CA2162187C - Bridge between two buses of a computer system that latches signals from the bus for use on the bridge and responds according to the bus protocols - Google Patents

Bridge between two buses of a computer system that latches signals from the bus for use on the bridge and responds according to the bus protocols

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Publication number
CA2162187C
CA2162187C CA002162187A CA2162187A CA2162187C CA 2162187 C CA2162187 C CA 2162187C CA 002162187 A CA002162187 A CA 002162187A CA 2162187 A CA2162187 A CA 2162187A CA 2162187 C CA2162187 C CA 2162187C
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CA
Canada
Prior art keywords
bus
control signals
bridge
pci
slave
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
CA002162187A
Other languages
French (fr)
Other versions
CA2162187A1 (en
Inventor
Sagi Katz
William Alan Wall
Amy Kulik
Daniel R. Cronin, Iii
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International Business Machines Corp
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International Business Machines Corp
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Publication date
Application filed by International Business Machines Corp filed Critical International Business Machines Corp
Publication of CA2162187A1 publication Critical patent/CA2162187A1/en
Application granted granted Critical
Publication of CA2162187C publication Critical patent/CA2162187C/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06FELECTRIC DIGITAL DATA PROCESSING
    • G06F13/00Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06FELECTRIC DIGITAL DATA PROCESSING
    • G06F13/00Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
    • G06F13/38Information transfer, e.g. on bus
    • G06F13/40Bus structure
    • G06F13/4004Coupling between buses
    • G06F13/4027Coupling between buses using bus bridges
    • G06F13/405Coupling between buses using bus bridges where the bridge performs a synchronising function
    • G06F13/4054Coupling between buses using bus bridges where the bridge performs a synchronising function where the function is bus cycle extension, e.g. to meet the timing requirements of the target bus

Abstract

A computer system having an ISA bus and a PCI bus is provided with a PCI to ISA
bridge having certain imbedded functions performed by PCI slaves on the bridge. In order to implement the bridge in slow CMOS technology, the PCI control signals are latched on the bridge. Since the PCI slaves on the bridge cannot respond with control signals on the PCI bus fast enough to satisfy the PCI bus protocol due to this latching, a logic device is provided on the bridge. The logic device monitors the unlatched master-slave control signals carried on the PCI bus, and in appropriate situations, drives the control signals on the PCI
bus (within the time specified by the PCI bus protocol) that the PCI slaves would normally drive but are unable to within the time necessary to meet the PCI bus protocol.

Description

A BRIDGE BETWI~N TWO BUSES OF A COMPUTER SYSTEM
THAT LATCHES SIGNALS FROM THE BUS FOR USE ON THE BRIDGE
AND RESPONDS ACCORDING TO THE BUS PROTOCOLS

BACKGROUND OF THE INVENTION

Field of the Invention The present invention relates to the field of digital computer systems, and moreparticularly, to a bus interface (a bridge) between two busses.

Desc~ lion of Related Art In computer systems, electronic chips and other components are connected with one another by buses. A variety of components can be connected to the bus providing intercommunication between all of the devices that are connected to the bus. One type of bus which has gained wide industry acceptance is the industry standard architecture (ISA) bus. The ISA bus has twenty-four (24) memory address lines which therefore provides support for up to sixteen (l fi) megabytes of memory. The wide acceptance of the ISA bus has resulted in a very large percentage of (levices being designed for use on the ISA bus.
However, higher-speed input/output devices commonly used in computer systems require faster buses.
A solution to the general problem of sending and receiving data from the processor to any high-speed input device is a local bus. Unlike the ISA bus, which opcrates relatively slowly with limited bandwidth, a local bus communicates at system speed and carries data in 32-bit blocks. Local bus machines remove from the main system bus those interfaces that need quick response, such as memory, display, and disk drives. One such local bus that is gaining acceptance in the industry is thc peripheral component interconllect (PCI) bus. The PCI bus can be a 32 or 64-bit pathway f~r high-speed data transfer. Essentially, the PCI
bus is a parallel data path provided in addition to an ISA l~us. The system processor and 216218~

memory can be attaehed directly to the PCT bus, for example. Other deviees such as graph;c display adapters, disk controllers, sound cards, ele. ean also attach directly or indirectly (e.g., through a host bridge) to the PCI hus.
A bridge chip is provide(l between the PCI hus and the ISA bus in order to provide eommunication between devices on the lwo huses. The hridge chip essentially translates the ISA bus cycles to PCI bus cycles, and vice versa.
Many of the devices attached to the PCI hus and the TSA bus are "master" devicesthat can eonduet proeessing indereIldently of the bus or other deviees. Certain deviees eoupled to the buses are considere~l to he "slave~" (?r "targets" that accept commands and respond to requests of a mastel. Many ~Ievices are able to SCtVC as both a master and a slave in eertain eireumstanees.
It is desirable to provi(le the bri(lge chil~ helweell lhe PCI hus and the ISA bus with eertain funetionality, sueh as scatte-r/gathering, integrated drive electronics (TDE) interfacing, PCI arbitration, etc. For at Ieast some of these purposes, the bridge chip eontains slaves. These slaves need lo respond to the PCI hus aeeording to the PCI bus protoeol, set forth in the PCI Speeifieation. However, to provi(le the desired funetionality in the bridge ehip within the specified respollse time r equired by the PCI bus is problematieal if the bridge ehip is implcmented in a relat;ively inexpensive and slower teehnology, such as a 0.8 microll CMOS technology. The problem arises due to the need to latch the signals that are received from the PCI hus as inputs lo the bridge ehip as well as those signals sent to the PCI bus from lhe hridge chip to allow the slaves implemented in the slower technology to make use of the signal~. Tlle lwo clock latency created by the latching is incompatible with tlle PCT bu!; rrolocol.
There is a need for a ~ystem which uses a bridge chip that provides desiIed functionality, and while implemented in a relati\!ely slowel technology, is able to maintain the PCI bus protocol.

These and other needs are mel by the present invention which provides a bridge coupled between first and second buses ror interfacing the first and second buses, the second bus carrying master-slave con~r(!l signal.s and l1aving a master coupled to the bus and a specified bus protocol. The bridge comprise~ an interllal latched third bus carrying latched master-slave control signals, at Ieast one slave, an(l a latch coupled between the second and third buses. This latch latche~ lhe masler-~lave control signals received from the second bus and the latched master-slave control signals received from the third bus. The bridge has a logic device coupled between the second and lhir(l buses, the logic device monitoring the states of the control signal~ on the seconcl l~us and driving at least one of the control signals on the secon(l bus according to the bus ptotocol in response to certain predetermined states of the monitore(l control sigl1al~i.
In certain preferred embodimenls of the invention, Ihe ~second bus is a peripheral controller interconnect (PCI) bu.s, and the hus protocol is a PCI bus protocol.
The present invention provide~ the cost advantage~s of a bridge that can be implemented in 0.2 micron CMOS tec}lnology, .since the control signals to and from the PCI
bus are latched for the PCI slaves on the bridge. At the .same time, however, PCI bus protocol is maintained by the logic device tllat monitors lhe unlatched control signals and responds to predetermined s~ate~ of the control signals accol(ling to the PCI bus protocol.
This frees the PCI slaves from havillg to respoll(l ullder cel-taill circumstances with control signals on the PCI bus within the time pelio(ls specirie(l by the PCI bus protocol.
The foregoing and other objecl~i, feat~lle~, aspect~ ail(l advantages of the present invention will become more appalent flom tlle followillg de~ailed description of the present invention when taken in conjunctioll witll lhe accnlllpanying ~llawings.

BRIEF DESCRIPTION OF THE DRA WIN(JS
Figure I is a perspective view of a computer system of the presellt invention.
Figure 2 is a block diagram of ~he computer system of Figurc I constructcd in accordance with an embodiment of the presellt invention.

21 62l 87 Fi~gure 3 is a bloek diagram Of a briclge chil- constructecl in accordanee with an embodiment of the present inventi~n.
Figures 4a-f are timing diagl ams of exemplaty signal ttansfets between the PCI bus and the bridge ehip of the present invention for clifreren~ situations.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT(S) With referenee now to the Figures and in pclrtieulal with refercnee to Figure I, a eonventional eomputer, or PC, designated 10, is o r tllc envil-onmcllt to whieh the invention has partieular utility. Computer 10 whicll l refelcll-ly, but nOt neccssarily, is of a type utilizing an IBM personal computer Or a simil3l syslelll, includes a console housing 12 in whieh a eireuit board eontaining the necessary circuitry inclucling a mieroproeessor and BIOS ehips, eontrollers, random aecess memory ancl olllel haldware are arranged. The eomputer will also inelucle a video display 14 an(l a keyboarcl 16 connected to the housing 12 through eable 18. Mass stol-age mecli3 includes a harcl clisk clrive within the housing and is non-aeeessible to the user, and user-accessible rlol-py disks, as well as, optionally, CD-ROM drives 20 and 22.
Figure 2 is a bloek diagram Of a computer syslem constructed in accordance with an embodiment of the presellt invcntion. The system inclucles a PCI l us 30, an ISA bus 32, with a plurality of ISA masters 36 an(l ISA slaves 3X. A plul ality of PCI memory slaves 40 (known as "targets" in the PCI prolocol, but hellcefol-l:ll rererred to as slaves) and PCI
masters 42 are eoupled to thc PCI bus 30.
The bridge ehip 34 eolltains an ISA intel-rclce 44 coutlled between the ISA bus 32 and an internal system bus 4~. A PCI hlterrace 4X i~ pl-oviclccl belween the PCI bus 30 and the system bus 46. The briclge chip 34 also hcs .1 DMA contloller 50 and programmable I/O (PIO) registers 52. Among other fullctiolls, Ihe bridge chip 34 provides an interface between the PCI bus 30 anci ~he ISA bus 32. Thc ISA in~errace 44 translates ISA bus eyeles into a system bus cyele ror use hy lhe bridge chir) 34. Among other funetion.s, the PCI interfaee 4X eonverts PCI bus cycles flom the PCI bus 30 into system bus cycles for the bridge chip 34. The DMA controller 50 provi(les DMA control of memory accesses within the system.
Figure 3 is a block diagram Of elements Or the PCI intcrface 48 that allow the bridge chip 34 to be implemented ;n a slow technology and still resp(?nd according to the PCI
protocol. It wil] be understood by th(lse of ordillaly skill in the art that the PCI interface 48 includes other elements rOr perfol mhlg the PCI cycles/internal system bus cycles translation, but these other elements ale not illustrc3ted S(l as not to obscure the present inventlon.
The PCI interface 48 is couple(l lo a pl~lr-ality of PCI slaves 64, 66, 68 located on the bridge chip 34. These PCI slaves 64 - 6X perrorm the variolls de~irecl functions that can be imbedded in the bridgc chip 34, such as sc.lttel/gather, IDE interfacing, PCI arbitration, etc. Since the bridge chip 34 is implemellte(i in slow technology to provide a reasonable cost chip, the PCI slaves 64- 6X are also irnl-lemented in the slow technology and cannot normally detect and respond to unlatche(l control sigll.lls On the PCI bus 30. The PCI slaves 64 - 68 on the bridge chip 34 thererore require thclt the control xignals to and from the PCI
bus 30 be latched.
The latching of the signals by the PCI interface 4X to all(l from the PCI bus 30 is provided by a PCI latch 60, formed hy conventi-)llal lalches. The latch 60 is coupled to the PCI bus 30 to receive a frame xignal (FRAMF#), all inili,ltor ready signal (IRDY#); and to send a target ready signal (TRDY~)"a stol- ~ignal (STOP#), and a device select signal (DEVSEL#). The latch 60 is also couple(l lo an inlei-llal lalched PCI bus 62 and provides latched versions of the above signals On lhe latclle(l PCI bus (2. The latched signals are designated as L_FRAMF#, I _IRDY~ l RDY~, I,_DEVSEL# ancl L_STOP#.
The latching of the sigllal~ hl botll dilccliol1s a(l(ls a two clock latency to the communication cycles between tlle PCI master 42 all(l the PCI ~laves 64 - 68. The PCI bus 30 is not designed to have a two cklck latency an(l maintain the protocol.
In order to overcome the latency prohlem brought about by the need to latch the signals in both directions, the PCl latch 4X Of the r~re~ent invelltion is provided with a PCI
interface ]ogic device 70 that is coupled ~o the PCI bus 30. As will be clescribed in more detail in the following, the PCI interrace logic device 70 monitors the external PCI control signals and the slave control signals and dt-ives the control signals on the PCI bus 30 according to the PCI bus protocol.
The con~lguration of the logic (levice 70 is sr~ecific to the particular bus with which the logic device 70 is being used, such as tlle examr)le of the PCI bus 30 in this illustrative embodiment. A state machine is ~?rovided for each or ~he STOP#, DEVSEL#, and TRDY#
signals for maintaining the PCI bus ~?rotocol. The conriguration or the state machines to perform the functions of moniloring an(l clriving the contl-ol signals according to the PCI
bus protocol is readi]y accomplished hy one of ordinary skill in the art.
Some of the problems that may arise clue lo the interfacing of the slaves 64 - 6X to the latched PCI bus 62 include: (I) slaves stol~l ing atlem~?ted bursts when slave TRDY#
is asserted with external FRAME# deasserte(l; (2) non-burst transfers; and (3) slaves stopping attempted bursts whell slave TRDY# is asscrte(l llrior to external FRAME#
deasserted, etc.
Although the PCI signals and bus l-rotocol are well-known to those of ordinary skill in the art, the meaning of the signals that are shown in the timing diagrams of Figur~ 4a-f will be briefly described.
The FRAME# s;gnal is asserte(l 't?y a mastel (or "initiator") to indicate to the slaves that the master is starting a lrallsactioll.
The IRDY# signal (Initiator Rcady) is assel^ted by a master to indicate that themaster is ready to send or receive dala.
The DEVSEL~ (Device Select) signal i.s asscl~e(l hy a s1.1ve to acknowledge to the master that the slave is aware lllat it is ~he ~Ievice selected to l~errorm the tran~saction with the master.
The TRDY# (Target Ready) signal is asselle(l by a slavc to indicate that the slave (or "target") is ready to sencl or receive dala.
The STOP# signal is asserted hy a slave to in(licate to a master that it is not able to handle a transaction.

In the exemplary embodiment -r thc r?tcscnt invcnti(ln, lhe logic device 70 takes over control of the DEVSEL# STOP# an(l TRDY# signals (tho.se .signals sent from a slave) under six different circumstanccs. The rirst of these i~ when a master 42 tries to burst to a non-bursting slave (such as PCI slave 64~ wilh a late IRDY#. The timing diagram for this situation is provided in Figure 4a. (In all (!I` lhe liming diagrams the prefix L_ means latched signals internal lo the bri(lge chip 34 whel-eas no prefix inclicates an unlatched signal external to the bridge chip 34. Also a dashe(l line indicates a signal that has been driven by the logic device 7().) Since the PCI slave 64 does not know whether the transfer is a burst transfer or a noll-blltst transfel-? lhe PCI slave 64 asserts L_STOP# in the fourth clock of the cycle. The STOP~ sign.ll is senl orr chip to the PCI bus 30 in the fifth clock of the cycle. In ordcr to scll~l dat.l lllc masler 42 drives the IRDY# signal active The master 42 also sees the a.sser~e(l STOP# 011 tllC sixth clock and therefore drives FRAME# inactive to terminale llle cycle. The signal TRDY# 111USt Ollly be asserted for one clock since the PCI slave 64 cloes not sur?polt a bursl transaction. Therefore the PCI
interface logic device 70 deasserts TRDY# on the sixlh clock. After the FRAME# is deasserted the PCI protocol requiles that DEVSEL# TRDY# and STOP# (the slave signals) all be deasserted. The PCI pro~ocol lhcrerore requires that the STOP# and DEVSEL# signals be deasserted in the cl--ck al`ter Ihe deassertioll of FRAME# i.e. in the seventh clock. Without the PCI interrace logic de\/ice 70 of ~he present invention these signals would not be driven inactive until lhe nillth clock, since the latched L_FRAME#
signal is not seen by the PCI slave 64 unli Mlle sevelllll clock rexpollded to in the eighth clock and sent off chip in the nintll clock. The PCI sl.lve ~l4 thus (loes not become aware that the cycle has to be termhlale(l ill SUrriCiClll (illlC lo rcsl-oll(l according to the PCI bus protocol.
The PCI interface logic ~Ievice 70 ~hicll is m(llliloling the unlatche(J (extcrnal) control signals recognizes the inacli~;e FRAM E# sign<ll as a circum.stance requiring termination of the cycle. Accor(lingly~ the PCI intelrclce logic device 70 drives the STOP#
DEVSEL# and TRDY# inaclive in ~he seventll clock Illeleby maintaining the PCI bus protocol.

The operation of the PCI interface logic 70 to dtive the control signals in the other ~Ive circumstances should llOW be apparent from the a~ove descriptioll and the remaining timing diagrams. The situation in Figurc 4b, for cxamplc OCCUIS when a master 42 tries to burst to a non-bursting slave ~4 with late IRDY# alld the cycle must be terminated with a target abort. A target abort is defined by I he slave cleasserting L_DEVSEL# and asserting L_STOP#. After receiving lhe STOP# signal in the fifth clock, the FRAME#
signal is driven inactive by the master. l he STOP# signal must be driven inactive by the PCI interface logic device 70 in the nexl clock (DEVSEI # an(i TRDY# are alreadyinactive) to maintain the bus protocol.
The third circumstance (Figurc 4c) occurs ~hctl thc Illa'itCr 42 iS bursting with an immediate IRDY#, and the PCI slave 64 r~erforms a targel abort by driving L_DEVSEL#
inactive and L_STOP# active. In tllis case, the PCI hus l-rotocol requires that the FRAME# signal be driven active (perro~med by lhe mastel 42) ancl the STOP# signal be driven inactive (by the PCI interface logic device 70~ one clock after the FRAME# signal is driven inactive after the targel abolt. The PCI interrclce logic device 70, which has been monitoring the unlatched signals, needs ~o drive only the STOP# signal to inactive since the DEVSEL# and TRDY# are alrea(ly inactive.
The fourth circumstance (Figurc 4d) occurs whell the m3ster 42 performs a non-bursting transfer with a late IRDY# signal alld thele is a target abort. In this case, the FRAME# signal is driven inactive by the masler 42 after Ille nlaster 42 sees the STOP#
signal active. Once again, the STOP# sigl1al is dlivel1 hlactive l~y the PCI interface logic device 70 one clock after the FRAME# is dC.lSSCI tcd in 01 (ICI ~O maintain the bus protocol.
Otherwise, the L_STOP# xignal ~oul(l nl-l be dl iVCIl inaclivc 011 thc PCI bus 30 for another two clock cycles, which woul~l violate thc l'CI l-us l~lotocol.
The f~lfth circumstance (Figure 4e) occurs when lhe master 42 performs a non-bursting transfer and there is 110 l,argcl ahorl,. In lhis case, the PCI slave 64 asserts L_STOP# in the fourlh clock, seen by ~hc mastcr 42 as STOP# in the fifth c]ock. The master 42 responds by deasserting FRAME# in thc sixlll clock. The STOP#, TRDY# and DEVSEL# signals must all be deasserted in the sevelltl1 clock since the FRAME# signal was deasserted in the sixth clock. Since the PCI slave 64 cannot di ive these signals inactive soon enough, due to the latching of the signals, the PCI inlerface logic device 70 drives the signals inactive to maintain the PCI bus protocol.
The sixth circumstance (Figurc 41~ occuls whell the master performs a bursting transfer to a non-bursting slave 64, with an imme(liate lRDY# signal. The L_STOP# signal is asserted by the PCI slave 64 in the l`ourtll clock, seen by lhe master 42 in the fifth clock which eauses the master to deasserl FRAME#. Arter FRAME# has been deasserted, the DEVSEL# and STOP# have to be driven inaclive in the SiXtll cloclc to maintain the PCI
bus protocol, the TRDY# signal alreacly heing inactive in thi.5 c3se.
As can be appreciated l~y lhe above ex~lmples, the present invention provides a PCI
interface logic device 70 that monitors tlle unlatclle(l, external control signals and under certain cireumstanees, takes OVCI the lask or clriving the exlernal slave signals on the PCI
bus 30 aceording to the PCI bus prolocol. This allows llle bridge chip 34, containing the PCI slaves 64 - 6X, to bc implemente(l in a slow, relatively inexpensive technology using latched signals, while maintaining the PCI bus protocol.
Although the present invention has been described and illustrated in detail, it is clearly understood that the s<lme is by way of illustlatioll an(l example only and is not to be taken by way of limitation, tlle spil it ~nd scor)e Or lhe pl-esent invention being limitcd only by the terms of the appell(led claitlls.

Claims (36)

1. A computer system comprising:
a first bus;
a second bus carrying master-slave control signals and having a specified bus protocol;
at least one master coupled to the second bus;
a bridge coupled between the first, and second buses for interfacing the first and second buses, the bridge including:
an internal latched third bus carrying latched master-slave control signals;
at least one slave;
a latch coupled between the second and third buses and latching the master-slave control signals received from the second bus and the latched master-slave control signals received from the third bus;
a logic device coupled between the second and third buses, the logic device monitoring the states of the control signals on the second bus and driving at least one of the control signals on the second bus according to the bus protocol in response to certain predetermined states of the monitored control signals.
2. The system of Claim 1, wherein the second bus is a peripheral controller interconnect (PCI) bus, and the bus protocol is a PCI bus protocol.
3. The system of Claim 2, wherein the slave is a PCI slave.
4. The system of Claim 3, wherein the third bus is an internal latched PCI
bus.
5. The system of Claim 4, wherein the control signals include a target ready signal, a device select signal and a stop signal, the logic device driving at least one of these control signals in response to the certain predetermined states of the monitored control signals.
6. The system of Claim 5, wherein the monitored control signals include a frame signal and an initiator ready signal.
7. The system of Claim 6, wherein the bridge is formed by slow CMOS
technology.
8. The system of Claim 5, wherein the logic device includes a separate state machine for each of the respective target ready, device select and stop signals.
9. The system of Claim 6, wherein the predetermined state includes a deassertion of the frame signal, the logic device driving any active target ready, device select and stop signals inactive in response to the deassertion of the frame signal.
10. A bridge coupled between first and second buses for interfacing the first and second buses, the second bus carrying master-slave control signals and having a master coupled to the bus and a specified bus protocol, the bridge comprising:
an internal latched third bus carrying latched master-slave control signals;
at least one slave;
a latch coupled between the second and third buses and latching the master-slave control signals received from the second bus and the latched master-slave control signals received from the third bus;
a logic device coupled between the second and third buses, the logic device monitoring the states of the control signals on the second bus and driving at least one of the control signals on the second bus according to the bus protocol in response to certain predetermined states of the monitored control signals.
11. The bridge of Claim 10, wherein the second bus is a peripheral controller interconnect (PCI) bus, and the bus protocol is a PCI bus protocol.
12. The bridge of Claim 11, wherein the slave is a PCI slave.
13. The bridge of Claim 12, wherein the third bus is an internal latched PCI
bus.
14. The bridge of Claim 13, wherein the control signals include a target ready signal, a device select signal and a stop signal, the logic device driving at least one of these control signals in response to the certain predetermined states of the monitored control signals.
15. The bridge of Claim 14, wherein the monitored control signals include a frame signal and an initiator ready signal.
16. The system of Claim 15, wherein the bridge is formed by slow CMOS
technology.
17. The bridge of Claim 14, wherein the logic device includes a separate state machine for each of the respective target ready, device select and stop signals.
18. The bridge of Claim 15, wherein the predetermined state includes a deassertion of the frame signal, the logic device driving any active target, ready, device select and stop signals inactive in response to the deassertion of the frame signal.
19. A computer system comprising:
a first bus;
a second bus carrying control signals and having a specified bus protocol;
at least one master coupled to the second bus;
a bridge coupled between the first and second buses for interfacing the first and second buses, the bridge including:
a third bus carrying latched control signals received from the second bus;
at least one slave coupled to the third bus and receiving latched control signals from the third bus;
a latch coupled between the second and third buses and latching control signals sent from the second bus to the third bus, and latching control signals sent from the third bus to the second bus;
a logic device coupled between the second and third buses, the logic device sending, in response to receiving predetermined unlatched master control signals from the master coupled to the second bus, predetermined unlatched slave control signals to the master on the second bus, wherein the predetermined unlatched master control signals are for a predetermined type of data transfer between the master coupled to the second bus and the slave coupled to the third bus.
20. The system of claim 19, wherein the second bus is a peripheral controller interconnect (PCI) bus, and the bus protocol is a PCI bus protocol.
21. The system of claim 19, wherein the slave is a PCI slave.
22. The system of claim 21, wherein the third bus is an internal latched PCI
bus.
23. The system of claim 22, wherein the control signals include a target ready signal, a device select signal and a stop signal, the logic device driving at least one of these control signals in response to the certain predetermined states of the monitored control signals.
24. The system of claim 23, wherein the monitored control signals include a frame signal and an initiator ready signal.
25. The system of claim 24, wherein the bridge is formed by slow CMOS
technology.
26. The system of claim 23, wherein the logic device includes a separate state machine for each of the respective target ready, device select and stop signals.
27. The system of claim 24, wherein the predetermined state includes a deassertion of the frame signal, the logic device driving any active target ready, device select and stop signals inactive in response to the deassertion of the frame signal.
28. A bridge coupled between first and second buses for interfacing the first and second buses, the second bus carrying control signals and having a master coupled to the bus and a specified bus protocol, the bridge comprising:
a third bus carrying latched control signals received from the second bus;
at least one slave coupled to the third bus and receiving latched control signals from the third bus;
a latch coupled between the second and third buses and latching control signals sent from the second bus to third bus, and latching control signals sent from the third bus to the second bus;
a logic device coupled between the second and third buses, the logic device sending, in response to receiving predetermined unlatched master control signals from the master coupled to the second bus, predetermined unlatched slave control signals to the master on the second bus, wherein the predetermined unlatched master control signals are for a predetermined type of data transfer between the master coupled to the second bus and the slave coupled to the third bus.
29. The bridge of claim 28, wherein the second bus is a peripheral controller interconnect (PCI) bus, and the bus protocol is a PCI bus protocol.
30. The bridge of claim 29, wherein the slave is a PCI slave.
31. The bridge of claim 30, wherein the third bus is an internal latched PCI bus.
32. The bridge of claim 31, wherein the control signals include a target ready signal, a device select signal and a stop signal, the logic device driving at least one of these control signals in response to the certain predetermined states of the monitored control signals.
33. The bridge of claim 32, wherein the monitored control signals include a frame signal and an initiator ready signal.
34. The system of claim 33, wherein the bridge is formed by slow CMOS
technology.
35. The bridge of claim 32, wherein the logic device includes a separate state machine for each of the respective target ready, device select and stop signals.
36. The bridge of claim 33, wherein the predetermined state includes a deassertion of the frame signal, the logic device driving any active target ready, device select and stop signals inactive in response to the deassertion of the frame signal.
CA002162187A 1994-11-30 1995-11-06 Bridge between two buses of a computer system that latches signals from the bus for use on the bridge and responds according to the bus protocols Expired - Fee Related CA2162187C (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US08/351,186 US5664124A (en) 1994-11-30 1994-11-30 Bridge between two buses of a computer system that latches signals from the bus for use on the bridge and responds according to the bus protocols
US08/351,186 1994-11-30

Publications (2)

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HU217405B (en) 2000-01-28
PL180351B1 (en) 2001-01-31
CZ9701508A3 (en) 2002-05-15
HUT76791A (en) 1997-11-28
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EP0795158A1 (en) 1997-09-17
WO1996017303A1 (en) 1996-06-06
EP0795158B1 (en) 1999-01-27
BR9505207A (en) 1997-09-16
KR100192724B1 (en) 1999-06-15
ATE176341T1 (en) 1999-02-15
JPH08235103A (en) 1996-09-13
CA2162187A1 (en) 1996-05-31
KR960018934A (en) 1996-06-17
CN1153352A (en) 1997-07-02
CN1089463C (en) 2002-08-21
JP3838278B2 (en) 2006-10-25
US5664124A (en) 1997-09-02
PL320020A1 (en) 1997-09-01
DE69507636D1 (en) 1999-03-11
DE69507636T2 (en) 1999-08-05

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