21152-AB [INTEL]
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INTEL 
21152 PCI-to-PCI Bridge
Preliminary Datasheet
October 1998
Notice: This document contains information on products in the design phase of development. Do not final-
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Verify with your local Intel sales office that you have the latest datasheet before finalizing a design.
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Copyright © Intel Corporation, 1998
*Third-party brands and names are the property of their respective owners.
21152 PCI-to-PCI Bridge Preliminary Datasheet
Contents
1
Introduction.................................................................................................................................... 1-1
1.1
1.2
1.3
Features............................................................................................................................ 1-1
Architecture..................................................................................................................... 1-4
Data Path ......................................................................................................................... 1-6
1.3.1
1.3.2
1.3.3
Posted Write Queue .......................................................................................... 1-6
Delayed Transaction Queue.............................................................................. 1-7
Read Data Queue .............................................................................................. 1-7
2
Signal Pins ..................................................................................................................................... 2-1
2.1
2.2
2.3
2.4
2.5
2.6
2.7
Primary PCI Bus Interface Signals.................................................................................. 2-2
Secondary PCI Bus Interface Signals.............................................................................. 2-5
Secondary Bus Arbitration Signals ................................................................................. 2-7
Clock Signals................................................................................................................... 2-7
Reset Signals ................................................................................................................... 2-8
Miscellaneous Signals ..................................................................................................... 2-8
Nand Tree Signals ........................................................................................................... 2-9
3
4
Pin Assignment .............................................................................................................................. 3-1
3.1
3.2
Pin Location List (Numeric)............................................................................................ 3-2
Pin Signal List (Alphanumeric)....................................................................................... 3-5
PCI Bus Operation ......................................................................................................................... 4-1
4.1
4.2
Types of Transactions...................................................................................................... 4-1
Address Phase.................................................................................................................. 4-2
4.2.1
4.2.2
Single Address Phase........................................................................................ 4-2
Dual Address Phase .......................................................................................... 4-2
4.3
4.4
4.5
Device Select (DEVSEL#) Generation ........................................................................... 4-3
Data Phase ....................................................................................................................... 4-3
Write Transactions........................................................................................................... 4-3
4.5.1
4.5.2
4.5.3
4.5.4
4.5.5
4.5.6
Posted Write Transactions ................................................................................ 4-4
Memory Write and Invalidate Transactions...................................................... 4-6
Delayed Write Transactions.............................................................................. 4-7
Write Transaction Address Boundaries ............................................................ 4-9
Buffering Multiple Write Transactions............................................................. 4-9
Fast Back-to-Back Write Transactions ........................................................... 4-10
4.6
4.7
Read Transactions ......................................................................................................... 4-11
4.6.1
4.6.2
4.6.3
4.6.4
4.6.5
4.6.6
Prefetchable Read Transactions ...................................................................... 4-11
Nonprefetchable Read Transactions ............................................................... 4-12
Read Prefetch Address Boundaries................................................................. 4-12
Delayed Read Requests................................................................................... 4-13
Delayed Read Completion with Target........................................................... 4-13
Delayed Read Completion on Initiator Bus .................................................... 4-14
Configuration Transactions ........................................................................................... 4-17
4.7.1
4.7.2
4.7.3
4.7.4
Type 0 Access to the 21152 ............................................................................ 4-18
Type 1 to Type 0 Translation.......................................................................... 4-18
Type 1 to Type 1 Forwarding ......................................................................... 4-20
Special Cycles ................................................................................................. 4-20
21152 PCI-to-PCI Bridge Preliminary Datasheet
iii
4.8
Transaction Termination................................................................................................ 4-21
4.8.1
4.8.2
4.8.3
Master Termination Initiated by the 21152..................................................... 4-22
Master Abort Received by the 21152.............................................................. 4-22
Target Termination Received by the 21152.................................................... 4-24
4.8.3.1 Delayed Write Target Termination Response .................................. 4-24
4.8.3.2 Posted Write Target Termination Response ..................................... 4-25
4.8.3.3 Delayed Read Target Termination Response ................................... 4-25
Target Termination Initiated by the 21152 ..................................................... 4-27
4.8.4.1 Target Retry ...................................................................................... 4-27
4.8.4.2 Target Disconnect.............................................................................4-28
4.8.4.3 Target Abort...................................................................................... 4-28
4.8.4
5
Address Decoding.......................................................................................................................... 5-1
5.1
5.2
Address Ranges ............................................................................................................... 5-1
I/O Address Decoding ..................................................................................................... 5-1
5.2.1
5.2.2
I/O Base and Limit Address Registers .............................................................. 5-2
ISA Mode.......................................................................................................... 5-3
5.3
5.4
Memory Address Decoding............................................................................................. 5-4
5.3.1
5.3.2
5.3.3
Memory-Mapped I/O Base and Limit Address Registers................................. 5-5
Prefetchable Memory Base and Limit Address Registers................................. 5-7
Prefetchable Memory 64-Bit Addressing Registers.......................................... 5-8
VGA Support................................................................................................................... 5-9
5.4.1
5.4.2
VGA Mode........................................................................................................ 5-9
VGA Snoop Mode............................................................................................. 5-9
6
7
Transaction Ordering ..................................................................................................................... 6-1
6.1
6.2
6.3
6.4
Transactions Governed by Ordering Rules ..................................................................... 6-1
General Ordering Guidelines........................................................................................... 6-2
Ordering Rules................................................................................................................. 6-3
Data Synchronization ...................................................................................................... 6-4
Error Handling ............................................................................................................................... 7-1
7.1
7.2
Address Parity Errors....................................................................................................... 7-1
Data Parity Errors ............................................................................................................ 7-2
7.2.1
7.2.2
7.2.3
7.2.4
Configuration Write Transactions to 21152 Configuration Space.................... 7-2
Read Transactions ............................................................................................. 7-2
Delayed Write Transactions.............................................................................. 7-3
Posted Write Transactions................................................................................. 7-5
7.3
7.4
Data Parity Error Reporting Summary ............................................................................ 7-7
System Error (SERR#) Reporting ................................................................................. 7-14
8
9
Exclusive Access............................................................................................................................ 8-1
8.1
8.2
8.3
Concurrent Locks ............................................................................................................ 8-1
Acquiring Exclusive Access Across the 21152............................................................... 8-1
Ending Exclusive Access................................................................................................. 8-3
PCI Bus Arbitration ....................................................................................................................... 9-1
9.1
9.2
Primary PCI Bus Arbitration ........................................................................................... 9-1
Secondary PCI Bus Arbitration ....................................................................................... 9-1
9.2.1
9.2.2
Secondary Bus Arbitration Using the Internal Arbiter...................................... 9-2
Secondary Bus Arbitration Using an External Arbiter...................................... 9-3
iv
21152 PCI-to-PCI Bridge Preliminary Datasheet
9.2.3
Bus Parking....................................................................................................... 9-3
10
11
Clocks .......................................................................................................................................... 10-1
10.1
10.2
Primary and Secondary Clock Inputs............................................................................ 10-1
Secondary Clock Outputs.............................................................................................. 10-2
10.2.1 Disabling Unused Secondary Clock Outputs.................................................. 10-2
Reset............................................................................................................................................. 11-1
11.1
11.2
11.3
Primary Interface Reset ................................................................................................. 11-1
Secondary Interface Reset ............................................................................................. 11-1
Chip Reset ..................................................................................................................... 11-2
12
13
PCI Power Management .............................................................................................................. 12-1
Configuration Space Registers..................................................................................................... 13-1
13.1
PCI-to-PCI Bridge Standard Configuration Registers .................................................. 13-3
13.1.1 Vendor ID Register — Offset 00h .................................................................. 13-3
13.1.2 Device ID Register — Offset 02h................................................................... 13-3
13.1.3 Command Register — Offset 04h................................................................... 13-4
13.1.4 Status Register — Offset 06h.......................................................................... 13-6
13.1.5 Revision ID Register — Offset 08h................................................................ 13-7
13.1.6 Programming Interface Register — Offset 09h .............................................. 13-7
13.1.7 Subclass Code Register — Offset 0Ah........................................................... 13-7
13.1.8 Base Class Code Register — Offset 0Bh........................................................ 13-8
13.1.9 Cache Line Size Register — Offset 0Ch ........................................................ 13-8
13.1.10 Primary Latency Timer Register — Offset 0Dh............................................. 13-8
13.1.11 Header Type Register — Offset 0Eh .............................................................. 13-9
13.1.12 Primary Bus Number Register — Offset 18h ................................................. 13-9
13.1.13 Secondary Bus Number Register — Offset 19h ............................................. 13-9
13.1.14 Subordinate Bus Number Register — Offset 1Ah........................................ 13-10
13.1.15 Secondary Latency Timer Register — Offset 1Bh ....................................... 13-10
13.1.16 I/O Base Address Register — Offset 1Ch .................................................... 13-11
13.1.17 I/O Limit Address Register — Offset 1Dh ................................................... 13-11
13.1.18 Secondary Status Register — Offset 1Eh ..................................................... 13-12
13.1.19 Memory Base Address Register — Offset 20h............................................. 13-13
13.1.20 Memory Limit Address Register — Offset 22h............................................ 13-13
13.1.21 Prefetchable Memory Base Address Register — Offset 24h........................ 13-14
13.1.22 Prefetchable Memory Limit Address Register — Offset 26h....................... 13-14
13.1.23 Prefetchable Memory Base Address Upper 32 Bits
Register — Offset 28h .................................................................................. 13-15
13.1.24 Prefetchable Memory Limit Address Upper 32 Bits
Register — Offset 2Ch.................................................................................. 13-15
13.1.25 I/O Base Address Upper 16 Bits Register — Offset 30h.............................. 13-16
13.1.26 I/O Limit Address Upper 16 Bits Register — Offset 32h............................. 13-16
13.1.27 Capabilities Pointer Register — Offset 34h.................................................. 13-17
13.1.28 Interrupt Pin — Offset 3Dh .......................................................................... 13-17
13.1.29 Bridge Control — Offset 3Eh ....................................................................... 13-18
13.1.30 Capability ID Register — Offset DCh.......................................................... 13-21
13.1.31 Next Item Register — Offset DDh ............................................................... 13-21
13.1.32 Power Management Capabilities Registers — Offset DEh .......................... 13-22
13.1.33 Power Management Control and Status Registers — Offset E0h ................ 13-23
21152 PCI-to-PCI Bridge Preliminary Datasheet
v
13.1.34 PPB Support Extensions Registers — Offset E2h ........................................ 13-24
13.1.35 Data Register — Offset E3h.......................................................................... 13-24
Device-Specific Configuration Registers .................................................................... 13-25
13.2.1 Chip Control Register — Offset 40h............................................................. 13-25
13.2.2 Diagnostic Control Register — Offset 41h................................................... 13-26
13.2.3 Arbiter Control Register — Offset 42h......................................................... 13-26
13.2.4 p_serr_l Event Disable Register -— Offset 64h............................................ 13-27
13.2.5 Secondary Clock Control Register — Offset 68h......................................... 13-28
13.2.6 p_serr_l Status Register — Offset 6Ah......................................................... 13-29
13.2
14
15
Diagnostic Nand Tree .................................................................................................................. 14-1
Electrical Specifications...............................................................................................................15-1
15.1
15.2
15.3
15.4
PCI Electrical Specification Conformance.................................................................... 15-1
Absolute Maximum Ratings.......................................................................................... 15-1
DC Specifications ..........................................................................................................15-2
AC Timing Specifications ............................................................................................. 15-2
15.4.1 Clock Timing Specifications........................................................................... 15-3
15.4.2 PCI Signal Timing Specifications................................................................... 15-4
15.4.3 Reset Timing Specifications............................................................................ 15-5
16
A
Mechanical Specifications ........................................................................................................... 16-1
Configuration Register Values After Reset .................................................................................. A-1
Support, Products, and Documentation...............................................................................................
Figures
1-1
1-2
1-3
1-4
3-1
4-1
4-2
4.3
21152 on the System Board...............................................................................1-2
21152 with Option Cards....................................................................................1-3
21152 Block Diagram.........................................................................................1-4
21152 Downstream Data Path ...........................................................................1-6
21152 Pinout Diagram .......................................................................................3-1
Flow-Through Posted Memory Write Transaction..............................................4-5
Downstream Delayed Write Transaction............................................................4-8
Multiple Memory Write Transactions Posted and Initiated as Fast
Back-to-Back Transactions on the Target Bus.................................................4-10
Nonprefetchable Delayed Read Transaction ...................................................4-14
Prefetchable Delayed Read Transaction .........................................................4-15
Flow-Through Prefetchable Read Transaction ................................................4-16
Configuration Transaction Address Formats....................................................4-17
Delayed Write Transaction Terminated with Master Abort...............................4-23
Delayed Read Transaction Terminated with Target Abort...............................4-26
I/O Transaction Forwarding Using Base and Limit Addresses...........................5-2
I/O Transaction Forwarding in ISA Mode...........................................................5-4
Memory Transaction Forwarding Using Base and Limit Registers ....................5-6
Secondary Arbiter Example ...............................................................................9-2
p_clk and s_clk Relative Timing .....................................................................10-1
21152 Configuration Space..............................................................................13-2
PCI Clock Signal AC Parameter Measurements..............................................15-3
4.4
4-5
4-6
4-7
4.8
4.9
5-1
5-2
5-3
9-1
10-1
13-1
15-1
vi
21152 PCI-to-PCI Bridge Preliminary Datasheet
15-2
16-1
PCI Signal Timing Measurement Conditions....................................................15-4
160-Pin PQFP Package ...................................................................................16-1
Tables
1-1
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9
3-1
3-2
3-3
3-4
4-1
4-2
4.3
21152 Function Blocks.......................................................................................1-5
Signal Pin Functional Groups.............................................................................2-1
Signal Type Abbreviations..................................................................................2-1
Primary PCI Bus Interface Signals (Sheet 1 of 3) .............................................2-2
Secondary PCI Bus Interface Signals (Sheet 1 of 2) ........................................2-5
Secondary PCI Bus Arbitration Signals..............................................................2-7
Clock Signals......................................................................................................2-7
Reset Signals .....................................................................................................2-8
Miscellaneous Signals........................................................................................2-8
Nand Tree Signals..............................................................................................2-9
Signal Type Abbreviations..................................................................................3-2
Pin Location List (Numeric) (Sheet 1 of 3) .........................................................3-2
Signal Type Abbreviations..................................................................................3-5
Pin Signal List (Alphanumeric) (Sheet 1 of 3) ....................................................3-5
21152 PCI Transactions.....................................................................................4-1
Write Transaction Forwarding ............................................................................4-3
Write Transaction Disconnect Address Boundaries...........................................4-9
Read Transaction Prefetching..........................................................................4-11
Read Prefetch Address Boundaries.................................................................4-12
Device Number to IDSEL s_ad Pin Mapping...................................................4-19
21152 Response to Delayed Write Target Termination ...................................4-24
21152 Response to Posted Write Target Termination .....................................4-25
21152 Response to Delayed Read Target Termination...................................4-25
Summary of Transaction Ordering .....................................................................6-3
Setting the Primary Interface Detected Parity Error Bit......................................7-7
Setting the Secondary Interface Detected Parity Error Bit .................................7-8
Setting the Primary Interface Data Parity Detected Bit ....................................7-9
Setting the Secondary Interface Data Parity Detected Bit................................7-10
Assertion of p_perr_l .......................................................................................7-11
Assertion of s_perr_l .....................................................................................7-12
Assertion of p_serr_l for Data Parity Errors.....................................................7-13
Power Management Transitions ......................................................................12-1
Absolute Maximum Ratings..............................................................................15-1
Functional Operating Range ............................................................................15-1
DC Parameters ...............................................................................................15-2
PCI Clock Signal AC Parameters.....................................................................15-3
PCI Signal Timing.............................................................................................15-4
Reset Timing Specifications.............................................................................15-5
160-Pin PQFP Package Dimensions ...............................................................16-2
Configuration Register Values After Reset........................................................ A-1
4.4
4.5
4.6
4.7
4.8
4.9
6-1
7-1
7-2
7-3
7-4
7-5
7-6
7-7
12-1
15-1
15-2
15-3
15-4
15-5
15-6
16-1
A-1
21152 PCI-to-PCI Bridge Preliminary Datasheet
vii
Introduction
1
The 21152 is a second-generation PCI-to-PCI bridge and is fully compliant with PCI Local Bus
Specification, Revision 2.1. The 21152 is pin-to-pin compatible with the 21052, which is fully
compliant with PCI Local Bus Specification, Revision 2.0.The 21152 provides full support for
delayed transactions, enabling buffering of memory read, I/O, and configuration transactions. The
21152 has separate posted write, read data, and delayed transaction queues with significantly more
buffering capability than first-generation bridges. In addition, the 21152 supports bi-directional
buffering of simultaneous multiple posted write and delayed transactions.Among the features
provided by the 21152 are a programmable 2-level secondary bus arbiter, individual secondary
clock software control, and enhanced address decoding. The 21152 has sufficient clock and
arbitration pins to support four PCI bus master devices directly on its secondary interface.
The 21152 allows the two PCI buses to operate concurrently. This means that a master and a target
on the same PCI bus can communicate while the other PCI bus is busy. This traffic isolation may
increase system performance in applications such as multimedia.
1.1
Features
The 21152 has the following features:
• Complies fully with Revision 2.1 of the PCI Local Bus Specification,
• Complies fully with Revision 1.1 of the PCI-to-PCI Bridge Architecture Specification,
• Complies fully with the Advanced Configuration Power Interface (ACPI) Specification
1
• Complies fully with the PCI Power Management Specification, Revision 1.0
• Implements delayed transactions for all PCI configuration, I/O, and memory read
commands—up to three transactions simultaneously in each direction
• Allows 88 bytes of buffering (data and address) for posted memory write commands in each
direction—up to three transactions simultaneously in each direction
• Allows 72 bytes of read data buffering in each direction
• Provides concurrent primary and secondary bus operation to isolate traffic
• Provides five secondary clock outputs
— Low skew, permitting direct drive of option slots
— Individual clock control through configuration space
• Provides arbitration support for four secondary bus devices
— A programmable 2-level arbiter
— Hardware disable control, permitting use of an external arbiter
• Provides enhanced address decoding
— A 32-bit I/O address range
1. 21152–AB and later revisions only. The 21152–AA does not implement this feature.
21152 PCI-to-PCI Bridge Preliminary Datasheet
1-1
Introduction
— A 32-bit memory-mapped I/O address range
— A 64-bit prefetchable memory address range
— ISA-aware mode for legacy support in the first 64 KB of I/O address range
— VGA addressing and VGA palette snooping support
• Supports PCI transaction forwarding for the following commands
— All I/O and memory commands
— Type 1 to Type 1 configuration commands
— Type 1 to Type 0 configuration commands (downstream only)
— All Type 1 to special cycle configuration commands
• Includes downstream lock support
• Supports both 5 V and 3.3 V signaling environments
The 21152 makes it possible to extend a system’s load capability limit beyond that of a single PCI
bus by allowing motherboard designers to add more PCI devices, or more PCI option card slots,
than a single PCI bus can support. Figure 1-1 illustrates the use of two 21152 PCI-to-PCI bridges
on a system board. Each 21152 that is added to the board creates a new PCI bus that provides
support for the additional PCI slots or devices.
Figure 1-1.
21152 on the System Board
PCI
Option Slots
CPU
Memory
and
21152
Cache
PCI Bus
PCI
Option Slots
Core
Logic
Graphics
ISA or EISA
Option Slots
PCI Bus
21152
PCI Bus
ISA or
EISA
SCSI
LAN
ISA or EISA Bus
Bridge
Support
Chip
Diskette
Keyboard
Serial
Parallel
TOY Clock
Audio
LJ-04888 .AI4
1-2
21152 PCI-to-PCI Bridge Datasheet
Introduction
Option card designers can use the 21152 to implement multiple-device PCI option cards. Without a
PCI-to-PCI bridge, PCI loading rules would limit option cards to one device. The PCI Local Bus
Specification loading rules limit PCI option cards to a single connection per PCI signal in the
option card connector. However, the 21152 overcomes this restriction by providing, on the option
card, an independent PCI bus to which up to four devices can be attached.
Figure 1-2 shows how the 21152 enables the design of a multicomponent option card.
Figure 1-2. 21152 with Option Cards
PCI Bus
P
PCI Bus
21152
S
LAN
Chip
LAN
Chip
LAN
Chip
LAN
Chip
Note:
P – Primary Interface
S – Secondary Interface
LJ-04889.AI4
21152 PCI-to-PCI Bridge Preliminary Datasheet
1-3
Introduction
1.2
Architecture
The 21152 internal architecture consists of the following major functions:
• PCI interface control logic for the primary and secondary PCI interfaces
• Data path and data path control logic
• Configuration register and configuration control logic
• Secondary bus arbiter
Figure 1-3 shows the major functional blocks of the 21152.
Figure 1-3. 21152 Block Diagram
Secondary Data
Secondary Control
Secondary Data
Secondary
Arbiter
Secondary
Arbiter
Primary
and
Primary-
to-
Secondary
Control
Secondary
Data Path
Configuration
Registers
Clocks and
Reset
Secondary-
to-
Primary
Data Path
Primary
Request
and Grant
85%
Primary Data
Primary Control
Primary Data
LJ-04939.AI4
1-4
21152 PCI-to-PCI Bridge Datasheet
Introduction
Table 1-1 describes the major functional blocks of the 21152.
Table 1-1.
21152 Function Blocks
Function Block
Description
Primary and Secondary Control
PCI interface control logic. This block contains state machines and
control logic for the primary target interface, the primary master
interface, the secondary target interface, and the secondary master
interface. This block also contains logic that interfaces to the data
path and the configuration block.
Primary-to-Secondary Data Path
Secondary-to-Primary Data Path
Data path for data received on the primary interface and driven on the
secondary interface. This block is used for write transactions initiated
on the primary PCI bus and for returning read data for read
transactions initiated on the secondary PCI bus. This block contains
logic to store and, for posted write transactions, to increment the
address of the current transaction. This block also performs bus
command and configuration address format translations.
Data path for data received on the secondary interface and driven on
the primary interface. This block is used for write transactions initiated
on the secondary PCI bus and for returning read data for read
transactions initiated on the primary PCI bus. This block contains logic
to store and, for posted write transactions, to increment the address of
the current transaction. This block also performs bus command and
configuration address format translations.
Configuration Registers
Configuration space registers and corresponding control logic. These
registers are accessible from the primary interface only.
Secondary Bus Arbiter Control
Logic for secondary bus arbitration. This block receives
s_req_l<3:0>, as well as the 21152 secondary bus request, and
drives one of the s_gnt_l<3:0> lines or the 21152 secondary bus
grant.
21152 PCI-to-PCI Bridge Preliminary Datasheet
1-5
Introduction
1.3
Data Path
The data path consists of a primary-to-secondary data path for transactions and data flowing in the
downstream direction and a secondary-to-primary data path for transactions and data flowing in the
upstream direction.
Both data paths have the following queues:
• Posted write queue
• Delayed transaction queue
• Read data queue
To prevent deadlocks and to maintain data coherency, a set of ordering rules is imposed on the
forwarding of posted and delayed transactions across the 21152. The queue structure, along with
the order in which the transactions in the queues are initiated and completed, supports these
ordering requirements. Chapter 6 describes the 21152 ordering rules in detail.
See Chapter 4 for a detailed description of 21152 PCI bus operation.
Figure 1-4 shows the 21152 data path for the downstream direction, and the following sections
describe the data path queues.
Figure 1-4. 21152 Downstream Data Path
Delayed
Transaction
Queue
Address
Control
s_ad
p_ad
Posted Write Data Queue
Delayed Read Data Queue
LJ-04634.AI4
1.3.1
Posted Write Queue
The posted write queue contains the address and data of memory write transactions targeted for the
opposite interface. The posted write transaction can consist of an arbitrary number of data phases,
subject to the amount of space in the queue and disconnect boundaries. The posted write queue can
contain multiple posted write transactions. The number of posted write transactions that can be
queued at one time is dependent upon their burst size. The posted write queue consists of 88 bytes
in each direction.
1-6
21152 PCI-to-PCI Bridge Datasheet
Introduction
1.3.2
Delayed Transaction Queue
For a delayed write request transaction, the delayed transaction queue contains the address, bus
command, 1 Dword of write data, byte enable bits, and parity. When the delayed write transaction
is completed on the target bus, the write completion status is added to the corresponding entry.
For a delayed read request transaction, the delayed transaction queue contains the address and bus
command, and for nonprefetchable read transactions, the byte enable bits. When the delayed read
transaction is completed on the target bus, the read completion status corresponding to that
transaction is added to the delayed request entry. Read data is placed in the read data queue.
The delayed transaction queue can hold up to three transactions (any combination of read and write
transactions).
1.3.3
Read Data Queue
The read data queue contains read data transferred from the target during a delayed read
completion. Read data travels in the opposite direction of the transaction. The
primary-to-secondary read data queue contains read data corresponding to a delayed read
transaction residing in the secondary-to-primary delayed transaction queue. The
secondary-to-primary read data queue contains read data corresponding to a delayed read
transaction in the primary-to-secondary delayed transaction queue. The amount of read data per
transaction depends on the amount of space in the queue and disconnect boundaries.
Read data for up to three transactions, subject to the burst size of the read transactions and available
queue space, can be stored. The read data queue for the 21152 consists of 72 bytes in each direction.
21152 PCI-to-PCI Bridge Preliminary Datasheet
1-7
Signal Pins
2
This chapter provides detailed descriptions of the 21152 signal pins, grouped by function.
Table 2-1 describes the signal pin functional groups, and the following sections describe the signals
in each group.
Table 2-1.
Signal Pin Functional Groups
Function
Description
Primary PCI bus interface signal
pins
All PCI pins required by the PCI-to-PCI Bridge Architecture Specification,
Revision 1.1.
Secondary PCI bus interface signal All PCI pins required by the PCI-to-PCI Bridge Architecture Specification,
pins
Revision 1.1.
Secondary PCI bus arbiter signal
pins
Four request/grant pairs of pins for the secondary PCI bus.
An arbiter enable control pin.
Clock signal pins
Two clock inputs (one for each PCI interface).
Five clock outputs (for four external secondary PCI bus devices and also
for the 21152).
Reset signal pins
A primary interface reset input. A secondary interface reset output.
Two input voltage signaling level pins.
Miscellaneous signal pins
Nand tree signal pins
An input and an output for the Nand tree diagnostic mechanism.
Table 2-2 defines the signal type abbreviations used in the signal tables:
Table 2-2.
Signal Type Abbreviations
Signal Type
Description
I
Standard input only.
Standard output only.
Tristate bidirectional.
O
TS
Sustained tristate. Active low signal must be pulled high for one cycle
when deasserting.
STS
OD
Standard open drain.
Note: The _l signal name suffix indicates that the signal is asserted when it is at a low voltage level and
corresponds to the "#" suffix in the PCI Local Bus Specification. If this suffix is not present, the
signal is asserted when it is at a high voltage level.
21152 PCI-to-PCI Bridge Preliminary Datasheet
2-1
Signal Pins
2.1
Primary PCI Bus Interface Signals
Table 2-3 describes the primary PCI bus interface signals.
Table 2-3.
Primary PCI Bus Interface Signals (Sheet 1 of 3)
Signal Name
p_ad<31:0>
Type
Description
TS
Primary PCI interface address/data. These signals are a multiplexed address
and data bus. During the address phase or phases of a transaction, the initiator
drives a physical address on p_ad<31:0>. During the data phases of a
transaction, the initiator drives write data, or the target drives read data, on
p_ad<31:0>. When the primary PCI bus is idle, the 21152 drives p_ad to a valid
logic level when p_gnt_l is asserted.
p_cbe_l<3:0>
TS
Primary PCI interface command/byte enables. These signals are a
multiplexed command field and byte enable field. During the address phase or
phases of a transaction, the initiator drives the transaction type on p_cbe_l<3:0>.
When there are two address phases, the first address phase carries the dual
address command and the second address phase carries the transaction type.
For both read and write transactions, the initiator drives byte enables on
p_cbe_l<3:0> during the data phases. When the primary PCI bus is idle, the
21152 drives p_cbe_l to a valid logic level when p_gnt_l is asserted.
p_par
TS
Primary PCI interface parity. Signal p_par carries the even parity of the 36 bits
of p_ad<31:0> and p_cbe_l<3:0> for both address and data phases. Signal
p_par is driven by the same agent that has driven the address (for address
parity) or the data (for data parity). Signal p_par contains valid parity one cycle
after the address is valid (indicated by assertion of p_frame_l), or one cycle after
data is valid (indicated by assertion of p_irdy_l for write transactions and
p_trdy_l for read transactions). Signal p_par is driven by the device driving read
or write data one cycle after p_ad is driven. Signal p_par is tristated one cycle
after the p_ad lines are tristated. Devices receiving data sample p_par as an
input to check for possible parity errors. When the primary PCI bus is idle, the
21152 drives p_par to a valid logic level when p_gnt_l is asserted (one cycle
after the p_ad bus is parked).
p_frame_l
p_irdy_l
STS
STS
Primary PCI interface FRAME#. Signal p_frame_l is driven by the initiator of a
transaction to indicate the beginning and duration of an access on the primary
PCI bus. Signal p_frame_l assertion (falling edge) indicates the beginning of a
PCI transaction. While p_frame_l remains asserted, data transfers can continue.
The deassertion of p_frame_l indicates the final data phase requested by the
initiator. When the primary PCI bus is idle, p_frame_l is driven to a deasserted
state for one cycle and then is sustained by an external pull-up resistor.
Primary PCI interface IRDY#. Signal p_irdy_l is driven by the initiator of a
transaction to indicate the initiator’s ability to complete the current data phase on
the primary PCI bus. During a write transaction, assertion of p_irdy_l indicates
that valid write data is being driven on the p_ad bus. During a read transaction,
assertion of p_irdy_l indicates that the initiator is able to accept read data for the
current data phase. Once asserted during a given data phase, p_irdy_l is not
deasserted until the data phase completes. When the primary bus is idle,
p_irdy_l is driven to a deasserted state for one cycle and then is sustained by an
external pull-up resistor.
p_trdy_l
STS
Primary PCI interface TRDY#. Signal p_trdy_l is driven by the target of a
transaction to indicate the target’s ability to complete the current data phase on
the primary PCI bus. During a write transaction, assertion of p_trdy_l indicates
that the target is able to accept write data for the current data phase. During a
read transaction, assertion of p_trdy_l indicates that the target is driving valid
read data on the p_ad bus. Once asserted during a given data phase, p_trdy_l is
not deasserted until the data phase completes. When the primary bus is idle,
p_trdy_l is driven to a deasserted state for one cycle and then is sustained by an
external pull-up resistor.
2-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
Signal Pins
Table 2-3.
Primary PCI Bus Interface Signals (Sheet 2 of 3)
Signal Name
p_devsel_l
Type
Description
STS
Primary PCI interface DEVSEL#. Signal p_devsel_l is asserted by the target,
indicating that the device is accepting the transaction. As a target, the 21152
performs positive decoding on the address of a transaction initiated on the
primary bus to determine whether to assert p_devsel_l. As an initiator of a
transaction on the primary bus, the 21152 looks for the assertion of p_devsel_l
within five cycles of p_frame_l assertion; otherwise, the 21152 terminates the
transaction with a master abort. When the primary bus is idle, p_devsel_l is
driven to a deasserted state for one cycle and then is sustained by an external
pull-up resistor.
p_stop_l
STS
Primary PCI interface STOP#. Signal p_stop_l is driven by the target of the
current transaction, indicating that the target is requesting the initiator to stop the
current transaction on the primary bus.
•
When p_stop_l is asserted in conjunction with p_trdy_l and p_devsel_l
assertion, a disconnect with data transfer is being signaled.
•
When p_stop_l and p_devsel_l are asserted, but p_trdy_l is deasserted, a
target disconnect without data transfer is being signaled. When this occurs
on the first data phase, that is, no data is transferred during the transaction,
this is referred to as a target retry.
•
When p_stop_l is asserted and p_devsel_l is deasserted, the target is
signaling a target abort.
When the primary bus is idle, p_stop_l is driven to a deasserted state for one
cycle and then is sustained by an external pull-up resistor.
p_lock_l
I
Primary PCI interface LOCK#. Signal p_lock_l is deasserted during the first
address phase of a transaction and is asserted one clock cycle later by an
initiator attempting to perform an atomic operation that may take more than one
PCI transaction to complete. The 21152 samples p_lock_l as a target and can
propagate the lock across to the secondary bus. The 21152 does not drive
p_lock_l as an initiator; that is, the 21152 does not propagate locked
transactions upstream. When released by an initiator, p_lock_l is driven to a
deasserted state for one cycle and then is sustained by an external pull-up
resistor.
p_idsel
I
Primary PCI interface IDSEL#. Signal p_idsel is used as the chip select line for
Type 0 configuration accesses to 21152 configuration space. When p_idsel is
asserted during the address phase of a Type 0 configuration transaction, the
21152 responds to the transaction by asserting p_devsel_l.
p_perr_l
STS
Primary PCI interface PERR#. Signal p_perr_l is asserted when a data parity
error is detected for data received on the primary interface. The timing of
p_perr_l corresponds to p_par driven one cycle earlier and p_ad and p_cbe_l
driven two cycles earlier. Signal p_perr_l is asserted by the target during write
transactions, and by the initiator during read transactions. When the primary bus
is idle, p_perr_l is driven to a deasserted state for one cycle and then is
sustained by an external pull-up resistor.
21152 PCI-to-PCI Bridge Preliminary Datasheet
2-3
Signal Pins
Table 2-3.
Primary PCI Bus Interface Signals (Sheet 3 of 3)
Signal Name
p_serr_l
Type
Description
OD
Primary PCI interface SERR#. Signal p_serr_l can be driven low by any device
on the primary bus to indicate a system error condition. The 21152 can assert
p_serr_l for the following reasons:
•
•
•
•
•
•
•
•
•
Address parity error
Posted write data parity error on target bus
Secondary bus s_serr_l assertion
Master abort during posted write transaction
Target abort during posted write transaction
Posted write transaction discarded
Delayed write request discarded
Delayed read request discarded
Delayed transaction master timeout
Signal p_serr_l is pulled up through an external resistor
p_req_l
p_gnt_l
TS
I
Primary PCI bus REQ#. Signal p_req_l is asserted by the 21152 to indicate to
the primary bus arbiter that it wants to start a transaction on the primary bus.
Primary PCI bus GNT#. When asserted, p_gnt_l indicates to the 21152 that
access to the primary bus is granted. The 21152 can start a transaction on the
primary bus when the bus is idle and p_gnt_l is asserted. When the 21152 has
not requested use of the bus and p_gnt_l is asserted, the 21152 must drive
p_ad, p_cbe_l, and p_par to valid logic levels.
2-4
21152 PCI-to-PCI Bridge Preliminary Datasheet
Signal Pins
2.2
Secondary PCI Bus Interface Signals
Table 2-4 describes the secondary PCI bus interface signals.
Table 2-4.
Secondary PCI Bus Interface Signals (Sheet 1 of 2)
Signal Name
s_ad<31:0>
Type
Description
TS
Secondary PCI interface address/data. These signals are a multiplexed
address and data bus. During the address phase or phases of a transaction, the
initiator drives a physical address on s_ad<31:0>. During the data phases of a
transaction, the initiator drives write data, or the target drives read data, on
s_ad<31:0>. When the secondary PCI bus is idle, the 21152 drives s_ad to a
valid logic level when its secondary bus grant is asserted.
s_cbe_l<3:0>
TS
TS
Secondary PCI interface command/byte enables. These signals are a
multiplexed command field and byte enable field. During the address phase or
phases of a transaction, the initiator drives the transaction type on s_cbe_l<3:0>.
When there are two address phases, the first address phase carries the dual
address command and the second address phase carries the transaction type. For
both read and write transactions, the initiator drives byte enables on s_cbe_l<3:0>
during the data phases. When the secondary PCI bus is idle, the 21152 drives
s_cbe_l to a valid logic level when its secondary bus grant is asserted.
s_par
Secondary PCI interface parity. Signal s_par carries the even parity of the 36
bits of s_ad<31:0> and s_cbe_l<3:0> for both address and data phases. Signal
s_par is driven by the same agent that has driven the address (for address
parity) or the data (for data parity). Signal s_par contains valid parity one cycle
after the address is valid (indicated by assertion of s_frame_l), or one cycle after
data is valid (indicated by assertion of s_irdy_l for write transactions and
s_trdy_l for read transactions). Signal s_par is driven by the device driving read
or write data one cycle after s_ad is driven. Signal s_par is tristated one cycle
after the s_ad lines are tristated. Devices receive data sample s_par as an input
to check for possible parity errors. When the secondary PCI bus is idle, the 21152
drives s_par to a valid logic level when its secondary bus grant is asserted (one
cycle after the s_ad bus is parked).
s_frame_l
STS
STS
Secondary PCI interface FRAME#. Signal s_frame_l is driven by the initiator of
a transaction to indicate the beginning and duration of an access on the
secondary PCI bus. Signal s_frame_l assertion (falling edge) indicates the
beginning of a PCI transaction. While s_frame_l remains asserted, data transfers
can continue. The deassertion of s_frame_l indicates the final data phase
requested by the initiator. When the secondary PCI bus is idle, s_frame_l is
driven to a deasserted state for one cycle and then is sustained by an external
pull-up resistor.
s_irdy_l
Secondary PCI interface IRDY#. Signal s_irdy_l is driven by the initiator of a
transaction to indicate the initiator’s ability to complete the current data phase on
the secondary PCI bus. During a write transaction, assertion of s_irdy_l indicates
that valid write data is being driven on the s_ad bus. During a read transaction,
assertion of s_irdy_l indicates that the initiator is able to accept read data for the
current data phase. Once asserted during a given data phase, s_irdy_l is not
deasserted until the data phase completes. When the secondary bus is idle,
s_irdy_l is driven to a deasserted state for one cycle and then is sustained by an
external pull-up resistor.
s_trdy_l
STS
Secondary PCI interface TRDY#. Signal s_trdy_l is driven by the target of a
transaction to indicate the target’s ability to complete the current data phase on
the secondary PCI bus. During a write transaction, assertion of s_trdy_l indicates
that the target is able to accept write data for the current data phase. During a
read transaction, assertion of s_trdy_l indicates that the target is driving valid
read data on the s_ad bus. Once asserted during a given data phase, s_trdy_l is
not deasserted until the data phase completes. When the secondary bus is idle,
s_trdy_l is driven to a deasserted state for one cycle and then is sustained by an
external pull-up resistor.
21152 PCI-to-PCI Bridge Preliminary Datasheet
2-5
Signal Pins
Table 2-4.
Secondary PCI Bus Interface Signals (Sheet 2 of 2)
Signal Name
s_devsel_l
Type
Description
STS
Secondary PCI interface DEVSEL#. Signal s_devsel_l is asserted by the
target, indicating that the device is accepting the transaction. As a target, the
21152 performs positive decoding on the address of a transaction initiated on the
secondary bus in order to determine whether to assert s_devsel_l. As an initiator
of a transaction on the secondary bus, the 21152 looks for the assertion of
s_devsel_l within five cycles of s_frame_l assertion; otherwise, the 21152
terminates the transaction with a master abort. When the secondary bus is idle,
s_devsel_l is driven to a deasserted state for one cycle and then is sustained by
an external pull-up resistor.
s_stop_l
STS
Secondary PCI interface STOP#. Signal s_stop_l is driven by the target of the
current transaction, indicating that the target is requesting the initiator to stop the
current transaction on the secondary bus.
•
When s_stop_l is asserted in conjunction with s_trdy_l and s_devsel_l
assertion, a disconnect with data transfer is being signaled.
•
When s_stop_l and s_devsel_l are asserted, but s_trdy_l is deasserted, a
target disconnect without data transfer is being signaled. When this occurs
on the first data phase, that is, no data is transferred during the transaction,
this is referred to as a target retry.
•
When s_stop_l is asserted and s_devsel_l is deasserted, the target is
signaling a target abort.
When the secondary bus is idle, s_stop_l is driven to a deasserted state for one
cycle and then is sustained by an external pull-up resistor.
s_lock_l
s_perr_l
s_serr_l
STS
STS
I
Secondary PCI interface LOCK#. Signal s_lock_l is deasserted during the first
address phase of a transaction and is asserted one clock cycle later by the 21152
when it is propagating a locked transaction downstream. The 21152 does not
propagate locked transactions upstream. The 21152 continues to assert s_lock_l
until the address phase of the next locked transaction, or until the lock is
released. When the lock is released, s_lock_l is driven to a deasserted state for
one cycle and then is sustained by an external pull-up resistor.
Secondary PCI interface PERR#. Signal s_perr_l is asserted when a data
parity error is detected for data received on the secondary interface. The timing of
s_perr_l corresponds to s_par driven one cycle earlier and s_ad driven two
cycles earlier. Signal s_perr_l is asserted by the target during write transactions,
and by the initiator during read transactions. When the secondary bus is idle,
s_perr_l is driven to a deasserted state for one cycle and then is sustained by an
external pull-up resistor.
Secondary PCI interface SERR#. Signal s_serr_l can be driven low by any
device except the 21152 on the secondary bus to indicate a system error
condition. The 21152 samples s_serr_l as an input and conditionally forwards it
to the primary bus on p_serr_l. The 21152 does not drive s_serr_l. Signal
s_serr_l is pulled up through an external resistor.
2-6
21152 PCI-to-PCI Bridge Preliminary Datasheet
Signal Pins
2.3
Secondary Bus Arbitration Signals
Table 2-5 describes the secondary bus arbitration signals.
.
Table 2-5.
Secondary PCI Bus Arbitration Signals
Signal Name
s_req_l<3:0>
Type
Description
I
Secondary PCI interface REQ#s. The 21152 accepts four request inputs,
s_req_l<3:0>, into its secondary bus arbiter. The 21152 request input to the
arbiter is an internal signal. Each request input can be programmed to be in either
a high priority rotating group or a low priority rotating group. An asserted level on
an s_req_l pin indicates that the corresponding master wants to initiate a
transaction on the secondary PCI bus. If the internal arbiter is disabled (s_cfn_l
tied high), s_req_l<0> is reconfigured to be an external secondary grant input for
the 21152. In this case, an asserted level on s_req_l<0> indicates that the 21152
can start a transaction on the secondary PCI bus if the bus is idle.
s_gnt_l<3:0>
TS
Secondary PCI interface GNT#s. The 21152 secondary bus arbiter can assert
one of four secondary bus grant outputs, s_gnt_l<3:0>, to indicate that an
initiator can start a transaction on the secondary bus if the bus is idle. The
21152’s secondary bus grant is an internal signal. A programmable 2-level
rotating priority algorithm is used. If the internal arbiteris disabled (s_cfn_l tied
high), s_gnt_l<0> is reconfigured to be an external secondary bus request output
for the 21152. The 21152 asserts this signal whenever it wants to start a
transaction on the secondary bus.
s_cfn_l
I
Secondary PCI central function enable. When tied low, s_cfn_l enables the
21152 secondary bus arbiter. When tied high, s_cfn_l disables the internal
arbiter. An external secondary bus arbiter must then be used. Signal s_req_l<0>
is reconfigured to be the 21152 secondary bus grant input, and s_gnt_l<0> is
reconfigured to be the 21152 secondary bus request output, when an external
arbiter is used. Secondary bus parking is done when s_req_l<0> is asserted, the
secondary bus is idle, and the 21152 does not want to initiate a transaction.
2.4
Clock Signals
Table 2-6 describes the clock signals.
Table 2-6.
Clock Signals
Signal Name
p_clk
Type
Description
I
Primary interface PCI CLK. Provides timing for all transactions on the primary
PCI bus. All primary PCI inputs are sampled on the rising edge of p_clk, and all
primary PCI outputs are driven from the rising edge of p_clk. Frequencies
supported by the 21152 range from 0 MHz to 33 MHz.
s_clk
I
Secondary interface PCI CLK. Provides timing for all transactions on the
secondary PCI bus. All secondary PCI inputs are sampled on the rising edge of
s_clk, and all secondary PCI outputs are driven from the rising edge of s_clk.
Frequencies supported by the 21152 range from 0 MHz to 33 MHz.
s_clk_o<4:0>
O
Secondary interface PCI CLK outputs. Signals s_clk_o<4:0> are 5 clock
outputs generated from the primary interface clock input, p_clk. These clocks
operate at the same frequency of p_clk. When these clocks are used, one of the
clock outputs must be fed back to the secondary clock input, s_clk. Unused clock
outputs can be disabled by writing the secondary clock disable bits in
configuration space; otherwise, terminate them electrically.
21152 PCI-to-PCI Bridge Preliminary Datasheet
2-7
Signal Pins
2.5
Reset Signals
Table 2-7 describes the reset signals.
Table 2-7.
Reset Signals
Signal Name
bpcca
Type
Description
I
Bus power/clock control management pin. When tied high and when the
21152 is placed in the D3hot power state, enables the 21152 to place the
secondary bus in the B2 power state. The 21152 will disable the secondary
clocks and drive them to 0. When tied low, placing the 21152 in the D3hot power
state has no effect on the secondary bus clocks.
p_rst_l
s_rst_l
I
Primary PCI bus RST#. Signal p_rst_l forces the 21152 to a known state. All
register state is cleared, and all primary PCI bus outputs are tristated. Signal
p_rst_l is asynchronous to p_clk.
O
Secondary PCI bus RST#. Signal s_rst_l is driven by the 21152 and acts as the
PCI reset for the secondary bus. The 21152 asserts s_rst_l when any of the
following conditions are met:
•
•
Signal p_rst_l is asserted.
The secondary reset bit in the bridge control register in configuration space is
set.
•
The chip reset bit in the diagnostic control register in configuration space is
set.
When the 21152 asserts s_rst_l, it tristates all secondary control signals and
drives zeros on s_ad, s_cbe_l, and s_par. Signal s_rst_l remains asserted until
p_rst_l is deasserted, and the secondary reset bit is clear. Assertion of s_rst_l
by itself does not clear register state, and configuration registers are still
accessible from the primary PCI interface.
a.
21152–AB and later revisions only.
2.6
Miscellaneous Signals
Table 2-8 describes the miscellaneous signals.
Table 2-8.
Miscellaneous Signals
Signal Name
p_vio
Type
Description
I
Primary interface I/O voltage. This signal must be tied to either 3.3 V or 5 V,
corresponding to the signaling environment of the primary PCI bus as described
in the PCI Local Bus Specification, Revision 2.1. When any device on the primary
PCI bus uses 5-V signaling levels, tie p_vio to 5 V. Signal p_vio is tied to 3.3 V
only when all the devices on the primary bus use 3.3-V signaling levels.
s_vio
I
Secondary interface I/O voltage. This signal must be tied to either 3.3 V or 5 V,
corresponding to the signaling environment of the secondary PCI bus as described
in the PCI Local Bus Specification, Revision 2.1. When any device on the
secondary PCI bus uses 5-V signaling levels, tie s_vio to 5 V. Signal s_vio is tied
to 3.3 V only when all the devices on the secondary bus use 3.3-V signaling levels.
2-8
21152 PCI-to-PCI Bridge Preliminary Datasheet
Signal Pins
2.7
Nand Tree Signals
Table 2-9 describes the Nand tree signals.
Table 2-9.
Nand Tree Signals
Signal Name
Type
Description
goz_l
I
Diagnostic tristate control. This signal, when asserted, tristates all
bidirectional and tristatable output pins.
nand_out
O
Nand tree diagnostic output. This signal is dedicated to the diagnostic
Nand tree. The Nand tree starts at s_cfn_l and runs clockwise. All
inputs, except p_clk and s_clk, are used in the Nand tree. The goz_l
signal should be asserted when the Nand tree mechanism is used.
21152 PCI-to-PCI Bridge Preliminary Datasheet
2-9
Pin Assignment
3
This chapter describes the 21152 pins. It provides numeric and alphanumeric lists of the pins and
includes a diagram showing 21152 pin assignment.
Figure 3-1 shows the 21152 pins. Table 3-2 lists pins by location in numeric order and Table 3-4
lists pins by signal names in alphanumeric order.
Figure 3-1. 21152 Pinout Diagram
vss
s_par
120
115
110
105
100
95
vdd
vss
p_ad<8>
s_serr_l
s_perr_l
s_lock_l
s_stop_l
s_devsel_l
vdd
s_trdy_l
s_irdy_l
s_frame_l
vss
s_cbe_l<2>
s_ad<16>
vdd
s_ad<17>
s_ad<18>
s_ad<19>
vss
s_ad<20>
s_ad<21>
s_ad<22>
vdd
s_ad<23>
s_cbe_l<3>
s_ad<24>
vss
s_ad<25>
s_ad<26>
vdd
s_ad<27>
s_ad<28>
s_ad<29>
vss
p_ad<9>
vdd
p_ad<10>
p_ad<11>
5
p_ad<12>
vss
p_ad<13>
10
15
20
25
30
35
40
p_ad<14>
p_ad<15>
vdd
p_cbe_l<1>
p_par
p_serr_l
p_perr_l
vss
p_lock_l
p_stop_l
p_devsel_l
p_trdy_l
vdd
p_irdy_l
p_frame_l
21152
p_cbe_l<2>
vss
p_ad<16>
p_ad<17>
p_ad<18>
vdd
90
Scaled@92%
p_ad<19>
p_ad<20>
p_ad<21>
s_ad<30>
s_ad<31>
s_req_l<0>
s_req_l<1>
s_req_l<2>
vdd
vss
85
p_ad<22>
p_ad<23>
p_idsel
p_cbe_l<3>
vss
*
21152-AB and later revisions only.
This is a vss pin for the 21152-AA.
LJ-04892.AI4
21152 PCI-to-PCI Bridge Preliminary Datasheet
3-1
Pin Assignment
3.1
Pin Location List (Numeric)
Table 3-1 provides the signal type abbreviations used in Table 3-2. Table 3-2 lists the 21152 pins in
numeric order, showing the location, signal name, and signal type of each pin.
Table 3-1.
Signal Type Abbreviations
Signal Type
Description
I
Standard input only.
Standard output only.
Power.
O
P
TS
Tristate bidirectional.
Sustained tristate. Active low signal must be pulled high for one cycle when
deasserting.
STS
OD
Standard open drain.
Table 3-2.
Pin Location List (Numeric) (Sheet 1 of 3)
PQFP
Location
PQFP
Location
Signal Name
Type
Signal Name
Type
1
vss
P
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
s_ad<23>
s_cbe_l<3>
s_ad<24>
vss
TS
TS
TS
P
2
s_par
TS
I
3
s_serr_l
s_perr_l
s_lock_l
s_stop_l
s_devsel_l
vdd
4
STS
STS
STS
STS
P
5
s_ad<25>
s_ad<26>
vdd
TS
TS
P
6
7
8
s_ad<27>
s_ad<28>
s_ad<29>
vss
TS
TS
TS
P
9
s_trdy_l
s_irdy_l
s_frame_l
vss
STS
STS
STS
P
10
11
12
13
14
15
16
17
18
19
20
21
22
23
s_ad<30>
s_ad<31>
s_req_l<0>
s_req_l<1>
s_req_l<2>
vdd
TS
TS
I
s_cbe_l<2>
s_ad<16>
vdd
TS
TS
P
I
s_ad<17>
s_ad<18>
s_ad<19>
vss
TS
TS
TS
P
I
P
vss
P
s_req_l<3>
s_gnt_l<0>
s_gnt_l<1>
s_gnt_l<2>
vdd
I
s_ad<20>
s_ad<21>
s_ad<22>
vdd
TS
TS
TS
P
TS
TS
TS
P
3-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
Pin Assignment
Table 3-2.
Pin Location List (Numeric) (Sheet 2 of 3)
PQFP
Location
PQFP
Location
Signal Name
Type
Signal Name
Type
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
s_gnt_l<3>
s_rst_l
s_cfn_l
vss
TS
O
I
84
p_ad<23>
p_ad<22>
vss
TS
TS
P
85
86
P
87
p_ad<21>
p_ad<20>
p_ad<19>
vdd
TS
TS
TS
P
s_clk
I
88
s_vio
I
89
s_clk_o<0>
vss
O
P
90
91
p_ad<18>
p_ad<17>
p_ad<16>
vss
TS
TS
TS
P
s_clk_o<1>
vdd
O
P
92
93
s_clk_o<2>
vss
O
P
94
95
p_cbe_l<2>
p_frame_l
p_irdy_l
vdd
TS
STS
STS
P
s_clk_o<3>
vdd
O
P
96
97
s_clk_o<4>
nand_out
goz_l
O
O
I
98
99
p_trdy_l
p_devsel_l
p_stop_l
p_lock_l
vss
STS
STS
STS
STS
P
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
p_rst_l
vss
I
P
p_clk
I
p_vio
I
p_perr_l
p_serr_l
p_par
STS
OD
TS
TS
P
p_gnt_l
p_req_l
p_ad<31>
vss
I
TS
TS
P
p_cbe_l<1>
vdd
p_ad<30>
p_ad<29>
p_ad<28>
vdd
TS
TS
TS
P
p_ad<15>
p_ad<14>
p_ad<13>
vss
TS
TS
TS
P
p_ad<27>
p_ad<26>
p_ad<25>
p_ad<24>
vdd
TS
TS
TS
TS
P
p_ad<12>
p_ad<11>
p_ad<10>
vdd
TS
TS
TS
P
p_ad<9>
p_ad<8>
vss
TS
TS
P
vss
P
p_cbe_l<3>
p_idsel
TS
I
vdd
P
21152 PCI-to-PCI Bridge Preliminary Datasheet
3-3
Pin Assignment
Table 3-2.
Pin Location List (Numeric) (Sheet 3 of 3)
PQFP
Location
PQFP
Location
Signal Name
Type
Signal Name
Type
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
vss
P
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
s_ad<5>
s_ad<6>
vss
TS
TS
P
p_cbe_l<0>
p_ad<7>
p_ad<6>
vdd
TS
TS
TS
P
s_ad<7>
s_cbe_l<0>
s_ad<8>
vdd
TS
TS
TS
P
p_ad<5>
p_ad<4>
vss
TS
TS
P
s_ad<9>
s_ad<10>
s_ad<11>
vss
TS
TS
TS
P
p_ad<3>
p_ad<2>
vdd
TS
TS
P
p_ad<1>
p_ad<0>
s_ad<0>
vss
TS
TS
TS
P
s_ad<12>
s_ad<13>
vdd
TS
TS
P
s_ad<14>
s_ad<15>
vss
TS
TS
P
s_ad<1>
s_ad<2>
s_ad<3>
vdd
TS
TS
TS
P
s_cbe_l<1>
bpcc1
TS
I
s_ad<4>
TS
vdd
P
1. Pertains to the 21152–AB and later revisions only. For the 21152–AA, this pin is vss.
3-4
21152 PCI-to-PCI Bridge Preliminary Datasheet
Pin Assignment
3.2
Pin Signal List (Alphanumeric)
Table 3-3 provides the signal type abbreviations used in Table 3-4. Table 3-4 lists the 21152 signal
names in alphanumeric order, showing the signal name, location, and signal type of each pin.
Table 3-3.
Signal Type Abbreviations
Signal Type
Description
I
Standard input only.
Standard output only.
Power.
O
P
TS
Tristate bidirectional.
Sustained tristate. Active low signal must be pulled high for one cycle when
deasserting.
STS
OD
Standard open drain.
Table 3-4.
Pin Signal List (Alphanumeric) (Sheet 1 of 3)
Pin
Name
PQFP
Location
Pin
Name
PQFP
Location
Type
Type
bpcc1
159
63
I
p_ad<20>
p_ad<21>
p_ad<22>
p_ad<23>
p_ad<24>
p_ad<25>
p_ad<26>
p_ad<27>
p_ad<28>
p_ad<29>
p_ad<30>
p_ad<31>
p_cbe_l<0>
p_cbe_l<1>
p_cbe_l<2>
p_cbe_l<3>
p_clk
88
87
85
84
79
78
77
76
74
73
72
70
122
107
95
82
66
100
96
68
83
97
102
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
I
goz_l
I
nand_out
p_ad<0>
p_ad<1>
p_ad<2>
p_ad<3>
p_ad<4>
p_ad<5>
p_ad<6>
p_ad<7>
p_ad<8>
p_ad<9>
p_ad<10>
p_ad<11>
p_ad<12>
p_ad<13>
p_ad<14>
p_ad<15>
p_ad<16>
p_ad<17>
p_ad<18>
p_ad<19>
62
O
133
132
130
129
127
126
124
123
118
117
115
114
113
111
110
109
93
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
p_devsel_l
p_frame_l
p_gnt_l
STS
STS
I
92
p_idsel
I
91
p_irdy_l
STS
STS
89
p_lock_l
21152 PCI-to-PCI Bridge Preliminary Datasheet
3-5
Pin Assignment
Table 3-4.
Pin Signal List (Alphanumeric) (Sheet 2 of 3)
Pin
Name
PQFP
Location
Pin
Name
PQFP
Location
Type
Type
p_par
106
104
69
TS
STS
TS
I
s_ad<29>
s_ad<30>
s_ad<31>
s_cbe_l<0>
s_cbe_l<1>
s_cbe_l<2>
s_cbe_l<3>
s_cfn_l
33
35
36
145
158
13
25
49
51
53
55
57
59
61
7
TS
TS
TS
TS
TS
TS
TS
I
p_perr_l
p_req_l
p_rst_l
64
p_serr_l
p_stop_l
p_trdy_l
p_vio
105
101
99
OD
STS
STS
I
67
s_ad<0>
s_ad<1>
s_ad<2>
s_ad<3>
s_ad<4>
s_ad<5>
s_ad<6>
s_ad<7>
s_ad<8>
s_ad<9>
s_ad<10>
s_ad<11>
s_ad<12>
s_ad<13>
s_ad<14>
s_ad<15>
s_ad<16>
s_ad<17>
s_ad<18>
s_ad<19>
s_ad<20>
s_ad<21>
s_ad<22>
s_ad<23>
s_ad<24>
s_ad<25>
s_ad<26>
s_ad<27>
s_ad<28>
134
136
137
138
140
141
142
144
146
148
149
150
152
153
155
156
14
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
TS
s_clk
I
s_clk_o<0>
s_clk_o<1>
s_clk_o<2>
s_clk_o<3>
s_clk_o<4>
s_devsel_l
s_frame_l
s_gnt_l<0>
s_gnt_l<1>
s_gnt_l<2>
s_gnt_l<3>
s_irdy_l
O
O
O
O
O
STS
STS
TS
TS
TS
TS
STS
STS
TS
STS
I
11
43
44
45
47
10
5
s_lock_l
s_par
2
s_perr_l
4
s_req_l<0>
s_req_l<1>
s_req_l<2>
s_req_l<3>
s_rst_l
37
38
39
42
48
3
16
I
17
I
18
I
20
O
21
s_serr_l
I
22
s_stop_l
s_trdy_l
6
STS
STS
I
24
9
26
s_vio
52
8
28
vdd
P
29
vdd
15
23
30
P
31
vdd
P
32
vdd
P
3-6
21152 PCI-to-PCI Bridge Preliminary Datasheet
Pin Assignment
Table 3-4.
Pin Signal List (Alphanumeric) (Sheet 3 of 3)
Pin
Name
PQFP
Location
Pin
Name
PQFP
Location
Type
Type
vdd
vdd
vdd
vdd
vdd
vdd
vdd
vdd
vdd
vdd
vdd
vdd
vdd
vdd
vdd
vdd
vdd
vss
vss
vss
40
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
vss
vss
vss
vss
vss
vss
vss
vss
vss
vss
vss
vss
vss
vss
vss
vss
vss
vss
vss
vss
27
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
P
46
34
56
41
60
50
75
54
80
58
90
65
98
71
108
116
120
125
131
139
147
154
160
1
81
86
94
103
112
119
121
128
135
143
151
157
12
19
1. Pertains to the 21152–AB and later revisions only. For the 21152–AA, this pin is vss.
21152 PCI-to-PCI Bridge Preliminary Datasheet
3-7
PCI Bus Operation
4
This chapter presents detailed information about PCI transactions, transaction forwarding across
the 21152, and transaction termination.
4.1
Types of Transactions
This section provides a summary of PCI transactions performed by the 21152.
Table 4-1 lists the command code and name of each PCI transaction. The Master and Target
columns indicate 21152 support for each transaction when the 21152 initiates transactions as a
master, on the primary bus and on the secondary bus, and when the 21152 responds to transactions
as a target, on the primary bus and on the secondary bus.
Table 4-1.
21152 PCI Transactions
21152 Initiates as Master
21152 Responds as Target
Type of Transaction
Primary
Secondary
Primary
Secondary
0000 Interrupt acknowledge
0001 Special cycle
0010 I/O read
No
No
No
No
No
No
Yes
Yes
Yes
No
Yes
Yes
Yes
No
Yes
Yes
No
Yes
Yes
No
0011 I/O write
0100 Reserved
0101 Reserved
No
No
No
No
0110 Memory read
0111 Memory write
1000 Reserved
Yes
Yes
No
Yes
Yes
No
Yes
Yes
No
Yes
Yes
No
1001 Reserved
No
No
No
No
1010 Configuration read
1011 Configuration write
1100 Memory read multiple
1101 Dual address cycle
1110 Memory read line
1111 Memory write and invalidate
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Type 1
Yes
Yes
Yes
Yes
Type 1
Yes
Yes
Yes
Yes
As indicated in Table 4-1, the following PCI commands are not supported by the 21152:
• The 21152 never initiates a PCI transaction with a reserved command code and, as a target, the
21152 ignores reserved command codes.
• The 21152 never initiates an interrupt acknowledge transaction and, as a target, the 21152
ignores interrupt acknowledge transactions. Interrupt acknowledge transactions are expected
to reside entirely on the primary PCI bus closest to the host bridge.
• The 21152 does not respond to special cycle transactions and cannot guarantee delivery of a special
cycle transaction to downstream buses, due to the broadcast nature of the special cycle command,
and the inability to control the transaction as a target. To generate special cycle transactions on other
PCI buses, either upstream or downstream, a Type 1 configuration command must be used.
• The 21152 does not generate Type 0 configuration transactions on the primary interface, nor does
it respond to Type 0 configuration transactions on the secondary PCI interface. The PCI-to-PCI
Bridge Architecture Specification does not support configuration from the secondary bus.
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-1
PCI Bus Operation
4.2
Address Phase
The standard PCI transaction consists of one or two address phases, followed by one or more data
phases. An address phase always lasts one PCI clock cycle. The first address phase is designated by
an asserting (falling) edge on the FRAME# signal.
The number of address phases depends on whether the address is 32 bits or 64 bits.
4.2.1
4.2.2
Single Address Phase
A 32-bit address uses a single address phase. This address is driven on AD<31:0>, and the bus
command is driven on C/BE#<3:0>. The 21152 supports the linear increment address mode only,
which is indicated when the low 2 address bits are equal to 0. If either of the low 2 address bits is
nonzero, the 21152 automatically disconnects the transaction after the first data transfer.
Dual Address Phase
Dual address transactions are PCI transactions that contain two address phases specifying a 64-bit
address.
The first address phase is denoted by the asserting edge of FRAME#.
The second address phase always follows on the next clock cycle.
For a 32-bit interface, the first address phase contains dual address command code on the C/BE#<3:0>
lines, and the low 32 address bits on the AD<31:0> lines. The second address phase consists of the
specific memory transaction command code on the C/BE#<3:0> lines, and the high 32 address bits on
the AD<31:0> lines. In this way, 64-bit addressing can be supported on 32-bit PCI buses.
The PCI-to-PCI Bridge Architecture Specification supports the use of dual address transactions in
the prefetchable memory range only. See Section 5.3.3 for a discussion of prefetchable address
space. The 21152 supports dual address transactions in both the upstream and the downstream
direction. The 21152 supports a programmable 64-bit address range in prefetchable memory for
downstream forwarding of dual address transactions. Dual address transactions falling outside the
prefetchable address range are forwarded upstream, but not downstream. Prefetching and posting
are performed in a manner consistent with the guidelines given in this specification for each type of
memory transaction in prefetchable memory space.
The 21152 uses the following transaction command codes:
• Memory write
• Memory write and invalidate
• Memory read
• Memory read line
• Memory read multiple
Use of other transaction codes may result in a master abort.
Any memory transactions addressing the first 4 GB space should use a single address phase; that is,
the high 32 bits of a dual address transaction should never be 0.
4-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
4.3
4.4
Device Select (DEVSEL#) Generation
The 21152 always performs positive address decoding when accepting transactions on either the
primary or secondary buses. The 21152 never subtractively decodes. Medium DEVSEL# timing is
used on both interfaces.
Data Phase
The address phase or phases of a PCI transaction are followed by one or more data phases. A data
phase is completed when IRDY# and either TRDY# or STOP# are asserted. A transfer of data
occurs only when both IRDY# and TRDY# are asserted during the same PCI clock cycle. The last
data phase of a transaction is indicated when FRAME# is deasserted and both TRDY# and IRDY#
are asserted, or when IRDY# and STOP# are asserted. See Section 4.8 for further discussion of
transaction termination.
Depending on the command type, the 21152 can support multiple data phase PCI transactions. For a
detailed description of how the 21152 imposes disconnect boundaries, see Section 4.5.4 for a
description of write address boundaries and Section 4.6.3 for a description of read address boundaries.
4.5
Write Transactions
Write transactions are treated as either posted write or delayed write transactions.
Table 4-2 shows the method of forwarding used for each type of write operation.
Table 4-2.
Write Transaction Forwarding
Type of Transaction
Type of Forwarding
Memory write
Posted
Posted
Delayed
Delayed
Memory write and invalidate
I/O write
Type 1 configuration write
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-3
PCI Bus Operation
4.5.1
Posted Write Transactions
Posted write forwarding is used for memory write and, for memory write and invalidate
transactions.
When the 21152 determines that a memory write transaction is to be forwarded across the bridge, the
21152 asserts DEVSEL# with medium timing and TRDY# in the same cycle, provided that enough
buffer space is available in the posted data queue for the address and at least 8 Dwords of data. This
enables the 21152 to accept write data without obtaining access to the target bus. The 21152 can
accept 1 Dword of write data every PCI clock cycle; that is, no target wait states are inserted. This
write data is stored in internal posted write buffers and is subsequently delivered to the target.
The 21152 continues to accept write data until one of the following events occurs:
• The initiator terminates the transaction by deasserting FRAME# and IRDY#.
• An internal write address boundary is reached, such as a cache line boundary or an aligned
4 KB boundary, depending on the transaction type.
• The posted write data buffer fills up.
• The 21152 ends the transaction on the target bus when one of the following conditions is met:
• All posted write data has been delivered to the target.
• The target returns a target disconnect or target retry (the 21152 starts another transaction to
deliver the rest of the write data).
• The target returns a target abort (the 21152 discards remaining write data).
• The master latency timer expires, and the 21152 no longer has the target bus grant (the 21152
starts another transaction to deliver remaining write data).
When one of the last two events occurs, the 21152 returns a target disconnect to the requesting
initiator on this data phase to terminate the transaction.
Section 4.8.3.2 provides detailed information about how the 21152 responds to target termination
during posted write transactions.
Once the posted write data moves to the head of the posted data queue, the 21152 asserts its request
on the target bus. This can occur while the 21152 is still receiving data on the initiator bus. When
the grant for the target bus is received and the target bus is detected in the idle condition, the 21152
asserts FRAME# and drives the stored write address out on the target bus. On the following cycle,
the 21152 drives the first Dword of write data and continues to transfer write data until all write
data corresponding to that transaction is delivered, or until a target termination is received. As long
as write data exists in the queue, the 21152 can drive 1 Dword of write data each PCI clock cycle;
that is, no master wait states are inserted. If write data is flowing through the 21152 and the initiator
stalls, the 21152 may have to insert wait states on the target bus if the queue empties.
4-4
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
Figure 4-1 shows a memory write transaction in flow-through mode, where data is being removed
from buffers on the target interface while more data is being transferred into the buffers on the
master interface.
Figure 4-1. Flow-Through Posted Memory Write Transaction
CY0
CY2
CY4
CY6
CY8
CY10
CY12
CY14
CY16
Cycle
p_clk
CY1
CY3
CY5
CY7
CY9
CY11
CY13
CY15
CY17
< 15ns >
Addr
7
Data
Data
Data
Data
Data
Data
Data
Data
Data
Data
p_ad
Byte Enables
p_cbe_l
p_frame_l
p_irdy_l
p_devsel_l
p_trdy_l
p_stop_l
s_clk
Addr
7
Data
Data
Data
Data
Data
Data
Data
Data
Data
Data
s_ad
Byte Enables
s_cbe_l
s_frame_l
s_irdy_l
s_devsel_l
s_trdy_l
s_stop_l
86%
LJ-04843.AI4
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-5
PCI Bus Operation
4.5.2
Memory Write and Invalidate Transactions
Posted write forwarding is used for memory write and invalidate transactions.
Memory write and invalidate transactions guarantee transfer of entire cache lines. If the write
buffer fills before an entire cache line is transferred, the 21152 disconnects the transaction and
converts it to a memory write transaction.
The 21152 disconnects memory write and invalidate commands at aligned cache line boundaries.
The cache line size value in the 21152 cache line size register gives the number of Dwords in a
cache line. For the 21152 to generate memory write and invalidate transactions, this cache line size
value must be written to a value that is a nonzero power of 2 and less than or equal to 16 (that is, 1,
2, 4, 8, or 16 Dwords).
If the cache line size does not meet the memory write and invalidate conditions, that is, the value is
0, or is not a power of 2, or is greater than 16 Dwords, the 21152 treats the memory write and
invalidate command as a memory write command. In this case, when the 21152 forwards the
memory write and invalidate transaction to the target bus, it converts the command code to a
memory write code and does not observe cache line boundaries.
If the value in the cache line size register does meet the memory write and invalidate conditions,
that is, the value is a nonzero power of 2 less than or equal to 16 Dwords, the 21152 returns a target
disconnect to the initiator either on a cache line boundary or when the posted write buffer fills.
For a cache line size of 16 Dwords, the 21152 disconnects a memory write and invalidate transaction
on every cache line boundary. When the cache line size is 1, 2, 4, or 8 Dwords, the 21152 accepts
another cache line if at least 8 Dwords of empty space remains in the posted write buffer. If less than
Dwords of empty space remains, the 21152 disconnects on that cache line boundary.
When the memory write and invalidate transaction is disconnected before a cache line boundary is
reached, typically because the posted write buffer fills, the transaction is converted to a memory
write transaction.
4-6
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
4.5.3
Delayed Write Transactions
Delayed write forwarding is used for I/O write transactions and for Type 1 configuration write
transactions.
A delayed write transaction guarantees that the actual target response is returned back to the
initiator without holding the initiating bus in wait states. A delayed write transaction is limited to a
single Dword data transfer.
When a write transaction is first detected on the initiator bus, and the 21152 forwards it as a
delayed transaction, the 21152 claims the access by asserting DEVSEL# and returns a target retry
to the initiator. During the address phase, the 21152 samples the bus command, address, and
address parity one cycle later. After IRDY# is asserted, the 21152 also samples the first data
Dword, byte enable bits, and data parity. This information is placed into the delayed transaction
queue. The transaction is queued only if no other existing delayed transactions have the same
address and command, and if the delayed transaction queue is not full. When the delayed write
transaction moves to the head of the delayed transaction queue and all ordering constraints with
posted data are satisfied (see Chapter 6), the 21152 initiates the transaction on the target bus. The
21152 transfers the write data to the target.
If the 21152 receives a target retry in response to the write transaction on the target bus, it continues
to repeat the write transaction until the data transfer is completed, or until an error condition is
encountered.
24
If the 21152 is unable to deliver write data after 2 attempts, the 21152 ceases further write
attempts and returns a target abort to the initiator. The delayed transaction is removed from the
delayed transaction queue. The 21152 also asserts p_serr_l if the primary SERR# enable bit is set
in the command register. See Section 7.4 for information on the assertion of p_serr_l.
When the initiator repeats the same write transaction (same command, address, byte enable bits,
and data), and the completed delayed transaction is at the head of the queue, the 21152 claims the
access by asserting DEVSEL# and returns TRDY# to the initiator, to indicate that the write data
was transferred. If the initiator requests multiple Dwords, the 21152 also asserts STOP# in
conjunction with TRDY# to signal a target disconnect. Note that only those bytes of write data with
valid byte enable bits are compared. If any of the byte enable bits are turned off (driven high), the
corresponding byte of write data is not compared.
If the initiator repeats the write transaction before the data has been transferred to the target, the
21152 returns a target retry to the initiator. The 21152 continues to return a target retry to the
initiator until write data is delivered to the target, or until an error condition is encountered. When
the write transaction is repeated, the 21152 does not make a new entry into the delayed transaction
queue. Section 4.8.3.1 provides detailed information about how the 21152 responds to target
termination during delayed write transactions.
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-7
PCI Bus Operation
Figure 4-2 shows a delayed write transaction forwarded downstream across the 21152.
Figure 4-2. Downstream Delayed Write Transaction
CY0
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CY8
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CY14
Cycle
p_clk
CY1
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CY5
CY7
CY9
CY11
CY13
< 15ns >
Addr
3
Data
Addr
3
Data
Addr
Data
p_ad
Byte Enables
Byte Enables
3
Byte Enables
p_cbe_l
p_frame_l
p_irdy_l
p_devsel_l
p_trdy_l
p_stop_l
s_clk
Addr
Data
s_ad
3
Byte Enables
s_cbe_l
s_frame_l
s_irdy_l
s_devsel_l
s_trdy_l
s_stop_l
LJ-04844.AI4
The 21152 implements a discard timer that starts counting when the delayed write completion is at
the head of the delayed transaction queue. The initial value of this timer can be set to one of two
values, selectable through both the primary and secondary master time-out bits in the bridge
control register. If the initiator does not repeat the delayed write transaction before the discard
timer expires, the 21152 discards the delayed write transaction from the delayed transaction queue.
The 21152 also conditionally asserts p_serr_l (see Section 7.4).
4-8
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
4.5.4
Write Transaction Address Boundaries
The 21152 imposes internal address boundaries when accepting write data. The aligned address
boundaries are used to prevent the 21152 from continuing a transaction over a device address
boundary and to provide an upper limit on maximum latency. The 21152 returns a target disconnect to
the initiator when it reaches the aligned address boundaries under the conditions shown in Table 4.3.
Table 4.3
Write Transaction Disconnect Address Boundaries
Type of Transaction
Condition
Aligned Address Boundary
Delayed write
All
Disconnects after one data transfer
Memory write
disconnect control
bit = 01
Posted memory write
Posted memory write
4 KB aligned address boundary
Memory write
disconnect control
bit = 11
Disconnects at cache line boundary
4 KB aligned address boundary
Cache line size ≠
Posted memory write and
invalidate
1, 2, 4, 8, 16
nth cache line boundary, where a cache line
boundary is reached and less than 8 free
Dwords of posted write buffer space remains
Cache line size =
1, 2, 4, 8
Posted memory write and
invalidate
Posted memory write and
invalidate
Cache line size = 16
16-Dword aligned address boundary
1. The memory write disconnect control bit is located in the chip control register at offset 40h in configuration
space.
4.5.5
Buffering Multiple Write Transactions
The 21152 continues to accept posted memory write transactions as long as space for at least
1 Dword of data in the posted write data buffer remains. If the posted write data buffer fills before
the initiator terminates the write transaction, the 21152 returns a target disconnect to the initiator.
Delayed write transactions are posted as long as at least one open entry in the 21152 delayed
transaction queue exists. Therefore, several posted and delayed write transactions can exist in data
buffers at the same time.
See Chapter 6 for information about how multiple posted and delayed write transactions are ordered.
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-9
PCI Bus Operation
4.5.6
Fast Back-to-Back Write Transactions
The 21152 can recognize and post fast back-to-back write transactions. When the 21152 cannot accept
the second transaction because of buffer space limitations, it returns a target retry to the initiator.
When the 21152 has posted multiple write transactions, it can initiate fast back-to-back write
transactions if the fast back-to-back enable bit is set in the command register for upstream write
transactions, and in the bridge control register for downstream write transactions. The 21152 does
not perform write combining or merging.
Figure 4.3 shows how multiple memory write transactions can be posted and then initiated as fast
back-to-back transactions on the target bus.
Figure 4.3
Multiple Memory Write Transactions Posted and Initiated as Fast Back-to-Back
Transactions on the Target Bus
CY0
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CY16
Cycle
p_clk
CY1
CY3
CY5
CY7
CY9
CY11
CY13
CY15
CY17
< 15ns >
Addr1
7
Data
Data
Data
Data
Addr2
7
Data
Data
Data
Data
p_ad
Byte Enables 1
Byte Enables 2
p_cbe_l
p_frame_l
p_irdy_l
p_devsel_l
p_trdy_l
p_stop_l
s_clk
Addr1
Data
Data
Data
Data
Addr2
7
Data
Data
Data
Data
s_ad
7
Byte Enables 1
Byte Enables 2
s_cbe_l
s_frame_l
s_irdy_l
s_devsel_l
s_trdy_l
s_stop_l
86%
LJ-04845.AI4
4-10
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
4.6
Read Transactions
Delayed read forwarding is used for all read transactions crossing the 21152.
Delayed read transactions are treated as either prefetchable or nonprefetchable.
Table 4.4 shows the read behavior, prefetchable or nonprefetchable, for each type of read
operation.
Table 4.4
Read Transaction Prefetching
Type of Transaction
Read Behavior
I/O read
Prefetching never done
Prefetching never done
Configuration read
Downstream: Prefetching used if address in prefetchable space
Upstream: Prefetching used if prefetch disable is off (default)
Memory read
Memory read line
Prefetching always used
Prefetching always used
Memory read multiple
See Section 5.3 for detailed information about prefetchable and nonprefetchable address spaces.
4.6.1
Prefetchable Read Transactions
A prefetchable read transaction is a read transaction where the 21152 performs speculative Dword
reads, transferring data from the target before it is requested from the initiator. This behavior allows
a prefetchable read transaction to consist of multiple data transfers. However, byte enable bits
cannot be forwarded for all data phases as is done for the single data phase of the nonprefetchable
read transaction. For prefetchable read transactions, the 21152 forces all byte enable bits to be
turned on for all data phases.
Prefetchable behavior is used for memory read line and memory read multiple transactions, as well
as for memory read transactions that fall into prefetchable memory space.
The amount of data that is prefetched depends on the type of transaction. The amount of
prefetching may also be affected by the amount of free buffer space available in the 21152, and by
any read address boundaries encountered.
Prefetching should not be used for those read transactions that have side effects in the target device,
that is, control and status registers, FIFOs, and so on. The target device’s base address register or
registers indicate if a memory address region is prefetchable.
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-11
PCI Bus Operation
4.6.2
Nonprefetchable Read Transactions
A nonprefetchable read transaction is a read transaction where the 21152 requests 1—and only
1—Dword from the target and disconnects the initiator after delivery of the first Dword of read
data. Unlike prefetchable read transactions, the 21152 forwards the read byte enable information
for the data phase.
Nonprefetchable behavior is used for I/O and configuration read transactions, as well as for
memory read transactions that fall into nonprefetchable memory space.
If extra read transactions could have side effects, for example, when accessing a FIFO, use
nonprefetchable read transactions to those locations. Accordingly, if it is important to retain the
value of the byte enable bits during the data phase, use nonprefetchable read transactions. If these
locations are mapped in memory space, use the memory read command and map the target into
nonprefetchable (memory-mapped I/O) memory space to utilize nonprefetching behavior.
4.6.3
Read Prefetch Address Boundaries
The 21152 imposes internal read address boundaries on read prefetching. When a read transaction
reaches one of these aligned address boundaries, the 21152 stops prefetching data, unless the target
signals a target disconnect before the read prefetch boundary is reached. When the 21152 finishes
transferring this read data to the initiator, it returns a target disconnect with the last data transfer,
unless the initiator completes the transaction before all prefetched read data is delivered. Any
leftover prefetched data is discarded.
Prefetchable read transactions in flow-through mode prefetch to the nearest aligned 4KB address
boundary, or until the initiator deasserts FRAME#. Section 4.6.6 describes flow-through mode
during read operations.
Table 4.5 shows the read prefetch address boundaries for read transactions during
non-flow-through mode.
Table 4.5
Read Prefetch Address Boundaries
Prefetch Aligned
Type of Transaction
Address Space
Cache Line Size
Address Boundary
Configuration read
I/O read
—
—
1 Dword (no prefetch)
1 Dword (no prefetch)
1 Dword (no prefetch)
—
—
Memory read
Memory read
Nonprefetchable
Prefetchable
—
CLS ≠ 1, 2, 4, 8
16-Dword aligned
address boundary
Memory read
Prefetchable
—
CLS = 1, 2, 4, 8
Cache line address
boundary
Memory read line
CLS ≠ 1, 2, 4, 8
16-Dword aligned
address boundary
Memory read line
—
—
—
CLS = 1, 2, 4, 8
CLS ≠ 1, 2, 4, 8
CLS = 1, 2, 4, 8
Cache line boundary
Queue full
Memory read multiple
Memory read multiple
Second cache line
boundary
4-12
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
4.6.4
Delayed Read Requests
The 21152 treats all read transactions as delayed read transactions, which means that the read
request from the initiator is posted into a delayed transaction queue. Read data from the target is
placed in the read data queue directed toward the initiator bus interface and is transferred to the
initiator when the initiator repeats the read transaction.
When the 21152 accepts a delayed read request, it first samples the read address, read bus
command, and address parity. When IRDY# is asserted, the 21152 then samples the byte enable
bits for the first data phase. This information is entered into the delayed transaction queue. The
21152 terminates the transaction by signaling a target retry to the initiator. Upon reception of the
target retry, the initiator is required to continue to repeat the same read transaction until at least one
data transfer is completed, or until a target response other than a target retry (target abort, or master
abort) is received.
4.6.5
Delayed Read Completion with Target
When the delayed read request reaches the head of the delayed transaction queue, and all
previously queued posted write transactions have been delivered, the 21152 arbitrates for the target
bus and initiates the read transaction, using the exact read address and read command captured
from the initiator during the initial delayed read request. If the read transaction is a nonprefetchable
read, the 21152 drives the captured byte enable bits during the next cycle. If the transaction is a
prefetchable read transaction, it drives all byte enable bits to 0 for all data phases. If the 21152
receives a target retry in response to the read transaction on the target bus, it continues to repeat the
read transaction until at least one data transfer is completed, or until an error condition is
encountered. If the transaction is terminated via normal master termination or target disconnect
after at least one data transfer has been completed, the 21152 does not initiate any further attempts
to read more data.
24
If the 21152 is unable to obtain read data from the target after 2 attempts, the 21152 ceases
further read attempts and returns a target abort to the initiator. The delayed transaction is removed
from the delayed transaction queue. The 21152 also asserts p_serr_l if the primary SERR# enable
bit is set in the command register. See Section 7.4 for information on the assertion of p_serr_l.
Once the 21152 receives DEVSEL# and TRDY# from the target, it transfers the data read to the
opposite direction read data queue, pointing toward the opposite interface, before terminating the
transaction. For example, read data in response to a downstream read transaction initiated on the
primary bus is placed in the upstream read data queue. The 21152 can accept 1 Dword of read data
each PCI clock cycle; that is, no master wait states are inserted. The number of Dwords transferred
during a delayed read transaction depends on the conditions given in Table 4.5 (assuming no
disconnect is received from the target).
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-13
PCI Bus Operation
4.6.6
Delayed Read Completion on Initiator Bus
When the transaction has been completed on the target bus, and the delayed read data is at the head
of the read data queue, and all ordering constraints with posted write transactions have been
satisfied, the 21152 transfers the data to the initiator when the initiator repeats the transaction. For
memory read transactions, the 21152 aliases the memory read, memory read line, and memory read
multiple bus commands when matching the bus command of the transaction to the bus command in
the delayed transaction queue. The 21152 returns a target disconnect along with the transfer of the
last Dword of read data to the initiator. If the initiator terminates the transaction before all read data
has been transferred, the remaining read data left in data buffers is discarded.
Figure 4.4 shows a nonprefetchable delayed read transaction.
Figure 4.4
Nonprefetchable Delayed Read Transaction
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p_clk
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< 15ns >
Addr
2
Addr
2
Addr
Data
p_ad
Byte Enables
Byte Enables
2
Byte Enables
p_cbe_l
p_frame_l
p_irdy_l
p_devsel_l
p_trdy_l
p_stop_l
s_clk
Addr
Data
s_ad
2
Byte Enables
s_cbe_l
s_frame_l
s_irdy_l
s_devsel_l
s_trdy_l
s_stop_l
LJ-04846.AI4
4-14
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
Figure 4-5 shows a prefetchable delayed read transaction.
Figure 4-5. Prefetchable Delayed Read Transaction
CY0
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CY14
Data
CY16
Data
CY18
Data
CY20
Data
Cycle
p_clk
CY1
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CY7
CY9
CY11
CY13
Data
CY15
Data
CY17
Data
CY19
Data
CY21
< 15ns >
Addr
6
Addr
6
Addr
6
p_ad
Byte Enables
Byte Enables
Byte Enables
p_cbe_l
p_frame_l
p_irdy_l
p_devsel_l
p_trdy_l
p_stop_l
s_clk
Addr
Data
Data
Data
Data
0
Data
Data
Data
Data
s_ad
6
s_cbe_l
s_frame_l
s_irdy_l
s_devsel_l
s_trdy_l
s_stop_l
73%
LJ-04847.AI4
When the master repeats the transaction and starts transferring prefetchable read data from 21152
data buffers while the read transaction on the target bus is still in progress and before a read
boundary is reached on the target bus, the read transaction starts operating in flow-through mode.
Because data is flowing through the data buffers from the target to the initiator, long read bursts can
then be sustained. In this case, the read transaction is allowed to continue until the initiator
terminates the transaction, or until an aligned 4 KB address boundary is reached, or until the buffer
fills, whichever comes first. When the buffer empties, the 21152 reflects the stalled condition to the
initiator by deasserting TRDY# until more read data is available; otherwise, the 21152 does not
insert any target wait states. When the initiator terminates the transaction, the deassertion of
FRAME# on the initiator bus is forwarded to the target bus. Any remaining read data is discarded.
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-15
PCI Bus Operation
Figure 4-6 shows a flow-through prefetchable read transaction.
Figure 4-6. Flow-Through Prefetchable Read Transaction
CY0
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CY4
CY6
CY8
CY10
CY12
CY14
CY16
CY18
Cycle
p_clk
CY1
CY3
CY5
CY7
CY9
CY11
CY13
CY15
CY17
CY19
<15ns>
Addr
6
Addr
Data
Data
Data
Data
p_ad
Byte Enables
6
Byte Enables
p_cbe_l
p_frame_l
p_irdy_l
p_devsel_l
p_trdy_l
p_stop_l
s_clk
Addr
Data
Data
Data
Data
Data
Data
Data
Data
Data
Data
s_ad
6
0
s_cbe_l
s_frame_l
s_irdy_l
s_devsel_l
s_trdy_l
s_stop_l
78%
LJ-04848.AI4
The 21152 implements a discard timer that starts counting when the delayed read completion is at
the head of the delayed transaction queue, and the read data is at the head of the read data queue.
The initial value of this timer can be set to one of two values, selectable through both the primary
and secondary master time-out value bits in the bridge control register. If the initiator does not
repeat the read transaction before the discard timer expires, the 21152 discards the read transaction
and the read data from its queues. The 21152 also conditionally asserts p_serr_l (see Section 7.4).
The 21152 has the capability to post multiple delayed read requests, up to a maximum of three in
each direction. If an initiator starts a read transaction that matches the address and read command
of a read transaction that is already queued, the current read command is not posted as it is already
contained in the delayed transaction queue.
See Chapter 6 for a discussion of how delayed read transactions are ordered when crossing the
21152.
4-16
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
4.7
Configuration Transactions
Configuration transactions are used to initialize a PCI system. Every PCI device has a
configuration space that is accessed by configuration commands. All 21152 registers are accessible
in configuration space only.
In addition to accepting configuration transactions for initialization of its own configuration space,
the 21152 also forwards configuration transactions for device initialization in hierarchical PCI
systems, as well as for special cycle generation.
To support hierarchical PCI bus systems, two types of configuration transactions are specified:
Type 0 and Type 1.
Type 0 configuration transactions are issued when the intended target resides on the same PCI bus
as the initiator. A Type 0 configuration transaction is identified by the configuration command and
the lowest 2 bits of the address set to 00b.
Type 1 configuration transactions are issued when the intended target resides on another PCI bus,
or when a special cycle is to be generated on another PCI bus. A Type 1 configuration command is
identified by the configuration command and the lowest 2 address bits set to 01b.
Figure 4-7 shows the address formats for Type 0 and Type 1 configuration transactions.
Figure 4-7. Configuration Transaction Address Formats
31
11 10
08 07
02 01 00
Reserved
Func. No.
Register No.
0 0
Type 0
31
24 23
16 15
11 10
08 07
02 01 00
Reserved
Bus Number
Device Number Func. No.
Register No.
0 1
Type 1
LJ-04638.A14
The register number is found in both Type 0 and Type 1 formats and gives the Dword address of the
configuration register to be accessed. The function number is also included in both Type 0 and
Type 1 formats and indicates which function of a multifunction device is to be accessed. For
single-function devices, this value is not decoded. Type 1 configuration transaction addresses also
include a 5-bit field designating the device number that identifies the device on the target PCI bus
that is to be accessed. In addition, the bus number in Type 1 transactions specifies the PCI bus to
which the transaction is targeted.
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-17
PCI Bus Operation
4.7.1
Type 0 Access to the 21152
The 21152 configuration space is accessed by a Type 0 configuration transaction on the primary
interface. The 21152 configuration space cannot be accessed from the secondary bus. The 21152
responds to a Type 0 configuration transaction by asserting p_devsel_l when the following
conditions are met during the address phase:
• The bus command is a configuration read or configuration write transaction.
• Low 2 address bits p_ad<1:0> must be 00b.
• Signal p_idsel must be asserted.
The function code is ignored because the 21152 is a single-function device.
The 21152 limits all configuration accesses to a single Dword data transfer and returns a target
disconnect with the first data transfer if additional data phases are requested. Because read
transactions to 21152 configuration space do not have side effects, all bytes in the requested Dword
are returned, regardless of the value of the byte enable bits.
Type 0 configuration write and read transactions do not use 21152 data buffers; that is, these
transactions are completed immediately, regardless of the state of the data buffers.
The 21152 ignores all Type 0 transactions initiated on the secondary interface.
4.7.2
Type 1 to Type 0 Translation
Type 1 configuration transactions are used specifically for device configuration in a hierarchical PCI bus
system. A PCI-to-PCI bridge is the only type of device that should respond to a Type 1 configuration
command. Type 1 configuration commands are used when configuration access is intended for a PCI
device residing on a PCI bus other than the one where the Type 1 transaction is generated.
The 21152 performs a Type 1 to Type 0 translation when the Type 1 transaction is generated on the
primary bus and is intended for a device attached directly to the secondary bus. The 21152 must
convert the configuration command to a Type 0 format so that the secondary bus device can
respond to it. Type 1 to Type 0 translations are performed only in the downstream direction; that is,
the 21152 generates a Type 0 transaction only on the secondary bus, and never on the primary bus.
The 21152 responds to a Type 1 configuration transaction and translates it into a Type 0 transaction
on the secondary bus when the following conditions are met during the address phase:
• The low 2 address bits on p_ad<1:0> are 01b.
• The bus number in address field p_ad<23:16> is equal to the value in the secondary bus
number register in 21152 configuration space.
• The bus command on p_cbe_l<3:0> is a configuration read or configuration write transaction.
When the 21152 translates the Type 1 transaction to a Type 0 transaction on the secondary
interface, it performs the following translations to the address:
• Sets the low 2 address bits on s_ad<10> to 00b
• Decodes the device number and drives the bit pattern specified in Table 4.6 on s_ad<31:16>
for the purpose of asserting the device’s IDSEL signal
• Sets s_ad<15:11> to 0
• Leaves unchanged the function number and register number fields
4-18
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
The 21152 asserts a unique address line based on the device number. These address lines may be used
as secondary bus IDSEL signals. The mapping of the address lines depends on the device number in
the Type 1 address bits p_ad<15:11>. Table 4.6 presents the mapping that the 21152 uses.
Table 4.6
Device Number to IDSEL s_ad Pin Mapping
Device Number p_ad<15:11>
Secondary IDSEL s_ad<31:16>
s_ad Bit
0h
00000
00001
00010
00011
00100
00101
00110
00111
0000 0000 0000 0001
0000 0000 0000 0010
0000 0000 0000 0100
0000 0000 0000 1000
0000 0000 0001 0000
0000 0000 0010 0000
0000 0000 0100 0000
0000 0000 1000 0000
0000 0001 0000 0000
0000 0010 0000 0000
0000 0100 0000 0000
0000 1000 0000 0000
0001 0000 0000 0000
0010 0000 0000 0000
0100 0000 0000 0000
1000 0000 0000 0000
0000 0000 0000 0000
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
—
1h
2h
3h
4h
5h
6h
7h
8h
01000
01001
01010
01011
01100
01101
01110
9h
Ah
Bh
Ch
Dh
Eh
Fh
01111
10h–1Eh
10000–11110
Generate special cycle (p_ad<7:2> = 00h)
0000 0000 0000 0000 (p_ad<7:2> ≠ 00h)
1Fh
11111
—
The 21152 can assert up to 16 unique address lines to be used as IDSEL signals for up to 16 devices
on the secondary bus, for device numbers ranging from 0 through 15. Because of electrical loading
constraints of the PCI bus, more than 16 IDSEL signals should not be necessary. However, if
device numbers greater than 15 are desired, some external method of generating IDSEL lines must
be used, and no upper address bits are then asserted. The configuration transaction is still translated
and passed from the primary bus to the secondary bus. If no IDSEL pin is asserted to a secondary
device, the transaction ends in a master abort.
The 21152 forwards Type 1 to Type 0 configuration read or write transactions as delayed
transactions. Type 1 to Type 0 configuration read or write transactions are limited to a single 32-bit
data transfer.
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-19
PCI Bus Operation
4.7.3
Type 1 to Type 1 Forwarding
Type 1 to Type 1 transaction forwarding provides a hierarchical configuration mechanism when
two or more levels of PCI-to-PCI bridges are used.
When the 21152 detects a Type 1 configuration transaction intended for a PCI bus downstream
from the secondary bus, the 21152 forwards the transaction unchanged to the secondary bus.
Ultimately, this transaction is translated to a Type 0 configuration command or to a special cycle
transaction by a downstream PCI-to-PCI bridge. Downstream Type 1 to Type 1 forwarding occurs
when the following conditions are met during the address phase:
• The low 2 address bits are equal to 01b.
• The bus number falls in the range defined by the lower limit (exclusive) in the secondary bus
number register and the upper limit (inclusive) in the subordinate bus number register.
• The bus command is a configuration read or write transaction.
The 21152 also supports Type 1 to Type 1 forwarding of configuration write transactions upstream
to support upstream special cycle generation. A Type 1 configuration command is forwarded
upstream when the following conditions are met:
• The low 2 address bits are equal to 01b.
• The bus number falls outside the range defined by the lower limit (inclusive) in the secondary
bus number register and the upper limit (inclusive) in the subordinate bus number register.
• The device number in address bits AD<15:11> is equal to 11111b.
• The function number in address bits AD<10:8> is equal to 111b.
• The bus command is a configuration write transaction.
The 21152 forwards Type 1 to Type 1 configuration write transactions as delayed transactions.
Type 1 to Type 1 configuration write transactions are limited to a single data transfer.
4.7.4
Special Cycles
The Type 1 configuration mechanism is used to generate special cycle transactions in hierarchical
PCI systems. Special cycle transactions are ignored by a PCI-to-PCI bridge acting as a target and
are not forwarded across the bridge. Special cycle transactions can be generated from Type 1
configuration write transactions in either the upstream or the downstream direction.
The 21152 initiates a special cycle on the target bus when a Type 1 configuration write transaction
is detected on the initiating bus and the following conditions are met during the address phase:
• The low 2 address bits on AD<1:0> are equal to 01b.
• The device number in address bits AD<15:11> is equal to 11111b.
• The function number in address bits AD<10:8> is equal to 111b.
• The register number in address bits AD<7:2> is equal to 000000b.
• The bus number is equal to the value in the secondary bus number register in configuration
space for downstream forwarding or equal to the value in the primary bus number register in
configuration space for upstream forwarding.
• The bus command on C/BE# is a configuration write command.
4-20
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
When the 21152 initiates the transaction on the target interface, the bus command is changed from
configuration write to special cycle. The address and data are forwarded unchanged. Devices that
use special cycles ignore the address and decode only the bus command. The data phase contains
the special cycle message. The transaction is forwarded as a delayed transaction, but in this case
the target response is not forwarded back (because special cycles result in a master abort). Once the
transaction is completed on the target bus, through detection of the master abort condition, the
21152 responds with TRDY# to the next attempt of the configuration transaction from the initiator.
If more than one data transfer is requested, the 21152 responds with a target disconnect operation
during the first data phase.
4.8
Transaction Termination
This section describes how the 21152 returns transaction termination conditions back to the
initiator.
• Normal termination
Normal termination occurs when the initiator deasserts FRAME# at the beginning of the last
data phase, and deasserts IRDY# at the end of the last data phase in conjunction with either
TRDY# or STOP# assertion from the target.
• Master abort
A master abort occurs when no target response is detected. When the initiator does not detect a
DEVSEL# from the target within five clock cycles after asserting FRAME#, the initiator
terminates the transaction with a master abort. If FRAME# is still asserted, the initiator
deasserts FRAME# on the next cycle, and then deasserts IRDY# on the following cycle.
IRDY# must be asserted in the same cycle in which FRAME# deasserts. If FRAME# is
already deasserted, IRDY# can be deasserted on the next clock cycle following detection of
the master abort condition.
The target can terminate transactions with one of the following types of termination:
• Normal termination—TRDY# and DEVSEL# asserted in conjunction with FRAME#
deasserted and IRDY# asserted.
• Target retry—STOP# and DEVSEL# asserted without TRDY# during the first data phase. No
data transfers occur during the transaction. This transaction must be repeated.
• Target disconnect with data transfer—STOP# and DEVSEL# asserted with TRDY#. Signals
that this is the last data transfer of the transaction.
• Target disconnect without data transfer—STOP# and DEVSEL# asserted without TRDY#
after previous data transfers have been made. Indicates that no more data transfers will be
made during this transaction.
• Target abort—STOP# asserted without DEVSEL# and without TRDY#. Indicates that the
target will never be able to complete this transaction. DEVSEL# must be asserted for at least
one cycle during the transaction before the target abort is signaled.
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-21
PCI Bus Operation
4.8.1
Master Termination Initiated by the 21152
The 21152, as an initiator, uses normal termination if DEVSEL# is returned by the target within
five clock cycles of the 21152’s assertion of FRAME# on the target bus. As an initiator, the 21152
terminates a transaction when the following conditions are met:
• During a delayed write transaction, a single Dword is delivered.
• During a nonprefetchable read transaction, a single Dword is transferred from the target.
• During a prefetchable read transaction, a prefetch boundary is reached.
• For a posted write transaction, all write data for the transaction is transferred from 21152 data
buffers to the target.
• For a burst transfer, with the exception of memory write and invalidate transactions, the master
latency timer expires and the 21152’s bus grant is deasserted.
• The target terminates the transaction with a retry, disconnect, or target abort.
If the 21152 is delivering posted write data when it terminates the transaction because the master
latency timer expires, it initiates another transaction to deliver the remaining write data. The
address of the transaction is updated to reflect the address of the current Dword to be delivered.
If the 21152 is prefetching read data when it terminates the transaction because the master latency
timer expires, it does not repeat the transaction to obtain more data.
4.8.2
Master Abort Received by the 21152
If the 21152 initiates a transaction on the target bus and does not detect DEVSEL# returned by the
target within five clock cycles of the 21152’s assertion of FRAME#, the 21152 terminates the
transaction with a master abort. The 21152 sets the received master abort bit in the status register
corresponding to the target bus.
For delayed read and write transactions, when the master abort mode bit in the bridge control
register is 0, the 21152 returns TRDY# on the initiator bus and, for read transactions, returns
FFFF FFFFh as data.
When the master abort mode bit is 1, the 21152 returns target abort on the initiator bus. The 21152
also sets the signaled target abort bit in the register corresponding to the initiator bus.
4-22
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
Figure 4.8 shows a delayed write transaction that is terminated with a master abort.
Delayed Write Transaction Terminated with Master Abort
Figure 4.8
CY0
CY2
CY4
CY6
CY8
CY10
CY12
CY14
CY16
Cycle
p_clk
CY1
CY3
CY5
CY7
CY9
CY11
CY13
CY15
< 15ns >
Addr
3
Data
Addr
3
Data
Addr
3
Data
p_ad
Byte Enables
Byte Enables
Byte Enables
p_cbe_l
p_frame_l
p_irdy_l
p_devsel_l
p_trdy_l
p_stop_l
s_clk
Addr
3
Data
s_ad
Byte Enables
s_cbe_l
s_frame_l
s_irdy_l
s_devsel_l
s_trdy_l
s_stop_l
91% LJ-04849.AI4
When a master abort is received in response to a posted write transaction, the 21152 discards the
posted write data and makes no more attempts to deliver the data. The 21152 sets the received
master abort bit in the status register when the master abort is received on the primary bus, or it sets
the received master abort bit in the secondary status register when the master abort is received on
the secondary interface. When a master abort is detected in response to a posted write transaction
and the master abort mode bit is set, the 21152 also asserts p_serr_l if enabled by the SERR#
enable bit in the command register and if not disabled by the device-specific p_serr_l disable bit
for master abort during posted write transactions [that is, master abort mode = 1; SERR# enable
bit = 1; and p_serr_l disable bit for master aborts = 0].
Note: When the 21152 performs a Type 1 to special cycle translation, a master abort is the expected
termination for the special cycle on the target bus. In this case, the master abort received bit is not
set, and the Type 1 configuration transaction is disconnected after the first data phase.
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-23
PCI Bus Operation
4.8.3
Target Termination Received by the 21152
When the 21152 initiates a transaction on the target bus and the target responds with DEVSEL#,
the target can end the transaction with one of the following types of termination:
• Normal termination (upon deassertion of FRAME#)
• Target retry
• Target disconnect
• Target abort
The 21152 handles these terminations in different ways, depending on the type of transaction being
performed.
4.8.3.1
Delayed Write Target Termination Response
When the 21152 initiates a delayed write transaction, the type of target termination received from
the target can be passed back to the initiator.
Table 4.7 shows the 21152 response to each type of target termination that occurs during a delayed
write transaction.
Table 4.7
21152 Response to Delayed Write Target Termination
Target Termination 21152 Response
Return disconnect to initiator with first data transfer only if multiple data phases
requested.
Normal
Target retry
Return target retry to initiator. Continue write attempts to target.
Return disconnect to initiator with first data transfer only if multiple data phases
requested.
Target disconnect
Return target abort to initiator.
Target abort
Set received target abort bit in target interface status register.
Set signaled target abort bit in initiator interface status register.
The 21152 repeats a delayed write transaction until one of the following conditions is met:
• The 21152 completes at least one data transfer.
• The 21152 receives a master abort.
• The 21152 receives a target abort.
24
• The 21152 makes 2 write attempts resulting in a response of target retry.
24
After the 21152 makes 2 attempts of the same delayed write transaction on the target bus, the 21152
asserts p_serr_l if the primary SERR# enable bit is set in the command register and the
implementation-specific p_serr_l disable bit for this condition is not set in the p_serr_l event disable
register. The 21152 stops initiating transactions in response to that delayed write transaction. The
delayed write request is discarded. Upon a subsequent write transaction attempt by the initiator, the
21152 returns a target abort. See Section 7.4 for a description of system error conditions.
4-24
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
4.8.3.2
Posted Write Target Termination Response
When the 21152 initiates a posted write transaction, the target termination cannot be passed back to
the initiator.
Table 4.8 shows the 21152 response to each type of target termination that occurs during a posted
write transaction.
Table 4.8
21152 Response to Posted Write Target Termination
Target Termination 21152 Response
Normal
No additional action.
Target retry
Target disconnect
Repeat write transaction to target.
Initiate write transaction to deliver remaining posted write data.
Set received target abort bit in the target interface status register. Assert p_serr_l if
enabled, and set the signaled primary status register.
Target abort
Note that when a target retry or target disconnect is returned and posted write data associated with
that transaction remains in the write buffers, the 21152 initiates another write transaction to attempt
to deliver the rest of the write data. In the case of a target retry, the exact same address will be
driven as for the initial write transaction attempt. If a target disconnect is received, the address that
is driven on a subsequent write transaction attempt is updated to reflect the address of the current
Dword. If the initial write transaction is a memory write and invalidate transaction, and a partial
delivery of write data to the target is performed before a target disconnect is received, the 21152
uses the memory write command to deliver the rest of the write data because less than a cache line
will be transferred in the subsequent write transaction attempt.
24
After the 21152 makes 2 write transaction attempts and fails to deliver all the posted write data
associated with that transaction, the 21152 asserts p_serr_l if the primary SERR# enable bit is set
in the command register and the device-specific p_serr_l disable bit for this condition is not set in
the p_serr_l event disable register. The write data is discarded. See Section 7.4 for a discussion of
system error conditions.
4.8.3.3
Delayed Read Target Termination Response
When the 21152 initiates a delayed read transaction, the abnormal target responses can be passed
back to the initiator. Other target responses depend on how much data the initiator requests.
Table 4.9 shows the 21152 response to each type of target termination that occurs during a delayed
read transaction.
Table 4.9
21152 Response to Delayed Read Target Termination
Target Termination 21152 Response
If prefetchable, target disconnect only if initiator requests more data than read from
target. If nonprefetchable, target disconnect on first data phase.
Normal
Target retry
Reinitiate read transaction to target.
Target disconnect
If initiator requests more data than read from target, return target disconnect to initiator.
Return target abort to initiator.
Target abort
Set received target abort bit in the target interface status register.
Set signaled target abort bit in the initiator interface status register.
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-25
PCI Bus Operation
Figure 4.9 shows a delayed read transaction that is terminated with a target abort.
Delayed Read Transaction Terminated with Target Abort
Figure 4.9
CY0
CY2
CY4
CY6
CY8
CY10
CY12
CY14
Cycle
p_clk
CY1
CY3
CY5
CY7
CY9
CY11
CY13
< 15ns >
Addr
2
Addr
2
Addr
p_ad
Byte Enables
Byte Enables
2
Byte Enables
p_cbe_l
p_frame_l
p_irdy_l
p_devsel_l
p_trdy_l
p_stop_l
s_clk
Addr
s_ad
2
Byte Enables
s_cbe_l
s_frame_l
s_irdy_l
s_devsel_l
s_trdy_l
s_stop_l
LJ-04850.AI4
The 21152 repeats a delayed read transaction until one of the following conditions is met:
• The 21152 completes at least one data transfer.
• The 21152 receives a master abort.
• The 21152 receives a target abort.
24
• The 21152 makes 2 read attempts resulting in a response of target retry.
24
After the 21152 makes 2 attempts of the same delayed read transaction on the target bus, the
21152 asserts p_serr_l if the primary SERR# enable bit is set in the command register and the
implementation-specific p_serr_l disable bit for this condition is not set in the p_serr_l event
disable register. The 21152 stops initiating transactions in response to that delayed read transaction.
The delayed read request is discarded. Upon a subsequent read transaction attempt by the initiator,
the 21152 returns a target abort. See Section 7.4 for a description of system error conditions.
4-26
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Operation
4.8.4
Target Termination Initiated by the 21152
The 21152 can return a target retry, target disconnect, or target abort to an initiator for reasons other
than detection of that condition at the target interface.
4.8.4.1
Target Retry
The 21152 returns a target retry to the initiator when it cannot accept write data or return read data
as a result of internal conditions. The 21152 returns a target retry to an initiator when any of the
following conditions is met:
• For delayed write transactions:
— The transaction is being entered into the delayed transaction queue.
— The transaction has already been entered into the delayed transaction queue, but target
response has not yet been received.
— Target response has been received but has not progressed to the head of the return queue.
— The delayed transaction queue is full, and the transaction cannot be queued.
— A transaction with the same address and command has been queued.
— A locked sequence is being propagated across the 21152, and the write transaction is not a
locked transaction.
• For delayed read transactions:
— The transaction is being entered into the delayed transaction queue.
— The read request has already been queued, but read data is not yet available.
— Data has been read from the target, but it is not yet at the head of the read data queue, or a
posted write transaction precedes it.
— The delayed transaction queue is full, and the transaction cannot be queued.
— A delayed read request with the same address and bus command has already been queued.
— A locked sequence is being propagated across the 21152, and the read transaction is not a
locked transaction.
— The 21152 is currently discarding previously prefetched read data.
• For posted write transactions:
— The posted write data buffer does not have enough space for address and at least 1 Dword
of write data.
— A locked sequence is being propagated across the 21152, and the write transaction is not a
locked transaction.
When a target retry is returned to the initiator of a delayed transaction, the initiator must repeat the
transaction with the same address and bus command as well as the data if this is a write transaction,
within the time frame specified by the master time-out value; otherwise, the transaction is
discarded from the 21152 buffers.
21152 PCI-to-PCI Bridge Preliminary Datasheet
4-27
PCI Bus Operation
4.8.4.2
Target Disconnect
The 21152 returns a target disconnect to an initiator when one of the following conditions is met:
• The 21152 hits an internal address boundary.
• The 21152 cannot accept any more write data.
• The 21152 has no more read data to deliver.
See Section 4.5.4 for a description of write address boundaries, and Section 4.6.3 for a description
of read address boundaries.
4.8.4.3
Target Abort
The 21152 returns a target abort to an initiator when one of the following conditions is met:
• The 21152 is returning a target abort from the intended target.
• The 21152 is unable to obtain delayed read data from the target or to deliver delayed write data
24
to the target after 2 attempts.
When the 21152 returns a target abort to the initiator, it sets the signaled target abort bit in the status
register corresponding to the initiator interface.
4-28
21152 PCI-to-PCI Bridge Preliminary Datasheet
Address Decoding
5
The 21152 uses three address ranges that control I/O and memory transaction forwarding. These
address ranges are defined by base and limit address registers in the 21152 configuration space.
This chapter describes these address ranges, as well as ISA-mode and VGA-addressing support.
5.1
Address Ranges
The 21152 uses the following address ranges that determine which I/O and memory transactions
are forwarded from the primary PCI bus to the secondary PCI bus, and from the secondary bus to
the primary bus:
• One 32-bit I/O address range
• One 32-bit memory-mapped I/O (nonprefetchable memory)
• One 64-bit prefetchable memory address range
Transactions falling within these ranges are forwarded downstream from the primary PCI bus to
the secondary PCI bus. Transactions falling outside these ranges are forwarded upstream from the
secondary PCI bus to the primary PCI bus.
The 21152 uses a flat address space; that is, it does not perform any address translations. The
address space has no “gaps” — addresses that are not marked for downstream forwarding are
always forwarded upstream.
5.2
I/O Address Decoding
The 21152 uses the following mechanisms that are defined in the 21152 configuration space to
specify the I/O address space for downstream and upstream forwarding:
• I/O base and limit address registers
• The ISA enable bit
• The VGA mode bit
• The VGA snoop bit
This section provides information on the I/O address registers and ISA mode. Section 5.4 provides
information on the VGA modes.
To enable downstream forwarding of I/O transactions, the I/O enable bit must be set in the
command register in 21152 configuration space. If the I/O enable bit is not set, all I/O transactions
initiated on the primary bus are ignored. To enable upstream forwarding of I/O transactions, the
master enable bit must be set in the command register. If the master enable bit is not set, the 21152
ignores all I/O and memory transactions initiated on the secondary bus. Setting the master enable
bit also allows upstream forwarding of memory transactions.
Caution: If any 21152 configuration state affecting I/O transaction forwarding is changed by a configuration
write operation on the primary bus at the same time that I/O transactions are ongoing on the
secondary bus, the 21152 response to the secondary bus I/O transactions is not predictable.
Configure the I/O base and limit address registers, ISA enable bit, VGA mode bit, and VGA snoop
bit before setting the I/O enable and master enable bits, and change them subsequently only when
the primary and secondary PCI buses are idle.
21152 PCI-to-PCI Bridge Preliminary Datasheet
5-1
Address Decoding
5.2.1
I/O Base and Limit Address Registers
The 21152 implements one set of I/O base and limit address registers in configuration space that define
an I/O address range for downstream forwarding. The 21152 supports 32-bit I/O addressing, which
allows I/O addresses downstream of the 21152 to be mapped anywhere in a 4 GB I/O address space.
I/O transactions with addresses that fall inside the range defined by the I/O base and limit registers
are forwarded downstream from the primary PCI bus to the secondary PCI bus. I/O transactions
with addresses that fall outside this range are forwarded upstream from the secondary PCI bus to
the primary PCI bus.
The I/O range can be turned off by setting the I/O base address to a value greater than that of the
I/O limit address. When the I/O range is turned off, all I/O transactions are forwarded upstream,
and no I/O transactions are forwarded downstream.
Figure 5-1 illustrates transaction forwarding within and outside the I/O address range.
Figure 5-1. I/O Transaction Forwarding Using Base and Limit Addresses
Primary
Interface
Secondary
Interface
I/O Limit
I/O Base
4KB
Multiple
I/O Address Space
LJ-04636.AI4
The 21152 I/O range has a minimum granularity of 4 KB and is aligned on a 4 KB boundary. The
maximum I/O range is 4 GB in size.
The I/O base register consists of an 8-bit field at configuration address 1Ch, and a 16-bit field at
address 30h. The top 4 bits of the 8-bit field define bits <15:12> of the I/O base address. The
bottom 4 bits read only as 1h to indicate that the 21152 supports 32-bit I/O addressing. Bits <11:0>
of the base address are assumed to be 0, which naturally aligns the base address to a 4 KB
boundary. The 16 bits contained in the I/O base upper 16 bits register at configuration offset 30h
define AD<31:16> of the I/O base address. All 16 bits are read/write. After primary bus reset or
chip reset, the value of the I/O base address is initialized to 0000 0000h.
5-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
Address Decoding
The I/O limit register consists of an 8-bit field at configuration offset 1Dh and a 16-bit field at
offset 32h. The top 4 bits of the 8-bit field define bits <15:12> of the I/O limit address. The bottom
4 bits read only as 1h to indicate that 32-bit I/O addressing is supported. Bits <11:0> of the limit
address are assumed to be FFFh, which naturally aligns the limit address to the top of a 4 KB I/O
address block. The 16 bits contained in the I/O limit upper 16 bits register at configuration offset
32h define AD<31:16> of the I/O limit address. All 16 bits are read/write. After primary bus reset
or chip reset, the value of the I/O limit address is reset to 0000 0FFFh.
Note: The initial states of the I/O base and I/O limit address registers define an I/O range of 0000 0000h
to 0000 0FFFh, which is the bottom 4 KB of I/O space. Write these registers with their appropriate
values before setting either the I/O enable bit or the master enable bit in the command register in
configuration space.
5.2.2
ISA Mode
The 21152 supports ISA mode by providing an ISA enable bit in the bridge control register in
configuration space. ISA mode modifies the response of the 21152 inside the I/O address range in
order to support mapping of I/O space in the presence of an ISA bus in the system. This bit only
affects the response of the 21152 when the transaction falls inside the address range defined by the
I/O base and limit address registers, and only when this address also falls inside the first 64 KB of
I/O space (address bits <31:16> are 0000h).
When the ISA enable bit is set, the 21152 does not forward downstream any I/O transactions
addressing the top 768 bytes of each aligned 1 KB block. Only those transactions addressing the
bottom 256 bytes of an aligned 1 KB block inside the base and limit I/O address range are
forwarded downstream. Transactions above the 64 KB I/O address boundary are forwarded as
defined by the address range defined by the I/O base and limit registers.
Accordingly, if the ISA enable bit is set, the 21152 forwards upstream those I/O transactions
addressing the top 768 bytes of each aligned 1 KB block within the first 64 KB of I/O space. The
master enable bit in the command configuration register must also be set to enable upstream
forwarding. All other I/O transactions initiated on the secondary bus are forwarded upstream only
if they fall outside the I/O address range.
When the ISA enable bit is set, devices downstream of the 21152 can have I/O space mapped into
the first 256 bytes of each 1 KB chunk below the 64 KB boundary, or anywhere in I/O space above
the 64 KB boundary.
21152 PCI-to-PCI Bridge Preliminary Datasheet
5-3
Address Decoding
Figure 5-2 illustrates I/O forwarding when the ISA enable bit is set
Figure 5-2. I/O Transaction Forwarding in ISA Mode.
Primary
Interface
Secondary
Interface
5000h - FFFFh
4D00h - 4FFFh
4C00h - 4CFFh
4900h - 4BFFh
4800h - 48FFh
4500h - 47FFh
4400h - 44FFh
4100h - 43FFh
4000h - 40FFh
5000h - FFFFh
I/O Address Space
Note:
In this example:
I/O Base Address = 0000 4000h
I/O Limit Address = 0000 4 FFFh
ISA Enable = 1
A5933-01
5.3
Memory Address Decoding
The 21152 has three mechanisms for defining memory address ranges for forwarding of memory
transactions:
• Memory-mapped I/O base and limit address registers
• Prefetchable memory base and limit address registers
• VGA mode
This section describes the first two mechanisms. Section 5.4.1 describes VGA mode.
To enable downstream forwarding of memory transactions, the memory enable bit must be set in
the command register in 21152 configuration space. To enable upstream forwarding of memory
transactions, the master enable bit must be set in the command register. Setting the master enable
bit also allows upstream forwarding of I/O transactions.
Caution: If any 21152 configuration state affecting memory transaction forwarding is changed by a
configuration write operation on the primary bus at the same time that memory transactions are
ongoing on the secondary bus, 21152 response to the secondary bus memory transactions is not
predictable. Configure the memory-mapped I/O base and limit address registers, prefetchable memory
5-4
21152 PCI-to-PCI Bridge Preliminary Datasheet
Address Decoding
base and limit address registers, and VGA mode bit before setting the memory enable and master
enable bits, and change them subsequently only when the primary and secondary PCI buses are idle.
5.3.1
Memory-Mapped I/O Base and Limit Address Registers
Memory-mapped I/O is also referred to as nonprefetchable memory. Memory addresses that cannot
automatically be prefetched but that can conditionally prefetch based on command type should be
mapped into this space. Read transactions to nonprefetchable space may exhibit side effects; this
space may have non-memory-like behavior. The 21152 prefetches in this space only if the memory
read line or memory read multiple commands are used; transactions using the memory read
command are limited to a single data transfer.
The memory-mapped I/O base address and memory-mapped I/O limit address registers define an
address range that the 21152 uses to determine when to forward memory commands. The 21152
forwards a memory transaction from the primary to the secondary interface if the transaction
address falls within the memory-mapped I/O address range. The 21152 ignores memory
transactions initiated on the secondary interface that fall into this address range. Any transactions
that fall outside this address range are ignored on the primary interface and are forwarded upstream
from the secondary interface (provided that they do not fall into the prefetchable memory range or
are not forwarded downstream by the VGA mechanism).
The memory-mapped I/O range supports 32-bit addressing only. The PCI-to-PCI Bridge
Architecture Specification does not provide for 64-bit addressing in the memory-mapped I/O space.
The memory-mapped I/O address range has a granularity and alignment of 1 MB. The maximum
memory-mapped I/O address range is 4 GB.
The memory-mapped I/O address range is defined by a 16-bit memory-mapped I/O base address
register at configuration offset 20h and by a 16-bit memory-mapped I/O limit address register at
offset 22h. The top 12 bits of each of these registers correspond to bits <31:20> of the memory
address. The low 4 bits are hardwired to 0. The low 20 bits of the memory-mapped I/O base
address are assumed to be 0 0000h, which results in a natural alignment to a 1MB boundary. The
low 20 bits of the memory-mapped I/O limit address are assumed to be F FFFFh, which results in
an alignment to the top of a 1MB block.
Note: The initial state of the memory-mapped I/O base address register is 0000 0000h. The initial state of
the memory-mapped I/O limit address register is 000F FFFFh. Note that the initial states of these
registers define a memory-mapped I/O range at the bottom 1MB block of memory. Write these
registers with their appropriate values before setting either the memory enable bit or the master
enable bit in the command register in configuration space.
To turn off the memory-mapped I/O address range, write the memory-mapped I/O base address
register with a value greater than that of the memory-mapped I/O limit address register.
21152 PCI-to-PCI Bridge Preliminary Datasheet
5-5
Address Decoding
Figure 5-3 shows how transactions are forwarded using both the memory-mapped I/O range and
the prefetchable memory range.
Figure 5-3. Memory Transaction Forwarding Using Base and Limit Registers
Primary
Interface
Secondary
Interface
DAC
DAC
DAC
Prefetchable Memory Limit
Prefetchable Memory Base
1MB
Multiple
DAC
4GB
SAC
SAC
SAC
SAC
SAC
Memory-Mapped I/O Limit
Memory-Mapped I/O Base
SAC
SAC
1MB
Multiple
SAC
Memory Address Space
Note:
DAC – Dual Address Cycle
SAC – Single Address Cycle
LJ-04639.AI4
5-6
21152 PCI-to-PCI Bridge Preliminary Datasheet
Address Decoding
5.3.2
Prefetchable Memory Base and Limit Address Registers
Locations accessed in the prefetchable memory address range must have true memory-like
behavior and must not exhibit side effects when read. This means that extra reads to a prefetchable
memory location must have no side effects. The 21152 prefetches for all types of memory read
commands in this address space.
The prefetchable memory base address and prefetchable memory limit address registers define an
address range that the 21152 uses to determine when to forward memory commands. The 21152
forwards a memory transaction from the primary to the secondary interface if the transaction
address falls within the prefetchable memory address range. The 21152 ignores memory
transactions initiated on the secondary interface that fall into this address range. The 21152 does
not respond to any transactions that fall outside this address range on the primary interface and
forwards those transactions upstream from the secondary interface (provided that they do not fall
into the memory-mapped I/O range or are not forwarded by the VGA mechanism).
The prefetchable memory range supports 64-bit addressing and provides additional registers to
define the upper 32 bits of the memory address range, the prefetchable memory base address upper
32 bits register, and the prefetchable memory limit address upper 32 bits register. For address
comparison, a single address cycle (32-bit address) prefetchable memory transaction is treated like
a 64-bit address transaction where the upper 32 bits of the address are equal to 0. This upper 32-bit
value of 0 is compared to the prefetchable memory base address upper 32 bits register and the
prefetchable memory limit address upper 32 bits register. The prefetchable memory base address
upper 32 bits register must be 0 in order to pass any single address cycle transactions downstream.
Section 5.3.3 further describes 64-bit addressing support.
The prefetchable memory address range has a granularity and alignment of 1 MB. The maximum
24
memory address range is 4 GB when 32-bit addressing is used, and 2 bytes when 64-bit
addressing is used.
The prefetchable memory address range is defined by a 16-bit prefetchable memory base address
register at configuration offset 24h and by a 16-bit prefetchable memory limit address register at
offset 28h. The top 12 bits of each of these registers correspond to bits <31:20> of the memory
address. The low 4 bits are hardwired to 1h, indicating 64-bit address support. The low 20 bits of
the prefetchable memory base address are assumed to be 0 0000h, which results in a natural
alignment to a 1 MB boundary. The low 20 bits of the prefetchable memory limit address are
assumed to be F FFFFh, which results in an alignment to the top of a 1 MB block.
Note: The initial state of the prefetchable memory base address register is 0000 0000h. The initial state of
the prefetchable memory limit address register is 000F FFFFh. Note that the initial states of these
registers define a prefetchable memory range at the bottom 1 MB block of memory. Write these
registers with their appropriate values before setting either the memory enable bit or the master
enable bit in the command register in configuration space.
To turn off the prefetchable memory address range, write the prefetchable memory base address
register with a value greater than that of the prefetchable memory limit address register. The entire
base value must be greater than the entire limit value, meaning that the upper 32 bits must be
considered. Therefore, to disable the address range, the upper 32 bits registers can both be set to the
same value, while the lower base register is set greater than the lower limit register; otherwise, the
upper 32-bit base must be greater than the upper 32-bit limit.
21152 PCI-to-PCI Bridge Preliminary Datasheet
5-7
Address Decoding
5.3.3
Prefetchable Memory 64-Bit Addressing Registers
The 21152 supports 64-bit memory address decoding for forwarding of dual-address memory
transactions. The dual-address cycle is used to support 64-bit addressing. The first address phase of a
dual-address transaction contains the low 32 address bits, and the second address phase contains the
high 32 address bits. During a dual-address cycle transaction, the upper 32 bits must never be 0—use
the single address cycle commands for transactions addressing the first 4GB of memory space.
The 21152 implements the prefetchable memory base address upper 32 bits register and the
prefetchable memory limit address upper 32 bits register to define a prefetchable memory address
range greater than 4 GB. The prefetchable address space can then be defined in three different
ways:
• Residing entirely in the first 4 GB of memory
• Residing entirely above the first 4 GB of memory
• Crossing the first 4 GB memory boundary
If the prefetchable memory space on the secondary interface resides entirely in the first 4GB of
memory, both upper 32 bits registers must be set to 0. The 21152 ignores all dual-address cycle
transactions initiated on the primary interface and forwards all dual-address transactions initiated
on the secondary interface upstream.
If the secondary interface prefetchable memory space resides entirely above the first 4 GB of
memory, both the prefetchable memory base address upper 32 bits register and the prefetchable
memory limit address upper 32 bits register must be initialized to nonzero values. The 21152
ignores all single address memory transactions initiated on the primary interface and forwards all
single address memory transactions initiated on the secondary interface upstream (unless they fall
within the memory-mapped I/O or VGA memory range). A dual-address memory transaction is
forwarded downstream from the primary interface if it falls within the address range defined by the
prefetchable memory base address, prefetchable memory base address upper 32 bits, prefetchable
memory limit address, and prefetchable memory limit address upper 32 bits registers. If the
dual-address transaction initiated on the secondary interface falls outside this address range, it is
forwarded upstream to the primary interface. The 21152 does not respond to a dual-address
transaction initiated on the primary interface that falls outside this address range, or to a
dual-address transaction initiated on the secondary interface that falls within the address range.
If the secondary interface prefetchable memory space straddles the first 4 GB address boundary,
the prefetchable memory base address upper 32 bits register is set to 0, while the prefetchable
memory limit address upper 32 bits register is initialized to a nonzero value. Single address cycle
memory transactions are compared to the prefetchable memory base address register only. A
transaction initiated on the primary interface is forwarded downstream if the address is greater than
or equal to the base address. A transaction initiated on the secondary interface is forwarded
upstream if the address is less than the base address. Dual-address transactions are compared to the
prefetchable memory limit address and the prefetchable memory limit address upper 32 bits
registers. If the address of the dual-address transaction is less than or equal to the limit, the
transaction is forwarded downstream from the primary interface and is ignored on the secondary
interface. If the address of the dual-address transaction is greater than this limit, the transaction is
ignored on the primary interface and is forwarded upstream from the secondary interface.
The prefetchable memory base address upper 32 bits register is located at configuration Dword
offset 28h, and the prefetchable memory limit address upper 32 bits register is located at
configuration Dword offset 2Ch. Both registers are reset to 0. See Figure 5-3 for an illustration of
how transactions are forwarded using both the memory-mapped I/O range and the prefetchable
memory range.
5-8
21152 PCI-to-PCI Bridge Preliminary Datasheet
Address Decoding
5.4
VGA Support
The 21152 provides two modes for VGA support:
• VGA mode, supporting VGA-compatible addressing
• VGA snoop mode, supporting VGA palette forwarding
5.4.1
VGA Mode
When a VGA-compatible device exists downstream from the 21152, set the VGA mode bit in the
bridge control register in configuration space to enable VGA mode. When the 21152 is operating in
VGA mode, it forwards downstream those transactions addressing the VGA frame buffer memory
and VGA I/O registers, regardless of the values of the 21152 base and limit address registers. The
21152 ignores transactions initiated on the secondary interface addressing these locations.
The VGA frame buffer consists of the following memory address range:
000A 0000h–000B FFFFh
Read transactions to frame buffer memory are treated as nonprefetchable. The 21152 requests only
a single data transfer from the target, and read byte enable bits are forwarded to the target bus.
The VGA I/O addresses consist of the following I/O addresses:
• 3B0h–3BBh
• 3C0h–3DFh
These I/O addresses are aliased every 1 KB throughout the first 64 KB of I/O space. This means that
address bits <15:10> are not decoded and can be any value, while address bits <31:16> must be all 0s.
VGA BIOS addresses starting at C0000h are not decoded in VGA mode.
5.4.2
VGA Snoop Mode
The 21152 provides VGA snoop mode, allowing for VGA palette write transactions to be
forwarded downstream. This mode is used when a graphics device downstream from the 21152
needs to snoop or respond to VGA palette write transactions. To enable the mode, set the VGA
snoop bit in the command register in configuration space.
Note that the 21152 claims VGA palette write transactions by asserting DEVSEL# in VGA snoop
mode.
When the VGA snoop bit is set, the 21152 forwards downstream transactions with the following
I/O addresses:
• 3C6h
• 3C8h
• 3C9h
21152 PCI-to-PCI Bridge Preliminary Datasheet
5-9
Address Decoding
Note that these addresses are also forwarded as part of the VGA compatibility mode previously
described. Again, address bits <15:10> are not decoded, while address bits <31:16> must be equal
to 0, which means that these addresses are aliased every 1 KB throughout the first 64 KB of I/O
space.
Note: If both the VGA mode bit and the VGA snoop bit are set, the 21152 behaves in the same way as if
only the VGA mode bit were set.
5-10
21152 PCI-to-PCI Bridge Preliminary Datasheet
Transaction Ordering
6
To maintain data coherency and consistency, the 21152 complies with the ordering rules set forth in
the PCI Local Bus Specification, Revision 2.1, for transactions crossing the bridge.
This chapter describes the ordering rules that control transaction forwarding across the 21152. For
a more detailed discussion of transaction ordering, see Appendix E of the PCI Local Bus
Specification, Revision 2.1.
6.1
Transactions Governed by Ordering Rules
Ordering relationships are established for the following classes of transactions crossing the 21152:
• Posted write transactions, comprised of memory write and memory write and invalidate
transactions.
Posted write transactions complete at the source before they complete at the destination; that
is, data is written into intermediate data buffers before it reaches the target.
• Delayed write request transactions, comprised of I/O write and configuration write transactions.
Delayed write requests are terminated by target retry on the initiator bus and are queued in the
delayed transaction queue. A delayed write transaction must complete on the target bus before
it completes on the initiator bus.
• Delayed write completion transactions, also comprised of I/O write and configuration write
transactions.
Delayed write completion transactions have been completed on the target bus, and the target
response is queued in the 21152 buffers. A delayed write completion transaction proceeds in
the direction opposite that of the original delayed write request; that is, a delayed write
completion transaction proceeds from the target bus to the initiator bus.
• Delayed read request transactions, comprised of all memory read, I/O read, and configuration
read transactions.
Delayed read requests are terminated by target retry on the initiator bus and are queued in the
delayed transaction queue.
• Delayed read completion transactions, comprised of all memory read, I/O read, and
configuration read transactions.
Delayed read completion transactions have been completed on the target bus, and the read data
has been queued in the 21152 read data buffers. A delayed read completion transaction
proceeds in the direction opposite that of the original delayed read request; that is, a delayed
read completion transaction proceeds from the target bus to the initiator bus.
The 21152 does not combine or merge write transactions:
• The 21152 does not combine separate write transactions into a single write transaction—this
optimization is best implemented in the originating master.
• The 21152 does not merge bytes on separate masked write transactions to the same Dword
address—this optimization is also best implemented in the originating master.
• The 21152 does not collapse sequential write transactions to the same address into a single write
transaction—the PCI Local Bus Specification does not permit this combining of transactions.
21152 PCI-to-PCI Bridge Preliminary Datasheet
6-1
Transaction Ordering
6.2
General Ordering Guidelines
Independent transactions on the primary and secondary buses have a relationship only when those
transactions cross the 21152.
The following general ordering guidelines govern transactions crossing the 21152:
• The ordering relationship of a transaction with respect to other transactions is determined
when the transaction completes, that is, when a transaction ends with a termination other than
target retry.
• Requests terminated with target retry can be accepted and completed in any order with respect
to other transactions that have been terminated with target retry. If the order of completion of
delayed requests is important, the initiator should not start a second delayed transaction until
the first one has been completed. If more than one delayed transaction is initiated, the initiator
should repeat all the delayed transaction requests, using some fairness algorithm. Repeating a
delayed transaction cannot be contingent on completion of another delayed transaction;
otherwise, a deadlock can occur.
• Write transactions flowing in one direction have no ordering requirements with respect to
write transactions flowing in the other direction. The 21152 can accept posted write
transactions on both interfaces at the same time, as well as initiate posted write transactions on
both interfaces at the same time.
• The acceptance of a posted memory write transaction as a target can never be contingent on
the completion of a nonlocked, nonposted transaction as a master. This is true of the 21152 and
must also be true of other bus agents; otherwise, a deadlock can occur.
• The 21152 accepts posted write transactions, regardless of the state of completion of any
delayed transactions being forwarded across the 21152.
6-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
Transaction Ordering
6.3
Ordering Rules
Table 6-1 shows the ordering relationships of all the transactions and refers by number to the
ordering rules that follow.
Table 6-1.
Summary of Transaction Ordering
Posted Delayed Read
Delayed Write
Request
Yes5
Delayed Read
Completion
Delayed Write
Completion
↓ Pass→
Write
No1
No2
Request
Yes5
No
Posted write
Yes5
Yes
Yes
No
Yes5
Yes
Yes
No
Delayed read request
No
Delayed write request
No4
No
No
Delayed read completion No3
Yes
Yes
Yes
Delayed write completion Yes
Yes
No
No
Note: The superscript accompanying some of the table entries refers to any applicable ordering rule listed
in this section. Many entries are not governed by these ordering rules; therefore, the
implementation can choose whether or not the transactions pass each other.
The entries without superscripts reflect the 21152’s implementation choices.
The following ordering rules describe the transaction relationships. Each ordering rule is followed by
an explanation, and the ordering rules are referred to by number in Table 6-1. These ordering rules
apply to posted write transactions, delayed write and read requests, and delayed write and read
completion transactions crossing the 21152 in the same direction. Note that delayed completion
transactions cross the 21152 in the direction opposite that of the corresponding delayed requests.
1. Posted write transactions must complete on the target bus in the order in which they were
received on the initiator bus.
The subsequent posted write transaction can be setting a flag that covers the data in the first
posted write transaction; if the second transaction were to complete before the first transaction,
a device checking the flag could subsequently consume stale data.
2. A delayed read request traveling in the same direction as a previously queued posted write
transaction must push the posted write data ahead of it. The posted write transaction must
complete on the target bus before the delayed read request can be attempted on the target bus.
The read transaction can be to the same location as the write data, so if the read transaction
were to pass the write transaction, it would return stale data.
3. A delayed read completion must “pull” ahead of previously queued posted write data traveling
in the same direction. In this case, the read data is traveling in the same direction as the write
data, and the initiator of the read transaction is on the same side of the 21152 as the target of
the write transaction. The posted write transaction must complete to the target before the read
data is returned to the initiator.
The read transaction can be to a status register of the initiator of the posted write data and
therefore should not complete until the write transaction is complete.
4. Delayed write requests cannot pass previously queued posted write data.
As in the case of posted memory write transactions, the delayed write transaction can be
setting a flag that covers the data in the posted write transaction; if the delayed write request
were to complete before the earlier posted write transaction, a device checking the flag could
subsequently consume stale data.
21152 PCI-to-PCI Bridge Preliminary Datasheet
6-3
Transaction Ordering
5. Posted write transactions must be given opportunities to pass delayed read and write requests
and completions.
Otherwise, deadlocks may occur when bridges that support delayed transactions are used in
the same system with bridges that do not support delayed transactions. A fairness algorithm is
used to arbitrate between the posted write queue and the delayed transaction queue.
6.4
Data Synchronization
Data synchronization refers to the relationship between interrupt signaling and data delivery. The
PCI Local Bus Specification, Revision 2.1, provides the following alternative methods for
synchronizing data and interrupts:
• The device signaling the interrupt performs a read of the data just written (software).
• The device driver performs a read operation to any register in the interrupting device before
accessing data written by the device (software).
• System hardware guarantees that write buffers are flushed before interrupts are forwarded.
The 21152 does not have a hardware mechanism to guarantee data synchronization for posted write
transactions. Therefore, all posted write transactions must be followed by a read operation, either
from the device to the location just written (or some other location along the same path), or from
the device driver to one of the device registers.
6-4
21152 PCI-to-PCI Bridge Preliminary Datasheet
Error Handling
7
The 21152 checks, forwards, and generates parity on both the primary and secondary interfaces. To
maintain transparency, the 21152 always tries to forward the existing parity condition on one bus to the
other bus, along with address and data. The 21152 always attempts to be transparent when reporting
errors, but this is not always possible, given the presence of posted data and delayed transactions.
To support error reporting on the PCI bus, the 21152 implements the following:
• PERR# and SERR# signals on both the primary and secondary interfaces
• Primary status and secondary status registers
• The device-specific p_serr_l event disable register
• The device-specific p_serr_l status register
This chapter provides detailed information about how the 21152 handles errors. It also describes
error status reporting and error operation disabling.
7.1
Address Parity Errors
The 21152 checks address parity for all transactions on both buses (all address and all bus commands).
When the 21152 detects an address parity error on the primary interface, the following occurs:
• If the parity error response bit is set in the command register, the 21152 does not claim the
transaction with p_devsel_l; this may allow the transaction to terminate in a master abort.
If the parity error response bit is not set, the 21152 proceeds normally and accepts the
transaction if it is directed to or across the 21152.
• The 21152 sets the detected parity error bit in the status register.
• The 21152 asserts p_serr_l and sets the signaled system error bit in the status register, if both
of the following conditions are met:
— The SERR# enable bit is set in the command register.
— The parity error response bit is set in the command register.
When the 21152 detects an address parity error on the secondary interface, the following occurs:
• If the parity error response bit is set in the bridge control register, the 21152 does not claim the
transaction with s_devsel_l; this may allow the transaction to terminate in a master abort.
If the parity error response bit is not set, the 21152 proceeds normally and accepts the
transaction if it is directed to or across the 21152.
• The 21152 sets the detected parity error bit in the secondary status register.
• The 21152 asserts p_serr_l and sets the signaled system error bit in the status register, if both
of the following conditions are met:
— The SERR# enable bit is set in the command register.
— The parity error response bit is set in the bridge control register.
21152 PCI-to-PCI Bridge Preliminary Datasheet
7-1
Error Handling
7.2
Data Parity Errors
When forwarding transactions, the 21152 attempts to pass the data parity condition from one
interface to the other unchanged, whenever possible, to allow the master and target devices to
handle the error condition.
The following sections describe, for each type of transaction, the sequence of events that occurs when
a parity error is detected and the way in which the parity condition is forwarded across the 21152.
7.2.1
Configuration Write Transactions to 21152 Configuration
Space
When the 21152 detects a data parity error during a Type 0 configuration write transaction to 21152
configuration space, the following events occur:
• If the parity error response bit is set in the command register, the 21152 asserts p_trdy_l and
writes the data to the configuration register. The 21152 also asserts p_perr_l.
• If the parity error response bit is not set, the 21152 does not assert p_perr_l.
• The 21152 sets the detected parity error bit in the status register, regardless of the state of the
parity error response bit.
7.2.2
Read Transactions
When the 21152 detects a parity error during a read transaction, the target drives data and data
parity, and the initiator checks parity and conditionally asserts PERR#.
For downstream transactions, when the 21152 detects a read data parity error on the secondary bus,
the following events occur:
• The 21152 asserts s_perr_l two cycles following the data transfer, if the secondary interface
parity error response bit is set in the bridge control register.
• The 21152 sets the detected parity error bit in the secondary status register.
• The 21152 sets the data parity detected bit in the secondary status register, if the secondary
interface parity error response bit is set in the bridge control register.
• The 21152 forwards the bad parity with the data back to the initiator on the primary bus.
If the data with the bad parity is prefetched and is not read by the initiator on the primary bus,
the data is discarded and the data with bad parity is not returned to the initiator.
• The 21152 completes the transaction normally.
7-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
Error Handling
For upstream transactions, when the 21152 detects a read data parity error on the primary bus, the
following events occur:
• The 21152 asserts p_perr_l two cycles following the data transfer, if the primary interface
parity error response bit is set in the command register.
• The 21152 sets the detected parity error bit in the primary status register.
• The 21152 sets the data parity detected bit in the primary status register, if the primary
interface parity error response bit is set in the command register.
• The 21152 forwards the bad parity with the data back to the initiator on the secondary bus.
If the data with the bad parity is prefetched and is not read by the initiator on the secondary
bus, the data is discarded and the data with bad parity is not returned to the initiator.
• The 21152 completes the transaction normally.
The 21152 returns to the initiator the data and parity that was received from the target. When the
initiator detects a parity error on this read data and is enabled to report it, the initiator asserts
PERR# two cycles after the data transfer occurs. It is assumed that the initiator takes responsibility
for handling a parity error condition; therefore, when the 21152 detects PERR# asserted while
returning read data to the initiator, the 21152 does not take any further action and completes the
transaction normally.
7.2.3
Delayed Write Transactions
When the 21152 detects a data parity error during a delayed write transaction, the initiator drives
data and data parity, and the target checks parity and conditionally asserts PERR#.
For delayed write transactions, a parity error can occur at the following times:
• During the original delayed write request transaction
• When the initiator repeats the delayed write request transaction
• When the 21152 completes the delayed write transaction to the target
When a delayed write transaction is normally queued, the address, command, address parity, data,
byte enable bits, and data parity are all captured and a target retry is returned to the initiator. When
the 21152 detects a parity error on the write data for the initial delayed write request transaction,
the following events occur:
• If the parity error response bit corresponding to the initiator bus is set, the 21152 asserts
TRDY# to the initiator and the transaction is not queued. If multiple data phases are requested,
STOP# is also asserted to cause a target disconnect. Two cycles after the data transfer, the
21152 also asserts PERR#.
If the parity error response bit is not set, the 21152 returns a target retry and queues the
transaction as usual. Signal PERR# is not asserted. In this case, the initiator repeats the
transaction.
• The 21152 sets the detected parity error bit in the status register corresponding to the initiator
bus, regardless of the state of the parity error response bit.
Note: If parity checking is turned off and data parity errors have occurred for queued or subsequent
delayed write transactions on the initiator bus, it is possible that the initiator’s reattempts of the
write transaction may not match the original queued delayed write information contained in the
delayed transaction queue. In this case, a master timeout condition may occur, possibly resulting in
a system error (p_serr_l assertion).
21152 PCI-to-PCI Bridge Preliminary Datasheet
7-3
Error Handling
For downstream transactions, when the 21152 is delivering data to the target on the secondary bus
and s_perr_l is asserted by the target, the following events occur:
• The 21152 sets the secondary interface data parity detected bit in the secondary status register,
if the secondary parity error response bit is set in the bridge control register.
• The 21152 captures the parity error condition to forward it back to the initiator on the primary bus.
Similarly, for upstream transactions, when the 21152 is delivering data to the target on the primary
bus and p_perr_l is asserted by the target, the following events occur:
• The 21152 sets the primary interface data parity detected bit in the status register, if the
primary parity error response bit is set in the command register.
• The 21152 captures the parity error condition to forward it back to the initiator on the
secondary bus.
A delayed write transaction is completed on the initiator bus when the initiator repeats the write
transaction with the same address, command, data, and byte enable bits as the delayed write
command that is at the head of the posted data queue. Note that the parity bit is not compared when
determining whether the transaction matches those in the delayed transaction queues.
Two cases must be considered:
• When parity error is detected on the initiator bus on a subsequent reattempt of the transaction
and was not detected on the target bus
• When parity error is forwarded back from the target bus
For downstream delayed write transactions, when the parity error is detected on the initiator bus
and the 21152 has write status to return, the following events occur:
• The 21152 first asserts p_trdy_l and then asserts p_perr_l two cycles later, if the primary
interface parity error response bit is set in the command register.
• The 21152 sets the primary interface parity error detected bit in the status register.
• Because there was not an exact data and parity match, the write status is not returned and the
transaction remains in the queue.
Similarly, for upstream delayed write transactions, when the parity error is detected on the initiator
bus and the 21152 has write status to return, the following events occur:
• The 21152 first asserts s_trdy_l and then asserts s_perr_l two cycles later, if the secondary
interface parity error response bit is set in the bridge control register.
• The 21152 sets the secondary interface parity error detected bit in the secondary status register.
• Because there was not an exact data and parity match, the write status is not returned and the
transaction remains in the queue.
For downstream transactions, in the case where the parity error is being passed back from the target
bus and the parity error condition was not originally detected on the initiator bus, the following
events occur:
• The 21152 asserts p_perr_l two cycles after the data transfer, if both of the following are true:
— The primary interface parity error response bit is set in the command register.
— The secondary interface parity error response bit is set in the bridge control register.
• The 21152 completes the transaction normally.
7-4
21152 PCI-to-PCI Bridge Preliminary Datasheet
Error Handling
For upstream transactions, in the case where the parity error is being passed back from the target
bus and the parity error condition was not originally detected on the initiator bus, the following
events occur:
• The 21152 asserts s_perr_l two cycles after the data transfer, if both of the following are true:
— The primary interface parity error response bit is set in the command register.
— The secondary interface parity error response bit is set in the bridge control register.
• The 21152 completes the transaction normally.
7.2.4
Posted Write Transactions
During downstream posted write transactions, when the 21152, responding as a target, detects a
data parity error on the initiator (primary) bus, the following events occur:
• The 21152 asserts p_perr_l two cycles after the data transfer, if the primary interface parity
error response bit is set in the command register.
• The 21152 sets the primary interface parity error detected bit in the status register.
• The 21152 captures and forwards the bad parity condition to the secondary bus.
• The 21152 completes the transaction normally.
Similarly, during upstream posted write transactions, when the 21152, responding as a target,
detects a data parity error on the initiator (secondary) bus, the following events occur:
• The 21152 asserts s_perr_l two cycles after the data transfer, if the secondary interface parity
error response bit is set in the bridge control register.
• The 21152 sets the secondary interface parity error detected bit in the secondary status register.
• The 21152 captures and forwards the bad parity condition to the primary bus.
• The 21152 completes the transaction normally.
During downstream write transactions, when a data parity error is reported on the target
(secondary) bus by the target’s assertion of s_perr_l, the following events occur:
• The 21152 sets the data parity detected bit in the secondary status register, if the secondary
interface parity error response bit is set in the bridge control register.
• The 21152 asserts p_serr_l and sets the signaled system error bit in the status register, if all of
the following conditions are met:
— The SERR# enable bit is set in the command register.
— The device-specific p_serr_l disable bit for posted write parity errors is not set.
— The secondary interface parity error response bit is set in the bridge control register.
— The primary interface parity error response bit is set in the command register.
— The 21152 did not detect the parity error on the primary (initiator) bus; that is, the parity
error was not forwarded from the primary bus.
21152 PCI-to-PCI Bridge Preliminary Datasheet
7-5
Error Handling
During upstream write transactions, when a data parity error is reported on the target (primary) bus
by the target’s assertion of p_perr_l, the following events occur:
• The 21152 sets the data parity detected bit in the status register, if the primary interface parity
error response bit is set in the command register.
• The 21152 asserts p_serr_l and sets the signaled system error bit in the status register, if all of
the following conditions are met:
— The SERR# enable bit is set in the command register.
— The secondary interface parity error response bit is set in the bridge control register.
— The primary interface parity error response bit is set in the command register.
— The 21152 did not detect the parity error on the secondary (initiator) bus; that is, the parity
error was not forwarded from the secondary bus.
The assertion of p_serr_l is used to signal the parity error condition in the case where the initiator
does not know that the error occurred. Because the data has already been delivered with no errors,
there is no other way to signal this information back to the initiator.
If the parity error was forwarded from the initiating bus to the target bus, p_serr_l is not asserted.
7-6
21152 PCI-to-PCI Bridge Preliminary Datasheet
Error Handling
7.3
Data Parity Error Reporting Summary
In the previous sections, the 21152’s responses to data parity errors are presented according to the
type of transaction in progress. This section organizes the 21152’s responses to data parity errors
according to the status bits that the 21152 sets and the signals that it asserts.
Table 7-1 shows setting the detected parity error bit in the status register, corresponding to the
primary interface. This bit is set when the 21152 detects a parity error on the primary interface.
Table 7-1.
Setting the Primary Interface Detected Parity Error Bit
Primary/Secondary
Primary Detected
Parity Error Bit
Bus Where Error
Was Detected
Parity Error
Response Bits
Transaction Type
Direction
0
0
1
0
1
0
0
0
1
0
0
0
Read
Downstream
Downstream
Upstream
Primary
x/x1
x/x
x/x
x/x
x/x
x/x
x/x
x/x
x/x
x/x
x/x
x/x
Read
Secondary
Primary
Read
Read
Upstream
Secondary
Primary
Posted write
Posted write
Posted write
Posted write
Delayed write
Delayed write
Delayed write
Delayed write
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
Primary
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
1. x = don’t care
21152 PCI-to-PCI Bridge Preliminary Datasheet
7-7
Error Handling
Table 7-2 shows setting the detected parity error bit in the secondary status register, corresponding
to the secondary interface. This bit is set when the 21152 detects a parity error on the secondary
interface.
Table 7-2.
Setting the Secondary Interface Detected Parity Error Bit
Secondary
Detected Parity
Error Bit
Primary/Secondary
Parity Error
Response Bits
Bus Where Error
Was Detected
Transaction Type
Direction
0
1
0
0
0
0
0
1
0
0
0
1
Read
Downstream
Downstream
Upstream
Primary
x/x1
x/x
x/x
x/x
x/x
x/x
x/x
x/x
x/x
x/x
x/x
x/x
Read
Secondary
Primary
Read
Read
Upstream
Secondary
Primary
Posted write
Posted write
Posted write
Posted write
Delayed write
Delayed write
Delayed write
Delayed write
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
Primary
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
1. x = don’t care
7-8
21152 PCI-to-PCI Bridge Preliminary Datasheet
Error Handling
Table 7-3 shows setting the data parity detected bit in the status register, corresponding to the
primary interface. This bit is set under the following conditions:
• The 21152 must be a master on the primary bus.
• The parity error response bit in the command register, corresponding to the primary interface,
must be set.
• The p_perr_l signal is detected asserted or a parity error is detected on the primary bus.
Table 7-3.
Setting the Primary Interface Data Parity Detected Bit
Primary/Secondary
Primary Data
Parity Detected Bit Transaction Type
Bus Where Error
Was Detected
Parity Error
Response Bits
Direction
0
0
1
0
0
0
1
0
0
0
1
0
Read
Downstream
Downstream
Upstream
Primary
x/x1
x/x
1/x
x/x
x/x
x/x
1/x
x/x
x/x
x/x
1/x
x/x
Read
Secondary
Primary
Read
Read
Upstream
Secondary
Primary
Posted write
Posted write
Posted write
Posted write
Delayed write
Delayed write
Delayed write
Delayed write
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
Primary
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
1. x = don’t care
21152 PCI-to-PCI Bridge Preliminary Datasheet
7-9
Error Handling
Table 7-4 shows setting the data parity detected bit in the secondary status register, corresponding
to the secondary interface. This bit is set under the following conditions:
• The 21152 must be a master on the secondary bus.
• The parity error response bit in the bridge control register, corresponding to the secondary
interface, must be set.
• The s_perr_l signal is detected asserted or a parity error is detected on the secondary bus.
Table 7-4.
Setting the Secondary Interface Data Parity Detected Bit
Primary/Secondary
Secondary Data
Parity Detected Bit Transaction Type
Bus Where Error
Was Detected
Parity Error
Response Bits
Direction
0
1
0
0
0
1
0
0
0
1
0
0
Read
Downstream
Downstream
Upstream
Primary
x/x1
x/1
x/x
x/x
x/x
x/1
x/x
x/x
x/x
x/1
x/x
x/x
Read
Secondary
Primary
Read
Read
Upstream
Secondary
Primary
Posted write
Posted write
Posted write
Posted write
Delayed write
Delayed write
Delayed write
Delayed write
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
Primary
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
1. x = don’t care
7-10
21152 PCI-to-PCI Bridge Preliminary Datasheet
Error Handling
Table 7-5 shows assertion of p_perr_l. This signal is set under the following conditions:
• The 21152 is either the target of a write transaction or the initiator of a read transaction on the
primary bus.
• The parity error response bit in the command register, corresponding to the primary interface,
must be set.
• The 21152 detects a data parity error on the primary bus or detects s_perr_l asserted during
the completion phase of a downstream delayed write transaction on the target (secondary) bus.
Table 7-5.
Assertion of p_perr_l
Primary/Secondary
Bus Where Error
Was Detected
Parity Error
Response Bits
p_perr_l
Transaction Type
Direction
1 (deasserted)
Read
Downstream
Downstream
Upstream
Primary
x/x1
x/x
1/x
x/x
1/x
x/x
x/x
x/x
1/x
1/1
x/x
x/x
1
Read
Secondary
Primary
0 (asserted)
Read
1
0
1
1
1
0
02
1
1
Read
Upstream
Secondary
Primary
Posted write
Posted write
Posted write
Posted write
Delayed write
Delayed write
Delayed write
Delayed write
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
Primary
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
1. x = don’t care.
2. The parity error was detected on the target (secondary) bus but not on the initiator (primary) bus.
21152 PCI-to-PCI Bridge Preliminary Datasheet
7-11
Error Handling
Table 7-6 shows assertion of s_perr_l. This signal is set under the following conditions:
• The 21152 is either the target of a write transaction or the initiator of a read transaction on the
secondary bus.
• The parity error response bit in the bridge control register, corresponding to the secondary
interface, must be set.
• The 21152 detects a data parity error on the secondary bus or detects p_perr_l asserted during
the completion phase of an upstream delayed write transaction on the target (primary) bus.
Table 7-6.
Assertion of s_perr_l
Primary/Secondary
Bus Where Error
Was Detected
Parity Error
Response Bits
s_perr_l
Transaction Type
Direction
1 (deasserted)
Read
Downstream
Downstream
Upstream
Primary
x/x1
x/1
x/x
x/x
x/x
x/x
x/x
x/1
x/x
x/x
1/1
x/1
0 (asserted)
Read
Secondary
Primary
1
1
1
1
1
0
1
1
02
0
Read
Read
Upstream
Secondary
Primary
Posted write
Posted write
Posted write
Posted write
Delayed write
Delayed write
Delayed write
Delayed write
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
Primary
Downstream
Downstream
Upstream
Secondary
Primary
Upstream
Secondary
1. x = don’t care.
2. The parity error was detected on the target (primary) bus but not on the initiator (secondary) bus.
7-12
21152 PCI-to-PCI Bridge Preliminary Datasheet
Error Handling
Table 7-7 shows assertion of p_serr_l. This signal is set under the following conditions:
• The 21152 has detected p_perr_l asserted on an upstream posted write transaction or s_perr_l
asserted on a downstream posted write transaction.
• The 21152 did not detect the parity error as a target of the posted write transaction.
• The parity error response bit on the command register and the parity error response bit on the
bridge control register must both be set.
• The SERR# enable bit must be set in the command register.
Table 7-7.
Assertion of p_serr_l for Data Parity Errors
Primary/Secondary
Bus Where Error
Was Detected
Parity Error
Response Bits
p_serr_l
Transaction Type
Direction
1 (deasserted)
Read
Downstream
Downstream
Upstream
Primary
x/x1
x/x
x/x
x/x
x/x
1/1
1/1
x/x
x/x
x/x
x/x
x/x
1
Read
Secondary
Primary
1
Read
1
Read
Upstream
Secondary
Primary
1
Posted write
Posted write
Posted write
Posted write
Delayed write
Delayed write
Delayed write
Delayed write
Downstream
Downstream
Upstream
02 (asserted)
Secondary
Primary
03
1
Upstream
Secondary
Primary
1
Downstream
Downstream
Upstream
1
Secondary
Primary
1
1
Upstream
Secondary
1. x = don’t care.
2. The parity error was detected on the target (secondary) bus but not on the initiator (primary) bus.
3. The parity error was detected on the target (primary) bus but not on the initiator (secondary) bus.
21152 PCI-to-PCI Bridge Preliminary Datasheet
7-13
Error Handling
7.4
System Error (SERR#) Reporting
The 21152 uses the p_serr_l signal to report conditionally a number of system error conditions in
addition to the special case parity error conditions described in Section 7.2.3.
Whenever the assertion of p_serr_l is discussed in this document, it is assumed that the following
conditions apply:
• For the 21152 to assert p_serr_l for any reason, the SERR# enable bit must be set in the
command register.
• Whenever the 21152 asserts p_serr_l, the 21152 must also set the signaled system error bit in
the status register.
In compliance with the PCI-to-PCI Bridge Architecture Specification, the 21152 asserts p_serr_l
when it detects the secondary SERR# input, s_serr_l, asserted and the SERR# forward enable bit is
set in the bridge control register. In addition, the 21152 also sets the received system error bit in the
secondary status register.
The 21152 also conditionally asserts p_serr_l for any of the following reasons:
• Target abort detected during posted write transaction
• Master abort detected during posted write transaction
24
24
• Posted write data discarded after 2 attempts to deliver (2 target retries received)
• Parity error reported on target bus during posted write transaction (see previous section)
24
24
• Delayed write data discarded after 2 attempts to deliver (2 target retries received)
24
24
• Delayed read data cannot be transferred from target after 2 attempts (2 target retries
received)
• Master timeout on delayed transaction
The device-specific p_serr_l status register reports the reason for the 21152’s assertion of
p_serr_l.
Most of these events have additional device-specific disable bits in the p_serr_l event disable
register that make it possible to mask out p_serr_l assertion for specific events. The master timeout
condition has a SERR# enable bit for that event in the bridge control register and therefore does not
have a device-specific disable bit.
7-14
21152 PCI-to-PCI Bridge Preliminary Datasheet
Exclusive Access
8
This chapter describes the use of the LOCK# signal to implement exclusive access to a target for
transactions that cross the 21152.
8.1
8.2
Concurrent Locks
The primary and secondary bus lock mechanisms operate concurrently except when a locked
transaction crosses the 21152. A primary master can lock a primary target without affecting the
status of the lock on the secondary bus, and vice versa. This means that a primary master can lock a
primary target at the same time that a secondary master locks a secondary target.
Acquiring Exclusive Access Across the 21152
For any PCI bus, before acquiring access to the LOCK# signal and starting a series of locked
transactions, the initiator must first check that both of the following conditions are met:
• The PCI bus must be idle.
• The LOCK# signal must be deasserted.
The initiator leaves the LOCK# signal deasserted during the address phase (only the first address
phase of a dual address transaction) and asserts LOCK# one clock cycle later. Once a data transfer
is completed from the target, the target lock has been achieved.
Locked transactions can cross the 21152 only in the downstream direction, from the primary bus to
the secondary bus.
When the target resides on another PCI bus, the master must acquire not only the lock on its own
PCI bus but also the lock on every bus between its bus and the target’s bus. When the 21152
detects, on the primary bus, an initial locked transaction intended for a target on the secondary bus,
the 21152 samples the address, transaction type, byte enable bits, and parity, as described in
Section 4.6.4. It also samples the lock signal. Because a target retry is signaled to the initiator, the
initiator must relinquish the lock on the primary bus, and therefore the lock is not yet established.
The first locked transaction must be a read transaction. Subsequent locked transactions can be read
or write transactions. Posted memory write transactions that are a part of the locked transaction
sequence are still posted. Memory read transactions that are a part of the locked transaction
sequence are not prefetched.
When the locked delayed read request is queued, the 21152 does not queue any more transactions
until the locked sequence is finished. The 21152 signals a target retry to all transactions initiated
subsequent to the locked read transaction that are intended for targets on the other side of the
21152. The 21152 allows any transactions queued before the locked transaction to complete
before initiating the locked transaction.
21152 PCI-to-PCI Bridge Preliminary Datasheet
8-1
Exclusive Access
When the locked delayed read request transaction moves to the head of the delayed transaction
queue, the 21152 initiates the transaction as a locked read transaction by deasserting s_lock_l on
the secondary bus during the first address phase, and by asserting s_lock_l one cycle later. If
s_lock_l is already asserted (used by another initiator), the 21152 waits to request access to the
secondary bus until s_lock_l is sampled deasserted when the secondary bus is idle. Note that the
existing lock on the secondary bus could not have crossed the 21152; otherwise, the pending
queued locked transaction would not have been queued. When the 21152 is able to complete a data
transfer with the locked read transaction, the lock is established on the secondary bus.
When the initiator repeats the locked read transaction on the primary bus with the same address,
transaction type, and byte enable bits, the 21152 transfers the read data back to the initiator, and the
lock is then also established on the primary bus.
For the 21152 to recognize and respond to the initiator, the initiator’s subsequent attempts of the
read transaction must use the locked transaction sequence (deassert p_lock_l during address phase,
and assert p_lock_l one cycle later). If the LOCK# sequence is not used in subsequent attempts, a
master time-out condition may result. When a master time-out condition occurs, p_serr_l is
conditionally asserted (see Section 7.4), the read data and queued read transaction are discarded,
and the s_lock_l signal is deasserted on the secondary bus.
Once the intended target has been locked, any subsequent locked transactions initiated on the primary
bus that are forwarded by the 21152 are driven as locked transactions on the secondary bus.
When the 21152 receives a target abort or a master abort in response to the delayed locked read
transaction, this status is passed back to the initiator, and no locks are established on either the
target or the initiator bus. The 21152 resumes forwarding unlocked transactions in both directions.
When the 21152 detects, on the secondary bus, a locked delayed transaction request intended for a
target on the primary bus, the 21152 queues and forwards the transaction as an unlocked
transaction. The 21152 ignores s_lock_l for upstream transactions and initiates all upstream
transactions as unlocked transactions.
8-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
Exclusive Access
8.3
Ending Exclusive Access
After the lock has been acquired on both the primary and secondary buses, the 21152 must
maintain the lock on the secondary (target) bus for any subsequent locked transactions until the
initiator relinquishes the lock.
The only time a target retry causes the lock to be relinquished is on the first transaction of a locked
sequence. On subsequent transactions in the sequence, the target retry has no effect on the status of
the lock signal.
An established target lock is maintained until the initiator relinquishes the lock. The 21152 does not
know whether the current transaction is the last one in a sequence of locked transactions until the
initiator deasserts the p_lock_l signal at the end of the transaction.
When the last locked transaction is a delayed transaction, the 21152 has already completed the
transaction on the secondary bus. In this case, as soon as the 21152 detects that the initiator has
relinquished the p_lock_l signal by sampling it in the deasserted state while p_frame_l is
deasserted, the 21152 deasserts the s_lock_l signal on the secondary bus as soon as possible.
Because of this behavior, s_lock_l may not be deasserted until several cycles after the last locked
transaction has been completed on the secondary bus. As soon as the 21152 has deasserted
s_lock_l to indicate the end of a sequence of locked transactions, it resumes forwarding unlocked
transactions.
When the last locked transaction is a posted write transaction, the 21152 deasserts s_lock_l on the
secondary bus at the end of the transaction because the lock was relinquished at the end of the write
transaction on the primary bus.
When the 21152 receives a target abort or a master abort in response to a locked delayed
transaction, the 21152 returns a target abort when the initiator repeats the locked transaction. The
initiator must then deassert p_lock_l at the end of the transaction. The 21152 sets the appropriate
status bits, flagging the abnormal target termination condition (see Section 4.8). Normal
forwarding of unlock posted and delayed transactions is resumed.
When the 21152 receives a target abort or a master abort in response to a locked posted write
transaction, the 21152 cannot pass back that status to the initiator. The 21152 asserts p_serr_1
when a target abort or a master abort is received during a locked posted write transaction, if the
SERR# enable bit is set in the command register. Signal p_serr_1 is asserted for the master abort
condition if the master abort mode bit is set in the bridge control register (see Section 7.4).
21152 PCI-to-PCI Bridge Preliminary Datasheet
8-3
PCI Bus Arbitration
9
The 21152 must arbitrate for use of the primary bus when forwarding upstream transactions, and
for use of the secondary bus when forwarding downstream transactions. The arbiter for the primary
bus resides external to the 21152, typically on the motherboard. For the secondary PCI bus, the
21152 implements an internal arbiter. This arbiter can be disabled, and an external arbiter can be
used instead.
This chapter describes primary and secondary bus arbitration.
9.1
Primary PCI Bus Arbitration
The 21152 implements a request output pin, p_req_l, and a grant input pin, p_gnt_l, for primary
PCI bus arbitration. The 21152 asserts p_req_l when forwarding transactions upstream; that is, it
acts as initiator on the primary PCI bus.
For posted write transactions (see Section 4.5.1), p_req_l is asserted one cycle after s_devsel_l is
asserted. For delayed read and write requests, p_req_l is not asserted until the transaction request
has been completely queued in the delayed transaction queue (target retry has been returned to the
initiator) and is at the head of the delayed transaction queue.
When p_gnt_l is asserted low by the primary bus arbiter after the 21152 has asserted p_req_l, the
21152 initiates a transaction on the primary bus during the next PCI clock cycle. When p_gnt_l is
asserted to the 21152 when p_req_l is not asserted, the 21152 parks p_ad, p_cbe_l, and p_par by
driving them to valid logic levels. When the primary bus is parked at the 21152 and the 21152 then
has a transaction to initiate on the primary bus, the 21152 starts the transaction if p_gnt_l was
asserted during the previous cycle.
9.2
Secondary PCI Bus Arbitration
The 21152 implements an internal secondary PCI bus arbiter. This arbiter supports four external
masters in addition to the 21152. The internal arbiter can be disabled, and an external arbiter can be
used instead for secondary bus arbitration.
21152 PCI-to-PCI Bridge Preliminary Datasheet
9-1
PCI Bus Arbitration
9.2.1
Secondary Bus Arbitration Using the Internal Arbiter
To use the internal arbiter, the secondary bus arbiter enable pin, s_cfn_l, must be tied low. The
21152 has four secondary bus request input pins, s_req_l<3:0>, and four secondary bus output
grant pins, s_gnt_l<3:0>, to support external secondary bus masters. The 21152 secondary bus
request and grant signals are connected internally to the arbiter and are not brought out to external
pins when s_cfn_l is low.
The secondary arbiter supports a programmable 2-level rotating algorithm. Two groups of masters
are assigned, a high priority group and a low priority group. The low priority group as a whole
represents one entry in the high priority group; that is, if the high priority group consists of n
masters, then in at least every n +1 transactions the highest priority is assigned to the low priority
group. Priority rotates evenly among the low priority group. Therefore, members of the high
priority group can be serviced n transactions out of n +1, while one member of the low priority
group is serviced once every n +1 transactions. Figure 9-1 shows an example of an internal arbiter
where three masters, including the 21152, are in the high priority group, and two masters are in the
low priority group. Using this example, if all requests are always asserted, the highest priority
rotates among the masters in the following fashion (high priority members are given in italics, low
priority members, in boldface type):
B, m0, m1, m2, B, m0, m1, m3, B, m0, m1, m2, B, m0, m1, m3, and so on.
Figure 9-1. Secondary Arbiter Example
m1
lpg
m0
B
m2
Note:
B – 21152
mx – Bus Master Number
lpg – Low Priority Group
m3
Arbiter Control Register = 10 0000 0011b
LJ04643A.AI4
Each bus master, including the 21152, can be configured to be in either the low priority group or the
high priority group by setting the corresponding priority bit in the arbiter control register in
device-specific configuration space. Each master has a corresponding bit. If the bit is set to 1, the
master is assigned to the high priority group. If the bit is set to 0, the master is assigned to the low
priority group. If all the masters are assigned to one group, the algorithm defaults to a straight rotating
priority among all the masters. After reset, all external masters are assigned to the low priority group,
and the 21152 is assigned to the high priority group. The 21152 receives highest priority on the target
bus every other transaction, and priority rotates evenly among the other masters.
Priorities are reevaluated every time s_frame_l is asserted, that is, at the start of each new
transaction on the secondary PCI bus. From this point until the time that the next transaction starts,
the arbiter asserts the grant signal corresponding to the highest priority request that is asserted. If
a grant for a particular request is asserted, and a higher priority request subsequently asserts, the
arbiter deasserts the asserted grant signal and asserts the grant corresponding to the new higher
9-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Bus Arbitration
priority request on the next PCI clock cycle. When priorities are reevaluated, the highest priority is
assigned to the next highest priority master relative to the master that initiated the previous
transaction. The master that initiated the last transaction now has the lowest priority in its group.
If the 21152 detects that an initiator has failed to assert s_frame_l after 16 cycles of both grant
assertion and a secondary idle bus condition, the arbiter deasserts the grant. That master does not
receive any more grants until it deasserts its request for at least one PCI clock cycle.
To prevent bus contention, if the secondary PCI bus is idle, the arbiter never asserts one grant
signal in the same PCI cycle in which it deasserts another. It deasserts one grant, and then asserts
the next grant, no earlier than one PCI clock cycle later. If the secondary PCI bus is busy, that is,
either s_frame_l or s_irdy_l is asserted, the arbiter can deassert one grant and assert another grant
during the same PCI clock cycle.
9.2.2
Secondary Bus Arbitration Using an External Arbiter
The internal arbiter is disabled when the secondary bus central function control pin, s_cfn_l, is
pulled high. An external arbiter must then be used.
When s_cfn_l is tied high, the 21152 reconfigures two pins to be external request and grant pins.
The s_gnt_l<0> pin is reconfigured to be the 21152’s external request pin because it is an output.
The s_req_l<0> pin is reconfigured to be the external grant pin because it is an input. When an
external arbiter is used, the 21152 uses the s_gnt_l<0> pin to request the secondary bus. When the
reconfigured s_req_l<0> pin is asserted low after the 21152 has asserted s_gnt_l<0>, the 21152
initiates a transaction on the secondary bus one cycle later. If s_req_l<0> is asserted and the 21152
has not asserted s_gnt_l<0>, the 21152 parks the s_ad, s_cbe_l, and s_par pins by driving them to
valid logic levels.
The unused secondary bus grant outputs, s_gnt_l<3:1>, are driven high. Unused secondary bus
request inputs, s_req_l<3:1>, should be pulled high.
9.2.3
Bus Parking
Bus parking refers to driving the AD, C/BE#, and PAR lines to a known value while the bus is idle.
In general, the device implementing the bus arbiter is responsible for parking the bus or assigning
another device to park the bus. A device parks the bus when the bus is idle, its bus grant is asserted,
and the device’s request is not asserted. The AD and C/BE# signals should be driven first, with the
PAR signal driven one cycle later.
The 21152 parks the primary bus only when p_gnt_l is asserted, p_req_l is deasserted, and the
primary PCI bus is idle. When p_gnt_l is deasserted, the 21152 tristates the p_ad, p_cbe_l, and
p_par signals on the next PCI clock cycle. If the 21152 is parking the primary PCI bus and wants
to initiate a transaction on that bus, then the 21152 can start the transaction on the next PCI clock
cycle by asserting p_frame_l if p_gnt_l is still asserted.
If the internal secondary bus arbiter is enabled, the secondary bus is always parked at the last
master that used the PCI bus. That is, the 21152 keeps the secondary bus grant asserted to a
particular master until a new secondary bus request comes along. After reset, the 21152 parks the
secondary bus at itself until transactions start occurring on the secondary bus. If the internal arbiter
is disabled, the 21152 parks the secondary bus only when the reconfigured grant signal,
s_req_l<0>, is asserted and the secondary bus is idle.
21152 PCI-to-PCI Bridge Preliminary Datasheet
9-3
Clocks
10
This chapter provides information about the 21152 clocks.
10.1
Primary and Secondary Clock Inputs
The 21152 implements a separate clock input for each PCI interface. The primary interface is
synchronized to the primary clock input, p_clk, and the secondary interface is synchronized to the
secondary clock input, s_clk.
The 21152 operates at a maximum frequency of 33 MHz, and s_clk always operates at the same
frequency as p_clk.
The primary and secondary clock inputs must always maintain a synchronous relationship to each
other; that is, their edge relationships to each other are well defined. The maximum skew between
p_clk and s_clk rising edges is 7 ns, as is the maximum skew between p_clk and s_clk falling
edges. The minimum skew between p_clk and s_clk edges is 0 ns. The secondary clock edge must
never precede the primary clock edge. Figure 10-1 illustrates the timing relationship between the
primary and the secondary clock inputs.
Figure 10-1. p_clk and s_clk Relative Timing
t
t
skew
skew
p_clk
s_clk
LJ-04646.AI4
21152 PCI-to-PCI Bridge Preliminary Datasheet
10-1
Clocks
10.2
Secondary Clock Outputs
The 21152 has five secondary clock outputs, s_clk_o<4:0>, that can be used as clock inputs for up
to four external secondary bus devices and for the 21152 secondary clock input.
The s_clk_o outputs are derived from p_clk. The s_clk_o edges are delayed from p_clk edges by a
minimum of 0 ns and a maximum of 5 ns. The maximum skew between s_clk_o edges is 500 ps.
Therefore, to meet the p_clk and s_clk requirements stated in Section 10.1, no more than 2 ns of
delay is allowed for secondary clock etch returning to the device secondary clock inputs.
The rules for using secondary clocks are:
• Each secondary clock output is limited to one load.
• One of the secondary clock outputs must be used for the 21152 s_clk input.
• Intel recommends using an equivalent amount of etch on the board for all secondary clocks, to
minimize skew between them, and a maximum delay of the etch of 2 ns.
• Intel recommends terminating or disabling unused secondary clock outputs to reduce power
dissipation and noise in the system.
10.2.1
Disabling Unused Secondary Clock Outputs
When secondary clock outputs are not used, they can be individually disabled and driven high by
writing the secondary clock control register in configuration space.
10-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
Reset
11
This chapter describes the primary interface, secondary interface, and chip reset mechanisms.
11.1
Primary Interface Reset
The 21152 has one reset input, p_rst_l. When p_rst_l is asserted, the following events occur:
• The 21152 immediately tristates all primary and secondary PCI interface signals.
• The 21152 performs a chip reset.
• Registers that have default values are reset.
Appendix A lists the values of all configuration space registers after reset.
The p_rst_l asserting and deasserting edges can be asynchronous to p_clk and s_clk.
11.2
Secondary Interface Reset
The 21152 is responsible for driving the secondary bus reset signal, s_rst_l. The 21152 asserts
s_rst_l when any of the following conditions is met:
• Signal p_rst_l is asserted.
Signal s_rst_l remains asserted as long as p_rst_l is asserted.
• The secondary reset bit in the bridge control register is set.
Signal s_rst_l remains asserted until a configuration write operation clears the secondary reset
bit.
• The chip reset bit in the diagnostic control register is set.
Signal s_rst_l remains asserted until a configuration write operation clears the secondary reset
bit.
When s_rst_l is asserted, all secondary PCI interface control signals, including the secondary grant
outputs, are immediately tristated. Signals s_ad, s_cbe_l, and s_par are driven low for the duration
of s_rst_l assertion. All posted write and delayed transaction data buffers are reset; therefore, any
transactions residing in 21152 buffers at the time of secondary reset are discarded.
When s_rst_l is asserted by means of the secondary reset bit, the 21152 remains accessible during
secondary interface reset and continues to respond to accesses to its configuration space from the
primary interface.
21152 PCI-to-PCI Bridge Preliminary Datasheet
11-1
Reset
11.3
Chip Reset
The chip reset bit in the diagnostic control register can be used to reset the 21152 and secondary bus.
When the chip reset bit is set, all registers and chip state are reset and all signals are tristated. In
addition, s_rst_l is asserted, and the secondary reset bit is automatically set. Signal s_rst_l remains
asserted until a configuration write operation clears the secondary reset bit.
As soon as chip reset completes, within 20 PCI clock cycles after completion of the configuration
write operation that sets the chip reset bit, the chip reset bit automatically clears and the chip is
ready for configuration.
During chip reset, the 21152 is inaccessible.
11-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
PCI Power Management
12
The 21152–AB incorporates functionality that complies fully with the Advanced Configuration
Power Interface (ACPI) and the PCI Power Management Specification. These features include:
• PCI Power Management registers using the enhanced capabilities port (ECP) address
mechanism
• Support for D0, D3 , and D3
power management states
hot
cold
• Support for D0, D1, D2, D3 , and D3
power management states for devices behind the
cold
hot
bridge
• Support of the B2 secondary bus power state when in the D3 power management state
hot
The 21152–AA does not include these features.
Table 12-1 shows the states and related actions that the 21152 performs during power management
transitions. (No other transactions are permitted.)
Table 12-1. Power Management Transitions
Current State
Next State
Action
Power has been removed from the 21152. A
power-up reset must be performed to bring the 21152
to D0.
D0
D3cold
If enabled to do so by the bpcc pin, the 21152 will
disable the secondary clocks and drive them low.
D0
D0
D3hot
D2
Unimplemented power state. The 21152 will ignore
the write to the power state bits (power state remains
at D0).
Unimplemented power state. The 21152 will ignore
the write to the power state bits (power state remains
at D0).
D0
D1
D0
The 21152 enables secondary clock outputs and
performs an internal chip reset. Signal s_rst_l will not
be asserted. All registers will be returned to the reset
values and buffers will be cleared.
D3hot
Power has been removed from the 21152. A
power-up reset must be performed to bring the 21152
to D0.
D3hot
D3cold
D0
Power-up reset. The 21152 performs the standard
power-up reset functions as described in Chapter 11.
D3cold
PME# signals are routed from downstream devices around PCI-to-PCI bridges. PME# signals do
not pass through PCI-to-PCI bridges.
21152 PCI-to-PCI Bridge Preliminary Datasheet
12-1
Configuration Space Registers
13
This chapter provides a detailed description of the 21152 configuration space registers. The chapter is
divided into two sections: Section 13.1 describes the standard 21152 PCI-to-PCI bridge configuration
registers, and Section 13.2 describes the 21152 device-specific configuration registers.
The 21152 configuration space uses the PCI-to-PCI bridge standard format specified in the
PCI-to-PCI Bridge Architecture Specification. The header type at configuration address 0Eh reads
as 01h, indicating that this device uses the PCI-to-PCI bridge format.
The 21152 also contains device-specific registers, starting at address 40h. Use of these registers is
not required for standard PCI-to-PCI bridge implementations.
The configuration space registers can be accessed only from the primary PCI bus. To access a
register, perform a Type 0 format configuration read or write operation to that register. During the
Type 0 address phase, p_ad<7:2> indicates the Dword offset of the register. During the data phase,
p_cbe_l<3:0> selects the bytes in the Dword that is being accessed.
Caution: Software changes the configuration register values that affect 21152 behavior only during
initialization. Change these values subsequently only when both the primary and secondary PCI
buses are idle, and the data buffers are empty; otherwise, the behavior of the 21152 is unpredictable.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-1
Configuration Space Registers
Figure 13-1 shows a summary of configuration space.
Figure 13-1. 21152 Configuration Space
31
16 15
00
Device ID
Vendor ID
Command
00h
04h
Status
Class Code
Header Type
Revision ID
08h
0Ch
Primary
Latency Timer
Cache Line
Size
Reserved
Reserved
Reserved
10h
14h
Secondary
Latency Timer
Subordinate
Bus Number
Secondary
Bus Number
Primary
Bus Number
18h
Secondary Status
I/O Limit Address I/O Base Address 1Ch
Memory Limit Address
Memory Base Address
20h
24h
28h
2Ch
30h
34h
38h
3Ch
40h
Prefetchable Memory Limit Address
Prefetchable Memory Base Address
Prefetchable Memory Base Address Upper 32 Bits
Prefetchable Memory Limit Address Upper 32 Bits
I/O Limit Address Upper 16 Bits
Reserved*
I/O Base Address Upper 16 Bits
ECP Pointer*
Reserved
Bridge Control
Arbiter Control
Interrupt Pin
Reserved
Diagnostic
Control
Chip Control
Reserved
44h
48h
4Ch
50h
54h
58h
5Ch
60h
64h
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
p_serr_l
Event Disable
Reserved
Reserved
Reserved
Reserved
p_serr_l Status
Reserved
Next Item Ptr**
Secondary Clock Control
68h
6Ch -DBh
DCh
Power Management Capabilities**
PMCSR Bridge
Capability ID**
Power Management CSR**
Data
E0h
Support Extensions**
E4h - FFh
Reserved
* For 21152-AA only, these registers are R/W Subsystem ID and Subsystem Vendor ID.
** These are reserved for the 21152-AA.
A6013-01
13-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.1
PCI-to-PCI Bridge Standard Configuration Registers
This section provides a detailed description of the PCI-to-PCI bridge standard configuration
registers.
Each field has a separate description.
Fields that have the same configuration Dword address are selectable by turning on (driving low)
the appropriate byte enable bits on p_cbe_l during the data phase. To select all fields of a
configuration address, drive all byte enable bits low.
All reserved fields and registers are read only and always return 0.
13.1.1
Vendor ID Register — Offset 00h
This section describes the vendor ID register.
Dword address = 00h
Byte enable p_cbe_l<3:0> = xx00b
Dword
Bit
Name
R/W Description
15:0
Vendor ID
R
Identifies Intel Corporation as the vendor of this device.
Internally hardwired to be 1011h.
13.1.2
Device ID Register — Offset 02h
This section describes the device ID register.
Dword address = 00h
Byte enable p_cbe_l<3:0> = 00xxb
Dword
Bit
Name
R/W Description
31:16
Device ID
R
Identifies this device as the 21152.
Internally hardwired to be 24h.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-3
Configuration Space Registers
13.1.3
Command Register — Offset 04h
This section describes the command register.
These bits affect the behavior of the 21152 primary interface, except where noted. Some of the bits
are repeated in the bridge control register, to act on the secondary interface.
This register must be initialized by configuration software.
Dword address = 04h
Byte enable p_cbe_l<3:0> = xx00b
Dword
Bit
Name
R/W Description
0
I/O space enable
R/W Controls the 21152’s response to I/O transactions on the primary
interface.
When 0: The 21152 does not respond to I/O transactions initiated on the
primary bus.
When 1: The 21152’s response to I/O transactions initiated on the
secondary bus is enabled.
Reset value: 0.
1
2
Memory space
enable
R/W Controls the 21152’s response to memory transactions on the21152
primary interface.
When 0: The 21152 does not respond to memory transactions initiated
on the primary bus.
When 1: The 21152’s response to memory transactions initiated on the
primary bus is enabled.
Reset value: 0.
Master enable
R/W Controls the 21152’s ability to initiate memory and I/O transactions on the
primary bus on behalf of an initiator on the secondary bus. Forwarding of
configuration transactions is not affected.
When 0: The 21152 does not respond to I/O or memory transactions on
the secondary interface and does not initiate I/O or memory transactions
on the primary interface.
When 1: The 21152 is enabled to operate as an initiator on the primary
bus and responds to I/O and memory transactions initiated on the
secondary bus.
Reset value: 0.
3
4
Special cycle
enable
R
R
The 21152 ignores special cycle transactions, so this bit is read only and
returns 0.
Memory write and
invalidate enable
The 21152 generates memory write and invalidate transactions only
when operating on behalf of another master whose memory write and
invalidate transaction is crossing the 21152.
This bit is read only and returns 0.
13-4
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
Dword
Bit
Name
R/W Description
5
VGA snoop
enable
R/W Controls the 21152’s response to VGA-compatible palette write
transactions. VGA palette write transactions correspond to I/O
transactions whose address bits are as follows:
•
•
•
p_ad<9:0> are equal to 3C6h, 3C8h, and 3C9h.
p_ad<15:10> are not decoded.
p_ad<31:16> must be 0.
When 0: VGA palette write transactions on the primary interface are
ignored unless they fall inside the 21152’s I/O address range.
When 1: VGA palette write transactions on the primary interface are
positively decoded and forwarded to the secondary interface.
Reset value: 0.
6
Parity error
response
R/W Controls the 21152’s response when a parity error is detected on the
primary interface.
When 0: The 21152 does not assert p_perr_l, nor does it set the data
parity reported bit in the status register. The 21152 does not report
address parity errors by asserting p_serr_l.
When 1: The 21152 drives p_perr_l and conditionally sets the data parity
reported bit in the status register when a data parity error is detected
(see Chapter 7). The 21152 allows p_serr_l assertion when address
parity errors are detected on the primary interface.
Reset value: 0.
7
8
Wait cycle control
SERR# enable
R
Reads as 0 to indicate that the 21152 does not perform address or data
stepping.
R/W Controls the enable for p_serr_l on the primary interface.
When 0: Signal p_serr_l cannot be driven by the 21152.
When 1: Signal p_serr_l can be driven low by the 21152 under the
conditions described in Section 7.4.
Reset value: 0.
9
Fast back-to-back R/W Controls the ability of the 21152 to generate fast back-to-back
enable
transactions on the primary bus.
When 0: The 21152 does not generate back-to-back transactions on the
primary bus.
When 1: The 21152 is enabled to generate back-to-back transactions on
the primary bus.
Reset value: 0.
15:10
Reserved
R
Reserved. Returns 0 when read.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-5
Configuration Space Registers
13.1.4
Status Register — Offset 06h
This section describes the status register.
These bits affect the status of the 21152 primary interface. Bits reflecting the status of the
secondary interface are found in the secondary status register. W1TC indicates that writing 1 to a
bit sets that bit to 0. Writing 0 has no effect.
Dword address = 04h
Byte enable p_cbe_l<3:0> = 00xxb
Dword
Bit
Name
R/W
Description
19:16
20
Reserved
ECP
R
R
Reserved. Returns 0 when read.
Enhanced Capabilities Port (ECP) enable. Reads as 1 in the 21152–AB
and later revisions to indicate that the 21152–AB supports an enhanced
capabilities list. The 21152–AA reads as 0 to show that this capability is
not supported.
21
66-MHz
capable
R
Indicates whether the primary interface is 66 MHz capable.
Reads as 0 to indicate that the primary interface operates at a maximum
frequency of 33 MHz.
22
23
Reserved
R
R
Reserved. Returns 0 when read.
Fast
back-to-back
capable
Reads as 1 to indicate that the 21152 is able to respond to fast
back-to-back transactions on the primary interface.
24
Data parity
detected
R/W1TC
This bit is set to 1 when all of the following are true:
The 21152 is a master on the primary bus.
Signal p_perr_l is detected asserted, or a parity error is detected on the
primary bus.
The parity error response bit is set in the command register.
Reset value: 0.
26:25
DEVSEL#
timing
R
Indicates slowest response to a nonconfiguration command on the
primary interface.
Reads as 01b to indicate that the 21152 responds no slower than with
medium timing.
27
28
Signaled
target abort
R/W1TC
R/W1TC
This bit is set to 1 when the 21152 is acting as a target on the primary
bus and returns a target abort to the primary master.
Reset value: 0.
Received
target abort
This bit is set to 1 when the 21152 is acting as a master on the primary
bus and receives a target abort from the primary target.
Reset value: 0.
29
30
Received
master abort
R/W1TC
R/W1TC
This bit is set to 1 when the 21152 is acting as a master on the primary
bus and receives a master abort.
Signaled
This bit is set to 1 when the 21152 has asserted p_serr_l.
system error
Reset value: 0.
31
Detected
parity error
R/W1TC
This bit is set to 1 when the 21152 detects an address or data parity error
on the primary interface.
Reset value: 0.
13-6
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.1.5
Revision ID Register — Offset 08h
This section describes the revision ID register.
Dword address = 08h
Byte enable p_cbe_l<3:0> = xxx0b
Dword
Bit
Name
R/W Description
7:0
Revision ID
R
Indicates the revision number of this device. Revisions 00h through 02h
indicate 21152–AA. The 21152–AB starts at Rev. ID 03h.
13.1.6
Programming Interface Register — Offset 09h
This section describes the programming interface register.
Dword address = 08h
Byte enable p_cbe_l<3:0> = xx0xb
Dword
Bit
Name
R/W Description
15:8
Programming
interface
R
No programming interfaces have been defined for PCI-to-PCI bridges.
Reads as 0.
13.1.7
Subclass Code Register — Offset 0Ah
This section describes the subclass code register.
Dword address = 08h
Byte enable p_cbe_l<3:0> = x0xxb
Dword
Bit
Name
R/W Description
Reads as 04h to indicate that this bridge device is a PCI-to-PCI bridge.
23:16
Subclass code
R
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-7
Configuration Space Registers
13.1.8
Base Class Code Register — Offset 0Bh
This section describes the base class code register.
Dword address = 08h
Byte enable p_cbe_l<3:0> = 0xxxb
Dword
Bit
Name
R/W Description
Reads as 06h to indicate that this device is a bridge device.
31:24
Base class code
R
13.1.9
Cache Line Size Register — Offset 0Ch
This section describes the cache line size register.
Dword address = 0Ch
Byte enable p_cbe_l<3:0> = xxx0b
Dword
Bit
Name
R/W Description
7:0
Cache line size
R/W Designates the cache line size for the system in units of 32-bit Dwords.
Used for prefetching memory read transactions and for terminating
memory write and invalidate transactions.
The cache line size should be written as a power of 2. If the value is not a
power of 2 or is greater than 16, the 21152 behaves as if the cache line
size were 0.
Reset value: 0.
13.1.10 Primary Latency Timer Register — Offset 0Dh
This section describes the primary latency timer register.
Dword address = 0Ch
Byte enable p_cbe_l<3:0> = xx0xb
Dword
Bit
Name
R/W Description
15:8
Master latency
timer
R/W Master latency timer for the primary interface. Indicates the number of
PCI clock cycles from the assertion of p_frame_l to the expiration of the
timer when the 21152 is acting as a master on the primary interface. All
bits are writable, resulting in a granularity of one PCI clock cycle.
When 0: The 21152 relinquishes the bus after the first data transfer when
the 21152’s primary bus grant has been deasserted, with the exception of
memory write and invalidate transactions.
Reset value: 0.
13-8
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.1.11 Header Type Register — Offset 0Eh
This section describes the header type register.
Dword address = 0Ch
Byte enable p_cbe_l<3:0> = x0xxb
Dword
Bit
Name
R/W Description
23:16
Header type
R
Defines the layout of addresses 10h through 3Fh in configuration space.
Reads as 01h to indicate that the register layout conforms to the
standard PCI-to-PCI bridge layout.
13.1.12 Primary Bus Number Register — Offset 18h
This section describes the primary bus number register.
This register must be initialized by configuration software.
Dword address = 18h
Byte enable p_cbe_l<3:0> = xxx0b
Dword
Bit
Name
R/W Description
7:0
Primary bus
number
R/W Indicates the number of the PCI bus to which the primary interface is
connected. The 21152 uses this register to decode Type 1 configuration
transactions on the secondary interface that should either be converted
to special cycle transactions on the primary interface or passed upstream
unaltered.
Reset value: 0.
13.1.13 Secondary Bus Number Register — Offset 19h
This section describes the secondary bus number register.
This register must be initialized by configuration software.
Dword address = 18h
Byte enable p_cbe_l<3:0> = xx0xb
Dword
Bit
Name
R/W Description
15:8
Secondary bus
number
R/W Indicates the number of the PCI bus to which the secondary interface is
connected. The 21152 uses this register to determine when to respond to
and forward Type 1 configuration transactions on the primary interface,
and to determine when to convert them to Type 0 or special cycle
transactions on the secondary interface.
Reset value: 0.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-9
Configuration Space Registers
13.1.14 Subordinate Bus Number Register — Offset 1Ah
This section describes the subordinate bus number register.
This register must be initialized by configuration software.
Dword address = 18h
Byte enable p_cbe_l<3:0> = x0xxb
Dword
Bit
Name
R/W Description
23:16
Subordinate bus
number
R/W Indicates the number of the highest numbered PCI bus that is behind (or
subordinate to) the 21152. Used in conjunction with the secondary bus
number to determine when to respond to Type 1 configuration
transactions on the primary interface and pass them to the secondary
interface as a Type 1 configuration transaction.
Reset value: 0.
13.1.15 Secondary Latency Timer Register — Offset 1Bh
This section describes the secondary latency timer register.
Dword address = 18h
Byte enable p_cbe_l<3:0> = 0xxxb
Dword
Bit
Name
R/W Description
31:24
Secondary
latency timer
R/W Master latency timer for the secondary interface. Indicates the number of
PCI clock cycles from the assertion of s_frame_l to the expiration of the
timer when the 21152 is acting as a master on the secondary interface.
All bits are writable, resulting in a granularity of one PCI clock cycle.
When 0: The 21152 ends the transaction after the first data transfer when
the 21152’s secondary bus grant has been deasserted, with the
exception of memory write and invalidate transactions.
Reset value: 0.
13-10
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.1.16 I/O Base Address Register — Offset 1Ch
This section describes the I/O base address register.
This register must be initialized by configuration software.
Dword address = 1Ch
Byte enable p_cbe_l<3:0> = xxx0b
Dword
Bit
Name
R/W Description
3:0
32-bit indicator
R
The low 4 bits of this register read as 1h to indicate that the 21152
supports 32-bit I/O address decoding.
7:4
I/O base address
<15:12>
R/W Defines the bottom address of an address range used by the 21152 to
determine when to forward I/O transactions from one interface to the
other. The upper 4 bits are writable and correspond to address bits
<15:12>. The lower 12 bits of the address are assumed to be 0. The
upper 16 bits corresponding to address bits <31:16> are defined in the
I/O base address upper 16 bits register. The I/O address range adheres
to 4 KB alignment and granularity.
Reset value: 0.
13.1.17 I/O Limit Address Register — Offset 1Dh
This section describes the I/O limit address register.
This register must be initialized by configuration software.
Dword address = 1Ch
Byte enable p_cbe_l<3:0> = xx0xb
Dword
Bit
Name
R/W Description
11:8
32-bit indicator
R/W The low 4 bits of this register read as 1h to indicate that the 21152
supports 32-bit I/O address decoding.
15:12
I/O limit address
<15:12>
R/W Defines the top address of an address range used by the 21152 to
determine when to forward I/O transactions from one interface to the
other. The upper 4 bits are writable and correspond to address bits
<15:12>. The lower 12 bits of the address are assumed to be FFFh. The
upper 16 bits corresponding to address bits <31:16> are defined in the
I/O limit address upper 16 bits register. The I/O address range adheres to
4 KB alignment and granularity.
Reset value: 0.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-11
Configuration Space Registers
13.1.18 Secondary Status Register — Offset 1Eh
This section describes the secondary status register.
These bits reflect the status of the 21152 secondary interface. W1TC indicates that writing 1 to that
bit sets the bit to 0. Writing 0 has no effect.
Dword address = 1Ch
Byte enable p_cbe_l<3:0> = 00xxb
Dword
Bit
Name
R/W
Description
20:16
21
Reserved
R
R
Reserved. Returns 0 when read.
66 MHz
capable
Indicates whether the secondary interface is 66 MHz capable.
Reads as 0 to indicate that the secondary interface operates at a
maximum frequency of 33 MHz.
22
23
Reserved
R
R
Reserved. Returns 0 when read.
Fast
back-to-back
capable
Reads as 1 to indicate that the 21152 is able to respond to fast
back-to-back transactions on the secondary interface.
24
Data parity
detected
R/W1TC
This bit is set to 1 when all of the following are true:
•
•
The 21152 is a master on the secondary bus.
Signal s_perr_l is detected asserted, or a parity error is detected on
the secondary bus.
•
The parity error response bit is set in the bridge control register.
Reset value: 0.
26:25
27
DEVSEL#
timing
R
Indicates slowest response to a command on the secondary interface.
Reads as 01b to indicate that the 21152 responds no slower than with
medium timing.
Signaled
R/W1TC
R/W1TC
R/W1TC
R/W1TC
R/W1TC
This bit is set to 1 when the 21152 is acting as a target on the secondary
bus and returns a target abort to the secondary bus master.
target abort
Reset value: 0.
28
Received
target abort
This bit is set to 1 when the 21152 is acting as a master on the secondary
bus and receives a target abort from the secondary bus target.
Reset value: 0.
29
Received
master abort
This bit is set to 1 when the 21152 is acting as an initiator on the
secondary bus and receives a master abort.
Reset value: 0.
30
Received
system error
This bit is set to 1 when the 21152 detects the assertion of s_serr_l on
the secondary interface.
Reset value: 0.
31
Detected
parity error
This bit is set to 1 when the 21152 detects an address or data parity error
on the secondary interface.
Reset value: 0.
13-12
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.1.19 Memory Base Address Register — Offset 20h
This section describes the memory base address register.
This register must be initialized by configuration software.
Dword address = 20h
Byte enable p_cbe_l<3:0> = xx00b
Dword
Bit
Name
R/W Description
3:0
Reserved
R
The low 4 bits of this register are read only and return 0.
15:4
Memory base
address <31:20>
R/W Defines the bottom address of an address range used by the 21152 to
determine when to forward memory transactions from one interface to
the other. The upper 12 bits are writable and correspond to address bits
<31:20>. The lower 20 bits of the address are assumed to be 0. The
memory address range adheres to 1 MB alignment and granularity.
Reset value: 0.
13.1.20 Memory Limit Address Register — Offset 22h
This section describes the memory limit address register.
This register must be initialized by configuration software.
Dword address = 20h
Byte enable p_cbe_l<3:0> = 00xxb
Dword
Bit
Name
R/W Description
19:16
31:20
Reserved
R
The low 4 bits of this register are read only and return 0.
Memory limit
address <31:20>
R/W Defines the top address of an address range used by the 21152 to
determine when to forward memory transactions from one interface to
the other. The upper 12 bits are writable and correspond to address bits
<31:20>. The lower 20 bits of the address are assumed to be FFFFFh.
The memory address range adheres to 1 MB alignment and granularity.
Reset value: 0.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-13
Configuration Space Registers
13.1.21 Prefetchable Memory Base Address Register — Offset 24h
This section describes the prefetchable memory base address register.
This register must be initialized by configuration software.
Dword address = 24h
Byte enable p_cbe_l<3:0> = xx00b
Dword
Bit
Name
R/W Description
3:0
64-bit indicator
R
The low 4 bits of this register are read only and return 1h to indicate that
this range supports 64-bit addressing.
15:4
Prefetchable
memory base
address <31:20>
R/W Defines the bottom address of an address range used by the 21152 to
determine when to forward memory read and write transactions from one
interface to the other. The upper 12 bits are writable and correspond to
address bits <31:20>. The lower 20 bits of the address are assumed to
be 0. The memory base register upper 32 bits contains the upper half of
the base address. The memory address range adheres to 1 MB
alignment and granularity.
Reset value: 0.
13.1.22 Prefetchable Memory Limit Address Register — Offset 26h
This section describes the prefetchable memory limit address register.
This register must be initialized by configuration software.
Dword address = 24h
Byte enable p_cbe_l<3:0> = 00xxb
Dword
Bit
Name
R/W Description
19:16
64-bit indicator
R
The low 4 bits of this register are read only and return 1h to indicate that
this range supports 64-bit addressing.
31:20
Prefetchable
memory limit
address <31:20>
R/W Defines the top address of an address range used by the 21152 to
determine when to forward memory read and write transactions from one
interface to the other. The upper 12 bits are writable and correspond to
address bits <31:20>. The lower 20 bits of the address are assumed to
be FFFFFh. The memory limit upper 32 bits register contains the upper
half of the limit address. The memory address range adheres to 1 MB
alignment and granularity.
Reset value: 0.
13-14
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.1.23 Prefetchable Memory Base Address Upper 32 Bits Register
— Offset 28h
This section describes the prefetchable memory base address upper 32 bits register.
This register must be initialized by configuration software.
Dword address = 28h
Byte enable p_cbe_l<3:0> = 0000b
Dword
Bit
Name
R/W Description
31:0
Upper 32
R/W Defines the upper 32 bits of a 64-bit bottom address of an address range
used by the 21152 to determine when to forward memory read and write
transactions from one interface to the other. The memory address range
adheres to 1 MB alignment and granularity.
prefetchable
memory base
address <63:32>
Reset value: 0.
13.1.24 Prefetchable Memory Limit Address Upper 32 Bits Register
— Offset 2Ch
This section describes the prefetchable memory limit address upper 32 bits register.
This register must be initialized by configuration software.
Dword address = 2Ch
Byte enable p_cbe_l<3:0> = 0000b
Dword
Bit
Name
R/W Description
31:0
Upper 32
R/W Defines the upper 32 bits of a 64-bit top address of an address range
used by the 21152 to determine when to forward memory read and write
transactions from one interface to the other. Extra read transactions
should have no side effects. The memory address range adheres to
1 MB alignment and granularity.
prefetchable
memory limit
address <63:32>
Reset value: 0.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-15
Configuration Space Registers
13.1.25 I/O Base Address Upper 16 Bits Register — Offset 30h
This section describes the I/O base address upper 16 bits register.
This register must be initialized by configuration software.
Dword address = 30h
Byte enable p_cbe_l<3:0> = xx00b
Dword
Bit
Name
R/W Description
15:0
I/O base address
upper 16 bits
<31:16>
R/W Defines the upper 16 bits of a 32-bit bottom address of an address range
used by the 21152 to determine when to forward I/O transactions from
one interface to the other. The I/O address range adheres to 4 KB
alignment and granularity.
Reset value: 0.
13.1.26 I/O Limit Address Upper 16 Bits Register — Offset 32h
This section describes the I/O limit address upper 16 bits register.
This register must be initialized by configuration software.
Dword address = 32h
Byte enable p_cbe_l<3:0> = 00xxb
Dword
Bit
Name
R/W Description
31:16
I/O limit address
upper 16 bits
<31:16>
R/W Defines the upper 16 bits of a 32-bit top address of an address range
used by the 21152 to determine when to forward I/O transactions from
one interface to the other. The I/O address range adheres to 4 KB
alignment and granularity.
Reset value: 0.
13-16
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.1.27 Capabilities Pointer Register — Offset 34h
This section describes the capabilities pointer register.
Dword address = 34h
Byte enable p_cbe_l<3:0> = 0000b
Dword
Bit
Name
R/W Description
7:0
ECP_PTR
R
Enhanced Capabilities Port (ECP) offset pointer. Reads as DCh in the
21152–AB and later revisions to indicate that the first item, which
corresponds to the power management registers, resides at that
configuration offset. This is a R/W register with no side effects in the
21152–AA.
31:8
Reserved
R
Reserved. The 21152–AB and later revisions return 0 when read. This is
a R/W register with no side effects in the 21152–AA.
13.1.28 Interrupt Pin — Offset 3Dh
This section describes the interrupt pin register.
Dword address = 3Ch
Byte enable p_cbe_l<3:0> = xx0xb
Dword
Bit
Name
R/W Description
R Reads as 0 to indicate that the 21152 does not have an interrupt pin.
15:8
Interrupt pin
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-17
Configuration Space Registers
13.1.29 Bridge Control — Offset 3Eh
This section describes the bridge control register.
This register must be initialized by configuration software.
Dword address = 3Eh
Byte enable p_cbe_l<3:0> = 00xxb
Dword
Bit
Name
R/W
Description
16
Parity error
response
R/W
Controls the 21152’s response when a parity error is detected on the
secondary interface.
When 0: The 21152 does not assert s_perr_l, nor does it set the data
parity reported bit in the secondary status register. The 21152 does not
report address parity errors by asserting p_serr_l.
When 1: The 21152 drives s_perr_l and conditionally sets the data parity
reported bit in the secondary status register when a data parity error is
detected on the secondary interface (see Chapter 7). Also must be set to
1 to allow p_serr_l assertion when address parity errors are detected on
the secondary interface.
Reset value: 0.
17
18
SERR#
forward
enable
R/W
R/W
Controls whether the 21152 asserts p_serr_l when it detects s_serr_l
asserted.
When 0: The 21152 does not drive p_serr_l when it detects s_serr_l
asserted.
When 1: The 21152 asserts p_serr_l when s_serr_l is detected asserted
(the primary SERR# driver enable bit must also be set).
Reset value: 0.
ISA enable
Modifies the 21152’s response to ISA I/O addresses. Applies only to
those addresses falling within the I/O base and limit address registers
and within the first 64KB of PCI I/O space.
When 0: The 21152 forwards all I/O transactions downstream that fall
within the I/O base and limit address registers.
When 1: The 21152 ignores primary bus I/O transactions within the I/O
base and limit address registers and within the first 64 KB of PCI I/O
space that address the last 768 bytes in each 1 KB block. Secondary bus
I/O transactions are forwarded upstream if the address falls within the
last 768 bytes in each 1 KB block.
Reset value: 0.
13-18
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
Dword
Bit
Name
R/W
Description
19
VGA enable
R/W
Modifies the 21152’s response to VGA-compatible addresses.
When 0: VGA transactions are ignored on the primary bus unless they
fall within the I/O base and limit address registers and the ISA mode is 0.
When 1: The 21152 positively decodes and forwards the following
transactions downstream, regardless of the values of the I/O base and
limit registers, ISA mode bit, or VGA snoop bit:
•
•
Memory transactions addressing 000A0000h–000BFFFFh
I/O transaction addressing:
— p_ad<9:0> = 3B0h–3BBh and 3C0h–3DFh
— p_ad<15:10> are not decoded.
— p_ad<31:16> = 0000h.
I/O and memory space enable bits must be set in the command register.
The transactions listed here are ignored by the 21152 on the secondary
bus.
Reset value: 0.
20
21
Reserved
R
Reserved. Returns 0 when read.
Master abort R/W
mode
Controls the 21152’s behavior when a master abort termination occurs in
response to a transaction initiated by the 21152 on either the primary or
secondary PCI interface.
When 0: The 21152 asserts TRDY# on the initiator bus for delayed
transactions, and FFFF FFFFh for read transactions. For posted write
transactions, p_serr_l is not asserted.
When 1: The 21152 returns a target abort on the initiator bus for delayed
transactions. For posted write transactions, the 21152 asserts p_serr_l if
the SERR# enable bit is set in the command register.
Reset value: 0.
22
23
24
Secondary
bus reset
R/W
Controls s_rst_l on the secondary interface.
When 0: The 21152 deasserts s_rst_l.
When 1: The 21152 asserts s_rst_l. When s_rst_l is asserted, the data
buffers and the secondary interface are initialized back to reset
conditions. The primary interface and configuration registers are not
affected by the assertion of s_rst_l.
Reset value: 0.
Fast
back-to-back
enable
Controls the ability of the 21152 to generate fast back-to-back
transactions on the secondary interface.
When 0: The 21152 does not generate fast back-to-back transactions on
the secondary PCI bus.
When 1: The 21152 is enabled to generate fast back-to-back
transactions on the secondary PCI bus.
Reset value: 0.
Primary
master
time-out
R/W
Sets the maximum number of PCI clock cycles that the 21152 waits for
an initiator on the primary bus to repeat a delayed transaction request.
The counter starts once the delayed transaction completion is at the
head of the queue. If the master has not repeated the transaction at least
once before the counter expires, the 21152 discards the transaction from
its queues.
When 0: The primary master time-out value is 215 PCI clock cycles, or
0.983 ms for a 33-MHz bus.
When 1: The value is 210 PCI clock cycles, or 30.7 µs for a 33-MHz bus.
Reset value: 0.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-19
Configuration Space Registers
Dword
Bit
Name
R/W
Description
25
Secondary
master
timeout
R/W
Sets the maximum number of PCI clock cycles that the 21152 waits for
an initiator on the secondary bus to repeat a delayed transaction request.
The counter starts once the delayed transaction completion is at the
head of the queue. If the master has not repeated the transaction at least
once before the counter expires, the 21152 discards the transaction from
its queues.
When 0: The primary master time-out value is 215 PCI clock cycles, or
0.983 ms for a 33 MHz bus.
When 1: The value is 210 PCI clock cycles, or 30.7 µs for a 33 MHz bus.
Reset value: 0.
26
27
Master
timeout
status
R/W1TC
R/W
This bit is set to 1 when either the primary master time-out counter or the
secondary master time-out counter expires and a delayed transaction is
discarded from the 21152’s queues. Write 1 to clear.
Reset value: 0.
Master
timeout
SERR#
enable
Controls assertion of p_serr_l during a master timeout.
When 0: Signal p_serr_l is not asserted as a result of a master time-out.
When 1: Signal p_serr_l is asserted when either the primary master
time-out counter or the secondary master time-out counter expires and a
delayed transaction is discarded from the 21152’s queues. The SERR#
enable bit in the command register must also be set.
Reset value: 0.
31:28
Reserved
R
Reserved. Returns 0 when read.
13-20
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.1.30 Capability ID Register — Offset DCh
This section describes the capability ID register. (Implemented in the 21152-AB and later revisions
only. In the 21152-AA, this register is reserved.)
Dword address = DCh
Byte enable p_cbe_l<3:0> = xxx0b
Dword
Bits
Name
R/W Description
7:0
CAP_ID
R
Enhanced capabilities ID. Reads only as 01h to indicate that these are
power management enhanced capability registers.
13.1.31 Next Item Register — Offset DDh
This section describes the next item register. (Implemented in the 21152-AB and later revisions
only. In the 21152-AA, this register is reserved.)
Dword address = DCh
Byte enable p_cbe_l<3:0> = xx0x
Dword
Bit
Name
R/W Description
15:8
NEXT_ITEM
R
Next Item Pointer. Reads as 0 to indicate that there are not other ECP
registers.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-21
Configuration Space Registers
13.1.32 Power Management Capabilities Registers — Offset DEh
This section describes the power management capabilities registers. (Implemented in the
21152-AB and later revisions only. In the 21152-AA, this register is reserved.)
Dword address = DCh
Byte enable p_cbe_l<3:0> = 00xx
Dword
Bit
Name
R/W Description
18:16
PM_VER
R
Power Management Revision. Reads as 001 to indicate that this device
is compliant to Revision 1.0 of the PCI Power Management Interface
Specification.
19
20
21
PME#Clock
AUX
R
R
R
PME# Clock Required. Reads as 0 because this device does not support
the PME# pin.
Auxiliary Power Support. Reads as 0 because this device does not have
PME# support or an auxiliary power source.
DSI
Device-Specific Initialization. Reads as 0 to indicate that this device does
not have device-specific initialization requirements.
24:22
25
Reserved
D1
R
R
Reserved. Read as 000b.
D1 Power State Support. Reads as 0 to indicate that this device does not
support the D1 power management state.
26
D2
R
R
D2 Power State Support. Reads as 0 to indicate that this device does not
support the D2 power management state.
31:27
PME_SUP
PME# Support. Reads as 0 to indicate that this device does not support
the PME# pin.
13-22
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.1.33 Power Management Control and Status Registers — Offset
E0h
This section describes the power management control and status registers. (Implemented in the
21152-AB and later revisions only. In the 21152-AA, this register is reserved.)
Dword address = E0h
Byte enable p_cbe_l = xx00
Dword
Bit
Name
R/W Description
1:0
PWR_STATE
R/W Power State. Reflects the current power state of this device. If an
unimplemented power state is written to this register, the 21152
completes the write transaction, ignores the write data, and does not
change the value of this field. Writing a value of D0 when the previous
state was D3 will cause a chip reset to occur (without asserting s_rst_l).
00b: D0
01b: D1 (not implemented)
10b: D2 (not implemented)
11b: D3
Reset value: 00b
7:2
8
Reserved
PME_EN
DATA_SEL
R
R
R
Reserved. Reads as 00000b.
PME# Enable. Reads as 0 because the PME# pin is not implemented.
12:9
Data Select. Reads as 0000b because the data register is not
implemented.
14:13
15
DATA_
SCALE
R
R
Data Scale. Reads as 00b because the data register is not implemented.
PME_STAT
PME Status. Reads as 0 because the PME# pin is not implemented.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-23
Configuration Space Registers
13.1.34 PPB Support Extensions Registers — Offset E2h
This section describes the PPB support extensions registers. (Implemented in the 21152-AB and
later revisions only. In the 21152-AA, this register is reserved.)
Dword address = E0h
Byte enable p_cbe_l<3:0> = x0xx
Dword
Bit
Name
R/W Description
21:16
22
Reserved
B2_B3
R
R
Reserved. Read only as 000000b.
B2_B3 Support for D3hot. When the BPCC_En bit (bit 24) reads as 1, this
bit reads as 1 to indicate that the secondary bus clock outputs will be
stopped and driven low when this device is placed in D3hot. This bit is not
defined when the BPCC_En bit reads as 0.
23
BPCC_En
R
Bus Power/Clock Control Enable. When the bpcc pin is tied high, this bit
reads as a 1 to indicate that the bus power/clock control mechanism is
enabled, as described in B2_B3 (bit 23). When the bpcc pin is tied low,
this bit reads as a 0 to indicate that the bus power/clock control
mechanism is disabled (secondary clocks are not disabled when this
device is placed in D3hot).
13.1.35 Data Register — Offset E3h
This section describes the data register. (Implemented in the 21152-AB and later revisions only. In
the 21152-AA, this register is reserved.)
Dword address = E0h
Byte enable p_cbe_l<3:0> = 0xxx
Dword
Bit
Name
R/W Description
R Data register. This register is not implemented and reads 00h.
31:24
Data
13-24
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.2
Device-Specific Configuration Registers
This section provides a detailed description of the 21152 device-specific configuration registers.
Each field has a separate description.
Fields that have the same configuration address are selectable by turning on (driving low) the
appropriate byte enable bits on p_cbe_l during the data phase. To select all fields of a configuration
address, drive all byte enable bits low.
All reserved fields and registers are read only and always return 0.
13.2.1
Chip Control Register — Offset 40h
This section describes the chip control register.
Dword address = 40h
Byte enable p_cbe_l<3:0> = xxx0b
Dword
Bit
Name
R/W Description
0
1
Reserved
R
Reserved. Returns 0 when read.
Memory write
disconnect control
R/W Controls when the 21152, as a target, disconnects memory write
transactions.
When 0: The 21152 disconnects on queue full or on a 4KB boundary.
When 1: The 21152 disconnects on a cache line boundary, as well as
when the queue fills or on a 4KB boundary.
Reset value: 0.
3:2
4
Reserved
R
Reserved. Returns 0 when read.
Secondary bus
prefetch disable
R/W Controls the 21152’s ability to prefetch during upstream memory read
transactions.
When 0: The 21152 prefetches and does not forward byte enable bits
during memory read transactions.
When 1: The 21152 requests only one Dword from the target during
memory read transactions and forwards read byte enable bits. The
21152 returns a target disconnect to the requesting master on the first
data transfer. Memory read line and memory read multiple transactions
are still prefetchable.
Reset value: 0.
7:5
Reserved
R
Reserved. Returns 0 when read.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-25
Configuration Space Registers
13.2.2
Diagnostic Control Register — Offset 41h
This section describes the diagnostic control register.
W1TR indicates that writing 1 in this bit position causes a chip reset to occur. Writing 0 has no
effect.
Dword address = 40h
Byte enable p_cbe_l<3:0> = xx0xb
Dword
Bit
Name
R/W
Description
8
Chip reset R/W1TR
Chip and secondary bus reset control.
When 1: Causes the 21152 to perform a chip reset. Data buffers,
configuration registers, and both the primary and secondary interfaces
are reset to their initial state. The 21152 clears this bit once chip reset is
complete. The 21152 can then be reconfigured.
Secondary bus reset s_rst_l is asserted and the secondary reset bit in
the bridge control register is set when this bit is set. The secondary reset
bit in the bridge control register must be cleared in order to deassert
s_rst_l.
10:9
Test mode R/W
Controls the testability of the 21152’s internal counters. These bits are
used for chip test only. The value of these bits controls which bytes of the
counters are exercised:
•
•
•
•
00b = Normal functionality — all bits are exercised.
01b = Byte 1 is exercised.
10b = Byte 2 is exercised.
11b = Byte 0 is exercised.
Reset value: 00b.
15:11
Reserved
R
Reserved. Returns 0 when read.
13.2.3
Arbiter Control Register — Offset 42h
This section describes the arbiter control register.
Dword address = 40h
Byte enable p_cbe_l<3:0> = 00xxb
Dword
Bit
Name
R/W Description
25:16
Arbiter control
R/W Each bit controls whether a secondary bus master is assigned to the high
priority arbiter group or the low priority arbiter group. Bits <19:16>
correspond to request inputs s_req_l<3:0>, respectively. Bit <25>
corresponds to the 21152 as a secondary bus master.
When 0: Indicates that the master belongs to the low priority group.
When 1: Indicates that the master belongs to the high priority group.
Reset value: 10 0000 0000b.
31:26
Reserved
R
Reserved. Returns 0 when read.
13-26
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.2.4
p_serr_l Event Disable Register -— Offset 64h
This section describes the p_serr_l event disable register.
Dword address = 64h
Byte enable p_cbe_l<3:0> = xxx0b
Dword
Bit
Name
R/W Description
0
1
Reserved
R
Reserved. Returns 0 when read.
Posted write
parity error
R/W Controls the 21152’s ability to assert p_serr_l when a data parity error is
detected on the target bus during a posted write transaction.
When 0: Signal p_serr_l is asserted if this event occurs and the SERR#
enable bit in the command register is set.
When 1: Signal p_serr_l is not asserted if this event occurs.
Reset value: 0.
2
3
4
5
6
7
Posted write
nondelivery
R/W Controls the 21152’s ability to assert p_serr_l when it is unable to deliver
posted write data after 224 attempts.
When 0: Signal p_serr_l is asserted if this event occurs and the SERR#
enable bit in the command register is set.
When 1: Signal p_serr_l is not asserted if this event occurs.
Reset value: 0.
Target abort
during posted
write
R/W Controls the 21152’s ability to assert p_serr_l when it receives a target
abort when attempting to deliver posted write data.
When 0: Signal p_serr_l is asserted if this event occurs and the SERR#
enable bit in the command register is set.
When 1: Signal p_serr_l is not asserted if this event occurs.
Reset value: 0.
Master abort on
posted write
R/W Controls the 21152’s ability to assert p_serr_l when it receives a master
abort when attempting to deliver posted write data.
When 0: Signal p_serr_l is asserted if this event occurs and the SERR#
enable bit in the command register is set.
When 1: Signal p_serr_l is not asserted if this event occurs.
Reset value: 0.
Delayed write
nondelivery
R/W Controls the 21152’s ability to assert p_serr_l when it is unable to deliver
delayed write data after 224 attempts.
When 0: Signal p_serr_l is asserted if this event occurs and the SERR#
enable bit in the command register is set.
When 1: Signal p_serr_l is not asserted if this event occurs.
Reset value: 0.
Delayed read—no R/W Controls the 21152’s ability to assert p_serr_l when it is unable to
data from target
transfer any read data from the target after 224 attempts.
When 0: Signal p_serr_l is asserted if this event occurs and the SERR#
enable bit in the command register is set.
When 1: Signal p_serr_l is not asserted if this event occurs.
Reset value: 0.
Reserved
R
Reserved. Returns 0 when read.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-27
Configuration Space Registers
13.2.5
Secondary Clock Control Register — Offset 68h
This section describes the secondary clock control register.
Dword address = 68h
Byte enable p_cbe_l<3:0> = xx00b
Dword
Bit
Name
R/W Description
1:0
Clock 0 disable
R/W If either bit is 0: Signal s_clk_o<0> is enabled.
When both bits are 1: Signal s_clk_o<0> is disabled and driven high.
Upon secondary bus reset, these bits are initialized to 0.
3:2
5:4
7:6
8
Clock 1 disable
Clock 2 disable
Clock 3 disable
Clock 4 disable
Reserved
R/W If either bit is 0: Signal s_clk_o<1> is enabled.
When both bits are 1: Signal s_clk_o<1> is disabled and driven high.
Upon secondary bus reset, these bits are initialized to 0.
R/W If either bit is 0: Signal s_clk_o<2> is enabled.
When both bits are 1: Signal s_clk_o<2> is disabled and driven high.
Upon secondary bus reset, these bits are initialized to 0.
R/W If either bit is 0: Signal s_clk_o<3> is enabled.
When both bits are 1: Signal s_clk_o<3> is disabled and driven high.
Upon secondary bus reset, these bits are initialized to 0.
R/W When 0: Signal s_clk_o<4> is enabled.
When 1: Signal s_clk_o<4> is disabled and driven high.
Upon secondary bus reset, this bit is initialized to 0.
9:13
R
Reserved. Returns 1 when read.
13-28
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Space Registers
13.2.6
p_serr_l Status Register — Offset 6Ah
This section describes the p_serr_l status register.
This status register indicates the reason for the 21152’s assertion of p_serr_l.
Dword address = 68h
Byte enable p_cbe_l<3:0> = x0xxb
Dword
Bit
Name
R/W
Description
0
Address
R/W1TC
When 1: Signal p_serr_l was asserted because an address parity error
parity error
was detected on either the primary or secondary PCI bus.
Reset value: 0.
1
2
3
4
5
6
Posted write
data parity
error
R/W1TC
R/W1TC
R/W1TC
When 1: Signal p_serr_l was asserted because a posted write data
parity error was detected on the target bus.
Reset value: 0.
Posted write
nondelivery
When 1: Signal p_serr_l was asserted because the 21152 was unable
to deliver posted write data to the target after 224 attempts.
Reset value: 0.
Target abort
during
posted write
When 1: Signal p_serr_l was asserted because the 21152 received a
target abort when delivering posted write data.
Reset value: 0.
Master abort R/W1TC
during
posted write
When 1: Signal p_serr_l was asserted because the 21152 received a
master abort when attempting to deliver posted write data.
Reset value: 0.
Delayed
write
nondelivery
R/W1TC
When 1: Signal p_serr_l was asserted because the 21152 was unable
to deliver delayed write data after 224 attempts.
Reset value: 0.
Delayed
read—no
data from
target
R/W1TC
When 1: Signal p_serr_l was asserted because the 21152 was unable
to read any data from the target after 224 attempts.
Reset value: 0.
7
Delayed
transaction
master
R/W1TC
When 1: Signal p_serr_l was asserted because a master did not repeat
a read or write transaction before the master time-out counter expired
on the initiator’s PCI bus.
time-out
Reset to 0.
21152 PCI-to-PCI Bridge Preliminary Datasheet
13-29
Diagnostic Nand Tree
14
The 21152 implements two pins for testing purposes:
• The goz_l pin, when asserted, tristates all bidirectional pins.
• The nand_out pin is the output of a serial Nand tree connecting all chip inputs except p_clk
and s_clk. A pattern can be applied to chip inputs, and the nand_out pin verifies input pin
interconnect.
Before the Nand tree test mechanism is used, all bidirectional signals must first be tristated by
assertion of goz_l. Signal goz_l should remain asserted for the duration of the test.
Note: Any inputs tied high or low (for example, s_cfn_l), should be connected to power or ground
through a resistive device to allow the Nand tree test mechanism to be used.
The Nand tree begins at the s_cfn_l input, runs clockwise to p_rst_l, and then is output at
nand_out.
Intel recommends the following Nand tree test sequence:
1. Drive goz_l low.
2. Drive each input and bidirectional pin high, with the possible exception of p_clk and s_clk.
(Signals p_clk and s_clk are not included in the Nand tree.)
3. Starting with pin 49 (s_cfn_l), proceed clockwise and individually drive each pin low;
nand_out should toggle with each pin.
4. Turn off tester drivers.
5. Drive goz_l high.
6. Reset chip before proceeding with further testing.
21152 PCI-to-PCI Bridge Preliminary Datasheet
14-1
Electrical Specifications
15
This chapter specifies the following electrical behavior of the 21152:
• PCI electrical conformance
• Absolute maximum ratings
• dc specifications
• ac timing specifications
15.1
15.2
PCI Electrical Specification Conformance
The 21152 PCI pins conform to the basic set of PCI electrical specifications in the PCI Local Bus
Specification, Revision 2.1. See that document for a complete description of the PCI I/O protocol
and pin ac specifications.
Absolute Maximum Ratings
The 21152 is specified to operate at a maximum frequency of 33 MHz at a junction temperature (T )
j
not to exceed 125°C. Table 15-1 lists the absolute maximum ratings for the 21152. Stressing the
device beyond the absolute maximum ratings may cause permanent damage. These are stress ratings
only. Operating beyond the functional operating range is not recommended, and extended exposure
beyond the functional operating range may affect the reliability.
Table 15-1. Absolute Maximum Ratings
Parameter
Minimum
Maximum
Tj
—
125°C
Supply voltage, Vcc
—
3.9 V
Maximum voltage applied to signal pins
Maximum power, PWC
Storage temperature range, Tstg
—
5.5 V
—
1.2 W @ 33 MHz
125°C
–55°C
Table 15-2 lists the functional operating range.
Table 15-2. Functional Operating Range
Parameter
Supply voltage, Vcc
Minimum
Maximum
3.0 V
3.6 V
Operating ambient temperature, Ta 0°C
70°C
21152 PCI-to-PCI Bridge Preliminary Datasheet
15-1
Electrical Specifications
15.3
DC Specifications
Table 15-3 defines the dc parameters met by all 21152 signals under the conditions of the
functional operating range.
Table 15-3. DC Parameters
Symbol
Parameter
Condition
Minimum
Maximum
Unit
Vcc
Vil
Supply voltage
—
3.0
3.6
V
V
V
V
V
V
V
Low-level input voltage1
High-level input voltage1
Low-level output voltage2
Low-level output voltage3
High-level output voltage2
High-level output voltage3
—
–0.5
0.5 Vcc
—
0.3 Vcc
Vcc + 0.5 V
0.1 Vcc
0.55
Vih
—
Vol
Iout = 1500 µA
Iout = 6 mA
Iout = –500 µA
Iout = –2 mA
Vol5V
Voh
Voh5V
—
0.9 Vcc
2.4
—
—
Low-level input leakage
current1,4
Iil
0 < Vin < Vcc
—
±10
µA
Cin
Input pin capacitance
—
—
—
—
10.0
8.0
pF
pF
pF
CIDSEL
Cclk
p_idsel pin capacitance
p_clk, s_clk pin capacitance
—
5.0
12.0
1. Guarantees meeting the specification for the 5-V signaling environment.
2. For 3.3-V signaling environment.
3. For 5-V signaling environment.
4. Input leakage currents include high-Z output leakage for all bidirectional buffers with tristate
outputs.
Note: In Table 15-3, currents into the chip (chip sinking) are denoted as positive (+) current. Currents
from the chip (chip sourcing) are denoted as negative (–) current.
15.4
AC Timing Specifications
The next sections specify the following:
• Clock timing specifications
• PCI signal timing specifications
• Reset timing specifications
15-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
Electrical Specifications
15.4.1
Clock Timing Specifications
The ac specifications consist of input requirements and output responses. The input requirements consist
of setup and hold times, pulse widths, and high and low times. Output responses are delays from clock
to signal. The ac specifications are defined separately for each clock domain within the 21152.
Figure 15-1 shows the ac parameter measurements for the p_clk and s_clk signals, and Table 15-4
specifies p_clk and s_clk parameter values for clock signal ac timing. See also Figure 15-2 for a
further illustration of signal timing. Unless otherwise indicated, all ac parameters are guaranteed
when tested within the functional operating range of Table 15-2.
Figure 15-1. PCI Clock Signal AC Parameter Measurements
T
cyc
V
t1
V
T
t2
T
high
low
V
t3
p_clk
T
T
f
r
T
T
r
f
V
t1
T
T
V
high
low
t2
V
t3
s_clk
Note:
T
T
skew
skew
T
cyc
_
_
_
Vt1
2.0 V for 5-V clocks; 0.5 Vcc for 3.3-V clocks
1.5 V for 5-V clocks; 0.4 Vcc for 3.3-V clocks
0.8 V for 5-V clocks; 0.3 Vcc for 3.3-V clocks
Vt2
Vt3
LJ-04738.AI4
Table 15-4. PCI Clock Signal AC Parameters
Symbol
Parameter
Minimum
Maximum
Unit
Tcyc
Thigh
Tlow
p_clk,s_clk cycle time
p_clk, s_clk high time
p_clk, s_clk low time
p_clk, s_clk slew rate1
30
11
11
1
Infinity
ns
—
—
4
ns
ns
V/ns
Tsclk
Delay from p_clk to s_clk
0
7
ns
ns
ns
ns
ns
Tsclkr
Tsclkf
Tdskew
Tskew
p_clk rising to s_clk_o rising
p_clk falling to s_clk_o falling2
0
5
0
5
s_clk_0 duty cycle skew from p_clk duty cycle2
s_clk_0<x> to s_clk_0<y>
—
—
0.750
0.500
1. 0.2 V to 0.6 V .
cc
cc
2. Measured with 30-pF lumped load.
21152 PCI-to-PCI Bridge Preliminary Datasheet
15-3
Electrical Specifications
15.4.2
PCI Signal Timing Specifications
Figure 15-2 and Table 15-5 show the PCI signal timing specifications.
Figure 15-2. PCI Signal Timing Measurement Conditions
CLK
Output
Input
V
T
test
val
T
inval
Valid
T
T
on
off
Valid
T
su
T
h
Note:
_
Vtest
1.5 V for 5-V signals; 0.4 Vcc for 3.3-V signals
LJ-04739.AI4
Table 15-5. PCI Signal Timing
Symbol
Parameter
Minimum
Maximum
Unit
Tval
CLK to signal valid delay — bused signals1,2,3
CLK to signal valid delay — point-to-point
Float to active delay
2
11
12
—
28
—
—
—
ns
ns
ns
ns
ns
ns
ns
Tval(ptp)
Ton
2
2
Toff
Active to float delay
—
Tsu
Input setup time to CLK — bused signals
Input setup time to CLK—point-to-point
Input signal hold time from CLK
7
Tsu(ptp)
Th
10, 12
0
1. See Figure 15-2.
2. All primary interface signals are synchronized to p_clk. All secondary interface signals are synchronized to
s_clk.
3. Point-to-point signals are p_req_l, s_req_l<3:0>, p_gnt_l, and s_gnt_l<3:0>. Bused signals are p_ad,
p_cbe_l, p_par, p_perr_l, p_serr_l, p_frame_l, p_irdy_l, p_trdy_l, p_lock_l, p_devsel_l, p_stop_l,
p_idsel, s_ad, s_cbe_l, s_par, s_perr_l, s_serr_l, s_frame_l, s_irdy_l, s_trdy_l, s_lock_l, s_devsel_l,
s_stop_l.
15-4
21152 PCI-to-PCI Bridge Preliminary Datasheet
Electrical Specifications
15.4.3
Reset Timing Specifications
Table 15-6 shows the reset timing specifications for p_rst_l and s_rst_l.
Table 15-6. Reset Timing Specifications
Symbol
Parameter
Minimum
Maximum
Unit
Trst
p_rst_l active time after power stable
p_rst_l active time after p_clk stable
p_rst_l active-to-output float delay
s_rst_l active after p_rst_l assertion
s_rst_l active time after s_clk stable
s_rst_l deassertion after p_rst_l deassertion
p_rst_l slew rate1
1
—
—
40
40
—
25
—
µs
Trst-clk
Trst-off
Tsrst
100
—
µs
ns
—
ns
Tsrst-on
Tdsrst
100
20
50
µs
Cycles
mV/ns
1. Applies to rising (deasserting) edge only.
21152 PCI-to-PCI Bridge Preliminary Datasheet
15-5
Mechanical Specifications
16
The 21152 is contained in an industry-standard 160-pin plastic quad flat pack (PQFP) package,
shown in Figure 16-1.
Figure 16-1. 160-Pin PQFP Package
- A -
D
D1
Pin 1
b
160-Pin PQFP
E1
E
- B -
e
A
See Detail "A"
// 0.13
C
Datum Plane
Seating Plane
- H -
- C -
M
S
S
B
ddd C A
c c c
C
(A) A2
Detail "A"
Note:
R
- Basic Dimension
) - Reference Dimension
(
L
A1
0o - 7o
(LL)
c
LJ04449A.AI4
21152 PCI-to-PCI Bridge Preliminary Datasheet
16-1
Mechanical Specifications
Table 16-1 lists the 160-pin package dimensions in millimeters.
Table 16-1. 160-Pin PQFP Package Dimensions
Symbol
Dimension
Value (mm)
LL
e
Lead length
1.30 reference1
Lead pitch
0.65 BSC2
L
Foot length
0.65 minimum to 1.03 maximum
4.50
A
Package overall height
Package standoff height
Package thickness
Lead width
A1
A2
b
0.25 minimum
3.17 minimum to 3.67 maximum
0.22 minimum to 0.38 maximum
0.12 minimum to 0.23 maximum
0.10
c
Lead thickness
Coplanarity
ccc
ddd
D
Lead skew
0.13
Package overall width
Package width
Package overall length
Package length
Ankle radius
31.20 BSC2
D1
E
28.00 BSC2
31.20 BSC2
E1
R
28.00 BSC2
0.13 minimum to 0.30 maximum
1. The value for this measurement is for reference only.
2. ANSI Y14.5M-1982 American National Standard Dimensioning and Tolerancing, Section 1.3.2,
defines Basic Dimension (BSC) as: A numerical value used to describe the theoretically exact
size, profile, orientation, or location of a feature or datum target. It is the basis from which
permissible variations are established by tolerances on other dimensions, in notes, or in feature
control frames.
16-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
Configuration Register Values After
Reset
A
Table A-1 lists the value of the 21152 configuration registers after reset. Reserved registers are not
listed and are always read only as 0.
Table A-1. Configuration Register Values After Reset (Sheet 1 of 2)
Byte Address
Register Name
Reset Value
00–01h
02–03h
04–05h
06–07h
Vendor ID
Device ID
Command
Status
1011h
0024h
0000h
0280h1
0290h2
08h
Revision ID
Initially 00h3
060400h
00h
09–0Bh
0Ch
Class code
Cache line
0Dh
Primary master latency timer
Header type
00h
0Eh
01h
18h
Primary bus number
Secondary bus number
Subordinate bus number
Secondary master latency timer
I/O base
00h
19h
00h
1Ah
00h
1Bh
00h
1Ch
01h
1Dh
I/O limit
01h
1E–1Fh
20–21h
22–23h
24–25h
26–27h
28–2Bh
2C–2Fh
30–31h
32–33h
34–35h
Secondary status
0280h
0000h
0000h
0001h
0001h
00000000h
00000000h
0000h
0000h
Memory-mapped I/O base
Memory-mapped I/O limit
Prefetchable memory base
Prefetchable memory limit
Prefetchable memory base upper 32 bits
Prefetchable memory limit upper 32 bits
I/O base upper 16 bits
I/O limit upper 16 bits
Subsystem vendor ID
ECP pointer
0000h4
00DCh2
36–37h
3Dh
Subsystem ID
Interrupt pin
0000h
00h
3E–3Fh
Bridge control
0000h
21152 PCI-to-PCI Bridge Preliminary Datasheet
A-1
Configuration Register Values After Reset
Table A-1. Configuration Register Values After Reset (Sheet 2 of 2)
Byte Address
Register Name
Reset Value
40h
Chip control
00h
41h
Diagnostic control
00h
42–43h
64h
Arbiter control
0200h
00h
p_serr_l event disable
Secondary clock control
p_serr_l status
68–69h
6Ah
00h
00h
DCh
Power management capability ID
Next item
01h5
00h5
0001h5
0000h5
DDh
DE–DFh
E0–E1h
E2h
Power management capabilities
Power management CSR
PPB support extensions
C0h (bpcc = 1)5
00h (bpcc = 0)
E3h
Data register
00h5
1. 21152–AA.
2. 21152–AB and later revisions.
3. Dependent on revision of device. The first revision is read as 00h; subsequent revisions increment by 1.
4. 21152–AA only. In the 21152–AB, these registers are reserved.
5. 21152–AB and later revisions only. In the 21152–AA, these registers are reserved.
A-2
21152 PCI-to-PCI Bridge Preliminary Datasheet
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