section of up to 65,536 quad dwords that make up the receive packet descriptors resides in
main memory. The receive packet descriptors are aligned on a quad dword basis and can be placed
anywhere in the 32-bit address space through the receive descriptor base address (Table 9-C). A data
buffer is associated with each descriptor. The data buffer can be up to 8188 Bytes long and must be a
contiguous section of main memory. The host can set two different data buffer sizes through the receive
large buffer size (RLBS) and the receive small buffer size (RSBS) registers (Section 9.2.1). If an
incoming packet requires more space than the data buffer allows, packet descriptors are link-listed
together by the DMA to provide a chain of data buffers. Figure 9-3 shows an example of how three
descriptors were linked together for an incoming packet on HDLC channel 2. Figure 9-2 shows a similar
example. Channel 9 only required a single data buffer and therefore only one packet descriptor was used.
Packet descriptors can be either free (available for use by the DMA) or used (currently contain data that
needs to be processed by the host). The free-queue descriptors point to the free-packet descriptors. The
done-queue descriptors point to the used-packet descriptors.
Table 9-C. Receive Descriptor Address Storage
REGISTER
NAME
ADDRESS
Receive Descriptor Base Address 0 (lower word)
Receive Descriptor Base Address 1 (upper word)
RDBA0
RDBA1
0750h
0754h
Figure 9-3. Receive Descriptor Example
Base + 00h
Free Descriptor
Base + 10h Channel 2 First Buffer Descriptor
Base + 20h Channel 9 Single Buffer Descriptor
Free-Queue Descriptor
Address
Base + 30h
Base + 40h
Base + 50h
Base + 60h
Base + 70h
Base + 80h
Free Descriptor
Free Descriptor
Done-Queue Descriptor Pointer
Channel 2 Second Buffer Descriptor
Free Descriptor
Channel 2 Last Buffer Descriptor
Free Descriptor
Base + FFFD0h
Base + FFFF0h
Free Descriptor
Free Descriptor
Maximum of 65,536
Descriptors
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 9-4. Receive Packet Descriptors
dword 0
Data Buffer Address (32)
Byte Count (13) Next Descriptor Pointer (16)
Timestamp (24) HDLC Channel (8)
dword 1
BUFS (3)
dword 2
dword 3
unused (32)
Note: The organization of the receive descriptor is not affected by the enabling of Big Endian.
dword 0; Bits 0 to 31/Data Buffer Address. Direct 32-bit starting address of the data buffer that is associated
with this receive descriptor.
dword 1; Bits 0 to 15/Next Descriptor Pointer. This 16-bit value is the offset from the receive descriptor base
address of the next descriptor in the chain. Only valid if buffer status = 001 or 010. Note: This is an index, not
absolute address.
dword 1; Bits 16 to 28/Byte Count. Number of bytes stored in the data buffer. Maximum is 8188 Bytes (0000h =
0 Bytes / 1FFCh = 8188 Bytes).
dword 1; Bits 29 to 31/Buffer Status. Must be one of the three states listed below.
001 = first buffer of a multiple buffer packet
010 = middle buffer of a multiple buffer packet
100 = last buffer of a multiple or single buffer packet (equivalent to EOF)
dword 2; Bits 0 to 7/HDLC Channel Number. HDLC channel number, which can be from 1 to 256.
00000000 (00h) = HDLC channel number 1
11111111 (FFh) = HDLC channel number 256
dword 2; Bits 8 to 31/Timestamp. When each descriptor is written into memory by the DMA, this 24-bit
timestamp is provided to keep track of packet arrival times. The timestamp is based on the PCLK frequency
divided by 16. For a 33MHz PCLK, the timestamp increments every 485ns and rolls over every 8.13 seconds. For
a 25MHz clock, the timestamp increments every 640ns and rolls over every 10.7 seconds. The host can calculate
the difference in packets’ arrival times by knowing the PCLK frequency and then taking the difference in
timestamp readings between consecutive packet descriptors.
dword 3; Bits 0 to 31/Unused. Not written to by the DMA. Can be used by the host. Application Note: dword 3
is used by the transmit DMA and, in store and forward applications, the receive and transmit packet descriptors
have been designed to eliminate the need for the host to groom the descriptors before transmission. In these type of
applications, the host should not use dword 3 of the receive packet descriptor.
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DS31256 256-Channel, High-Throughput HDLC Controller
9.2.3 Free Queue
The host writes the 32-bit addresses of the available (free) data buffers and their associated packet
descriptors to the receive free queue. The descriptor space is indicated through a 16-bit pointer, which
the DMA uses along with the receive packet descriptor base address to find the exact 32-bit address of
the associated receive packet descriptor.
Figure 9-5. Receive Free-Queue Descriptor
dword 0
Free Data Buffer Address (32)
dword 1
Unused (16)
Free Packet Descriptor Pointer (16)
Note: The organization of the free queue is not affected by the enabling of Big Endian.
dword 0; Bits 0 to 31/Data Buffer Address. Direct 32-bit starting address of a free data buffer.
dword 1; Bits 0 to 15/Free Packet Descriptor Pointer. This 16-bit value is the offset from the receive descriptor
base address of the free descriptor space associated with the free data buffer in dword 0. Note: This is an index,
not an absolute address.
dword 1; Bits 16 to 31/Unused. Not used by the DMA. Can be set to any value by the host and is ignored by the
receive DMA.
The receive DMA reads from the receive free-queue descriptor circular queue which data buffers and
their associated descriptors are available for use by the DMA.
The receive free-queue descriptor is actually a set of two circular queues (Figure 9-6). There is one
circular queue that indicates where free large buffers and their associated free descriptors exist. There is
another circular queue that indicates where free small buffers and their associated free descriptors exist.
Large and Small Buffer Size Handling
Through the receive configuration-RAM buffer-size field, the DMA knows for a particular HDLC
channel whether the incoming packets should be stored in the large or the small free data buffers. The
host informs the DMA of the size of both the large and small buffers through the receive large and small
buffer size (RLBS/RSBS) registers. For example, when the DMA knows that data is ready to be written
onto the PCI bus, it checks to see if the data is to be sent to a large buffer or a small buffer, and then it
goes to the appropriate free-queue descriptor and pulls the next available free buffer address and free
descriptor pointer. If the host wishes to have only one buffer size, then the receive free queue small-
buffer start address is set equal to the receive free-queue end address. In the receive configuration RAM,
none of the active HDLC channels are configured for the small buffer size.
There are a set of internal addresses within the device to keep track of the addresses of the dual circular
queues in the receive free queue. These are accessed by the host and the DMA. On initialization, the host
configures all the registers shown in Table 9-E. After initialization, the DMA only writes to (changes)
the read pointers and the host only writes to the write pointers.
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DS31256 256-Channel, High-Throughput HDLC Controller
Empty Case
The receive free queue is considered empty when the read and write pointers are identical.
Receive Free-Queue Empty State
empty descriptor
empty descriptor
empty descriptor
read pointer > empty descriptor
empty descriptor
< write pointer
empty descriptor
empty descriptor
Full Case
The receive free queue is considered full when the read pointer is ahead of the write pointer by one
descriptor. Therefore, one descriptor must always remain empty.
Receive Free-Queue Full State
valid descriptor
valid descriptor
empty descriptor
read pointer > valid descriptor
valid descriptor
< write pointer
valid descriptor
valid descriptor
Table 9-D describes how to calculate the absolute 32-bit address of the read and write pointers for the
receive free queue.
Table 9-D. Receive Free-Queue Read/Write Pointer Absolute Address
Calculation
BUFFER
ALGORITHM
Absolute Address = Free Queue Base + Write Pointer x 8
Absolute Address = Free Queue Base + Read Pointer x 8
Large
Absolute Address = Free Queue Base + Small Buffer Start x 8 + Write Pointer x 8
Absolute Address = Free Queue Base + Small Buffer Start x 8 + Read Pointer x 8
Small
Table 9-E. Receive Free-Queue Internal Address Storage
REGISTER
NAME
RFQBA0
RFQBA1
RFQLBWP
RFQLBRP
RFQSBSA
RFQSBWP
RFQSBRP
RFQEA
ADDRESS
Receive Free-Queue Base Address 0 (lower word)
Receive Free-Queue Base Address 1 (upper word)
Receive Free-Queue Large Buffer Host Write Pointer
Receive Free-Queue Large Buffer DMA Read Pointer
Receive Free-Queue Small Buffer Start Address
Receive Free-Queue Small Buffer Host Write Pointer
Receive Free-Queue Small Buffer DMA Read Pointer
Receive Free-Queue End Address
0700h
0704h
0710h
0718h
070Ch
0714h
071Ch
0708h
Note: Both RFQSBSA and RFQEA are not absolute addresses, i.e., the absolute end address is “Base + RFQEA x 8.”
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 9-6. Receive Free-Queue Structure
Host Readied
Base + 00h
Base + 08h
Base + 10h
Base + 18h
Free-Queue Descriptor
DMA Acquired
Free-Queue Descriptor
Free-Queue Large Buffer
Host Write Pointer
DMA Acquired
Free-Queue Descriptor
Large
Buffer
Circular
Queue
DMA Acquired
Free-Queue Descriptor
Host Readied
Free-Queue Descriptor
Free-Queue Large Buffer
DMA Read Pointer
Base + 20h
Host Readied
Free-Queue Descriptor
Host Readied
Free-Queue Descriptor
Free-Queue Small Buffer
Start Address
Host Readied
Free Queue Descriptor
Free-Queue Small Buffer
Host Write Pointer
Small
DMA Acquired
Buffer
Circular
Queue
Free-Queue Descriptor
DMA Acquired
Free-Queue Descriptor
DMA Acquired
Free-Queue Descriptor
Host Readied
Free-Queue Descriptor
Free-Queue Small Buffer
DMA Read Pointer
Host Readied
Free-Queue Descriptor
Maximum of 65,536
Free-Queue Descriptors
Base + End Address
Once the receive DMA is activated (by setting the RDE control bit in the master configuration register,
see Section 5), it can begin reading data out of the free queue. It knows where to read data out of the free
queue by reading the read pointer and adding it to the base address to obtain the actual 32-bit address.
Once the DMA has read the free queue, it increments the read pointer by two dwords. A check must be
made to ensure the incremented address does not equal or exceed either the receive free-queue small-
buffer start address (in the case of the large buffer circular queue) or the receive free-queue end address
(in the case of the small buffer circular queue). If the incremented address does equal or exceed either of
these addresses, the incremented read pointer is set equal to 0000h.
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DS31256 256-Channel, High-Throughput HDLC Controller
Status/Interrupts
On each read of the free queue by the DMA, the DMA sets either the status bit for receive DMA large
buffer read (RLBR) or the status bit for receive DMA small buffer read (RSBR) in the status register for
DMA (SDMA). The DMA also checks the receive free-queue large-buffer host write pointer and the
receive free-queue small-buffer host write pointer to ensure that an underflow does not occur. If it does
occur, the DMA sets either the status bit for receive DMA large buffer read error (RLBRE) or the status
bit for receive DMA small buffer read error (RSBRE) in the status register for DMA (SDMA), and it
does not read the free queue nor does it increment the read pointer. In such a scenario, the receive FIFO
can overflow if the host does not provide free-queue descriptors. Each of the status bits can also (if
enabled) cause a hardware interrupt to occur. See Section 5 for more details.
Free-Queue Burst Reading
The DMA can read the free queue in bursts, which allows for a more efficient use of the PCI bus. The
DMA can grab messages from the free queue in groups rather than one at a time, freeing up the PCI bus
for more time-critical functions.
An internal FIFO stores up to 16 free-queue descriptors (32 dwords, as each descriptor occupies two
dwords). The free queue can either opeate in dual or singular circular queue mode. It can be divided into
large buffer and small buffer. The LBSA (large buffer starting address) and the LBEA (large buffer
ending address) form the large buffer queue, and the SBSA (small buffer starting address) and the
RFQEA (receive free-queue end address) form the small buffer queue. When the SBSA is not equal to
and greater than the RFQEA, the free queue is set up in a dual circular mode. If the SBSA is equal to the
FRQEA, the free queue is operating in a single queue mode. When the free queue is operated as a dual
circular queue supporting both large and small buffers, then the FIFO is cut into two 8-message FIFOs. If
the free queue is operated as a single circular queu supporting only the large buffers, then the FIFO is set
up as a single 16-descriptor FIFO. The host must configure the free-queue FIFO for proper operation
through the receive DMA queues control (RDMAQ) register (see the following).
When enabled through the receive free-queue FIFO-enable (RFQFE) bit, the free-queue FIFO does not
read the free queue until it reaches the low watermark. When the FIFO reaches the low watermark
(which is two descriptors in the dual mode or four descriptors in the single mode), it attempts to fill the
FIFO with additional descriptors by burst reading the free queue. Before it reads the free queue, it checks
(by examining the receive free-queue host write pointer) to ensure the free queue contains enough
descriptors to fill the free-queue FIFO. If the free queue does not have enough descriptors to fill the
FIFO, it only reads enough to keep from underflowing the free queue. If the FIFO detects that there are
no free-queue descriptors available for it to read, then it sets either the status bit for the receive DMA
large buffer read error (RLBRE) or the status bit for the receive DMA small buffer read error (RSBRE)
in the status register for DMA (SDMA); it does not read the free queue nor does it increment the read
pointer. In such a scenario, the receive FIFO can overflow if the host does not provide free-queue
descriptors. If the free-queue FIFO can read descriptors from the free queue, it burst reads them,
increments the read pointer, and sets either the status bit for receive DMA large buffer read (RLBR) or
the status bit for the receive DMA small buffer read (RSBR) in the status register for DMA (SDMA).
See Section 5 for more details on status bits.
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
RDMAQ
Register Description: Receive DMA Queues Control
Register Address:
0780h
Bit #
Name
Default
7
n/a
0
6
5
RDQF
0
4
RDQFE
0
3
RFQSF
0
2
RFQLF
0
1
n/a
0
0
RFQFE
0
n/a
0
Bit #
Name
Default
15
n/a
0
14
n/a
0
13
n/a
0
12
n/a
0
11
n/a
0
10
RDQT2
0
9
RDQT1
0
8
RDQT0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Receive Free-Queue FIFO Enable (RFQFE). To enable the DMA to burst read descriptors from the free
queue, this bit must be set to 1. If this bit is set to 0, descriptors are read one at a time.
0 = free-queue burst read disabled
1 = free-queue burst read enabled
Bit 2/Receive Free-Queue Large Buffer FIFO Flush (RFQLF). When this bit is set to 1, the internal large
buffer free-queue FIFO is flushed (currently loaded free-queue descriptors are lost). This bit must be set to 0 for
proper operation.
0 = FIFO in normal operation
1 = FIFO is flushed
Bit 3/Receive Free-Queue Small Buffer FIFO Flush (RFQSF). When this bit is set to 1, the internal small
buffer free-queue FIFO is flushed (currently loaded free-queue descriptors are lost). This bit must be set to 0 for
proper operation.
0 = FIFO in normal operation
1 = FIFO is flushed
Bit 4/Receive Done-Queue FIFO Enable (RDQFE). See Section 9.2.4 for details.
Bit 5/Receive Done-Queue FIFO Flush (RDQF). See Section 9.2.4 for details.
Bits 8 to 10/Receive Done-Queue Status Bit Threshold Setting (RDQT0 to RDQT2). See Section 9.2.4 for
details.
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9.2.4 Done Queue
The DMA writes to the receive done queue when it has filled a free data buffer with packet data and has
loaded the associated packet descriptor with all the necessary information. The descriptor location is
indicated through a 16-bit pointer that the host uses with the receive descriptor base address to find the
exact 32-bit address of the associated receive descriptor.
Figure 9-7. Receive Done-Queue Descriptor
dword 0
V
EOF
Status(3)
BUFCNT(3)
HDLC Channel (8)
Descriptor Pointer (16)
Note 1: The organization of the done queue is not affected by the enabling of Big Endian.
Note 2: Descriptor pointer is an index, not an absolute address.
dword 0; Bits 0 to 15/Descriptor Pointer. This 16-bit value is the offset from the receive descriptor base
address of a receive packet descriptor that has been readied by the DMA and is available for the host to begin
processing. Note: This is an index, not an absolute address.
dword 0; Bits 16 to 23/HDLC Channel Number. This is an HDLC channel number, which can be from 1 to
256.
00000000 (00h) = HDLC channel number 1
11111111 (FFh) = HDLC channel number 256
dword 0; Bits 24 to 26/Buffer Count (BUFCNT). If an HDLC channel has been configured to only write to
the done queue after a packet has been completely received (i.e., the threshold field in the receive DMA
configuration RAM is set to 000), then BUFCNT is always set to 000. If the HDLC channel has been
configured through the threshold field to write to the done queue after a programmable number of buffers
(from 1 to 7) has been filled, then BUFCNT corresponds to the number of buffers that have been written to
host memory. The BUFCNT is less than the threshold field value when the incoming packet does not require
the number of buffers specified in the threshold field.
000 = indicates that a complete packet has been received (only used when threshold = 000)
001 = 1 buffer has been filled
010 = 2 buffers have been filled
111 = 7 buffers have been filled
dword 0; Bits 27 to 29/Packet Status. These three bits report the final status of an incoming packet. They are
only valid when the EOF bit is set to 1 (EOF = 1).
000 = no error, valid packet received
001 = receive FIFO overflow (remainder of the packet discarded)
010 = CRC checksum error
011 = HDLC frame abort sequence detected (remainder of the packet discarded)
100 = nonaligned byte count error (not an integral number of bytes)
101 = long frame abort (max packet length exceeded; remainder of the packet discarded)
110 = PCI abort (remainder of the packet discarded)
111 = reserved state (never occurs in normal device operation)
dword 0; Bit 30/End of Frame (EOF). This bit is set to 1 when this receive descriptor is the last one in the
current descriptor chain. This indicates that a packet has been fully received or an error has been detected,
which has caused a premature termination.
dword 0; Bit 31/Valid Done-Queue Descriptor (V). This bit is set to 0 by the receive DMA. Instead of
reading the receive done-queue read pointer to locate completed done-queue descriptors, the host can use this
bit, since the DMA sets the bit to 0 when it is written into the queue. If the latter scheme is used, the host must
set this bit to 1 when the done queue descriptor is read.
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DS31256 256-Channel, High-Throughput HDLC Controller
The host reads from the receive done queue to find which data buffers and their associated descriptors
are ready for processing.
The receive done queue is circular. A set of internal addresses within the device that are accessed by the
host and the DMA keep track of the queue’s addresses. On initialization, the host configures all the
registers, as shown in Table 9-F. After initialization, the DMA only writes to (changes) the write pointer
and the host only writes to the read pointer.
Empty Case
The receive done queue is considered empty when the read and write pointers are identical.
Receive Done-Queue Empty State
empty descriptor
empty descriptor
empty descriptor
read pointer > empty descriptor < write pointer
empty descriptor
empty descriptor
empty descriptor
Full Case
The receive done queue is considered full when the read pointer is ahead of the write pointer by one
descriptor. Therefore, one descriptor must always remain empty.
Receive Done-Queue Full State
valid descriptor
valid descriptor
empty descriptor < write pointer
read pointer >
valid descriptor
valid descriptor
valid descriptor
valid descriptor
Table 9-F. Receive Done-Queue Internal Address Storage
REGISTER
NAME
ADDRESS
Receive Done-Queue Base Address 0 (lower word)
Receive Done-Queue Base Address 1 (upper word)
Receive Done-Queue DMA Write Pointer
Receive Done-Queue Host Read Pointer
Receive Done-Queue End Address
RDQBA0
RDQBA1
RDQWP
RDQRP
0730h
0734h
0740h
073Ch
0738h
0744h
RDQEA
Receive Done-Queue FIFO Flush Timer
RDQFFT
Note: Receive done-queue end address is not an absolute address. The absolute end address is “Base + RDQEA x 4.”
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 9-8. Receive Done-Queue Structure
DMA Readied
Done-Queue Descriptor
Base + 00h
Base + 04h
DMA Readied
Done-Queue Descriptor
Host Processed
Done-Queue Descriptor
Done-Queue DMA Write Pointer
Base + 08h
Base + 0Ch
Host Processed
Done-Queue Descriptor
Host Processed
Done-Queue Descriptor
Base + 10h
Base + 14h
DMA Readied
Done-Queue Descriptor
Done-Queue Host Read Pointer
Maximum of 65,536
DMA Readied
Done-Queue Descriptor
Done-Queue Descriptors
Base + End Address
Once the receive DMA is activated (through the RDE control bit in the master configuration register, see
Section 5), it can begin writing data to the done queue. It knows where to write data into the done queue
by reading the write pointer and adding it to the base address to obtain the actual 32-bit address. Once
the DMA has written to the done queue, it increments the write pointer by one dword. A check must be
made to ensure the incremented address does not exceed the receive done-queue end address. If the
incremented address exceeds this address, the incremented write pointer is set equal to 0000h (i.e., the
base address).
Status Bits/Interrupts
On writes to the done queue by the DMA, the DMA sets the status bit for the receive DMA done-queue
write (RDQW) in the SDMA. The host can configure the DMA to either set this status bit on each write
to the done queue or only after multiple (from 2 to 128) writes. The host controls this by setting the
RDQT0 to RDQT2 bits in the receive DMA queues control (RDMAQ) register. See the description of
the RDMAQ register at the end of Section 9.2.4 for more details. The DMA also checks the receive
done-queue host read pointer to ensure an overflow does not occur. If this does occur, the DMA then sets
the status bit for the receive DMA done-queue write error (RDQWE) in the status register for DMA
(SDMA), and it does not write to the done queue nor does it increment the write pointer. In such a
scenario, packets can be lost and unrecoverable. Each of the status bits can also (if enabled) cause a
hardware interrupt to occur. See Section 5 for more details.
Buffer Write Threshold Setting
In the DMA configuration RAM (Section 9.2.5), there is a host-controlled field called “threshold” (bits
RDT0 to RDT2) that informs the DMA when it should write to the done queue. The host has the option
to have the DMA place information in the done queue after a programmable number (from 1 to 7) data
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DS31256 256-Channel, High-Throughput HDLC Controller
buffers have been filled or wait until the completed packet data has been written. The DMA always
writes to the done queue when it has finished receiving a packet, even if the threshold has not been met.
Done-Queue Burst Writing
The DMA can write to the done queue in bursts, which allows for a more efficient use of the PCI bus.
The DMA can hand off descriptors to the done queue in groups rather than one at a time, freeing up the
PCI bus for more time-critical functions.
An internal FIFO stores up to eight done-queue descriptors (8 dwords as each descriptor occupies one
dword). The host must configure the FIFO for proper operation through the receive DMA queues-control
(RDMAQ) register (see the following).
When enabled through the receive done-queue FIFO-enable (RDQFE) bit, the done-queue FIFO does not
write to the done queue until it reaches the high watermark. When the done-queue FIFO reaches the high
watermark (which is six descriptors), it attempts to empty the done-queue FIFO by burst writing to the
done queue. Before it writes to the done queue, it checks (by examining the receive done-queue host read
pointer) to ensure the done queue has enough room to empty the done-queue FIFO. If the done queue
does not have enough room, then it only burst writes enough descriptors to keep from overflowing the
done queue. If the FIFO detects that there is no room for any descriptors to be written, it sets the status
bit for the receive DMA done-queue write error (RDQWE) in the status register for DMA (SDMA). It
does not write to the done queue nor does it increment the write pointer. In such a scenario, packets can
be lost and unrecoverable. If the done-queue FIFO can write descriptors to the done queue, it burst writes
them, increments the write pointer, and sets the status bit for the receive DMA done-queue write
(RDQW) in the status register for DMA (SDMA). See Section 5 for more details on status bits.
Done-Queue FIFO Flush Timer
To ensure the done-queue FIFO gets flushed to the done queue on a regular basis, the DMA uses the
receive done-queue FIFO flush timer (RDQFFT) to determine the maximum wait time between writes.
The RDQFFT is a 16-bit programmable counter that is decremented every PCLK divided by 256. It is
only monitored by the DMA when the receive done-queue FIFO is enabled (RDQFE = 1). For a 33MHz
PCLK, the timer is decremented every 7.76µs. For a 25MHz clock, it is decremented every 10.24µs.
Each time the DMA writes to the done queue it resets the timer to the count placed into it by the host. On
initialization, the host sets a value into the RDQFFT that indicates the maximum time the DMA should
wait in between writes to the done queue. For example, with a PCLK of 33MHz, the range of wait times
is from 7.8µs (RDQFFT = 0001h) to 508ms (RDQFFT = FFFFh). With a PCLK of 25MHz, the wait
times range from 10.2µs (RDQFFT = 0001h) to 671ms (RDQFFT = FFFFh).
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Register Name:
RDQFFT
Register Description: Receive Done-Queue FIFO Flush Timer
Register Address:
0744h
Bit #
Name
Default
7
TC7
0
6
TC6
0
5
TC5
0
4
TC4
0
3
TC3
0
2
TC2
0
1
TC1
0
0
TC0
0
Bit #
Name
Default
15
TC15
0
14
TC14
0
13
TC13
0
12
TC12
0
11
TC11
0
10
TC10
0
9
TC9
0
8
TC8
0
Note: Bits that are underlined are read-only, all other bits are read-write.
Bits 0 to 15/Receive Done-Queue FIFO Flush Timer Control Bits (TC0 to TC15). Please note that on system
reset, the timer is set to 0000h, which is defined as an illegal setting. If the receive done-queue FIFO is to be
activated (RDQFE = 1), then the host must first configure the timer to a proper state and then set the RDQFE bit to
one.
0000h = illegal setting
0001h = timer count resets to 1
FFFFh = timer count resets to 65,536
Register Name:
RDMAQ
Register Description: Receive DMA Queues Control
Register Address:
0780h
Bit #
7
n/a
0
6
n/a
0
5
RDQF
0
4
RDQFE
0
3
RFQSF
0
2
RFQLF
0
1
n/a
0
0
RFQFE
0
Name
Default
Bit #
Name
Default
15
n/a
0
14
n/a
0
13
n/a
0
12
n/a
0
11
n/a
0
10
RDQT2
0
9
RDQT1
0
8
RDQT0
0
Note: Bits that are underlined are read-only, all other bits are read-write.
Bit 0/Receive Free-Queue FIFO Enable (RFQFE). See Section 9.2.3 for details.
Bit 2/Receive Free-Queue Large Buffer FIFO Flush (RFQLF). See Section 9.2.3 for details.
Bit 3/Receive Free-Queue Small Buffer FIFO Flush (RFQSF). See Section 9.2.3 for details.
Bit 4/Receive Done-Queue FIFO Enable (RDQFE). To enable the DMA to burst write descriptors to the done
queue, this bit must be set to 1. If this bit is set to 0, messages are written one at a time.
0 = done-queue burst-write disabled
1 = done-queue burst-write enabled
Bit 5/Receive Done-Queue FIFO Flush (RDQF). When this bit is set to 1, the internal done-queue FIFO is
flushed by sending all data into the done queue. This bit must be set to 0 for proper operation.
0 = FIFO in normal operation
1 = FIFO is flushed
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Bits 8 to 10/Receive Done-Queue Status-Bit Threshold Setting (RDQT0 to RDQT2). These bits determine
when the DMA sets the receive DMA done-queue write (RDQW) status bit in the status register for DMA
(SDMA) register.
000 = set the RDQW status bit after each descriptor write to the done queue
001 = set the RDQW status bit after 2 or more descriptors are written to the done queue
010 = set the RDQW status bit after 4 or more descriptors are written to the done queue
011 = set the RDQW status bit after 8 or more descriptors are written to the done queue
100 = set the RDQW status bit after 16 or more descriptors are written to the done queue
101 = set the RDQW status bit after 32 or more descriptors are written to the done queue
110 = set the RDQW status bit after 64 or more descriptors are written to the done queue
111 = set the RDQW status bit after 128 or more descriptors are written to the done queue
9.2.5 DMA Channel Configuration RAM
There is a set of 768 dwords (3 dwords per channel times 256 channels) on-board the device that the host
uses to configure the DMA. It uses the DMA to store values locally when it is processing a packet. Most
of the fields within the DMA configuration RAM are for DMA use and the host never writes to these
fields. The host is only allowed to write (configure) to the lower word of dword 2 for each HDLC
channel. The host-configurable fields are denoted with a thick box as shown below.
Figure 9-9. Receive DMA Configuration RAM
msb
31
lsb
0
Receive DMA Configuration RAM
Current Packet Data Buffer Address (32)
000h
004h
008h
00Ch
010h
014h
HDLC
Channel 1
Start Descriptor Pointer (16)
Byte Count (13)
Current Descriptor Pointer (16)
Size
CH
EN
Threshold
Threshold(3)
FBF unused (5)
Unused (4)
(2)
Count (3)
Current Packet Data Buffer Address (32)
HDLC
Channel 2
Start Descriptor Pointer (16)
Byte Count (13)
Current Descriptor Pointer (16)
Size
CH
EN
Threshold
Count (3)
Unused (4)
Threshold(3
FBF unused (5)
(2)
BF4h
BF8h
BFCh
Current Packet Data Buffer Address (32)
HDLC
Start Descriptor Pointer (16)
Byte Count (13)
Current Descriptor Pointer (16)
Size
Channel 256
CH
EN
Threshold
Count (3)
Unused (4)
Threshold(3
FBF unused (5)
(2)
Fields shown within the thick box
are written by the Host; all other
fields are for usage by the DMA and
can only be read by the Host
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DS31256 256-Channel, High-Throughput HDLC Controller
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 0; Bits 0 to 31/Current Data Buffer Address. The current 32-bit address of the data buffer that is being
used. This address is used by the DMA to track where data should be written to as it comes in from the receive
FIFO.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 1; Bits 0 to 15/Current Descriptor Pointer. This 16-bit value is the offset from the receive descriptor
base address of the current receive descriptor being used by the DMA to describe the specifics of the data stored in
the associated data buffer.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 1; Bits 16 to 31/Starting Descriptor Pointer. This 16-bit value is the offset from the receive descriptor
base address of the first receive descriptor in a link-list chain of descriptors. This pointer is written into the done
queue by the DMA after a specified number of data buffers (see the threshold value below) have been filled.
- HOST MUST CONFIGURE -
dword 2; Bit 0/Channel Enable (CHEN). This bit is controlled by the host to enable and disable an HDLC
channel.
0 = HDLC channel disabled
1 = HDLC channel enabled
- HOST MUST CONFIGURE -
dword 2; Bits 1, 2/Buffer Size Select. These bits are controlled by the host to select the manner in which the
receive DMA stores incoming packet data.
00 = use large size data buffers only
01 = use small size data buffers only
10 = fill a small buffer first, followed then by large buffers as needed
11 = illegal state and should not be selected
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 2; Bits 3 to 6/DMA Reserved. These could be any value when read. They should be set to 0 when the host
writes to it.
- HOST MUST CONFIGURE -
dword 2; Bits 7 to 9/Threshold. These bits are controlled by the host to determine when the DMA should write
into the done queue that data is available for processing. They cannot be set to 000 when in transparent mode
(RTRANS = 1).
000 = DMA should write to the done queue only after packet reception is complete
001 = DMA should write to the done queue after 1 data buffer has been filled
010 = DMA should write to the done queue after 2 data buffers have been filled
011 = DMA should write to the done queue after 3 data buffers have been filled
100 = DMA should write to the done queue after 4 data buffers have been filled
101 = DMA should write to the done queue after 5 data buffers have been filled
110 = DMA should write to the done queue after 6 data buffers have been filled
111 = DMA should write to the done queue after 7 data buffers have been filled
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 2; Bits 10 to 14/DMA Reserved. These could be any value when read. They should be set to 0 when the
host writes to it.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 2; Bit 15/First Buffer Fill (FBF). This bit is set to 1 by the receive DMA when it is in the process of
filling the first buffer of a packet. The DMA uses this bit to determine when to switch to large buffers when the
buffer size-select field is set to 10.
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- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 2; Bits 16 to 28/Byte Count. The DMA uses these 13 bits to keep track of the number of bytes stored in
the data buffer. Maximum is 8188 Bytes (0000h = 0 Bytes / 1FFCh = 8188 Bytes).
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 2; Bits 29 to 31/Threshold Count. These bits keep track of the number of data buffers that have been
filled so that the receive DMA knows when, based on the host-controlled threshold, to write to the done queue.
000 = threshold count is 0 data buffers
001 = threshold count is 1 data buffer
010 = threshold count is 2 data buffers
011 = threshold count is 3 data buffers
100 = threshold count is 4 data buffers
101 = threshold count is 5 data buffers
110 = threshold count is 6 data buffers
111 = threshold count is 7 data buffers
Register Name:
RDMACIS
Register Description: Receive DMA Channel Configuration Indirect Select
Register Address:
0770h
Bit #
Name
Default
7
6
5
HCID5
0
4
HCID4
0
3
HCID3
0
2
HCID2
0
1
HCID1
0
0
HCID0
0
HCID7
0
HCID6
0
Bit #
Name
Default
15
IAB
0
14
IARW
0
13
n/a
0
12
n/a
0
11
n/a
0
10
RDCW2
0
9
RDCW1
0
8
RDCW0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 7/HDLC Channel ID (HCID0 to HCID7)
00000000 (00h) = HDLC channel number 1
11111111 (FFh) = HDLC channel number 256
Bits 8 to 10/Receive DMA Configuration RAM Word Select Bits 0 to 2 (RDCW0 to RDCW2)
000 = lower word of dword 0
001 = upper word of dword 0
010 = lower word of dword 1
011 = upper word of dword 1
100 = lower word of dword 2 (only word that the host can write to)
101 = upper word of dword 2
110 = illegal state
111 = illegal state
Bit 14/Indirect Access Read/Write (IARW). When the host wishes to read data from the internal receive DMA
configuration RAM, this bit should be written to 1 by the host. This causes the device to begin obtaining the data
from the channel location indicated by the HCID bits. During the read access, the IAB bit is set to 1. Once the data
is ready to be read from the RDMAC register, the IAB bit is set to 0. When the host wishes to write data to the
internal receive DMA configuration RAM, this bit should be written to 0 by the host. This causes the device to
take the data that is currently present in the RDMAC register and write it to the channel location indicated by the
HCID bits. When the device has completed the write, the IAB bit is set to 0.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit is set to 1 until the data is ready to be read. It is set to 0 when the data is
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DS31256 256-Channel, High-Throughput HDLC Controller
ready to be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the
write operation has completed.
Register Name:
RDMAC
Register Description: Receive DMA Channel Configuration
Register Address:
0774h
Bit #
Name
Default
7
D7
6
D6
5
D5
4
D4
3
D3
2
D2
1
D1
0
D0
Bit #
Name
Default
15
D15
14
D14
13
D13
12
D12
11
D11
10
D10
9
D9
8
D8
Note: Bits that are underlined are read-only, all other bits are read-write.
Bits 0 to 15/Receive DMA Configuration RAM Data (D0 to D15). Data that is written to or read from the
receive DMA configuration RAM.
9.3 Transmit Side
9.3.1 Overview
The transmit DMA uses a scatter-gather technique to read packet data from main memory. The host
keeps track of and decides from where (and when) the DMA should grab the outgoing packet data. A set
of descriptors that get handed back and forth between the host and the DMA can tell the DMA where to
obtain the packet data, and the DMA can tell the host when the data has been transmitted.
The transmit DMA operation has three main areas, as shown in Figure 9-10, Figure 9-11, and Table 9-G.
The host writes to the pending queue, informing the DMA which channels have packet data ready to be
transmitted. Associated with each pending-queue descriptor is a data buffer that contains the actual data
payload of the HDLC packet. The data buffers can be between 1 and 8188 Bytes in length (inclusive). If
an outgoing packet requires more memory than a data buffer contains, the host can link the data buffers
to handle packets of any size.
The done-queue descriptors contain information that the DMA wishes to pass to the host. The DMA
writes to the done queue when it has completed transmitting either a complete packet or data buffer (see
below for the discussion on the DMA update to the done queue). Through the done-queue descriptors,
the DMA informs the host about the status of the outgoing packet data. If an error occurs in the
transmission, the done queue can be used by the host to recover the packet data that did not get
transmitted and the host can then re-queue the packets for transmission.
If enabled, the DMA can burst read the pending-queue descriptors and burst write the done-queue
descriptors. This helps minimize PCI bus accesses, freeing the PCI bus up to do more time-critical
functions. See Sections 9.3.3 and 9.3.4 for more details on this feature.
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Table 9-G. Transmit DMA Main Operational Areas
DESCRIPTORS
FUNCTION
SECTION
A dedicated area of memory that describes the location and attributes of the
Packet
9.3.2
packet data.
A dedicated area of memory that the host writes to inform the DMA that
packet data is queued and ready for transmission.
A dedicated area of memory that the DMA writes to inform the host that the
packet data has been transmitted.
Pending Queue
Done Queue
9.3.3
9.3.4
Host Linking of Data Buffers
As previously mentioned, the data buffers are limited to a length of 8188 Bytes. If an outgoing packet
requires more memory space than the available data buffer contains, the host can link multiple data
buffers together to handle a packet length of any size. The host does this through the end-of-frame (EOF)
bit in the packet descriptor. Each data buffer has a one-to-one association with a packet descriptor. If the
host wants to link multiple data buffers together, the EOF bit is set to 0 in all but the last data buffer.
Figure 9-10 shows an example for HDLC channel 5 where the host has linked three data buffers
together. The transmit DMA knows where to find the next data buffer when the EOF bit is set to 0
through the next descriptor pointer field.
Host Linking of Packets (Packet Chaining)
The host also has the option to link multiple packets together in a chain. Through the chain valid (CV)
bit in the packet descriptor, the host can inform the transmit DMA that the next descriptor pointer field
contains the descriptor of another HDLC packet that is ready for transmission. The transmit DMA
ignores the CV bit until it sees EOF = 1, which indicates the end of a packet. If CV = 1 when EOF = 1,
this indicates to the transmit DMA that it should use the next descriptor pointer field to find the next
packet in the chain. Figure 9-12 shows an example of packet chaining. Each column represents a separate
packet chain. In column 1, three data buffers have been linked together by the host for packet #1, and the
host has created a packet chain by setting CV = 1 in the last descriptor of packet #1.
DMA Linking of Packets (Horizontal Link Listing)
The transmit DMA also has the ability to link packets together. Internally, the transmit DMA can store
up to two packet chains, but if the host places more packet chains into the pending queue, the transmit
DMA must begin linking these chains together externally. The transmit DMA does this by writing to
packet descriptors (Figure 9-12). If columns 1 and 2 were the only two packet chains queued for
transmission, then the transmit DMA would not need to link packet chains together, but as soon as
column 3 was queued for transmission, the transmit DMA had to store the third chain externally because
it had no more room internally. The transmit DMA links the packet chain in the third column to the one
in the second column by writing the first descriptor of the third chain in the next pending descriptor
pointer field of the first descriptor of the second column (it also sets the PV bit to 1). As shown in the
figure, this chaining was carried one step farther to link the fourth column to the third.
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Priority Packets
The host has the option to change the order in which packets are transmitted by the DMA. If the host sets
the priority packet (PRI) bit in the pending-queue descriptor to 1, the transmit DMA knows that this
packet is a priority packet and should be transmitted ahead of all standard packets. The rules for packet
transmission are as follows:
1) Priority packets are transmitted as soon as the current standard packet (not packet chain) finishes
transmission.
2) All priority packets are transmitted before any more standard packets are transmitted.
3) Priority packets are ordered on a first come, first served basis.
Figure 9-13 shows an example of a set of priority packets interrupting a set of standard packets. In the
example, the first priority packet chain (shown in column 2) was read by the transmit DMA from the
pending queue while it was transmitting standard packet #1. It waited until standard packet #1 was
complete and then began sending the priority packets. While column 2 was being sent, the priority
packet chains of columns 3 and 4 arrived in the pending queue, so the transmit DMA linked column four
to column three and then waited until all of the priority packets were transmitted before returning to the
standard packet chain in column 1. Note that the packet chain in column 1 was interrupted to transmit the
priority packets. In other words, the transmit DMA did not wait for the complete packet to finish
transmitting, only the current packet.
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Figure 9-10. Transmit DMA Operation
EOF = 1
Data Buffer Address
Transmitted
Data Buffer
for Channel 5
EOFCV # Bytes Next Desc. Ptr.
unused
CH #5
unused PV Next Pend. Desc.
Done-Queue Descriptors
(circular queue)
EOF = 0
Data Buffer Address
EOFCV # Bytes Next Desc. Ptr.
1st Transmitted
Data Buffer
00h Status CH#5 Free Desc. Ptr.
04h Status CH#1 Free Desc. Ptr.
08h Status CH# Free Desc. Ptr.
0Ch Status CH# Free Desc. Ptr.
10h Status CH# Free Desc. Ptr.
14h Status CH# Free Desc. Ptr.
unused
CH #1
for Channel 1
unused PV Next Pend. Desc.
EOF = 0
Data Buffer Address
EOFCV # Bytes Next Desc. Ptr.
2nd Transmitted
Data Buffer
unused
CH #1
for Channel 1
unused PV Next Pend. Desc.
EOF = 1
Data Buffer Address
EOFCV # Bytes Next Desc. Ptr.
Last Transmitted
Data Buffer
unused
CH #1
for Channel 1
unused PV Next Pend. Desc.
Open Descriptor Space
Available for Use by the Host
Open Descriptor Space
Available for Use by the Host
Pending-Queue Descriptors
(circular queue)
EOF = 0
Data Buffer Address
EOFCV # Bytes Next Desc. Ptr.
1st Queued
Data Buffer
for Channel 5
00h
04h
08h
0Ch
PRI
PRI
PRI
PRI
CH#5 Free Desc. Ptr.
CH#1 Free Desc. Ptr.
CH# Free Desc. Ptr.
CH# Free Desc. Ptr.
unused
CH #5
unused PV Next Pend. Desc.
EOF = 0
Data Buffer Address
EOFCV # Bytes Next Desc. Ptr.
2nd Queued
Data Buffer
for Channel 5
unused
CH #5
unused PV Next Pend. Desc.
EOF = 1
Data Buffer Address
EOFCV # Bytes Next Desc. Ptr.
Last Queued
Data Buffer
unused
CH #5
for Channel 5
unused PV Next Pend. Desc.
EOF = 0
Data Buffer Address
EOFCV # Bytes Next Desc. Ptr.
Queued
Data Buffer
for Channel 1
unused
CH #1
unused PV Next Pend. Desc.
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 9-11. Transmit DMA Memory Organization
Main Offboard Memory
(32-Bit Address Space)
Internal Registers
Free Data Buffer Space
Used Data Buffer Space
Pending-Queue Base Address (32)
Transmit Pending-Queue Descriptors:
Contains Index Pointers to Packet
Descriptors of Queued Data Buffers that
are Ready to be Transmitted
Pending-Queue Host Write Pointer (16)
Pending-Queue DMA Read Pointer (16)
Up to 64k dwords
Free-Queue Descriptors Allowed
Pending-Queue End Address (16)
Done-Queue Base Address (32)
Done-Queue DMA Write Pointer (16)
Done-Queue Host Read Pointer (16)
Transmit Done-Queue Descriptors:
Contains Index Pointers to Packet
Descriptors of Data Buffers that have
been Transmitted
Up to 64k dwords
Done-Queue Descriptors Allowed
Done-Queue End Address (16)
Descriptor Base Address (32)
Transmit Packet Descriptors:
Contains 32-Bit Addresses to Data
Buffers as well as Status/Control
Information and Links to Other Packet
Descriptors
Up to 64k quad dwords
Descriptors Allowed
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Figure 9-12. Transmit DMA Packet Handling
Transmit DMA Configuration RAM
Last Pending Descriptor Pointer
Next Pending Descriptor Pointer
Next Descriptor Pointer
Start Descriptor Pointer
Next Pending
Next Pending
Descriptor Pointer
stored within the
Packet Descriptor
Descriptor Pointer
stored within the
Packet Descriptor
1st Descriptor
(EOF=0/CV=0)
1st Descriptor
Last Descriptor
1st Descriptor
(EOF=0/CV=0)
(EOF=0/CV=0)
PV=1
(EOF=1/CV=0)
PV=1
Buffer 1
Packet 1
Buffer 1
Buffer 1
Buffer 1
Packet 6
Packet 3
Packet 5
2nd Descriptor
(EOF=0/CV=0)
2nd Descriptor
2nd Descriptor
(EOF=0/CV=0)
(EOF=0/CV=0)
Buffer 2
Buffer 2
Packet 1
Buffer 2
Packet 6
Packet 3
Last Descriptor
(EOF=1/CV=1)
Last Descriptor
Last Descriptor
(EOF=1/CV=0)
(EOF=1/CV=1)
Buffer 3
Packet 3
Last Descriptor
Buffer 3
Packet 1
Buffer 3
Packet 6
Last Descriptor
(EOF=1/CV=0)
(EOF=1/CV=0)
Buffer 1
Packet 4
Buffer 1
Packet 2
Packet Chain
Column 1
Packet Chain
Column 2
Packet Chain
Column 3
Packet Chain
Column 4
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 9-13. Transmit DMA Priority Packet Handling
Transmit DMA Configuration RAM
Standard Queue Pointers
Priority Queue Pointers
Last Pending Descriptor Pointer
Next Pending Descriptor Pointer
Next Descriptor Pointer
Last Pending Descriptor Pointer
Next Pending Descriptor Pointer
Next Descriptor Pointer
Start Descriptor Pointer
See
Note 1
1st Descriptor
(EOF=0/CV=0)
Buffer 1
Packet 1
2nd Descriptor
(EOF=0/CV=0)
Buffer 2
Packet 1
Last Descriptor
(EOF=1/CV=1)
Next Pending
Descriptor Pointer
stored within the
Packet Descriptor
Buffer 3
Packet 1
1st Descriptor
(EOF=0/CV=0)
Last Descriptor
1st Descriptor
(EOF=0/CV=0)
(EOF=1/CV=0)
PV = 1
Service
Priority
Packets
Buffer 1
Pri. Packet 1
Buffer 1
Buffer 1
Pri. Packet 4
Pri. Packet 3
Last Descriptor
(EOF=1/CV=1)
2nd Descriptor
(EOF=0/CV=0)
Normal
Path if No
Priority
Packets
Had
Buffer 2
Pri. Packet 1
Buffer 2
Pri. Packet 4
Last Descriptor
(EOF=1/CV=0)
Last Descriptor
(EOF=1/CV=0)
Occurred
Buffer 1
Pri. Packet 2
Buffer 3
Pri. Packet 4
All Priority Packets Have Been Serviced
Last Descriptor
(EOF=1/CV=0)
Buffer 1
Packet 2
Standard
Priority
Priority
Priority
Packet Chain
Column 1
Packet Chain
Column 2
Packet Chain
Column 3
Packet Chain
Column 4
Note 1: The start descriptor pointer field in the transmit DMA configuration RAM is used by both the normal and
priority pending queues.
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DMA Updates to the Done Queue
The host has two options for when the transmit DMA should write descriptors that have completed
transmission to the done queue. On a channel-by-channel basis, through the done-queue select (DQS) bit
in the transmit DMA configuration RAM, the host can condition the DMA to:
1) Write to the done queue only when the complete HDLC packet has been transmitted (DQS = 0).
2) Write to the done queue when each data buffer has been transmitted (DQS = 1).
The status field in the done-queue descriptor is configured based on the setting of the DQS bit.
If DQS = 0, it is set to 000 when a packet has successfully completed transmission to the status field. If
DQS = 1, it is set to 001 when the first data buffer has successfully completed transmission to the status
field. The status field is set to 010 when each middle buffer (i.e., the second through the next to last) has
successfully completed transmission. The status field is set to 011 when the last data buffer of a packet
has successfully completed transmission.
Error Conditions
While processing packets for transmission, the DMA can encounter a number of error conditions, which
include the following:
• PCI error (an abort error)
• transmit FIFO underflow
• channel is disabled (CHEN = 0) in the transmit DMA configuration RAM
• channel number discrepancy between the pending queue and the packet descriptor
• Byte count of 0 Bytes in the packet descriptor
If any of these errors occur, the transmit DMA automatically disables the affected channel by setting the
channel enable (CHEN) bit in the transmit DMA configuration RAM to 0. Then it writes the current
descriptor into the done queue with the appropriate error status, as shown in Table 9-H.
Table 9-H. Done-Queue Error-Status Conditions
PACKET
ERROR DESCRIPTION
STATUS
100
101
110
111
Software provisioning error; this channel was not enabled
Descriptor error; either byte count = 0 or channel code inconsistent with pending queue
PCI error; either parity or abort
Transmit FIFO error; it has underflowed
Since the transmit DMA has disabled the channel, any remaining queued descriptors are not transmitted
and are written to the done queue with a packet status of 100 (i.e., reporting that the channel was not
enabled). At this point the host has two options. Option 1: It can wait until all of the remaining queued
descriptors are written to the done queue with an errored status, manually re-enable the channel by
setting the CHEN bit to 1, and then re-queue all of the affected packets. Option 2: As soon as it detects
an errored status, it can force the channel active again by setting the channel reset (CHRST) bit to 1 for
the next descriptor that it writes to the pending queue for the affected channel. As soon as the transmit
DMA detects that the CHRST is set to 1, it re-enables the channel by forcing the CHEN bit to 1. The
DMA does not re-enable the channel until it has finished writing all of the previously queued descriptors
to the done queue. Then the host can collect the errored descriptors as they arrive in the done queue and
re-queue them for transmission by writing descriptors to the pending queue, so the transmit DMA knows
where to find the packets that did not get transmitted (Note: The host must set the next-pending
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descriptor pointer and PV fields in the packet descriptor to 0 to ready them for transmission). The second
option allows the software a cleaner error-recovery technique. See Figure 9-14 for more details.
Figure 9-14. Transmit DMA Error Recovery Algorithm
Read Done Queue
Data Buffers and
Packet Descriptor
Space Available
for Reuse
No
Status = 1xx?
Yes
Set CHRST = 1 for
the Next Descriptor
Written to the
Pending Queue
Set the PV and the Next
Pending Descriptor Pointer
Fields to 0 in the Errored
Packet Descriptor
Place the Errored Packet
Descriptor Back into the
Pending Queue for
Retransmission
Host Actions
The host typically handles the transmit DMA as follows:
1) The host places readied packets into the pending queue.
2) The host either polls (or is interrupted) that some outgoing packets have completed transmission and
that it should read the done queue.
3) If done queue reports that an error was incurred and that a packet was not transmitted, the host must
requeue the packet for transmission.
Transmit DMA Actions
A typical scenario for the transmit DMA is as follows:
1) The transmit DMA constantly reads the pending queue looking for packets that are queued for
transmission.
2) The transmit DMA updates the done queue as packets or data buffers to complete transmission.
3) If an error occurs, the transmit DMA disables the channel and waits for the host to request that the
channel be enabled.
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9.3.2 Packet Descriptors
A contiguous section of up to 65,536 quad dwords that make up the transmit packet descriptors resides in
main memory. The transmit packet descriptors are aligned on a quad-dword basis and can be placed
anywhere in the 32-bit address space through the transmit descriptor base address (Table 9-I). A data
buffer is associated with each descriptor. The data buffer can be up to 8188 Bytes long and must be a
contiguous section of main memory. The host informs the DMA of data buffers’ actual sizes through the
byte count field that resides in the packet descriptor.
If an outgoing packet requires more space than the data buffer allows, then packet descriptors are link-
listed together by the host to provide a chain of data buffers. Figure 9-15 shows an example of how three
descriptors were linked together for an incoming packet on HDLC channel 7. Channel 3 only required a
single data buffer and thus only one packet descriptor was used. Figure 9-10 shows a similar example for
channels 5 and 1.
Packet descriptors can be either pending (i.e., queued up by the host and ready for transmission by the
DMA) or completed (i.e., have been transmitted by the DMA and are available for processing by the
host). Pending-packet descriptors are pointed to by the pending-queue descriptors and completed packet
descriptors are pointed to by the done-queue descriptors.
Table 9-I. Transmit Descriptor Address Storage
REGISTER
NAME
TDBA0
TDBA1
ADDRESS
0850h
Transmit Descriptor Base Address 0 (lower word)
Transmit Descriptor Base Address 1 (upper word)
0854h
Figure 9-15. Transmit Descriptor Example
Base + 00h CH 5 Single Sent Buffer Descriptor
Base + 10h CH 7 1st Queued Buffer Descriptor
Done-Queue Descriptor Pointer
Base + 20h
Base + 30h
Base + 40h
CH 3 Single Queued Buffer Desc.
CH 7 Sent 1st Buffer Descriptor
Free Descriptor
Pending-Queue Descriptor Address
Base + 50h CH 7 2nd Queued Buffer Descriptor
Base + 60h
Base + 70h
Base + 80h
Free Descriptor
CH 7 Last Queued Buffer Descriptor
CH 7 Last Sent Buffer Descriptor
Base + FFFD0h
Base + FFFF0h
Free Descriptor
Free Descriptor
Maximum of 65,536 Descriptors
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 9-16. Transmit Packet Descriptors
dword 0
Data Buffer Address (32)
Byte Count (13)
unused (24)
PV
dword 1
EOF
dword 2
CV
unused
Next Descriptor Pointer (16)
HDLC Channel (8)
dword 3
unused (15)
Next Pending Descriptor Pointer (16)
Note 1: The organization of the transmit descriptor is not affected by the enabling of Big Endian.
Note 2: The format of the transmit descriptor is almost identical to the receive descriptor; this lessens the burden of the host in preparing
descriptors in store-and-forward applications.
Note 3: Next descriptor pointer is an index, not an absolute address.
dword 0; Bits 0 to 31/Data Buffer Address. Direct 32-bit starting address of the data buffer that is associated
with this transmit descriptor.
dword 1; Bits 0 to 15/Next Descriptor Pointer. This 16-bit value is the offset from the transmit descriptor base
address of the next descriptor in the chain. Only valid if EOF = 0 (next descriptor in the same packet chain) or if
EOF = 1 and CV = 1 (first descriptor in the next packet).
dword 1; Bits 16 to 28/Byte Count. Number of bytes stored in the data buffer. Maximum is 8188 Bytes (0000h =
0 Bytes / 1FFCh = 8188 Bytes).
dword 1; Bit 29/Unused. This bit is ignored by the transmit DMA and can be set to any value.
dword 1; Bit 30/Chain Valid (CV). If CV is set to 1 when EOF = 1, then this indicates that the next descriptor
pointer field is valid and corresponds to the first descriptor of the next packet that is queued up for transmission.
The CV bit is ignored when EOF = 0.
dword 1; Bit 31/End of Frame (EOF). When set to 1, this bit indicates that the descriptor is the last buffer in the
current packet. When set to 0, this bit indicates that next descriptor pointer field is valid and points to the next
descriptor in the packet chain.
dword 2; Bits 0 to 7/HDLC Channel Number. HDLC channel number, which can be from 1 to 256.
00000000 (00h) = HDLC channel number 1
11111111 (FFh) = HDLC channel number 256
dword 2; Bits 8 to 31/Unused. These bits are ignored by the transmit DMA and can be set to any value.
dword 3; Bits 0 to 15/Next Pending Descriptor Pointer. This 16-bit value is the offset from the transmit
descriptor base address to another descriptor chain that is queued up for transmission. The transmit DMA can store
up to two queued packet chains internally, but additional packet chains must be stored as a link list by the transmit
DMA using this field. This field is only valid if PV = 1, and it should be set to 0000h by the host when the host is
preparing the descriptor.
dword 3; Bit 16/Pending Descriptor Valid (PV). If set, this bit indicates that the next pending descriptor pointer
field is valid and corresponds to the first descriptor of the next packet chain that is queued up for transmission.
This field is written to by the transmit DMA to link descriptors together and should always be set to 0 by the host.
dword 3; Bits 17 to 31/Unused. These bits are ignored by the transmit DMA and can be set to any value.
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DS31256 256-Channel, High-Throughput HDLC Controller
9.3.3 Pending Queue
The host writes to the transmit pending queue the location of the readied descriptor, channel number, and
control information. The descriptor space is indicated through a 16-bit pointer, which the DMA uses
with the transmit packet-descriptor base address to find the exact 32-bit address of the associated
transmit packet descriptor.
Figure 9-17. Transmit Pending-Queue Descriptor
dword 0
Unused (3)
Status(3)
CHRST
PRI
HDLC Channel (8)
Descriptor Pointer (16)
Note 1: The organization of the pending queue is not affected by the enabling of Big Endian.
Note 2: Decriptor pointer is an index, not an absolute address.
dword 0; Bits 0 to 15/Descriptor Pointer. This 16-bit value is the offset from the transmit descriptor base
address to the first descriptor in a packet chain (can be a single descriptor) that is queued up for transmission.
dword 0; Bits 16 to 23/HDLC Channel Number. HDLC channel number, which can be from 1 to 256.
00000000 (00h) = HDLC channel number 1
11111111 (FFh) = HDLC channel number 256
dword 0; Bit 24/Priority Packet (PRI). If this bit is set to 1, this indicates to the transmit DMA that the packet or
packet chain pointed to by the descriptor pointer field should be transmitted immediately after the current packet
transmission (whether it be standard or priority) is complete.
dword 0; Bit 25/Channel Reset (CHRST). Under normal operating conditions, this bit should always be set to 0.
When an error condition occurs and the transmit DMA places the channel into an out-of-service state by setting
the channel enable (CHEN) bit in the transmit DMA configuration register to 0, the host can force the channel
active again by setting the CHRST bit to 1. Only the first descriptor loaded into the pending queue after an error
condition should have CHRST set to 1; all subsequent descriptors (until another error condition occurs) should
have CHRST set to 0. The transmit DMA examines this bit and forces the channel active (CHEN = 1) if CHRST is
set to 1. If CHRST is set to 0, then the transmit DMA does not modify the state of the CHEN bit. See Section 9.2.2
for more details about how error conditions are handled.
dword 0; Bits 26 to 28/Packet Status. Not used by the DMA. Can be set to any value by the host and is ignored
by the transmit DMA. This field is used by the transmit DMA when it writes to the done queue to inform the host
of the status of the outgoing packet data.
dword 0; Bits 29 to 31/Unused. Not used by the DMA. Can be set to any value by the host and is ignored by the
transmit DMA.
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DS31256 256-Channel, High-Throughput HDLC Controller
The transmit DMA reads from the transmit pending-queue descriptor circular queue which data buffers
and their associated descriptors are ready for transmission. A set of internal addresses within the device
that are accessed by both the host and the DMA keep track of the circular queue addresses in the transmit
pending queue. On initialization, the host configures all of the registers shown in Table 9-J. After
initialization, the DMA only writes to (changes) the read pointers and the host only writes to the write
pointers.
Empty Case
The transmit pending queue is considered empty when the read and write pointers are identical.
Transmit Pending-Queue Empty State
empty descriptor
empty descriptor
empty descriptor
empty descriptor
empty descriptor
empty descriptor
empty descriptor
read pointer >
< write pointer
Full Case
The transmit pending queue is considered full when the read pointer is ahead of the write pointer by one
descriptor. Therefore, one descriptor must always remain empty.
Transmit Pending-Queue Full State
valid descriptor
valid descriptor
empty descriptor < write pointer
read pointer >
valid descriptor
valid descriptor
valid descriptor
valid descriptor
Table 9-J. Transmit Pending-Queue Internal Address Storage
REGISTER
NAME
ADDRESS
Transmit Pending-Queue Base Address 0 (lower word)
Transmit Pending-Queue Base Address 1 (upper word)
Transmit Pending-Queue Host Write Pointer
Transmit Pending-Queue DMA Read Pointer
Transmit Pending-Queue End Address
TPQBA0
TPQBA1
TPQWP
TPQRP
0800h
0804h
080Ch
0810h
0808h
TPQEA
Note: Transmit free-queue end address is not an absolute address. The absolute end address is “Base + TPQEA.”
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 9-18. Transmit Pending-Queue Structure
Host Readied
Base + 00h
Base + 04h
Base + 08h
Base + 0Ch
Pending-Queue Descriptor
Host Readied
Pending-Queue Descriptor
DMA Acquired
Pending-Queue Host Write Pointer
Pending-Queue DMA Read Pointer
Pending-Queue Descriptor
DMA Acquired
Pending-Queue Descriptor
DMA Acquired
Pending-Queue Descriptor
Base + 10h
Base + 14h
Host Readied
Pending-Queue Descriptor
Host Readied
Maximum of 65,536
Pending-Queue Descriptor
Base + End Address
Pending-Queue Descriptors
Once the transmit DMA is activated (by setting the TDE control bit in the master configuration register;
see Section 5), it can begin reading data out of the pending queue. It knows where to read the data by
reading the read pointer and adding it to the base address to obtain the actual 32-bit address. Once the
DMA has read the pending queue, it increments the read pointer by one dword. A check must be made to
ensure the incremented address does not exceed the transmit pending-queue end address. If the
incremented address does exceed this address, the incremented read pointer is set equal to 0000h.
Status/Interrupts
On each read of the pending queue by the DMA, the DMA sets the status bit for transmit DMA pending-
queue read (TPQR) in the status register for DMA (SDMA). The status bits can also (if enabled) cause
an hardware interrupt to occur. See Section 5 for more details.
Pending-Queue Burst Reading
The DMA can read the pending queue in bursts, which allows for a more efficient use of the PCI bus.
The DMA can grab descriptors from the pending queue in groups rather than one at a time, freeing up
the PCI bus for more time-critical functions.
An internal FIFO can store up to 16 pending-queue descriptors (16 dwords, since each descriptor
occupies one dword). The host must configure the pending-queue FIFO for proper operation through the
transmit DMA queues-control (TDMAQ) register (see the following).
When enabled through the transmit pending-queue FIFO-enable (TPQFE) bit, the pending-queue FIFO
does not read the pending queue until it is empty. When the pending queue is empty, it attempts to fill
the FIFO with additional descriptors by burst reading the pending queue. Before it reads the pending
queue, it checks (by examining the transmit pending-queue host write pointer) to ensure the pending
queue contains enough descriptors to fill the pending-queue FIFO. If the pending queue does not have
enough descriptors to fill the FIFO, it only reads enough to empty the pending queue. If the FIFO detects
that there are no pending-queue descriptors available for it to read, it waits and tries again later. If the
pending-queue FIFO can read descriptors from the pending queue, it burst reads them, increments the
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DS31256 256-Channel, High-Throughput HDLC Controller
read pointer, and sets the status bit for transmit DMA pending-queue read (TPQR) in the status register
for DMA (SDMA). See Section 5 for more details about status bits.
Register Name:
TDMAQ
Register Description: Transmit DMA Queues Control
Register Address:
0880h
Bit #
Name
Default
7
n/a
0
6
5
n/a
0
4
n/a
0
3
TDQF
0
2
TDQFE
0
1
TPQF
0
0
TPQFE
0
n/a
0
Bit #
Name
Default
15
n/a
0
14
n/a
0
13
n/a
0
12
n/a
0
11
n/a
0
10
TDQT2
0
9
TDQT1
0
8
TDQT0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Transmit Pending-Queue FIFO Enable (TPQFE). This bit must be set to 1 to enable the DMA to burst
read descriptors from the pending queue. If this bit is set to 0, descriptors are read one at a time.
0 = pending-queue burst read disabled
1 = pending-queue burst read enabled
Bit 1/Transmit Pending-Queue FIFO Flush (TPQF). When this bit is set to 1, the internal pending-queue FIFO
is flushed (currently loaded pending-queue descriptors are lost). This bit must be set to 0 for proper operation.
0 = FIFO in normal operation
1 = FIFO is flushed
Bit 2/Transmit Done-Queue FIFO Enable (TDQFE). See Section 9.3.4 for details.
Bit 3/Transmit Done-Queue FIFO Flush (TDQF). See Section 9.3.4 for details.
Bits 8 to 10/Transmit Done-Queue Status Bit Threshold Setting (TDQT0 to TDQT2). See Section 9.3.4 for
more details.
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DS31256 256-Channel, High-Throughput HDLC Controller
9.3.4 Done Queue
The DMA writes to the transmit done queue when it has finished either transmitting a complete packet
chain or a complete data buffer. This option is selected by the host when it configures the DQS field in
the transmit DMA configuration RAM (Section 9.3.5). The descriptor location is indicated in the done
queue through a 16-bit pointer that the host uses along with the transmit descriptor base address to find
the exact 32-bit address of the associated transmit descriptor.
Figure 9-19. Transmit Done-Queue Descriptor
dword 0
unused
Status (3)
CHRST
PRI
HDLC Channel (8)
Descriptor Pointer (16)
Note: The organization of the done queue is not affected by the enabling of Big Endian.
dword 0; Bits 0 to 15/Descriptor Pointer. This 16-bit value is the offset from the transmit descriptor base
address to either the first descriptor in a HDLC packet (can be a single descriptor) that has been transmitted
(DQS = 0) or the descriptor that corresponds to a single data buffer that has been transmitted (DQS = 1).
dword 0; Bits 16 to 23/HDLC Channel Number. HDLC channel number, which can be from 1 to 256.
00000000 (00h) = HDLC channel number 1
11111111 (FFh) = HDLC channel number 256
dword 0; Bit 24/Priority Packet (PRI). This field is meaningless in the done queue and could be set to any value.
See Section 9.3.3 for details.
dword 0; Bit 25/Channel Reset (CHRST). This field is meaningless in the done queue and could be set to any
value. See Section 9.3.3 for details.
dword 0; Bits 26 to 28/Packet Status. These three bits report the final status of an outgoing packet. All the error
states cause a HDLC abort sequence (eight 1s in a row, followed by continuous interfill bytes of either FFh or
7Eh) to be sent, and the channel is placed out of service by the transmit DMA, setting the channel enable (CHEN)
bit in the transmit DMA configuration RAM to 0. The status state of 000 is only used when the channel has been
configured by the host to write to the done queue only after a complete HDLC packet (can be a single data buffer)
has been transmitted (i.e., DQS = 0). The status states of 001, 010, and 011 are only used when the channel has
been configured by the host to write to the done queue after each data buffer has been transmitted (i.e., DQS = 1).
000 = packet transmission complete and the descriptor pointer field corresponds to the first
descriptor in a HDLC packet (can be a single descriptor) that has been transmitted (DQS = 0)
001 = first buffer transmission complete of a multi (or single) buffer packet (DQS = 1)
010 = middle buffer transmission complete of a multibuffer packet (DQS = 1)
011 = last buffer transmission complete of a multibuffer packet (DQS = 1)
100 = software provisioning error; this channel was not enabled
101 = descriptor error; either byte count = 0 or channel code inconsistent with pending queue
110 = PCI error
111 = transmit FIFO error; it has underflowed
dword 0; Bits 29 to 31/Unused. Not used by the DMA. Could be any value when read.
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DS31256 256-Channel, High-Throughput HDLC Controller
The host reads from the transmit done queue to find which data buffers and their associated descriptors
have completed transmission. The transmit done queue is circular queue. A set of internal addresses
within the device that are accessed by both the host and the DMA keep track of the circular queue
addresses in the transmit done queue. On initialization, the host configures all of the registers, as shown
in Table 9-K. After initialization, the DMA only writes to (changes) the write pointer and the host only
writes to the read pointer.
Empty Case
The transmit done queue is considered empty when the read and write pointers are identical.
Transmit Done-Queue Empty State
empty descriptor
empty descriptor
empty descriptor
empty descriptor
empty descriptor
empty descriptor
empty descriptor
read pointer >
< write pointer
Full Case
The transmit done queue is considered full when the read pointer is ahead of the write pointer by one
descriptor. Therefore, one descriptor must always remain empty.
Transmit Done-Queue Full State
valid descriptor
valid descriptor
empty descriptor < write pointer
read pointer >
valid descriptor
valid descriptor
valid descriptor
valid descriptor
Table 9-K. Transmit Done-Queue Internal Address Storage
REGISTER
NAME
ADDRESS
Transmit Done-Queue Base Address 0 (lower word)
Transmit Done-Queue Base Address 1 (upper word)
Transmit Done-Queue DMA Write Pointer
Transmit Done-Queue Host Read Pointer
Transmit Done-Queue End Address
TDQBA0
TDQBA1
TDQWP
TDQRP
TDQEA
TDQFFT
0830h
0834h
0840h
083Ch
0838h
0844h
Transmit Done-Queue FIFO Flush Timer
Note: Transmit done-queue end address is not an absolute address. The absolute end address is “Base + TDQEA x 4.”
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 9-20. Transmit Done-Queue Structure
DMA Readied
Base + 00h
Base + 04h
Base + 08h
Base + 0Ch
Done Queue Descriptor
DMA Readied
Done Queue Descriptor
Host Processed
Done Queue DMA Write Pointer
Done Queue Host Read Pointer
Done Queue Descriptor
Host Processed
Done Queue Descriptor
Host Processed
Done Queue Descriptor
Base + 10h
Base + 14h
DMA Readied
Done Queue Descriptor
DMA Readied
Maximum of 65536
Done Queue Descriptor
Done Queue Descriptors
Base + End Address
dmatdq
Once the transmit DMA is activated (through the TDE control bit in the master configuration register;
see Section 5 for more details), it can begin writing data to the done queue. It knows where to write data
into the done queue by reading the write pointer and adding it to the base address to obtain the actual 32-
bit address. Once the DMA writes to the done queue, it increments the write pointer by one dword. A
check must be made to ensure the incremented address does not exceed the transmit done-queue end
address. If the incremented address does exceed this address, the incremented write pointer is set equal to
0000h (i.e., the base address).
Status Bits/Interrupts
On writes to the done queue by the DMA, the DMA sets the status bit for the transmit DMA done-queue
write (TDQW) in the status register for DMA (SDMA). The host can configure the DMA to either set
this status bit on each write to the done queue or only after multiple (from 2 to 128) writes. The host
controls this by setting the TDQT0 to TDQT2 bits in the transmit DMA queues-control (TDMAQ)
register. See the description of the TDMAQ register at the end of this section for more details. The DMA
also checks the transmit done-queue host read pointer to ensure that an overflow does not occur. If this
does occur, the DMA sets the status bit for transmit DMA done-queue write error (TDQWE) in the status
register for DMA (SDMA), and it does not write to the done queue nor does it increment the write
pointer. In such a scenario, information on transmitted packets is lost and unrecoverable. Each of the
status bits can also (if enabled) cause a hardware interrupt to occur. See Section 5 for more details.
Done-Queue Burst Writing
The DMA can write to the done queue in bursts. This allows for a more efficient use of the PCI bus. The
DMA can hand off descriptors to the done queue in groups rather than one at a time, freeing up the PCI
bus for more time-critical functions.
An internal FIFO can store up to eight done-queue descriptors (8 dwords, since each descriptor occupies
one dword). The host must configure the FIFO for proper operation through the transmit DMA queues
control (TDMAQ) register (see the following).
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DS31256 256-Channel, High-Throughput HDLC Controller
When enabled through the transmit done-queue FIFO-enable (TDQFE) bit, the done-queue FIFO does
not write to the done queue until it reaches the high watermark. When the done-queue FIFO reaches the
high watermark (which is six descriptors), it attempts to empty the done-queue FIFO by burst writing to
the done queue. Before it writes to the done queue, it checks (by examining the transmit done-queue host
read pointer) to ensure the done queue has enough room to empty. If the done queue does not have
enough room, then it only burst writes enough descriptors to keep from overflowing. If the FIFO detects
that there is no room for any descriptors to be written, then it sets the status bit for transmit DMA done-
queue write error (TDQWE) in the SDMA and it does not write to the done queue nor does it increment
the write pointer. In such a scenario, information on transmitted packets is lost and unrecoverable. If the
done-queue FIFO can write descriptors to the done queue, then it burst writes them, increments the write
pointer, and sets the status bit for transmit DMA done-queue write (TDQW) in the SDMA. See Section 5
for more details about status bits.
Done-Queue FIFO Flush Timer
To ensure the done-queue FIFO gets flushed to the done queue on a regular basis, the transmit done-
queue FIFO flush timer (TDQFFT) is used by the DMA to determine the maximum wait time in between
writes. The TDQFFT is a 16-bit programmable counter that is decremented every PCLK divided by 256.
It is only monitored by the DMA when the transmit done-queue FIFO is enabled (TDQFE = 1). For a
33MHz PCLK, the timer is decremented every 7.76µs. For a 25MHz clock, it decrements every 10.24µs.
Each time the DMA writes to the done queue it resets the timer to the count placed into it by the host. On
initialization, the host sets a value into the TDQFFT that indicates the maximum time the DMA should
wait in between writes to the done queue. For example, with a PCLK of 33MHz, the range of wait times
is from 7.8µs (RDQFFT = 0001h) to 508ms (RDQFFT = FFFFh). With a PCLK of 25MHz, the wait
times range from 10.2µs (RDQFFT = 0001h) to 671ms (RDQFFT = FFFFh).
Register Name:
TDQFFT
Register Description: Transmit Done-Queue FIFO Flush Timer
Register Address:
0844h
Bit #
Name
Default
7
TC7
0
6
TC6
0
5
TC5
0
4
TC4
0
3
TC3
0
2
TC2
0
1
TC1
0
0
TC0
0
Bit #
Name
Default
15
TC15
0
14
TC14
0
13
TC13
0
12
TC12
0
11
TC11
0
10
TC10
0
9
TC9
0
8
TC8
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 15/Transmit Done-Queue FIFO Flush Timer Control Bits (TC0 to TC15). Please note that on system
reset, the timer is set to 0000h, which is defined as an illegal setting. If the receive done-queue FIFO is to be
activated (TDQFE = 1), the host must first configure the timer to a proper state and then set the TDQFE bit
to 1.
0000h = illegal setting
0001h = timer count resets to 1
FFFFh = timer count resets to 65,536
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
TDMAQ
Register Description: Transmit DMA Queues Control
Register Address:
0880h
Bit #
Name
Default
7
n/a
0
6
n/a
0
5
n/a
0
4
n/a
0
3
TDQF
0
2
TDQFE
0
1
TPQF
0
0
TPQFE
0
Bit #
15
n/a
0
14
n/a
0
13
n/a
0
12
n/a
0
11
n/a
0
10
TDQT2
0
9
TDQT1
0
8
TDQT0
0
Name
Default
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Transmit Pending-Queue FIFO Enable (TPQFE). See Section 9.3.3 for details.
Bit 1/Transmit Pending-Queue FIFO Flush (TPQLF). See Section 9.3.3 for details.
Bit 3/Transmit Done-Queue FIFO Enable (TDQFE). This bit must be set to 1 to enable the DMA to burst write
descriptors to the done queue. If this bit is set to 0, descriptors are written one at a time.
0 = done-queue burst write disabled
1 = done-queue burst write enabled
Bit 4/Transmit Done-Queue FIFO Flush (TDQF). When this bit is set to 1, the internal done-queue FIFO is
flushed by sending all data into the done queue. This bit must be set to 0 for proper operation.
0 = FIFO in normal operation
1 = FIFO is flushed
Bits 8 to 10/Transmit Done-Queue Status Bit Threshold Setting (TDQT0 to TDQT2). These bits determine
when the DMA sets the transmit DMA done-queue write (TDQW) status bit in the status register for DMA
(SDMA) register.
000 = set the TDQW status bit after each descriptor write to the done queue
001 = set the TDQW status bit after 2 or more descriptors are written to the done queue
010 = set the TDQW status bit after 4 or more descriptors are written to the done queue
011 = set the TDQW status bit after 8 or more descriptors are written to the done queue
100 = set the TDQW status bit after 16 or more descriptors are written to the done queue
101 = set the TDQW status bit after 32 or more descriptors are written to the done queue
110 = set the TDQW status bit after 64 or more descriptors are written to the done queue
111 = set the TDQW status bit after 128 or more descriptors are written to the done queue
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DS31256 256-Channel, High-Throughput HDLC Controller
9.3.5 DMA Configuration RAM
The device contains an on-board set of 1536 dwords (6 dwords per channel times 256 channels) that are
used by the host to configure the DMA and used by the DMA to store values locally when it is
processing a packet. Most of the fields within the DMA configuration RAM are for DMA use and the
host never writes to these fields. The host is only allowed to write (configure) to the lower word of
dword 1 for each HDLC channel. In Figure 9-21, the host-configurable fields are denoted with a thick
box.
Figure 9-21. Transmit DMA Configuration RAM
msb
31
lsb
0
Transmit DMA Configuration RAM
000h
004h
008h
00Ch
010h
014h
Current Packet Data Buffer Address (32)
PEND
PRI
un-
CH
unused (9)
EOF CV
DQS
PPP
Byte Count (13)
ST(2) ST(2)
used
EN
HDLC
Channel
1
Start Descriptor Pointer (16)
Next Descriptor Pointer (16)
Next Pending Descriptor Pointer (16)
Next Priority Descriptor Pointer (16)
Last Pending Descriptor Pointer (16)
unused (16)
Next Priority Pending Descriptor Pointer (16)
Last Priority Pending Descriptor Pointer (16)
17D8h
17DCh
17F0h
17F4h
17F8h
17FCh
Current Packet Data Buffer Address (32)
PEND
PRI
un-
CH
EN
HDLC
Channel
256
unused (9)
Start Descriptor Pointer (16)
CV
DQS
PPP
EOF
Byte Count (13)
ST(2) ST(2)
used
Next Descriptor Pointer (16)
Next Pending Descriptor Pointer (16)
Next Priority Descriptor Pointer (16)
Last Pending Descriptor Pointer (16)
unused (16)
Next Priority Pending Descriptor Pointer (16)
Last Priority Pending Descriptor Pointer (16)
Fields shown within the thick box
are written by the Host; all other
fields are for usage by the DMA and
can only be read by the Host
dmatcram
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DS31256 256-Channel, High-Throughput HDLC Controller
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 0; Bits 0 to 31/Current Data Buffer Address. This is the current 32-bit address of the data buffer that is
being used. This address is used by the DMA to keep track of where data should be read from as it is passed to the
transmit FIFO.
- HOST MUST CONFIGURE -
dword 1; Bit 0/Channel Enable (CHEN). This bit is controlled by both the host and the transmit DMA to enable
and disable a HDLC channel. The DMA automatically disables a channel when an error condition occurs (see
Section 9.2.1 for a discussion on error conditions). The DMA automatically enables a channel when it detects that
the channel reset (CHRST) bit in the pending-queue descriptor is set to 1.
0 = HDLC channel disabled
1 = HDLC channel enabled
- HOST MUST CONFIGURE -
dword 1; Bit 1/Done-Queue Select (DQS). This bit determines whether the transmit DMA writes to the done
queue only after a complete HDLC packet (which may be only a single buffer) has been transmitted (in which case
the descriptor pointer in the done queue corresponds to the first descriptor of the packet) or whether it should write
to the done queue after each data buffer has been transmitted (in which case the descriptor pointer in the done
queue corresponds to a single data buffer). The setting of this bit also affects the reporting of the status field in the
transmit done queue. When DQS = 0, the only nonerrored status possible is a setting of 000. When DQS = 1, then
the nonerrored settings of 001, 010, and 011 are possible.
0 = write to the done queue only after a complete HDLC packet has been transmitted
1 = write to the done queue after each data buffer is transmitted
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 1; Bit 2/Unused. This field is not used by the DMA and could be any value when read.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 1; Bits 3 to 15/Byte Count. The DMA uses these 13 bits to keep track of the number of bytes stored in the
data buffer. Maximum is 8188 Bytes (0000h = 0 Bytes / 1FFCh = 8188 Bytes).
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 1; Bit 16/Chain Valid (CV). This is an internal copy of the CV field that resides in the current packet
descriptor that the DMA is operating on. See Section 9.2.2 for more details on the CV bit.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 1; Bit 17/End of Frame (EOF). This is an internal copy of the EOF field that resides in the current Packet
Descriptor that the DMA is operating on. See Section 9.2.2 for more details about the EOF bit.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 1; Bits 18 to 19/Pending State (PENDST). This field is used by the transmit DMA to keep track of
queued descriptors as they arrive from the pending queue and for the DMA to know when it should create a
horizontal linked list of transmit descriptors and where it can find the next valid descriptor. This field handles
standard packets and the PRIST field handles priority packets.
State
Next Descriptor Pointer Field
Next Pending Descriptor Pointer Field
00
01
10
11
Not Valid
Valid
Not Valid
Valid
Not Valid
Not Valid
Valid
Valid
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DS31256 256-Channel, High-Throughput HDLC Controller
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 1; Bits 20 to 21/Priority State (PRIST). This field is used by the transmit DMA to keep track of queued
priority descriptors as they arrive from the pending queue, and for the DMA to know when it should create a
horizontal linked list of transmit priority descriptors and where it can find the next valid priority descriptor. This
field handles priority packets and the PENDST field handles standard packets.
State
Next Priority Descriptor Pointer Field
Next Priority Pending Descriptor Pointer Field
00
01
10
11
Not Valid
Valid
Not Valid
Valid
Not Valid
Not Valid
Valid
Valid
-FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 1; Bit 22/Processing Priority Packet (PPP). This bit is set to 1 when the DMA is currently processing a
priority packet.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 1; Bits 23 to 31/Unused. This field is not used by the DMA and could be any value when read.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 2; Bits 0 to 15/Next Descriptor Pointer. This 16-bit value is the offset from the transmit descriptor base
address of the next transmit packet descriptor for the packet that is currently being transmitted. Only valid if
EOF = 0 or if EOF = 1 and CV = 1.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 2; Bits 16 to 31/Start Descriptor Pointer. This 16-bit value is the offset from the transmit descriptor base
address of the first transmit packet descriptor for the packet that is currently being transmitted. If DQS = 0, then
this pointer is written back to the done queue when the packet has completed transmission. This field is used by
the DMA for processing standard as well as priority packets.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 3; Bits 0 to 15/Next Pending Descriptor Pointer. This 16-bit value is the offset from the transmit
descriptor base address of the first transmit packet descriptor for the packet that is queued up next for
transmission.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 3; Bits 16 to 31/Last Pending Descriptor Pointer. This 16-bit value is the offset from the transmit
descriptor base address of the first transmit packet descriptor for the packet that is queued up last for transmission.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 4; Bits 0 to 15/Next Priority Descriptor Pointer. This 16-bit value is the offset from the transmit
descriptor base address of the next transmit priority packet descriptor for the priority packet that is currently being
transmitted. Only valid if EOF = 0 or if EOF = 1 and CV = 1.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 4; Bits 16 to 31/Unused. This field is not used by the DMA and could be any value when read.
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 5; Bits 0 to 15/Last Priority Pending Descriptor Pointer. This 16-bit value is the offset from the
transmit descriptor base address of the first transmit priority packet descriptor for the priority packet that is queued
up last for transmission.
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DS31256 256-Channel, High-Throughput HDLC Controller
- FOR DMA USE ONLY/HOST CAN ONLY READ THIS FIELD -
dword 5; Bits 16 to 31/Next Priority Pending Descriptor Pointer. This 16-bit value is the offset from the
transmit descriptor base address of the first transmit priority packet descriptor for the packet priority that is queued
up next for transmission.
Register Name:
TDMACIS
Register Description: Transmit DMA Configuration Indirect Select
Register Address:
0870h
Bit #
7
6
5
HCID5
0
4
HCID4
0
3
HCID3
0
2
HCID2
0
1
HCID1
0
0
HCID0
0
Name
HCID7
0
HCID6
Default
0
Bit #
Name
Default
15
IAB
0
14
IARW
0
13
n/a
0
12
n/a
0
11
TDCW3
0
10
TDCW2
0
9
TDCW1
0
8
TDCW0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bits 0 to 7/HDLC Channel ID (HCID0 to HCID7)
00000000 (00h) = HDLC channel number 1
11111111 (FFh) = HDLC channel number 256
Bits 8 to 11/Transmit DMA Configuration RAM Word Select Bits 0 to 3 (TDCW0 to TDCW3)
0000 = lower word of dword 0
0001 = upper word of dword 0
0010 = lower word of dword 1 (only word that the host can write to)
0011 = upper word of dword 1
0100 = lower word of dword 2
0101 = upper word of dword 2
0110 = lower word of dword 3
0111 = upper word of dword 3
1000 = lower word of dword 4
1001 = upper word of dword 4
1010 = lower word of dword 5
1011 = upper word of dword 5
Bit 14/Indirect Access Read/Write (IARW). When the host wishes to read data from the internal transmit DMA
configuration RAM, the host should write this bit to 1. This causes the device to begin obtaining the data from the
channel location indicated by the HCID bits. During the read access, the IAB bit is set to 1. Once the data is ready
to be read from the TDMAC register, the IAB bit is set to 0. When the host wishes to write data to the internal
transmit DMA configuration RAM, this bit should be written to 0 by the host. This causes the device to take the
data that is currently present in the TDMAC register and write it to the channel location indicated by the HCID
bits. When the device has completed the write, the IAB bit is set to 0.
Bit 15/Indirect Access Busy (IAB). When an indirect read or write access is in progress, this read-only bit is set
to 1. During a read operation, this bit is set to 1 until the data is ready to be read. It is set to 0 when the data is
ready to be read. During a write operation, this bit is set to 1 while the write is taking place. It is set to 0 once the
write operation has completed.
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
TDMAC
Register Description: Transmit DMA Configuration
Register Address:
0874h
Bit #
Name
Default
7
D7
0
6
D6
0
5
D5
0
4
D4
0
3
D3
0
2
D2
0
1
D1
0
0
D0
0
Bit #
Name
Default
15
D15
0
14
D14
0
13
D13
0
12
D12
0
11
D11
0
10
D10
0
9
D9
0
8
D8
0
Note: Bits that are underlined are read only, all other bits are read-write.
Bits 0 to 15/Transmit DMA Configuration RAM Data (D0 to D15). Data that is written to or read from the
transmit DMA configuration RAM.
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DS31256 256-Channel, High-Throughput HDLC Controller
10. PCI BUS
10.1General Description of Operation
The PCI block interfaces the DMA block to an external high-speed bus. The PCI block complies with
Revision 2.1 (June 1, 1995) of the PCI Local Bus Specification. HDLC packet data always passes to and
from the DS31256 through the PCI bus. The user has the option to configure and monitor the internal
device registers either through the PCI bus (local bus bridge mode) or through the local bus (local bus
configuration mode). When the local bus bridge mode is used, the host on the PCI bus can also bridge to
the local bus and sets/monitors the PCI configuration registers. When the local bus configuration mode is
used, the CPU on the local bus sets/monitors the PCI configuration registers.
The PCI configuration registers (Figure 10-1) are described in detail in Section 10.2. The following notes
apply to the PCI configuration registers:
1) All unused locations (the shaded areas of Figure 10-1) return zeros when read.
2) Read-only locations can be written with either 1 or 0 with no effect.
3) All bits are read/write, unless otherwise noted.
Figure 10-1. PCI Configuration Memory Map
0x000
0x004
0x008
0x00C
0x010
Device ID
Status
Vendor ID
Command
Class Code
Header Type
Base Address for Device Configuration
Revision ID
Latency Timer
Cache Line Size
0x000
0x03C
Max. Latency
Min. Grant
Interrupt Pin
Interrupt Line
0x100
0x104
0x108
0x10C
0x110
Device ID
Status
Class Code
Header Type
Base Address for Local Bus
Vendor ID
Command
Revision ID
0x00000
0x13C
Interrupt Pin
Interrupt Line
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10.1.1 PCI Read Cycle
A read cycle on the PCI bus is shown in Figure 10-2. During clock cycle #1, the initiator asserts the
PFRAME signal and drives the address onto the PAD signal lines and the bus command (which would
be a read) onto the PCBE signal lines. The target reads the address and bus command and, if the address
matches its own, it then asserts the PDEVSEL signal and begins the bus transaction. During clock cycle
#2, the initiator stops driving the address onto the PAD signal lines and switches the PCBE signal lines
to indicate byte enables. It also asserts the PIRDY signal and begins monitoring the PDEVSEL and
PTRDY signals. During clock cycle #4, the target asserts PTRDY, indicating to the initiator that valid
data is available to be read on the PAD signal lines by the initiator. During clock cycle #5, the target is
not ready to provide data #2 because PTRDY is deasserted. During clock cycle #6, the target again
asserts PTRDY, informing the initiator to read data #2. During clock cycle #7, the initiator deasserts
PIRDY, indicating to the target that it is not ready to accept data. During clock cycle #8, the initiator
asserts PIRDY and acquires data #3. Also during clock cycle #8, the initiator deasserts PFRAME,
indicating to the target that the bus transaction is complete and no more data needs to be read. During
clock cycle #9, the target deasserts PTRDY and PDEVSEL and the initiator deasserts PIRDY.
The PXAS, PXDS, and PXBLAST signals are not part of a standard PCI bus. These PCI extension
signals are unique to the device and are useful in adapting the PCI bus to a proprietary bus scheme. They
are only asserted when the device is a bus master.
Figure 10-2. PCI Bus Read
PCLK
1
2
3
4
5
6
7
8
9
10
PFRAME
PAD
Address
CMD
data #1
data #2
data #3
BE #3
Byte Enable #1
BE #2
PCBE
PIRDY
PTRDY
PDEVSEL
PXAS
PXDS
PXBLAST
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10.1.2 PCI Write Cycle
A write cycle on the PCI bus is shown in Figure 10-3. During clock cycle #1, the initiator asserts the
PFRAME signal and drives the address onto the PAD signal lines and the bus command (which would
be a write) onto the PCBE signal lines. The target reads the address and bus command and, if the address
matches its own, it then asserts the PDEVSEL signal and begins the bus transaction. During clock cycle
#2, the initiator stops driving the address onto the PAD signal lines and begins driving data #1. It also
switches the PCBE signal lines to indicate the byte enable for data #1. The initiator asserts the PIRDY
signal and begins monitoring the PDEVSEL and PTRDY signals. During clock cycle #3, the initiator
detects that PDEVSEL and PTRDY are asserted, which indicates that the target has accepted data #1 and
the initiator begins driving the data and byte enable for data #2. During clock cycle #4, since PDEVSEL
and PTRDY are asserted, data #2 is written by the initiator to the target. During clock cycle #5, both
PIRDY and PTRDY are deasserted, indicating that neither the initiator nor the target are ready for data
#3 to be passed. During clock cycle #6, the initiator is ready so it asserts PIRDY and deasserts PFRAME,
which indicates that data #3 is the last one passed. During clock cycle #8, the target asserts PTRDY,
which indicates to the initiator that data #3 is ready to be accepted by the target. During clock cycle #9,
the initiator deasserts PIRDY and stops driving the PAD and PCBE signal lines. The target deasserts
PDEVSEL and PTRDY.
The PXAS, PXDS, and PXBLAST signals are not part of a standard PCI bus. These PCI extension
signals are unique to the device. They are useful in adapting the PCI bus to a proprietary bus scheme.
They are only asserted when the device is a bus master.
Figure 10-3. PCI Bus Write
PCLK
1
2
3
4
5
6
7
8
9
10
PFRAME
PAD
Address
CMD
data #1
BE #1
data #2
data #3
BE #2
BE #3
PCBE
PIRDY
PTRDY
PDEVSEL
PXAS
PXDS
PXBLAST
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10.1.3 PCI Bus Arbitration
The PCI bus can be arbitrated as shown in Figure 10-4. The initiator requests bus access by asserting
PREQ. A central arbiter grants the access some time later by asserting PGNT. Once the bus has been
granted, the initiator waits until both PIRDY and PFRAME are deasserted (i.e., an idle cycle) before
acquiring the bus and beginning the transaction. As shown in Figure 10-3, the bus was still being used
when it was granted and the device had to wait until clock cycle #6 before it acquired the bus and began
the transaction. The arbiter can deassert PGNT at any time and the initiator must relinquish the bus after
the current transfer is complete, which can be limited by the latency timer.
Figure 10-4. PCI Bus Arbitration Signaling Protocol
PCLK
1
2
3
4
5
6
7
8
9
10
PREQ
PGNT
PFRAME
Wait for PGNT Asserted
and then PFRAME and
PIRDY Deasserted
Bus is Acquired
Bus is Relinquished
10.1.4 PCI Initiator Abort
If a target fails to respond to an initiator by asserting PDEVSEL and PTRDY within 5 clock cycles, then
the initiator aborts the transaction by deasserting PFRAME and then, one clock later, by deasserting
PIDRY (Figure 10-5). If such a scenario occurs, it is reported through the master abort status bit in the
PCI command/status configuration register (Section 10.2).
Figure 10-5. PCI Initiator Abort
PCLK
1
2
3
4
5
6
7
8
9
10
PFRAME
PIRDY
PTRDY
PDEVSEL
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10.1.5 PCI Target Retry
Targets can terminate the requested bus transaction before any data is transferred because the target is
busy and temporarily unable to process the transaction. Such a termination is called a target retry and no
data is transferred. A target retry is signaled to the initiator by the assertion of PSTOP and not asserting
PTRDY on the initial data phase (Figure 10-6). When the DS31256 is a target, it only issues a target
retry when the host is accessing the local bus. This occurs when the local bus is operating in the
arbitration mode. It is busy at the instant the host requests access to the local bus. See Section 11.1 for
more details about the operation of the local bus.
Figure 10-6. PCI Target Retry
PCLK
1
2
3
4
5
6
7
8
9
10
PFRAME
PIRDY
PTRDY
PSTOP
PDEVSEL
10.1.6 PCI Target Disconnect
A target can prematurely terminate a transaction by asserting PSTOP (Figure 10-7). Depending on the
current state of the ready signals when PSTOP is asserted, data may or may not be transferred. The target
always deasserts PSTOP when it detects that the initiator has deasserted PFRAME. When the DS31256
is a target, it disconnects with data after the first data phase is complete, if the master attempts a burst
transaction. This is because the device does not support burst transactions when it is a target. When it is
an initiator and experiences a disconnect from the target, it attempts another bus transaction (if it still has
the bus granted) after waiting either one (disconnect without data) or two clock cycles (disconnect with
data).
Figure 10-7. PCI Target Disconnect
PCLK
1
2
3
4
5
6
7
8
9
10
PFRAME
PSTOP
PDEVSEL
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10.1.7 PCI Target Abort
Targets can also abort the current transaction, which means they do not wish for the initiator to attempt
the request again. No data is transferred in a target abort scenario. A target abort is signaled to the
initiator by the simultaneous assertion of PSTOP and deassertion of PDEVSEL (Figure 10-8). When the
DS31256 is a target, it only issues a target abort when the host is accessing the local bus. This occurs
when the host attempts a bus transaction with a combination of byte enables (PCBE) that are not
supported by the local bus. If such a scenario occurs, it reports through the target-abort-initiated status bit
in the PCI command/status configuration register (Section 10.2). See Section 11.1 for details about local
bus operation. When the DS31256 is a bus master, if it detects a target abort, it reports through the target
abort detected by master status bit in the PCI command/status configuration register (Section 10.2).
Figure 10-8. PCI Target Abort
PCLK
1
2
3
4
5
6
7
8
9
10
PFRAME
PTRDY
PSTOP
PDEVSEL
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10.1.8 PCI Fast Back-to-Back
Fast back-to-back transactions are two consecutive bus transactions without the usually required idle
cycle (PFRAME and PIRDY deasserted) between them. This can only occur when there is a guarantee
that there is not any contention on the signal lines. The PCI specification allows two types of fast back-
to-back transactions—those that access the same agent (Type 1) and those that do not (Type 2).
Figure 10-9 shows an example of a fast back-to-back transaction where no idle cycle exists. As a bus
master, the DS31256 cannot perform a Type 2 access. As a target, it can accept both types of fast back-
to-back transactions.
Figure 10-9. PCI Fast Back-To-Back
PCLK
1
2
3
4
5
6
7
8
9
10
PFRAME
PAD
data #1
BE #1
Address
CMD
data #2
BE #2
data #1
BE #1
data #2
BE #2
Address
CMD
PCBE
PIRDY
PTRDY
PDEVSEL
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10.2PCI Configuration Register Description
Register Name:
Register Description: PCI Vendor ID/Device ID Register 0
Register Address: 0x000
PVID0
LSB
Vendor ID (Read Only/Set to EAh)
Vendor ID (Read Only/Set to 13h)
Device ID (Read Only/Set to 34h)
Device ID (Read Only/Set to 31h)
MSB
Bits 0 to 15/Vendor ID. These read-only bits identify Dallas Semiconductor as the device’s manufacturer. The
vendor ID was assigned by the PCI Special Interest Group and is fixed at 13EAh.
Bits 16 to 31/Device ID. These read-only bits identify the DS31256 as the device being used. The device ID was
assigned by Dallas Semiconductor and is fixed at 3134h.
Register Name:
Register Description: PCI Command/Status Register 0
Register Address: 0x004
PCMD0
LSB
IOC
STEPC PARC VGA
MWEN
SCC
MASC
MSC
Reserved (Read Only/Set to All Zeros)
FBBEN
PSEC
FBBCT
MSB
PPE
UDF
PSE
66MHz
MABT
Reserved (Read Only/Set to All Zeros)
TABT DTS1 DTS0
TABTM
PARR
Note: Read-only bits in the PCMD0 register are underlined; all other bits are read-write.
The lower word (bits 0 to 15) of the PCMD0 register is the command portion and is used for PCI bus control.
When all bits in the lower word are set to 0, the device is logically disconnected from the bus for all accesses,
except for accesses to the configuration registers. The upper word (bits 16 to 31) is the status portion and is used
for status information. Reads to the status portion behave normally but writes are unique in that bits can be reset
(i.e., forced to 0) but not set (i.e., forced to 1). A bit in the status portion resets when 1 is written to that bit
position. Bit positions that have 0 written to them do not reset.
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10.2.1 Command Bits (PCMD0)
Bit 0/I/O Space Control (IOC). This read-only bit is forced to 0 by the device to indicate that it does not respond
to I/O space accesses.
Bit 1/Memory Space Control (MSC). This read/write bit controls whether or not the device responds to accesses
by the PCI bus to the memory space (the internal device configuration registers). When this bit is set to 0, the
device ignores accesses attempted to the internal configuration registers. When set to 1, the device allows accesses
to the internal configuration registers. This bit should be set to 0 when the local bus is operated in the
configuration mode. This bit is forced to 0 when a hardware reset is initiated through the PRST pin.
0 = ignore accesses to the internal device configuration registers
1 = allow accesses to the internal device configuration registers
Bit 2/Master Control (MASC). This read/write bit controls whether or not the device can act as a master on the
PCI bus. When this bit is set to 0, the device cannot act as a master. When it is set to 1, the device can act as a bus
master. This bit is forced to 0 when a hardware reset is initiated through the PRST pin.
0 = deny the device from operating as a bus master
1 = allow the device to operate as a bus master
Bit 3/Special Cycle Control (SCC). This read-only bit is forced to 0 by the device to indicate that it cannot
decode special cycle operations.
Bit 4/Memory Write and Invalidate Command Enable (MWEN). This read-only bit is forced to 0 by the
device to indicate that it cannot generate the memory write and invalidate command.
Bit 5/VGA Control (VGA). This read-only bit is forced to 0 by the device to indicate that it is not a VGA-
compatible device.
Bit 6/Parity Error Response Control (PARC). This read/write bit controls whether or not the device should
ignore parity errors. When this bit is set to 0, the device ignores any parity errors that it detects and continues to
operate normally. When this bit is set to 1, the device must act on parity errors. This bit is forced to 0 when a
hardware reset is initiated through the PRST pin.
0 = ignore parity errors
1 = act on parity errors
Bit 7/Address Stepping Control (STEPC). This read-only bit is forced to 0 by the device to indicate that it is not
capable of address/data stepping.
Bit 8/PCI System Error Control (PSEC). This read/write bit controls whether or not the device should enable
the PSERR output pin. When this bit is set to 0, the device disables the PSERR pin. When this bit is set to 1, the
device enables the PSERR pin. This bit is forced to 0 when a hardware reset is initiated through the PRST pin.
0 = disable the PSERR pin
1 = enable the PSERR pin
Bit 9/Fast Back-to-Back Master Enable (FBBEN). This read-only bit is forced to 0 by the device to indicate that
it is not capable of generating fast back-to-back transactions to different agents.
Bits 10 to 15/Reserved. These read-only bits are forced to 0 by the device.
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10.2.2 Status Bits (PCMD0)
The upper word in the PCMD0 register is the status portion, which reports events as they occur. As previously
mentioned, reads of the status portion occur normally but writes are unique in that bits can only be reset (i.e.,
forced to 0). This occurs when 1 is written to a bit position. Writes with a 0 to a bit position have no effect. This
allows individual bits to be reset.
Bits 16 to 20/Reserved. These read-only bits are forced to 0 by the device.
Bit 21/66MHz Capable (66MHz). This read-only bit is forced to 0 by the device to indicate that it is not capable
of running at 66MHz.
Bit 22/User-Definable Features Capable (UDF). This read-only bit is forced to 0 by the device to indicate that it
does not support user-definable features.
Bit 23/Fast Back-to-Back Capable Target (FBBCT). This read-only bit is forced to 1 by the device to indicate
that it is capable of accepting fast back-to-back transactions when the transactions are not from the same agent.
Bit 24/PCI Parity Error Reported (PARR). This read/write bit is set to 1 when the device is a bus master and
detects or asserts the PPERR signal when the PARC command bit is enabled. This bit can be reset (set to 0) by the
host by writing 1 to this bit.
0 = no parity errors have been detected
1 = parity errors detected
Bits 25, 26/Device Timing Select Bits 0 and 1 (DTS0 and DTS1). These read-only bits are forced to 01b by the
device to indicate that it is capable of the medium timing requirements for the PDEVSEL signal.
Bit 27/Target Abort Initiated (TABT). This read-only bit is forced to 0 by the device since it does not terminate
a bus transaction with a target abort when the device is a target.
Bit 28/Target Abort Detected by Master (TABTM). This read/write bit is set to 1 when the device is a bus
master and it detects that a bus transaction has been aborted by the target with a target abort. This bit can be reset
(set to 0) by the host by writing 1 to this bit.
Bit 29/Master Abort (MABT). This read/write bit is set to 1 when the device is a bus master and the bus
transaction is terminated with a master abort (except for special cycle). This bit can be reset (set to 0) by the host
by writing 1 to this bit.
Bit 30/PCI System Error Reported (PSE). This read/write bit is set to 1 when the device asserts the PSERR
signal. This bit can be reset (set to 0) by the host by writing 1 to this bit.
Bit 31/PCI Parity Error Reported (PPE). This read/write bit is set to 1 when the device detects a parity error
(even if parity is disabled through the PARC command bit). This bit can be reset (set to 0) by the host by writing 1
to this bit.
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
Register Description: PCI Revision ID/Class Code Register 0
Register Address: 0x008h
PRCC0
LSB
Revision ID (Read Only/Set to 00h)
Class Code (Read Only/Set to 00h)
Class Code (Read Only/Set to 80h)
Class Code (Read Only/Set to 02h)
MSB
Bits 0 to 7/Revision ID. These read-only bits identify the specific device revision, which is selected by Dallas
Semiconductor.
Bits 8 to 15/Class Code Interface. These read-only bits identify the subclass interface value for the device and
are fixed at 00h. See Appendix D of PCI Local Bus Specification Revision 2.1 for details.
Bits 16 to 23/Class Code Subclass. These read-only bits identify the subclass value for the device and are fixed at
80h, which indicate “Other Network Controller.” See Appendix D of PCI Local Bus Specification Revision 2.1 for
details.
Bits 24 to 31/Class Code Base Class. These read-only bits identify the base class value for the device and are
fixed at 02h, which indicate “Network Controllers.” See Appendix D of PCI Local Bus Specification Revision 2.1
for details.
Register Name:
Register Description: PCI Latency Timer/Header Type Register 0
Register Address: 0x00Ch
PLTH0
LSB
Cache Line Size
Latency Timer
Header Type (Read Only/Set to 80h)
BIST (Read Only/Set to 00h)
MSB
Bits 0 to 7/Cache Line Size. These read/write bits indicate the cache line size in terms of dwords. If the burst size
of a data read transaction exceeds this value, the PCI block uses the memory read multiple command. Valid
settings are 04h (4 dwords), 08h, 10h, 20h, and 40h (64 dwords). Other settings are interpreted as 00h. These bits
are forced to 0 when a hardware reset is initiated through the PRST pin.
Bits 8 to 15/Latency Timer. These read/write bits indicate the value of the latency timer (in terms of the number
of PCI clocks) for use when the device is a bus master. These bits are forced to 0 when a hardware reset is initiated
through the PRST pin.
Bits 16 to 23/Header Type. These read-only bits are forced to 80h, which indicate a multifunction device.
Bits 24 to 31/Built-In Self-Test (BIST). These read only bits are forced to 0.
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
Register Description: PCI Device Configuration Memory Base Address Register
Register Address: 0x010h
PDCM
LSB
MSI
Base Address (Read Only/Set to 0h)
Base Address
PF
TYPE1
TYPE0
Base Address (Read Only/Set to 0h)
Base Address
Base Address
MSB
Note: Read-only bits in the PDCM register are underlined; all other bits are read-write.
Bit 0/Memory Space Indicator (MSI). This read-only bit is forced to 0 to indicate that the internal device
configuration registers are mapped to memory space.
Bits 1, 2/Type 0, Type 1. These read-only bits are forced to 00b to indicate that the internal device configuration
registers can be mapped anywhere in the 32-bit address space.
Bit 3/Prefetchable (PF). This read-only bit is forced to 0 to indicate that prefetching is not supported by the
device for the internal device configuration registers.
Bits 4 to 11/Base Address. These read-only bits are forced to 0 to indicate that the internal device configuration
registers require 4kB of memory space.
Bits 12 to 31/Base Address. These read/write bits define the location of the 4kB memory space that is mapped to
the internal configuration registers. These bits correspond to the most significant bits of the PCI address space.
Register Name:
Register Description: PCI Interrupt Line and Pin/Minimum Grant/Maximum Latency Register 0
Register Address: 0x03Ch
PINTL0
LSB
Interrupt Line
Interrupt Pin (Read Only/Set to 01h)
Maximum Grant (Read Only/Set to 05h)
Maximum Latency (Read Only/Set to 0 Fh)
MSB
Bits 0 to 7/Interrupt Line. These read/write bits indicate and store interrupt line routing information. The device
does not use this information, it is only posted here for the host to use.
Bits 8 to 15/Interrupt Pin. These read-only bits are forced to 01h to indicate that PINTA is used as an interrupt.
Bits 16 to 23/Minimum Grant. These read-only bits are used to indicate to the host how long of a burst period
the device needs, assuming a clock rate of 33MHz. The values placed in these bits specify a period of time in
0.25µs increments. These bits are forced to 05h.
Bits 24 to 31/Maximum Latency. These read-only bits are used to indicate to the host how often the device needs
to gain access to the PCI bus. The values placed in these bits specify a period of time in 0.25µs increments. These
bits are forced to 0Fh.
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
Register Description: PCI Vendor ID/Device ID Register 1
Register Address: 0x100h
PVID1
LSB
Vendor ID (Read Only/Set to EAh)
Vendor ID (Read Only/Set to 13h)
Device ID (Read Only/Set to 34h)
Device ID (Read Only/Set to 31h)
MSB
Bits 0 to 15/Vendor ID. These read-only bits identify Dallas Semiconductor as the device’s manufacturer. The
vendor ID was assigned by the PCI Special Interest Group and is fixed at 13EAh.
Bits 16 to 31/Device ID. These read-only bits identify the DS31256 as the device being used. The device ID was
assigned by Dallas Semiconductor and is fixed at 3134h.
Register Name:
PCMD1
Register Description: PCI Command/Status Register 1
Register Address:
STEPC
0x104h
PARC
LSB
IOC
VGA
MWEN
SCC
MASC
MSC
Reserved (Read Only/Set to All Zeros)
66MHz
FBBEN
PSEC
FBBCT
MSB
UDF
PSE
Reserved (Read Only/Set to All Zeros)
PPE
MABT
TABTM
TABT DTS1 DTS0
PARR
Note: Read-only bits in the PCMD1 register are underlined; all other bits are read-write.
The lower word (bits 0 to 15) of the PCMD1 register is the command portion and is used for the PCI bus control.
When all bits in the lower word are set to 0, the device is logically disconnected from the bus for all accesses,
except for accesses to the configuration registers. The upper word (bits 16 to 31) is the status portion and is used
for status information. Reads to the status portion behave normally but writes are unique in that bits can be reset
(i.e., forced to 0) but not set (i.e., forced to 1). A bit in the status portion is reset when a 1 is written to that bit
position. Bit positions that have 0 written to them do not reset.
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10.2.3 Command Bits (PCMD1)
Bit 0/I/O Space Control (IOC). This read-only bit is forced to 0 by the device to indicate that it does not respond
to I/O space accesses.
Bit 1/Memory Space Control (MSC). This read/write bit controls whether or not the device responds to accesses
by the PCI bus to the memory space, which is the local bus. When this bit is set to 0, the device ignores accesses
attempted to the local bus. When set to 1, the device allows accesses to the local bus. This bit should be set to 0
when the local bus operates in configuration mode. This bit is forced to 0 when a hardware reset is initiated
through the PRST pin.
0 = ignore accesses to the local bus
1 = allow accesses to the bus
Bit 2/Master Control (MASC). This read-only bit is forced to 0 by the device since it cannot act as a bus master.
Bit 3/Special Cycle Control (SCC). This read-only bit is forced to 0 by the device to indicate that it cannot
decode special cycle operations.
Bit 4/Memory Write and Invalidate Command Enable (MWEN). This read-only bit is forced to 0 by the
device to indicate that it cannot generate the memory write and invalidate command.
Bit 5/VGA Control (VGA). This read-only bit is forced to 0 by the device to indicate that it is not a VGA-
compatible device.
Bit 6/Parity Error Response Control (PARC). This read/write bit controls whether or not the device should
ignore parity errors. When this bit is set to 0, the device ignores any parity errors that it detects and continues to
operate normally. When this bit is set to 1, the device must act on parity errors. This bit is forced to 0 when a
hardware reset is initiated through the PRST pin.
0 = ignore parity errors
1 = act on parity errors
Bit 7/Address Stepping Control (STEPC). This read-only bit is forced to 0 by the device to indicate that it is not
capable of address/data stepping.
Bit 8/PCI System Error Control (PSEC). This read/write bit controls whether or not the device should enable
the PSERR output pin. When this bit is set to 0, the device disables the PSERR pin. When this bit is set to 1, the
device enables the PSERR pin. This bit is forced to 0 when a hardware reset is initiated through the PRST pin.
0 = disable the PSERR pin
1 = enable the PSERR pin
Bit 9/Fast Back-to-Back Master Enable (FBBEN). This read-only bit is forced to 0 by the device to indicate that
it is not capable of generating fast back-to-back transactions to different agents.
Bits 10 to 15/Reserved. These read-only bits are forced to 0 by the device.
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10.2.4
Status Bits (PCMD1)
The upper word in the PCMD1 register is the status portion, which reports events as they occur. As mentioned
earlier, reads of the status portion occur normally, but writes are unique in that bits can only be reset (i.e., forced to
0). This occurs when a 1 is written to a bit position. Writes with a 0 to a bit position have no effect. This allows
individual bits to be reset.
Bits 16 to 20/Reserved. These read-only bits are forced to 0 by the device.
Bit 21/66MHz Capable (66MHz). This read-only bit is forced to 0 by the device to indicate that it is not capable
of running at 66MHz.
Bit 22/User-Definable Features Capable (UDF). This read-only bit is forced to 0 by the device to indicate that it
does not support user-definable features.
Bit 23/Fast Back-to-Back Capable Target (FBBCT). This read-only bit is forced to 1 by the device to indicate
that it is capable of accepting fast back-to-back transactions when the transactions are not from the same agent.
Bit 24/PCI Parity Error Reported (PARR). This read-only bit is forced to 0 by the device since the device
cannot act as a bus master.
Bits 25, 26/Device Timing Select Bits 0 and 1 (DTS0 and DTS1). These read-only bits are forced to 01b by the
device to indicate that they are capable of the medium timing requirements for the PDEVSEL signal.
Bit 27/Target Abort Initiated (TABT). This read/write bit is set to 1 when the device terminates a bus
transaction with a target abort. This occurs only when the local bus is operating in the bus arbitration mode and the
local bus does not have bus control when the host requests access. This bit can be reset (set to 0) by the host by
writing a 1 to this bit.
Bit 28/Target Abort Detected by Master (TABTM). This read-only bit is forced to 0 by the device since the
device cannot act as a bus master.
Bit 29/Master Abort (MABT). This read-only bit is forced to 0 by the device since the device cannot act as a bus
master.
Bit 30/PCI System Error Reported (PSE). This read/write bit is set to 1 when the device asserts the PSERR
signal (even if it is disabled through the PSEC command bit). This bit can be reset (set to 0) by the host by writing
1 to this bit.
Bit 31/PCI Parity Error Reported (PPE). This read/write bit is set to 1 when the device detects a parity error.
The host can reset this bit (set to 0) by writing a 1 to this bit.
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
Register Description: PCI Revision ID/Class Code Register 1
Register Address: 0x108h
PRCC1
LSB
Revision ID (Read Only/Set to 00h)
Class Code (Read Only/Set to 00h)
Class Code (Read Only/Set to 80h)
Class Code (Read Only/Set to 06h)
MSB
Bits 0 to 7/Revision ID. These read-only bits identify the specific device revision, selected by Dallas
Semiconductor.
Bits 8 to 15/Class Code Interface. These read-only bits identify the subclass interface value for the device and
are fixed at 00h. See Appendix D of PCI Local Bus Specification Revision 2.1 for details.
Bits 16 to 23/Class Code Subclass. These read-only bits identify the subclass value for the device and are fixed at
80h, indicating “Other Bridge Device.” See Appendix D of PCI Local Bus Specification Revision 2.1 for details.
Bits 24 to 31/Class Code Base Class. These read-only bits identify the base class value for the device and are
fixed at 06h, which indicate “Bridge Devices.” See Appendix D of PCI Local Bus Specification Revision 2.1 for
details.
Register Name:
PLTH1
Register Description: PCI Latency Timer/Header Type Register 1
Register Address: 0x10Ch
LSB
Cache Line Size (Read Only/Set to 00h)
Latency Timer (Read Only/Set to 00h)
Header Type (Read Only/Set to 80h)
BIST (Read Only/Set to 00h)
MSB
Bits 0 to 7/Cache Line Size. These read-only bits are forced to 0.
Bits 8 to 15/Latency Timer. These read-only bits are forced to 0 by the device since the device cannot act as a
bus master.
Bits 16 to 23/Header Type. These read-only bits are forced to 80h, which indicate a multifunction device.
Bits 24 to 31/Built-In Self-Test (BIST). These read-only bits are forced to 0.
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DS31256 256-Channel, High-Throughput HDLC Controller
Register Name:
Register Description: PCI Local Bus Memory Base Address Register
Register Address: 0x110h
PLBM
LSB
Base Address (Read Only/Set to 0h)
Base Address
PF
TYPE1
TYPE0
MSI
Base Address (Read Only/Set to 0h)
Base Address
Base Address
MSB
Note: Read-only bits in the PLBM register are underlined; all other bits are read-write.
Bit 0/Memory Space Indicator (MSI). This read-only bit is forced to 0 to indicate that the local bus is mapped to
memory space.
Bits 1 and 2/Type 0 and Type 1. These read-only bits are forced to 00b to indicate that the local bus can be
mapped anywhere in the 32 bit address space.
Bit 3/Prefetchable (PF). This read-only bit is forced to 0 to indicate that prefetching is not supported by the
device for the local bus.
Bits 4 to 19/Base Address. These read-only bits are forced to 0 to indicate that the local bus requires 1MB of
memory space.
Bits 20 to 31/Base Address. These read/write bits define the location of the 1MB memory space that is mapped to
the local bus. These bits correspond to the most significant bits of the PCI address space.
Register Name:
Register Description: PCI Interrupt Line and Pin/Minimum Grant/Maximum Latency Register 1
Register Address: 0x13Ch
PINTL1
LSB
Interrupt Line
Interrupt Pin (Read Only/Set to 01h)
Maximum Grant (Read Only/Set to 00h)
Maximum Latency (Read Only/Set to 00h)
MSB
Bits 0 to 7/Interrupt Line. These read/write bits indicate and store interrupt line routing information. The device
does not use this information, it is only posted here for the host to use.
Bits 8 to 15/Interrupt Pin. These read-only bits are forced to 01h to indicate that PINTA is used as an interrupt.
Bits 16 to 23/Minimum Grant. These read-only bits are forced to 0.
Bits 24 to 31/Maximum Latency. These read-only bits are forced to 0.
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DS31256 256-Channel, High-Throughput HDLC Controller
11. LOCAL BUS
11.1General Description
The local bus can operate in two modes, either as a PCI bridge (master mode) or as a configuration bus
(slave mode). This selection is made in hardware by connecting the LMS pin high or low. Figure 11-1
shows an example of the local bus operating in the PCI bridge mode. In this example, the host can access
the control ports on the T1/E1 devices through the local bus. Figure 11-2 also shows an example of the
PCI bridge mode, but the local bus arbitration is enabled, which allows a local CPU to control when the
host can have access to the local bus. To access the local bus, the host must first request the bus and then
wait until it is granted. Figure 11-3 features an example of the configuration mode. In this mode, the
CPU on the local bus configures and monitors the DS31256. In this mode, the host on the PCI/custom
bus cannot access the DS31256 and the PCI/custom bus is only used to transfer HDLC packet data to
and from the host.
Table 11-A lists all the local bus pins and their applications in both operating modes. The local bus
operates only in a nonmultiplexed fashion; it is not capable of operating as a multiplexed bus. For both
operating modes, the local bus can be set up for either Intel or Motorola type buses. This selection is
made in hardware by connecting the LIM pin high or low.
Table 11-A. Local Bus Signals
PCI BRIDGE
CONFIGURATION MODE
(LMS = 1)
SIGNAL
FUNCTION
MODE (LMS = 0)
LD[0:15]
LA[0:19]
Data Bus
Address Bus
Input on Read/Output on Write Input on Write/Output on Read
Output
Output
Input
Input
LWR (LR/W)
Bus Write (Read/Write Select)
LRD (LDS)
LBHE
Bus Read (Data Strobe)
Byte High Enable
Output
Output
Input
Input
Tri-stated
Input
LIM
Intel/Motorola Select
LINT
LMS
Interrupt
Mode Select
Bus Clock
Bus Ready
Chip Select
Input
Input
Output
Input
LCLK
LRDY
LCS
Output
Input
Tri-stated
Ignored
Input
Ignored
LHOLD (LBR)
Hold Request (Bus Request)
Output
Tri-stated
LHLDA (LBG)
Hold Acknowledge (Bus Grant)
Bus Acknowledge
Input
Ignored
LBGACK
Output
Tri-stated
Note: Signals shown in parentheses are active when Motorola mode (LIM = 1) is selected.
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 11-1. Bridge Mode
T1 / E1
Framer or
Transceiver
PCI /
Custom
Host
Bus
Processor
and Main
Memory
T1 / E1
Framer or
Transceiver
DS31256
T1 / E1
Framer or
Transceiver
T1 / E1
Framer or
Transceiver
Local Bus
Figure 11-2. Bridge Mode with Arbitration Enabled
PCI /
T1 / E1
Custom
Framer or
Bus
DS31256
Transceiver
Host
Processor
and Main
Memory
T1 / E1
Framer or
Transceiver
T1 / E1
Framer or
1. Request
Bus Access
2. Bus Access
Granted
1
2
Transceiver
T1 / E1
Framer or
Transceiver
3. Transaction
Occurs
3
Local Bus
Local CPU that Handles
Local RAM &
ROM
the Real-Time Tasks Required
by the T1 / E1 Interfaces
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 11-3. Configuration Mode
T1 / E1
Framer or
Transceiver
PCI /
DS31256
Custom
Bus
Host
Processor
and Main
Memory
No
T1 / E1
Framer or
Transceiver
Access
Allowed
T1 / E1
Framer or
Transceiver
Only Used to
Transfer HDLC
Data
T1 / E1
Framer or
Transceiver
Local Bus
CPU Configures and
Monitors Ds31256
Local RAM &
ROM
11.1.1
PCI Bridge Mode
In PCI bridge mode, data from the PCI bus can be transferred to the local bus. The local bus acts as a
“master” and creates all the necessary signals to control the bus. The user must configure the local bus
bridge mode control register (LBBMC), which is described in Section 11.2.
With 20 address lines, the local bus can address 1MB address space. The host on the PCI bus determines
where to map this 1MB address space within the 32-bit address space of the PCI bus by configuring the
base address in the PCI configuration registers (Section 10).
Bridge Mode 8-Bit and 16-Bit Access
During a bus access by the host, the local bus can determine how to map the four possible byte positions
from/to the PCI bus to/from the local bus data bus (LD) pins by examining the PCBE signals and the
local bus width (LBW) control bit that resides in the local bus bridge mode control (LBBMC) register. If
the local bus is used as an 8-bit bus (LBW = 1), then the host must only assert one of the PCBE signals.
The PCI data is mapped to/from the LD[7:0] signal lines; the LD[15:0] signal lines remain inactive. The
local bus block drives the A0 and A1 address lines according to the assertion of the PCBE signals by the
host. See Table 11-B for details. If the host asserts more than one of the PCBE signals when the local bus
is configured as an 8-bit bus, then the local bus rejects the access and the PCI block returns a target abort
to the host. See Section 10 for details about a target abort.
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DS31256 256-Channel, High-Throughput HDLC Controller
Table 11-B. Local Bus 8-Bit Width Address, LBHE Setting
LBHE
PCBE [3:0]
1110
A1
0
A0
0
1
1
1
1
1101
0
1
1011
0111
1
1
0
1
Note 1: All other possible states for PCBE cause the device to return a target abort to the host.
Note 2: The 8-bit data picked from the PCI bus is routed/sampled to/from the LD[7:0] signal lines.
Note 3: If no PCBE signals are asserted during an access, a target abort is not returned and no transaction occurs on the local bus.
If the local bus is used as 16-bit bus, the LBW control bit must be set to 0. In 16-bit accesses, the host
can either perform 16-bit access or an 8-bit access by asserting the appropriate PCBE signals (Table
11-C). For 16-bit access, the host enables the combination of either PCBE0/PCBE1 or PCBE2/PCBE3
and the local bus block maps the word from/to the PCI bus to/from the LD[15:0] signals. For 8-bit access
in the 16-bit bus mode, the host must assert just one of the PCBE0 to PCBE3 signals. If the host asserts a
combination of PCBE signals not supported by the local bus, the local bus rejects the access and the PCI
block returns a target abort to the host. See Section 10 for details on a target abort. Section 11.3 contains
a number of timing examples for the local bus.
Table 11-C. Local Bus 16-Bit Width Address, LD, LBHE Setting
8/16
A1
A0
LD[15:8]
LD[7:0]
Active
PCBE [3:0]
LBHE
1110
1101
1100
1011
0111
0011
8
8
0
0
0
1
1
1
0
1
0
0
1
0
1
0
0
1
0
0
Active
Active
16
8
Active
Active
8
Active
Active
16
Active
Note 1: All other possible states for PCBE cause the device to return a target abort to the host.
Note 2: The 16-bit data picked from the PCI bus is routed/sampled to/from the LD[7:0] and LD[15:8] signal lines as shown.
Note 3: If no PCBE signals are asserted during an access, a target abort is not returned and no transaction occurs on the local bus.
Bridge Mode Bus Arbitration
In bridge mode, the local bus can arbitrate for bus access. In order for this feature to operate, the host
must access the PCI bridge mode control register (LBBMC) and enable it through the LARBE control bit
(the default is bus arbitration disabled). If bus arbitration is enabled, then, before a bus transaction can
occur, the local bus first requests bus access by asserting the LHOLD (LBR) signal and then waits for the
bus to be granted from the local bus arbiter by sensing that the LHLDA (LBG) has been asserted. If the
host on the PCI bus attempts a local bus access when the local bus is not granted by the local bus master
(LBGACK is deasserted), the local bus block immediately informs the host by issuing a PCI target retry
that the local bus is busy and cannot be accessed at that time (in other words, come back later). See
Section 10 for details about the PCI target retry. When this happens, the local bus block does not attempt
the bus access and keeps the LA, LD, LBHE, LWR (LR/W), and LRD (LDS) signals tri-stated.
If the host attempts a local bus access when the bus is busy, the local bus block requests bus access, and,
after it has been granted, it seizes the bus for the time programmed into the local bus arbitration timer
(LAT0 to LAT3 in the LBBMC register), which can be from 32 to 1,048,576 clocks. As long as the local
bus has been granted and the arbitration timer has at least 16 clocks left, the host is allowed to access the
local bus. See Figure 11-4 and the timing examples in Section 11.3 for more details.
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DS31256 256-Channel, High-Throughput HDLC Controller
Bridge Mode Bus Transaction Timing
When the local bus is operated in PCI bridge mode, the bus transaction time can be determined either
from an external ready signal (LRDY) or from the PCI bridge mode control register (LBBMC), which
allows a bus transaction time of 1 to 11 LCLK cycles. If the total access time to the local bus exceeds 16
PCLK cycles, the PCI access times out and a PCI target retry is sent to the host. This only occurs when
LRDY has not been detected within 9 clocks. If this happens, the local bus error (LBE) status bit in the
status master (SM) register is set. Additional details about the LBE status bit can be found in Section 5.
More details about transaction timing can be found in Figure 10-4 and the timing examples in
Section 11.3.
Bridge Mode Interrupt
In the PCI bridge mode, the local bus can detect an external interrupt through the LINT signal. If the
local bus detects that the LINTA signal has been asserted, it then sets the LBINT status bit in the status
master (SM) register. Setting this status bit can cause a hardware interrupt to occur at the PCI bus
through the PINTA signal. This interrupt can be masked through the ISM register. See Section 5 for
more details.
11.1.2 Configuration Mode
In configuration mode, the local bus is used only to configure the device and obtain status information
from the device. It is also used to configure the PCI configuration registers and therefore the PCI bus
signal PIDSEL is disabled when the local bus is in the configuration mode. The DS31256 PCI
configuration registers can't be accessed via the PCI bus when the DS31256 is in Configuration mode
(LMS=1). In this mode no device registers are accessible via the PCI bus.
Data cannot be passed from the local bus to the PCI bus in this mode. The PCI bus is only used as a
high-speed I/O bus for the HDLC packet data. In this mode, bus arbitration, bus format, and the user-
settable bus transaction time features are disabled. All bus accesses are based on 16-bit addresses and 16-
bit data in this mode. The upper four addresses (LA[19:16]) are ignored and 8-bit data accesses are not
allowed. See Section 13 for the AC timing requirements.
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 11-4. Local Bus Access Flowchart
PCI Host Initiates a
Local Bus Access
No
Is Arbitration Enabled
for the Local Bus?
Yes
Request
the Bus
Is the Local Bus
Granted?
No
Yes
Are there 16 Clocks
Remaining?
No
Yes
Yes
Is the External Local Bus
Ready (LRDY) Being Used?
No
Start 9 Clock Timer
Local Bus Access
Progresses
LRDY Active?
Yes
No
Timer Expired?
No
Yes
Local Bus Access
Progresses
Set the LBE Status Bit
PCI Target Retry
Issued
Normal Access
Occurs
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DS31256 256-Channel, High-Throughput HDLC Controller
11.2Local Bus Bridge Mode Control Register Description
Register Name:
Register Description: Local Bus Bridge Mode Control
Register Address: 0040h
LBBMC
Note: This register can only be accessed through the PCI bus and therefore only in the PCI bridge mode. In configuration mode, this register
cannot be accessed. It is set to all zeros upon a hardware reset issued through the PRST pin. It is not affected by a software reset issued
through the RST control bit in the master reset and ID (MRID) register.
Bit #
Name
Default
7
n/a
0
6
LBW
0
5
LRDY3
0
4
LRDY2
0
3
LRDY1
0
2
LRDY0
0
1
LARBE
0
0
LCLKE
0
Bit #
Name
Default
15
n/a
0
14
n/a
0
13
n/a
0
12
n/a
0
11
LAT3
0
10
LAT2
0
9
LAT1
0
8
LAT0
0
Note: Bits that are underlined are read-only; all other bits are read-write.
Bit 0/Local Bus Clock Enable (LCLKE)
0 = tri-state the LCLK output signal pin
1 = allow LCLK to appear at the pin
Bit 1/Local Bus Arbitration Enable (LARBE). When enabled, the LHOLD (LBR), LBGACK, and LHLDA
(LBG) signal pins are active and the proper arbitration handshake sequence must occur for a proper bus
transaction. When disabled, the LHOLD (LBR), LBGACK, and LHLDA (LBG) signal pins are deactivated and
bus arbitration on the local bus is not invoked. Also, the arbitration timer is enabled (see the description of the
LAT0 to LAT3 bits) when LARBE is set to 1.
0 = local bus arbitration is disabled
1 = local bus arbitration is enabled
Bit 2/Local Bus Ready Control Bit 0 (LRDY0). LSB
Bit 3/Local Bus Ready Control Bit 1 (LRDY1)
Bit 4/Local Bus Ready Control Bit 2 (LRDY2)
Bit 5/Local Bus Ready Control Bit 3 (LRDY3). MSB. These control bits determine the duration of the local bus
transaction in the PCI bridge mode. The bus transaction can either be controlled through the external LRDY input
signal or through a predetermined period of 1 to 11 LCLK periods.
0000 = use the LRDY signal input pin to control the bus transaction
0001 = bus transaction is defined as 1 LCLK period
0010 = bus transaction is defined as 2 LCLK periods
0011 = bus transaction is defined as 3 LCLK periods
0100 = bus transaction is defined as 4 LCLK periods
0101 = bus transaction is defined as 5 LCLK periods
0110 = bus transaction is defined as 6 LCLK periods
0111 = bus transaction is defined as 7 LCLK periods
1000 = bus transaction is defined as 8 LCLK periods
1001 = bus transaction is defined as 9 LCLK periods
1010 = bus transaction is defined as 10 LCLK periods
1011 = bus transaction is defined as 11 LCLK periods
1100 = illegal state
1101 = illegal state
1110 = illegal state
1111 = illegal state
153 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Bit 6/Local Bus Width (LBW)
0 = 16 bits
1 = 8 bits
Bits 8 to 11/Local Bus Arbitration Timer Setting (LAT0 to LAT3). These four bits determine the total time the
local bus seizes the bus when it has been granted in the arbitration mode (LARBE = 1). This period is measured
from LHLDA (LBG) being detected to LBGACK inactive.
CONDITION
33MHz PCLK 25MHz PCLK
0000 = when granted, hold the bus for 32 LCLKs
0001 = when granted, hold the bus for 64 LCLKs
0010 = when granted, hold the bus for 128 LCLKs
0011 = when granted, hold the bus for 256 LCLKs
0100 = when granted, hold the bus for 512 LCLKs
1101 = when granted, hold the bus for 262,144 LCLKs
1110 = when granted, hold the bus for 524,288 LCLKs
1111 = when granted, hold the bus for 1,048,576 LCLKs
0.97µs
1.3µs
1.9µs
2.6µs
3.9µs
7.8µs
5.1µs
10.2µs
20.5µs
10.5ms
21.0ms
41.9ms
15.5µs
7.9ms
15.9ms
31.8ms
154 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
11.3Examples of Bus Timing for Local Bus PCI Bridge Mode Operation
Figure 11-5. 8-Bit Read Cycle
Intel Mode (LIM = 0)
Arbitration Enabled (LARBE = 1)
Bus Transaction Time = 4 LCLK (LRDY = 0100)
An attempted access by the host causes the local bus to request the bus. If bus access has not been granted
(LBGACK deasserted), the timing shown at the top of the page applies, with LHOLD being asserted. Once
LHLDA is detected, the local bus grabs the bus for 32 to 1,048,576 clocks and then releases it. If the bus has
already been granted (LBGACK asserted), the timing shown at the bottom of the page applies.
LCLK
LHOLD
LHLDA
32 to 1,048,576 LCLKs
LBGACK
Note: LA, LD, LBHE, LWR, and LRD are tri-stated.
1
2
3
4
LCLK
Tri-state
Address Valid
LA[19:0]
LD[7:0]
LD[15:8]
LBHE
LWR
Tri-State
Tri-State
Tri-State
LRD
155 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 11-6. 16-Bit Write Cycle
Intel Mode (LIM = 0)
Arbitration Enabled (LARBE = 1)
Bus Transaction Time = 4 LCLK (LRDY = 0100)
An attempted access by the host causes the local bus to request the bus. If bus access has not been granted
(LBGACK deasserted), the timing shown at the top of the page occurs, with LHOLD being asserted. Once
LHLDA is detected, the local bus grabs the bus for 32 to 1,048,576 clocks and then releases it. If the bus has
already been granted (LBGACK asserted), the timing shown at the bottom of the page applies.
LCLK
LHOLD
LHLDA
32 to 1,048,576 LCLKs
LBGACK
Note: LA, LD, LBHE, LWR, and LRD are tri-stated.
1
2
3
4
LCLK
Tri-State
Tri-State
Tri-State
Tri-State
Tri-State
Address Valid
Data Valid
LA[19:0]
LD[7:0]
LD[15:8]
LBHE
Data Valid
LRD
Tri-State
LWR
156 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 11-7. 8-Bit Read Cycle
Intel Mode (LIM = 0)
Arbitration Disabled (LARBE = 0)
Bus Transaction Time = Timed from LRDY (LRDY = 0000)
1
2
3
4
5
6
7
8
9
10
LCLK
Address Valid
LA[19:0]
LD[7:0]
LD[15:8]
LBHE
LWR
LRD
LRDY
Note: The LRDY signal must be detected by the 9th LCLK or the bus access attempted by the host is unsuccessful
and the LBE status bit is set.
157 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 11-8. 16-Bit Write (Only Upper 8 Bits Active) Cycle
Intel Mode (LIM = 0)
Arbitration Disabled (LARBE = 0)
Bus Transaction Time = Timed from LRDY (LRDY = 0000)
LCLK
1
2
3
4
5
6
7
8
9
10
Address Valid
LA[19:0]
LD[7:0]
LD[15:8]
Data Valid
LBHE
LRD
LWR
LRDY
Note: The LRDY signal must be detected by the 9th LCLK or the bus access attempted by the host is unsuccessful and the
LBE status bit is set.
158 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 11-9. 8-Bit Read Cycle
Motorola Mode (LIM = 1)
Arbitration Enabled (LARBE = 1)
Bus Transaction Time = 6 LCLK (LRDY = 0110)
An attempted access by the host causes the local bus to request the bus. If bus access has not been granted
(LBGACK deasserted), the timing shown at the top of the page occurs, with LBR being asserted. Once LBG is
detected, the local bus grabs the bus for 32 to 1,048,576 clocks and then releases it. If the bus has already been
granted (LBGACK asserted), the timing shown at the bottom of the page applies.
LCLK
LBR
LBG
32 to 1,048,576 LCLKs
LBGACK
Note: LA, LD, LBHE, LDS, and LR/W are tri-stated.
1
2
3
4
5
6
LCLK
Tri-State
Address Valid
LA[19:0]
LD[7:0]
LD[15:8]
Tri-State
Tri-State
Tri-State
LBHE
LR/W
LDS
159 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 11-10. 8-Bit Write Cycle
Motorola Mode (LIM = 1)
Arbitration Enabled (LARBE = 1)
Bus Transaction Time = 6 LCLK (LRDY = 0110)
An attempted access by the host causes the local bus to request the bus. If bus access has not been granted
(LBGACK deasserted), the timing shown at the top of the page occurs, with LBR being asserted. Once LBG is
detected, the local bus grabs the bus for 32 to 1,048,576 clocks and then releases it. If the bus has already been
granted (LBGACK asserted), the timing shown at the bottom of the page applies.
LCLK
LBR
LBG
32 to 1,048,576 LCLKs
LBGACK
Note: LA, LD, LBHE, LDS, and LR/W are tri-stated.
1
2
3
4
5
6
LCLK
Tri-State
Tri-State
Address Valid
LA[19:0]
LD[7:0]
LD[15:8]
Data Valid
Tri-State
Tri-State
LBHE
Tri-State
Tri-State
LR/W
LDS
160 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 11-11. 16-Bit Read Cycle
Motorola Mode (LIM = 1)
Arbitration Disabled (LARBE = 0)
Bus Transaction Time = Timed from LRDY (LRDY = 0000)
LCLK
1
2
3
4
5
6
7
8
9
10
Address Valid
LA[19:0]
LD[7:0]
LD[15:8]
LBHE
LR/W
LDS
LRDY
Note: The LRDY signal must be detected by the 9th LCLK or the bus access attempted by the host is unsuccessful and the LBE
161 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 11-12. 8-Bit Write Cycle
Motorola Mode (LIM = 1)
Arbitration Disabled (LARBE = 0)
Bus Transaction Time = Timed from LRDY (LRDY = 0000)
1
2
3
4
5
6
7
8
9
10
LCLK
Address Valid
LA[19:0]
LD[7:0]
LD[15:8]
Data Valid
Tri-State
LBHE
LR/W
LDS
LRDY
Note: The LRDY signal must be detected by the 9th LCLK or the bus access attempted by the host is unsuccessful and the LBE status
bit is set.
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DS31256 256-Channel, High-Throughput HDLC Controller
12. JTAG
12.1JTAG Description
The DS31256 supports the standard instruction codes SAMPLE/PRELOAD, BYPASS, and EXTEST.
Optional public instructions included are HIGHZ, CLAMP, and IDCODE. Figure 12-1 is a block
diagram. The DS31256 contains the following items, which meet the requirements set by the IEEE
1149.1 Standard Test Access Port and Boundary Scan Architecture:
Test Access Port (TAP)
TAP Controller
Bypass Register
Boundary Scan Register
Device Identification Register
Instruction Register
The TAP has the necessary interface pins JTCLK, JTRST, JTDI, JTDO, and JTMS. Details about these
pins can be found in Section 3.4. Refer to IEEE 1149.1-1990, IEEE 1149.1a-1993, and IEEE 1149.1b-
1994 for details about the Boundary Scan Architecture and the TAP.
Figure 12-1. Block Diagram
BOUNDARY
SCAN REGISTER
IDENTIFICATION
REGISTER
BYPASS
REGISTER
INSTRUCTION
REGISTER
SELECT
TEST ACCESS PORT
TRI-STATE
CONTROLLER
10k
10k
10k
JTDI
JTMS
JTCLK
JTDO
JTRST
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DS31256 256-Channel, High-Throughput HDLC Controller
12.2 TAP Controller State Machine Description
This section details the operation of the TAP controller state machine. See Figure 12-2 for details about
each of the states. The TAP controller is a finite state machine, which responds to the logic level at JTMS
on the rising edge of JTCLK.
Figure 12-2. TAP Controller State Machine
Test-Logic-Reset
1
0
1
1
Select
Select
1
Run-Test/Idle
DR-Scan
IR-Scan
0
0
0
1
1
Capture-DR
0
Capture-IR
0
Shift-DR
1
Shift-IR
1
0
1
0
1
Exit1-DR
0
Exit1-IR
0
Pause-DR
1
Pause-IR
0
0
0
0
0
Exit2-DR
1
Exit2-IR
1
Update-DR
Update-IR
1
0
1
0
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DS31256 256-Channel, High-Throughput HDLC Controller
Test-Logic-Reset. The TAP controller is in the Test-Logic-Reset state upon DS31256 power-up. The
instruction register contains the IDCODE instruction. All system logic on the DS31256 operates
normally.
Run-Test-Idle. Run-Test-Idle is used between scan operations or during specific tests. The instruction
and test registers remain idle.
Select-DR-Scan. All test registers retain their previous state. With JTMS low, a rising edge of JTCLK
moves the controller into the Capture-DR state and initiates a scan sequence. JTMS high moves the
controller to the Select-IR-Scan state.
Capture-DR. Data can be parallel loaded into the test data registers selected by the current instruction. If
the instruction does not call for a parallel load or the selected register does not allow parallel loads, the
test register remains at its current value. On the rising edge of JTCLK, the controller goes to the Shift-DR
state if JTMS is low or it goes to the Exit1-DR state if JTMS is high.
Shift-DR. The test data register selected by the current instruction is connected between JTDI and JTDO
and shifts data one stage toward its serial output on each rising edge of JTCLK. If a test register selected
by the current instruction is not placed in the serial path, it maintains its previous state.
Exit1-DR. While in this state, a rising edge on JTCLK with JTMS high puts the controller in the Update-
DR state, which terminates the scanning process. A rising edge on JTCLK with JTMS low puts the
controller in the Pause-DR state.
Pause-DR. Shifting of the test registers is halted while in this state. All test registers selected by the
current instruction retain their previous states. The controller remains in this state while JTMS is low. A
rising edge on JTCLK with JTMS high puts the controller in the Exit2-DR state.
Exit2-DR. While in this state, a rising edge on JTCLK with JTMS high puts the controller in the Update-
DR state and terminates the scanning process. A rising edge on JTCLK with JTMS low enters the Shift-
DR state.
Update-DR. A falling edge on JTCLK while in the Update-DR state latches the data from the shift
register path of the test registers into the data output latches. This prevents changes at the parallel output
because of changes in the shift register. A rising edge on JTCLK with JTMS low puts the controller in the
Run-Test-Idle state. With JTMS high, the controller enters the Select-DR-Scan state.
Select-IR-Scan. All test registers retain their previous states. The instruction register remains
unchanged during this state. With JTMS low, a rising edge on JTCLK moves the controller into the
Capture-IR state and initiates a scan sequence for the instruction register. JTMS high during a rising edge
on JTCLK puts the controller back into the Test-Logic-Reset state.
Capture-IR. The Capture-IR state is used to load the shift register in the instruction register with a fixed
value. This value is loaded on the rising edge of JTCLK. If JTMS is high on the rising edge of JTCLK,
the controller enters the Exit1-IR state. If JTMS is low on the rising edge of JTCLK, the controller enters
the Shift-IR state.
Shift-IR. In this state, the shift register in the instruction register is connected between JTDI and JTDO
and shifts data one stage for every rising edge of JTCLK toward the serial output. The parallel register as
165 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
well as all test registers remain at their previous states. A rising edge on JTCLK with JTMS high moves
the controller to the Exit1-IR state. A rising edge on JTCLK with JTMS low keeps the controller in the
Shift-IR state while moving data one stage through the instruction shift register.
Exit1-IR. A rising edge on JTCLK with JTMS low puts the controller in the Pause-IR state. If JTMS is
high on the rising edge of JTCLK, the controller enters the Update-IR state and terminates the scanning
process.
Pause-IR. Shifting of the instruction register is halted temporarily. With JTMS high, a rising edge on
JTCLK puts the controller in the Exit2-IR state. The controller remains in the Pause-IR state if JTMS is
low during a rising edge on JTCLK.
Exit2-IR. A rising edge on JTCLK with JTMS high puts the controller in the Update-IR state. The
controller loops back to the Shift-IR state if JTMS is low during a rising edge of JTCLK in this state.
Update-IR. The instruction shifted into the instruction shift register is latched into the parallel output on
the falling edge of JTCLK as the controller enters this state. Once latched, this instruction becomes the
current instruction. A rising edge on JTCLK with JTMS low puts the controller in the Run-Test-Idle state.
With JTMS high, the controller enters the Select-DR-Scan state.
12.3Instruction Register and Instructions
The instruction register contains a shift register as well as a latched parallel output, and is 3 bits in length.
When the TAP controller enters the Shift-IR state, the instruction shift register is connected between JTDI
and JTDO. While in the Shift-IR state, a rising edge on JTCLK with JTMS low shifts data one stage
toward the serial output at JTDO. A rising edge on JTCLK in the Exit1-IR state or the Exit2-IR state with
JTMS high moves the controller to the Update-IR state. The falling edge of that same JTCLK latches the
data in the instruction shift register to the instruction parallel output. Table 12-A shows instructions
supported by the DS31256 and their respective operational binary codes.
Table 12-A. Instruction Codes
INSTRUCTION
SELECTED REGISTER
INSTRUCTION CODES
SAMPLE/PRELOAD
Boundary Scan
010
111
000
011
100
001
BYPASS
Bypass
EXTEST
Boundary Scan
Bypass
CLAMP
HIGHZ
Bypass
IDCODE
Device Identification
SAMPLE/PRELOAD. SAMPLE/PRELOAD is a mandatory instruction for the IEEE 1149.1
specification that supports two functions. The digital I/Os of the DS31256 can be sampled at the
boundary scan register without interfering with the normal operation of the device by using the Capture-
DR state. SAMPLE/PRELOAD also allows the DS31256 to shift data into the boundary scan register
through JTDI using the Shift-DR state.
EXTEST. EXTEST allows testing of all interconnections to the DS31256. When the EXTEST
instruction is latched in the instruction register, the following actions occur. Once enabled through the
Update-IR state, the parallel outputs of all digital output pins are driven. The boundary scan register is
connected between JTDI and JTDO. The Capture-DR samples all digital inputs into the boundary scan
register.
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DS31256 256-Channel, High-Throughput HDLC Controller
BYPASS. When the BYPASS instruction is latched into the parallel instruction register, JTDI connects
to JTDO through the 1-bit bypass test register. This allows data to pass from JTDI to JTDO without
affecting the device’s normal operation.
IDCODE. When the IDCODE instruction is latched into the parallel instruction register, the
identification test register is selected. The device identification code loads into the identification register
on the rising edge of JTCLK following entry into the Capture-DR state. Shift-DR can be used to shift the
identification code out serially through JTDO. During Test-Logic-Reset, the identification code is forced
into the instruction register’s parallel output. The device ID code always has 1 in the LSB position. The
next 11 bits identify the manufacturer’s JEDEC number and number of continuation bytes followed by 16
bits for the device and 4 bits for the version. The device ID code for the DS31256 is 00006143h.
12.4Test Registers
IEEE 1149.1 requires a minimum of two test registers—the bypass register and the boundary scan
register. An optional identification register has been included in the DS31256 design that is used in
conjunction with the IDCODE instruction and the Test-Logic-Reset state of the TAP controller.
Bypass Register
This is a single 1-bit shift register used in conjunction with the BYPASS, CLAMP, and HIGHZ
instructions that provides a short path between JTDI and JTDO.
Boundary Scan Register
This register contains both a shift register path and a latched parallel output for all control cells and digital
I/O cells. Visit www.maxim-ic.com/telecom for a downloadable BDSL file that contains all bit identity
and definition information.
Identification Register
The identification register contains a 32-bit shift register and a 32-bit latched parallel output. This register
is selected during the IDCODE instruction and when the TAP controller is in the Test-Logic-Reset state.
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DS31256 256-Channel, High-Throughput HDLC Controller
13. AC CHARACTERISTICS
ABSOLUTE MAXIMUM RATINGS
Voltage Range on Any Lead with Respect to VSS (except VDD)…………………………………………….-0.3V to +5.5V
Supply Voltage (VDD) Range with Respect to VSS…....…………………………………………………….-0.3V to +3.63V
Operating Temperature/Ambient Temperature Under Bias………………………………………………….0°C to +70°C
Junction Temperature Under Bias……………………………………………………………………………………≤ 125°C
Storage Temperature Range………………………………………………………………………………..-55°C to +125°C
Soldering Temperature…………………………………………………………See IPC/JEDEC J-STD-020 Specification
ESD Tolerance (Note 1)……………………………………………………Class 2 (2000V→4000V HBM: 1.5kΩ, 100pF)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only,
and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is
not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
RECOMMENDED DC OPERATING CONDITIONS
(TA = 0°C to +70°C)
PARAMETER
SYMBOL
VIH
CONDITIONS
(Notes 2, 3)
(Note 2)
MIN
1.8
-0.3
3.0
TYP
MAX UNITS
V
V
Logic 1
Logic 0
Supply
5.5
+0.8
3.6
VIL
VDD
V
DC CHARACTERISTICS
(VDD = 3.0V to 3.6V, TA = 0°C to +70°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX UNITS
Supply Current at VDD = 3.6V
IDD
(Note 4)
500
7
0.6
770
mA
Lead Capacitance
CIO
pF
Schmitt Hysteresis
Input Leakage
VTH
IIL
V
-10
-500
-10
-4.0
+4.0
+10
+500
+10
(Note 5)
(Note 5)
(Note 6)
µA
µA
µA
mA
mA
pF
Input Leakage (with pullups)
Output Leakage
Output Current (2.4V)
Output Current (0.4V)
Output Capacitance
Output Capacitance
IILP
ILO
IOH
IOL
COUT
COUTB
(Note 1)
(Note 1)
25
50
pF
Note 1: COUTB refers to bus-related outputs (PCI and local bus); COUT refers to all other outputs.
Note 2: Assumes a reasonably noise-free environment.
Note 3: The PCI 2.1 Specification states that VIH should be VDD/2 in a 3.3V signaling environment, and 2.0V in a 5V signaling environment.
Note 4: Measured 550mA with RC0 to RC15 and TC0 to TC15 = 2.048MHz, PCLK = 33MHz, constant traffic on all ports.
Note 5: 0V < VIN < VDD
Note 6: Outputs in tri-state.
Note 7: The typical values listed above are not production tested.
Note 8: Dallas Semiconductor Communications devices are tested in accordance with ESDA STM 5.1-1998.
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DS31256 256-Channel, High-Throughput HDLC Controller
AC CHARACTERISTICS: LAYER 1 PORTS
(VDD = 3.0V to 3.6V, TA = 0°C to +70°C.)
PARAMETER
RC/TC Clock Period
SYMBOL CONDITIONS MIN
TYP
MAX
UNITS
(Note 9)
(Note 10)
(Note 9)
(Note 10)
(Note 9)
(Note 10)
(Note 9)
(Note 10)
100
19
40
8
t1
t2
t3
t4
t4
t5
t5
t6
ns
RC/TC Clock Low Time
ns
ns
ns
ns
ns
ns
ns
40
8
RC/TC Clock High Time
5
2
RD Setup Time to the Falling Edge or
Rising Edge of RC
RS/TS Setup Time from the Falling
Edge or Rising Edge of RC/TC
RD Hold Time from the Falling Edge or
Rising Edge of RC
(Note 9)
5
t1 - 10
t1 - 10
(Note 9)
(Note 10)
5
5
RS/TS Hold Time from the Falling Edge
(Note 9)
5
or Rising Edge of RC/TC
Delay from the Rising Edge or Falling
Edge of TC to Data Valid on TD
(Note 9)
(Note 10)
5
3
25
15
Note 9: Ports 0 to 15 in applications running up to 10MHz.
Note 10: Port 0, 1, or 2 running in applications up to 52MHz.
Note 11: Aggregate, maximum bandwidth and port speed for the DS31256 are directly proportional to PCLK frequency. Throughput
measurements are made at PCLK = 33MHz.
Figure 13-1. Layer 1 Port AC Timing Diagram
t1
t2
t3
RC[n] / TC[n]
Normal Mode
RC[n] / TC[n]
Inverted Mode
t4
t5
RD[n] / RS[n] /
TS[n]
t6
TD[n]
l1 ac
Note: TC and RC are independent of each other. In the above timing diagram, all the signals beginning with “T” reference the
transmit clock TC; all signals beginning with “R” reference the receive clock RC.
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DS31256 256-Channel, High-Throughput HDLC Controller
AC CHARACTERISTICS: LOCAL BUS IN BRIDGE MODE (LMS = 0)
(VDD = 3.0V to 3.6V, TA = 0°C to +70°C.)
PARAMETER
SYMBOL CONDITIONS MIN
TYP
MAX UNITS
Delay Time from the Rising Edge of PCLK
to Output Valid from Tri-state
Delay Time from the Rising Edge of PCLK
to Tri-State from Output Valid
Delay Time from the Rising Edge of PCLK
to Output Valid from an Already Active
Drive State
t1
t2
7
7
17
15
ns
ns
t3
6
14
ns
LD[15:0] Setup Time to the Rising Edge of
PCLK
t4
t5
t6
t7
t8
t9
1
5
1
5
4
5
ns
ns
ns
ns
ns
ns
LD[15:0] Hold Time from the Rising Edge
of PCLK
Input Setup Time to the Rising Edge of
PCLK
Input Hold Time from the Rising Edge of
PCLK
Delay Time from the Rising Edge of PCLK
to the Rising Edge of LCLK
Delay Time from the Falling Edge of
PCLK to the Falling Edge of LCLK
7
8
Figure 13-2. Local Bus Bridge Mode (LMS = 0) AC Timing Diagram
PCLK
t1
LA[19:0], LD[15:0], LBHE,
Data Valid
LWR (LR/W), LRD (DS)
Tri-state
t2
Tri-state
LA[19:0], LWR (LR/W),
LRD (LDS), LBHE
Data Valid
t3
LA[19:0], LWR (LR/W),
LRD (DS), LHOLD (LBR),
LBGACK
Data Valid
t5
t7
t4
t6
LD[15:0]
LINT, LRDY
LHLDA (LBG)
t8
LCLK
t9
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DS31256 256-Channel, High-Throughput HDLC Controller
AC CHARACTERISTICS: LOCAL BUS IN CONFIGURATION MODE (LMS = 1)
(VDD = 3.0V to 3.6V, TA = 0°C to +70°C.)
PARAMETER
SYMBOL CONDITIONS MIN
TYP
MAX UNITS
Setup Time for LA[15:0] Valid to LCS
t1
t2
t3
t4
t5
t6
0
0
ns
ns
Active
Setup Time for LCS Active to Either
LRD, LWR, or LDS Active
Delay Time from Either LRD or LDS
(Note 12)
(Note 13)
75
20
ns
ns
ns
ns
Active to LD[15:0] Valid
Hold Time from Either LRD, LWR, or
LDS Inactive to LCS Inactive
0
5
Hold Time from Either LRD or LDS
Inactive to LD[15:0] Tri-State
Wait Time from Either LWR or LDS
75
Active to Latch LD[15:0]
LD[15:0] Setup Time to Either LWR or
LDS Inactive
t7
t8
10
2
ns
ns
LD[15:0] Hold Time from Either LWR
or LDS Inactive
LA[15:0] Hold from Either LWR, LRD,
or LDS Inactive
t9
5
ns
ns
LRD, LWD, or LDS Inactive Time
t10
(Note 14)
65
Note 12: Given value for 33MHz PCLK. Calculated as 1.5 x (PCLK Period) + 30ns
Note 13: Given value for 33MHz PCLK. Calculated as 2 x (PCLK Period) + 15ns
Note 14: Given value for 33MHz PCLK. Calculated as 2 x (PCLK Period) + 5ns
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 13-3. Local Bus Configuration Mode (LMS = 1) AC Timing Diagrams
Intel Read Cycle
t9
t9
LA[15:0]
Address Valid
Data Valid
LD[15:0]
LWR
t5
t1
LCS
t2
t3
t4
t10
LRD
Intel Write Cycle
LA[15:0]
LD[15:0]
Address Valid
t7
t8
LRD
LCS
t1
t2
t6
t4
t10
LWR
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DS31256 256-Channel, High-Throughput HDLC Controller
Figure 13-4. Local Bus Configuration Mode (LMS = 1) AC Timing Diagrams
(continued)
Motorola Read Cycle
t9
LA[15:0]
Address Valid
Data Valid
LD[15:0]
t5
LR/W
t1
LCS
LDS
t2
t3
t4
t10
Motorola Write Cycle
t9
LA[15:0]
Address Valid
LD[15:0]
LR/W
LCS
t8
t7
t1
t2
t6
t4
t10
LDS
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DS31256 256-Channel, High-Throughput HDLC Controller
AC CHARACTERISTICS: PCI BUS INTERFACE
(VDD = 3.0V to 3.6V, TA = 0°C to +70°C.)
PARAMETER
PCLK Period
PCLK Low Time
SYMBOL CONDITIONS MIN
TYP MAX UNITS
t1
t2
t3
(Note 15)
30
12
12
40
ns
ns
ns
PCLK High Time
All PCI Inputs and I/O Setup Time to the
t4
t5
t6
t7
7
0
2
ns
ns
ns
ns
Rising Edge of PCLK
All PCI Inputs and I/O Hold Time from the
Rising Edge of PCLK
Delay from the Rising Edge of PCLK to
Data Valid on All PCI Outputs and I/O
Delay from the Rising Edge of PCLK to
Tri-State on All PCI Outputs and I/O
Delay from the Rising Edge of PCLK to
Active from Tri-State on All PCI Outputs
and I/O
(Note 16)
11
28
t8
2
ns
Note 15: Aggregate, maximum bandwidth and port speed for the DS31256 are directly proportional to PCLK frequency. Ensure that PCLK is
33MHz for maximum throughput.
Note 16: The PCI extension signals PABLAST, PXAS, and PXDS have a 15ns max. These signals are not part of the PCI Specification.
Figure 13-5. PCI Bus Interface AC Timing Diagram
t1
t2
t3
PCLK
t4
t5
PCI Input
& I/O
t6
PCI Output
& I/O
Data Valid
t7
Tri-State
PCI Output &
I/O to Tri-State
t8
PCI Output &
Tri-State
I/O from Tri-State
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DS31256 256-Channel, High-Throughput HDLC Controller
AC CHARACTERISTICS: JTAG TEST PORT INTERFACE
(VDD = 3.0V to 3.6V, TA = 0°C to +70°C.)
PARAMETER
SYMBOL CONDITIONS
MIN
TYP
MAX UNITS
JTCLK Clock Period
t1
t2
t3
1000
ns
ns
ns
JTCLK Clock Low Time
400
JTCLK Clock High Time
JTMS/JTDI Setup Time to the Rising
Edge of JTCLK
400
t4
t5
t6
50
50
2
ns
JTMS/JTDI Hold Time from the Rising
Edge of JTCLK
ns
Delay Time from the Falling Edge of
JTCLK to Data Valid on JTDO
50
ns
Figure 13-6. JTAG Test Port Interface AC Timing Diagram
t1
t2
t3
JTCLK
t4
t5
JTMS/JTDI
JTDO
t6
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DS31256 256-Channel, High-Throughput HDLC Controller
14. REVISION HISTORY
REVISION
DESCRIPTION
112102
New product release.
Corrected various typographical errors, including:
Lifted some usage restrictions
Changed maximum number of T1 links from 64 to 60
Added U12 as a Ground in Table 3-A.
Removed PCI t5 and VIH exceptions to PCI 2.1 compliance.
Changed 8191 to 8188 in Figure 9-1 to be dword consistent.
Changed Logic 1 minimum from 2.2V to 1.8V in Section 13.
Added typical supply current and increase the maximum in Section 13.
Added typical supply current and increase the maximum in Section 13.
Removed t5 compliance issue and added Note 16 in Section 13, PCI.
Added Chapter 15, Thermal Properties.
073103
Updated recommended components in Section 17:Applications.
Page 109: Removed “Chateau” from Figure 9-11.
Page 137, Bits 16 to 31/Device ID. These read-only bits identify the DS31256 as the device
being used. The device ID was assigned by Dallas Semiconductor and is fixed at 31256h. The
device ID is 3134, not 31256.
Page 142, Bits 16 to 31/Device ID. These read-only bits identify the DS31256 as the device
being used. The device ID was assigned by Dallas Semiconductor and is fixed at 31256h. The
device ID is 3134, not 31256.
101104
Page 151: Section 11.1.2 Configuration Mode. Added info about how data cannot be passed
from the local bus to the PCI bus in this mode—The DS31256 PCI configuration registers
cannot be accessed via the PCI bus when the DS31256 is in Configuration mode (LMS=1). In
this mode no device registers are accessible via the PCI bus.
Page 83: Added the last paragraph that states the DS31256 has no restrictions on the transmit
side, but lists the restrictions on the location and size of the receive buffers in host memory.
Page 90: Removed “Chateau” from Figure 9-2.
031405
012506
Added lead-free package information to Ordering Information table (page 1).
Section 3.3: Local Bus Signal Description:
•
Removed sentence “These signals are sampled on the rising edge of LCLK to
determine the internal device configuration register that the external host wishes to
access.” from LA0 to LA19 description.
•
•
Removed sentence “In configuration mode (LMS = 1), this signal is sampled on the
rising edge of LCLK.” from LWR(LR/W) description.
Removed sentence “In configuration mode (LMS = 1), this signal is sampled on the
rising edge of LCLK.” from LRD(LDS) description.
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DS31256 256-Channel, High-Throughput HDLC Controller
15. PACKAGE INFORMATION
(The package drawing(s) in this data sheet may not reflect the most current specifications. The package number provided for
each package is a link to the latest package outline information.)
15.1 256-pin PBGA (27mm x 27mm) (56-G6004-001)
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DS31256 256-Channel, High-Throughput HDLC Controller
16. THERMAL CHARACTERISTICS
Table 16-A. Thermal Properties, Natural Convection
PARAMETER
Ambient Temperature
Junction Temperature
Theta-JA (θJA), Still Air
Psi-JB (ΨJB), Still Air
Psi-JT (ΨJT), Still Air
CONDITIONS
(Note 1)
MIN
0
0
TYP
MAX
+70°C
+125°C
UNITS
°C
°C
°C/W
°C/W
°C/W
15.4
7.03
0.07
(Note 2)
Note 1: The package is mounted on a four-layer JEDEC standard test board with no airflow and dissipating maximum power.
Note 2: Theta-JA (θJA) is the junction-to-ambient thermal resistance, when the package is mounted on a four-layer JEDEC standard test board
with no airflow and dissipating maximum power.
Table 16-B. Thermal Properties vs. Airflow
FORCED AIR (m/s)
THETA-JA (θJA)
Psi-JB (ΨJB)
7.03°C/W
6.77°C/W
6.53°C/W
Psi-JT (ΨJT)
0.07°C/W
0.40°C/W
0.57°C/W
0
1
15.4°C/W
13.0°C/W
11.9°C/W
2.5
Figure 16-1. 27mm x 27mm PBGA with 256 Balls, 2oz Planes, +70°C
Ambient, Under Natural Convection at 3.0W
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DS31256 256-Channel, High-Throughput HDLC Controller
17. APPLICATIONS
This section describes some possible applications for the DS31256. There are numerous potential
configurations but only a few are shown. Users are encouraged to contact the factory for support of their
particular application. Email telecom.support@dalsemi.com or visit our website at
www.maxim-ic.com/telecom for more information.
The T1 and E1 channelized application examples in this section are one of two types. The first type is
where a single T1 or E1 data stream is routed to and from the DS31256. This is represented as a thin
arrow in the application examples (Figure 17-1). Figure 17-2 shows the electrical connections. The
second type is where four T1 or E1 data streams have been TDM into a single 8.192MHz data stream,
which is routed to and from the DS31256. This type is represented as a thick arrow in Figure 17-1.
Figure 17-3 shows the electrical connections.
Figure 17-1. Application Drawing Key
1x
SINGLE T1 OR E1 LINE AT 1.544MHz OR 2.048MHz
4x
QUAD (4) T1 OR 31 LINES BYTE INTERLEAVED AT 8.192MHz
Figure 17-2. Single T1/E1 Line Connection
RC
RCLK
RD
RS
RSER
RSYNC
DALLAS FRAMER
OR TRANSCEIVER
DS31256
TC
TD
TS
TCLK
TSER
TSYNC
(ELASTIC STORES
DISABLED)
Note: A looped timed application is shown. The transmit clock may be decoupled from the receive in timing master applications.
179 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
Figure 17-3. Quad T1/E1 Connection
17.1 16 Port T1 or E1 with 256 HDLC Channel Support
Figure 17-4 shows an application where 16 T1 or E1 links are framed and interfaced to a single DS31256.
The T1 lines can be either clear-channel or channelized. The DS21Q55 quad T1/E1/J1 single-chip
transceiver performs the line interface function and frames to the T1/E1/J1 line.
Figure 17-4. 16-Port T1 Application
Port 0
Port 1
Port 2
Port 3
Port 4
Port 5
Port 6
Port 7
Port 8
Port 9
Port 10
Port 11
Port 12
Port 13
Port 14
Port 15
DS21455
Four
T1 or E1Lines
Quad T1/E1
Transceiver
DS21455
Quad T1/E1
Transceiver
Four
T1 or E1Lines
DS31256
DS21455
Four
T1 or E1Lines
Quad T1/E1
Transceiver
DS21455
Four
T1 or E1Lines
Quad T1/E1
Transceiver
180 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
17.2 Dual T3 with 256 HDLC Channel Support
Figure 17-5 shows an application where two T3 lines are interfaced to a single DS31256. The T3 lines are
demultiplexed by DS3112 M13 devices and passed to the DS21FF42 4 x 4 16-channel T1 framer and
DS21FT42 4 x 3 12-channel T1 framer devices. The T1 framers locate the frame and multiframe
boundaries and interface to the DS31256 by aggregating four T1 lines into a single 8.192MHz data
stream, which then flows into and out of the DS31256. The T1 lines can be either clear channel or
channelized.
Figure 17-5. Dual T3 Application
1
DS21FF42
4 x 4
2
Port 0
Port 1
Port 2
Port 3
Port 4
Port 5
Port 6
Port 7
Port 8
Port 9
Port 10
Port 11
Port 12
Port 13
Port 14
Port 15
16-Channel
T1 Framer
16
T3
DS3112
M13
Line
17
18
DS21FT42
4 x 3
#1
Interface
12-Channel
DS3152
Dual
DS31256
T1 Framer
28
1
2
T3/E3
LIU
DS21FF42
4 x 4
16-Channel
T1 Framer
T3
16
DS3112
M13
Line
#2
17
18
DS21FT42
4 x 3
Interface
12-Channel
T1 Framer
28
181 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
17.3 Single T3 with 512 HDLC Channel Support
Figure 17-6 shows an application where a T3 line is interfaced to two DS31256s. The T3 line is
demultiplexed by the M13 block and passed to the DS21FF42 and DS21FT42 devices. The T1 framers
locate the frame and multiframe boundaries and interface to the DS31256. Aggregating four T1 lines into
a single 8.192MHz data stream is not required since the DS31256 has enough physical ports to support
the application, but aggregation could be done to cut down on the number of electrical connections
between the DS31256 and the T1 framers. The T1 lines can be either clear channel or channelized.
Figure 17-6. T3 Application (512 HDLC Channels)
Port 0
Port 1
Port 2
Port 3
Port 4
DS31256
DS21FF42
4 x 4
Port 5
Port 6
#1
16-Channel
Port 7
T1 Framer
Port 8
Port 9
1
2
Port 10
Port 11
Port 12
Port 13
Port 14
Port 15
16
DS3112
M13
Interface
17
18
Port 0
Port 1
Port 2
Port 3
Port 4
Port 5
Port 6
Port 7
Port 8
Port 9
Port 10
Port 11
Port 12
Port 13
Port 14
Port 15
28
DS21FT42
4 x 3
DS31256
#2
12-Channel
T1 Framer
182 of 183
DS31256 256-Channel, High-Throughput HDLC Controller
17.4 Single T3 with 672 HDLC Channel Support
Figure 17-7 shows an application where a fully channelized T3 line is interfaced to three DS31256s. The
T3 line is demultiplexed by the M13 block and passed to the DS21FF42 and DS21FT42 devices. The T1
framers locate the frame and multiframe boundaries and interface to the DS31256. Aggregating four T1
lines into a single 8.192MHz data stream is not required since the DS31256 has enough physical ports to
support the applicationm, but aggregation could be done to cut down on the number of electrical
connections between the DS31256 and the T1 framers. The T1 lines can be either clear channel or
channelized.
Figure 17-7. T3 Application (672 HDLC Channels)
Port 0
Port 1
Port 2
Port 3
DS31256
Port 4
Port 5
DS21FF42
Four x Four
16-Channel
T1 Framer
#1
Port 6
Port 7
Port 8
(Supports 10
T1 Lines)
Port 9
1
2
Port 10
Port 11
Port 12
Port 13
Port 14
Port 15
16
DS3112
M13
Interface
17
18
Port 0
Port 1
Port 2
Port 3
Port 4
Port 5
Port 6
Port 7
Port 8
Port 9
Port 10
Port 11
Port 12
Port 13
Port 14
Port 15
28
DS31256
#2
DS21FT42
Four x Three
12-Channel
T1 Framer
(Supports 10
T1 Lines)
Port 0
Port 1
Port 2
Port 3
Port 4
Port 5
Port 6
Port 7
Port 8
Port 9
Port 10
Port 11
Port 12
Port 13
Port 14
Port 15
DS31256
#3
(Supports 8
T1 Lines)
183 of 183
Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product.
No circuit patent licenses are implied. Maxim/Dallas Semiconductor reserves the right to change the circuitry and specifications without notice at any time.
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The Maxim logo is a registered trademark of Maxim Integrated Products, Inc. The Dallas logo is a registered trademark of Dallas Semiconductor Corp.
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