PCI
`YSTEM
`ARCHITECTURE
`
`FOURTH EDITIO
`
`MINDSHARE, INC
`Tom Shanley/ Don Anderso1
`
`PC SYSTEM
`, ARCHITECTURE
`SER IES
`
`1
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`Comcast, Ex. 1247
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`

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`PCI
`System
`Architecture,
`Fourth Edition
`
`MINDSHARE, INC.
`
`Don Anderson
`Tom Shanley
`• ....
`
`ADDISON-WESLEY
`
`An imprint of Addison Wesley Longman, Inc.
`Reading, Massachusetts " Menlo Park, California " New York
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`2
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`Many of the designations used by manufacturers and sellers to distinguish their prod(cid:173)
`ucts are claimed as trademarks. Where those designators appear in this book, and
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`
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`expressed or implied warranty' of any kind and assume no responsibility for errors or
`omissions. No liability is assumed for incidental or consequential damages in connec(cid:173)
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`Library of Congress Cataloging-in-Publication Data is available.
`
`ISBN: 0-201-30974-2
`
`Copyright ©1999 by MindShare, Inc.
`All rights reserved. No part of this publication may be reproduced, stored in a retrieval
`system, or transmitted, in any form or by any means, electronic, mechanical, photocopy(cid:173)
`ing, recording, or otherwise, without the prior written permission of the publisher.
`Printed in the United States of America. Published simultaneously in Canada.
`
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`Cover Designer: Simone R. Payment
`Set in 10 point Palatino by MindShare, Inc. .
`
`12 3 4 5 6 7 8 9-MA-0302010099
`First Printing, May 1999
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`

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`Intro To PCI
`
`Th is Chapter
`
`This chapter provides a brief history of PCI, introduces its major feature set, the
`concept of a PCI device versus a PCI function, and identifies the specifications
`that this book is based upon.
`
`The Next Chapter
`
`The next chapter provides an introduction to the PCI transfer mechanism,
`including a definition of the following basic concepts: burst transfers, the initia(cid:173)
`tor, targets, agents, single and multi-function devices, the PCI bus clock, the
`address phase, claiming the transaction, the data phase, transaction completion
`and the return of the bus to the idle state. It defines how a device must respond
`if the device that it is transferring data with exhibits a protocol violation. Finally,
`it introduces the "green" nature of PCI-power conservation is stressed in the
`spec.
`
`PCI Bus History
`
`Intel made the decision not to back the VESA VL standard because the emerg(cid:173)
`ing standard did not take a sufficiently long-term approach towards the prob(cid:173)
`lems presented at that time and those to be faced in the coming five years. In
`addition, the VL bus had very limited support for burst transfers, thereby limit(cid:173)
`ing the achievable throughput.
`
`Intel defined the PCI bus to ensure that the marketplace would not become
`crowded with various permutations of local bus architectures peculiar to a spe(cid:173)
`cific processor bus. The first release of the specification, version 1.0, became
`available on 6/22/92. Revision 2.0 became available in April of 1993. Revision
`2.1 was issued in Ql of 1995. The latest version, 2.2, was completed on Decem(cid:173)
`ber 18, 1998, and became available in February 0£1999.
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`Chapter 1: Intro To PCI
`
`Specifications Book is Based On
`
`This book is based on the documents indicated in Table 1-2 on page 13.
`
`Table 1-2: This Book is Based On The Following Documents
`
`PCI Local Bus Specification
`
`PCI-to-PCI Bridge Specification
`
`PCI System Design Guide
`
`PCI BIOS Specification
`
`PCI Bus Power Management Interface Specification
`
`PCI Hot-Plug Specification
`
`Obtaining PCI Bus Specification(s)
`
`•Revision<
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`2.2
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`1.1
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`1.0
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`2.1
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`1.1
`
`1.0
`
`The PCI bus specification, version 1.0, was developed by Intel Corporation. The
`specification is now managed by a consortium of industry partners known as
`the PCI Special Interest Group (SIG). MindShare, Inc. is a member of the SIG.
`The specifications are commercially available for purchase from the SIG. The
`latest revision of the specification (as of this printing) is 2.2. For information
`regarding the specifications and/ or SIG membership, contact:
`
`PCI Special Interest Group
`2575 N.E. Kathryn #17
`Hillsboro, Oregon 97124
`1-800-433-5177 (USA)
`503-693-6232 (International)
`503-693-8344 (Fax)
`pcisig@pcisig.com
`http:/ /www.pcisig.com
`
`13
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`
` Intro to PCI Bus
`Operation
`
`The Previous Chapter
`
`The previous chapter provided a brief history of PCI, introduced it’s major fea—
`ture set, the concept of a PCI device versus a PCI function, and identified the
`specifications that this book is based upon. It also provided information on con-
`tacting the PCI SIG.
`
`In This Chapter
`
`This chapter provides an introduction to the PCI transfer mechanism, including
`a definition of the following basic concepts: burst transfers, the initiator, targets,
`agents, single and multi—function devices, the PCI bus clock, the address phase,
`claiming the transaction, the data phase, transaction completion and the return
`of the bus to the idle state. It defines how a device must respond if the device
`that it is transferring data with exhibits a protocol violation. Finally, it intro-
`duces the ”green" nature of PCI—power conservation is stressed in the spec.
`
`The 'Next Chapter
`
`Unlike many buses, the PCI bus does not incorporate termination resistors at
`the physical end of the bus to absorb voltage changes and prevent the wave—
`front caused by a voltage change from being reflected back down the bus.
`Rather, PCI uses reflections to advantage. The next chapter provides an intro—
`duction to reflected—wave switching.
`
`
`Burst Transfer
`
`Refer to Figure 2-1 on page 16. A burst transfer is one consisting of a single
`address phase followed by two or more data phases. The bus master only has to
`arbitrate for bus ownership one time. The start address and transaction type are
`issued during the address phase. All deviceson the bus latch the address and
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`PCI System Architecture
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`transaction type and decode them to determine which is the target device. The
`target device latches the start address into an address counter (assuming it sup-
`ports burst mode—more on this later) and is responsible for incrementing the
`address from data phase to data phase.
`
`PCI data transfers can be accomplished using burst transfers. Many PCI bus
`masters and target devices are designed to support burst mode. It should be
`noted that a PCI target may be designed such that it can only handle single data
`phase transactions. When a bus master attempts to perform a burst transaction,
`the target forces the master to terminate the transaction at the completion of the
`first data phase. The master must re-arbitrate for the bus to attempt resumption »
`of the burst with the next data item. The target terminates each burst transfer
`attempt when the first data phase completes. This would yield very poor per-
`formance, but may be the correct approach for a device that doesn’t require high
`throughput. Each burst transfer consists of the following basic components:
`
`
`
`The address and transfer type are output during the address phase.
`O
`0 A data object (up to 32-bits in a 32~bit implementation or 64—bits in a 64—bit
`implementation) may then be transferred during each subsequent data
`phase.
`
`Assuming that neither the initiator (i.e., the master) nor the target device inserts
`wait states in each data phase, a data object (a dword or a quadword) may be
`transferred on the rising—edge of each PCI clock cycle. At a PCI bus clock fre-
`quency of 33MHZ, a transfer rate of 132Mbytes/ second may be achieved. A
`transfer rate of 264Mbytes / second may be achieved in a 64—bit implementation
`' when performing 64—bit transfers during each data phase. A 66MI-Iz PCI bus
`implementation can achieve 264 or 528Mbytes /second transfer rates using 32—
`or 64—bit transfers. This chapter introduces the burst mechanism used to per-
`forming block transfers over the PCI bus.
`
`Figure 2—1: Example Burst Data Transfer
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`
`
`Chapter 2: Intro to PCI Bus Operation
`
`
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`Initiator, Target and Agents
`
`There are two participants in every PCI burst transfer: the initiator and the tar—
`get. The initiator, or bus master, is the device that initiates a transfer. The terms
`bus master and initiator can be used interchangeably and frequently are in the
`PCI specification. The target is the device currently addressed by the initiator
`for the purpose of performing a data transfer. PCI initiator and target devices
`are commonly referred to as PCI-compliant agents in the spec.
`
`
`Single- Vs. Multi-Function PCI Devices
`
`A PCI physical device package may take the form of a component integrated
`onto the system board or may be implemented on a PCI add-in card. Each PCI
`package (referred to in the spec as a device) may incorporate from one to eight
`separate functions. A function is a logical device. This is analogous to a multi—
`function card found in any ISA, EISA or Micro Channel machine.
`
`0 A package containing one function is referred to as a single-function PCI
`device,
`
`0 while a package containing two or more PCI functions is referred to as a
`multi-function PCI device.
`
`Each function contains its own, individually—addressable configuration space,
`64 dwords in size. Its configuration registers are implemented in this space.
`Using these registers, the configuration software can automatically detect the
`function’s presence, determine its resource requirements (memory space, 10
`space, interrupt line, etc.), and can then assign resources to the function that are
`guaranteed not to conflict with the resources assigned to other devices
`
`
`PCI Bus Clock
`
`Refer to the CLK signal in Figure 2—2 on page 19. All actions on the PCI bus are
`synchronized to the PCI CLK signal. The frequency of the CLK signal may be
`anywhere from OMHZ to 33MH2. The revision 1 0 specification stated that all
`devices must support operation from 16 to 33MHZ, while recommending sup—
`port for operation down to OMHz (in other words, when the clock has been
`stopped as a power conservation strategy). The revision 2.x (x-— 1 or 2) PCI
`specification indicates that all PCI devices must support PCI operation within
`the OMHz to 33MHz range. Support for operation down to OMHZ provides
`
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`
`
`PCI System Architecture
`
`low—power and static debug capability. On a bus with a clock running at 33MHz
`Or slower, the PCI CLK frequency may be changed at any time and may be
`stopped (but only in the low state). Components integrated onto the system
`board may be designed to only operate at a single frequency and may require a
`policy of no frequency change (and the system board designer would ensure
`that the clock frequency remains unchanged). Devices on add—in cards must
`support operation from 0 through 33MHz (because the card must operate in
`any platform that it may be installed in).
`
`The revision 2.1 specification also defined PCI bus operation at speeds of up to
`66MHz. The chapter entitled "66MHz PCI Implementation" describes the opera—
`tional characteristics of the 66MHz PCI bus, embedded devices and add-in
`cards.
`
`
`Address Phase
`
`Refer to Figure 2-2 on page 19. Every PCI transaction (with the exception of a
`transaction using 64-bit addressing) starts offs/“with an address phase one PCI
`clock period in duration (the only exceptier‘i'is a transaction wherein the initia—
`tor uses 64-bit addressing delivereds-irttwo address phases and consuming two
`PCI clock periods—this topicgi’s“ [covered in ”64-bit Addressing” on page 287).
`During the address phasew‘the initiator identifies the target device (via the
`
`address) and the typ. ,
`fransaction (also referred to as the command type). The
`target devicegisidentified by driving a start address within its assigned range
`onto the PCI address / data bus. At the same time, the initiator identifies the
`type oftransaction by driving the command type onto the 4—bit wide PCI Com—
`mand /Byte Enable bus. The initiator also asserts thé‘FRAMEit signal to indicate
`the presence of a valid start address and transaction type on the bus. Since the
`initiator only presents the start address and command for one PCI clock cycle, it
`is the responsibility of every PCI target device to latch the address and com-
`mand on the next rising-edge of the clock so that it may subsequently be
`decoded.
`
`By decoding the address latched from the address bus and the command type
`latched from the Command /Byte Enable bus, a target device can determine if it
`is being addressed and the type of transaction in progress. It's important to note
`that the initiator only supplies a start address to the target (during the address
`phase). Upon completion of the address phase, the address / data bus becomes
`the data bus for the duration of the transaction and is used to transfer data in
`each of the data phases. It is the responsibility of the target to latch the start
`address and to auto—increment it (assuming that the target supports burst trans~
`fers) to point to thenext group of locations:s(adword or a quadword) during
`each subsequent data transfer.
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` Chapter 2: Intro to PCI Bus Operation
`
`
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`...... ..i.
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`
`r at deasserts
` Target keeps
`TRD
`and DEVSEL.
`TRDV# tie-asserted at
`least unill DEVSEL#
`
`assened.
`
`Data Transfers
`
` Tar etdevlce
`3589 s DEVSEL#
`
`
`
`Claiming the Transaction ,
`
`Refer to Figure 2-2 on page 19. When a PCI target determines that it is the target
`of a transaction, it must claim the transaction by asserting DEVSEL# (Device
`Select). If the initiator doesn’t sample DEVSEL# asserted within a predeter-
`mined amount of time, it aborts the transaction.
`
`
`
`Data Phase(s)
`
`Refer to Figure 2-2 on page 19. The data phase of a transaction is the period dur—
`ing which a data object is transferred between the initiator and the target. The
`number of data bytes to be transferred during a data phase is determined by the
`number of Command/Byte Enable signals that‘are asserted by the initiator dur-
`ing the data phase.
`I
`" ‘
`
`
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`Figure 2-2: Typical PCI Transaction
`
`
`
`IiI|
`
`Inltlator starts
`
`transaction by
`
`CLK
`asserting FRAME# driving
`II
`address onto AIS bus
`and command unto CIBE bus
`
`
`
`
`: _q _
`i
`' ,
`
`'
`
`-
`.
`:
`:
`:
`i
`i
`.
`.
`
`Targets latch and
`decode address
`and command
`
`
`
`
`
`TurnAround cycle.
`
`
`Initiator stops driving
`AD bus
`>
`
`Initiator stops driving
`command and starts
`driving byte enables
`
`
`.
`|
`nltlamrdeassms
`FRAME# Indicating
`that it's readylto complete
`|ast da
`phase
`.
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`10
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`
`
`PCI System Architecture
`
`Each data phase is at least one PCI clock period in duration. Both the initiator
`and the target must indicate that they are ready to complete a data phase, or the
`data phase is extended by a wait state one PCI CLK period in duration. The PCI
`bus defines ready signal lines used by both the initiator (IRDY#) and the target
`(TRDY#) for this purpose.
`
`ransaction Duration
`
`0
`= 2
`‘ T
`
`The initiator doesn’t issue a transfer count to the target. Rather, in each data
`phase it indicates whether it’s ready to transfer the current data item and, if it is,
`whether it’s the final. data item. FRAME# is asserted at the start of the address
`phase and remains asserted until the initiator is ready (asserts IRDY#) to com-
`plete the final data phase. When the target samples IRDY# asserted and
`FRAME# deasserted in a data phase, it realizes that this is the final data phase.
`However, the data phase will not complete until the target has also asserted the
`TRDY# signal.
`
`
`Transaction Completion and Return of Bus to Idle State
`
`Refer to Figure 2-2 on page 19. The initiator indicates that the last data transfer
`(of a burst transfer) is in progress by deasserting FRAME# and asserting IRDY#.
`When the last data transfer has been completed, the initiator returns the PCI bus
`to the idle state by deasserting its ready line (IRDY#).
`
`If another bus master had previously been granted ownershipof the bus by the
`PCI bus arbiter and was waiting for the current initiator to surrender the bus, it
`can detect that the bus has returned to the idle state by detecting FRAME# and
`IRDY# both deasserted on the same rising-edge of the PCI clock (on the rising-
`edge of clock nine in the figure).
`
`
`RespOnse to Illegal Behavior
`
`The PCI specification does not encourage the device designer to actively Check
`for protocol violations. If a device does detect a violation, however, the follow—
`ing policy is advised.
`
`Upon detection of illegal use of bus protocol, all PCI devices should be designed
`to gracefully return to the idle state (i.e., cease driving all bus signals and return
`its target or master state machine to the quiescent state) as quickly as possible.
`The good device (as opposed to the evil one) should attempt to stay operational
`so it can participate in future transactions.
`L
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`;
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` Chapter 2:intro-tofret/Bus:, pe
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`The specification is understandably vague on this point. It depends on the '_
`nature of the protocol violation as to whether the devices can gracefully return L
`to their idle states and still function properly. As an example, the specification
`cites the case where the initiator simultaneously deasserts FRAME# and IRDY#
`(an illegal action). In this case, when the target detects this illegal end to the
`transaction, it is suggested that the target deassert all target—related signals and
`return its state machine to the idle state. In the event that a protocol violation
`leaves a target device questioning its ability to function correctly in the future, it
`can respond to all future access attempts with a Target Abort (explained in ”Tar-
`get Abort” on page 194). If the target thinks that the protocol violation has not
`impaired its ability to function correctly, it just surrenders all signals, returns to
`the idle state, and does not indicate any type of error.
`
`
`
`“Green” Machine
`
`In keeping with the goal of low power consumption, the specification calls for
`low—power, CMOS output drivers and receivers to be used by PCI devices.
`
`The next chapter introduces the reflected-wave switching used in the PCI bus
`environment to permit low—power, CMOS drivers to successfully drive the bus.
`
`If the address/ data bus and command/byte enable signals are permitted to
`float (around the switching region of the CMOS input buffers which exist in
`every PCI device) for extended periods of time, the receiver inputs would oscil-
`late and draw excessive current. This is a violation of the spec. To prevent this
`from happening, it is a rule in PCI that the address/ data bus, the command/
`byte enables, and the parity signal must not be permitted to float for extended
`periods of time. Since the bus is normally driven most of the time, it may be
`assumed that the pre-charged bus (precharged by the last entity to drive the
`bus) will retain its state while not being driven for brief periods of time during
`turnaround cycles (turnaround cycles are described in the chapter entitled
`”Read Transfers” on page 123).
`
`”Bus Parking” on page 65 describes the mechanism utilized to prevent the bus
`from floating when the bus is idle. The chapters entitled “Read Transfers” on
`page 123 and ”Write Transfers” on page 135 describe the mechanism utilized
`during data phases with wait states. The chapter entitled "The 64-bit PCI Exten-
`sion" describes the mechanism utilized to keep the upper half of the bus from
`floating when its not in use (during a 32—bit transfer).
`
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