1、INTERNATIONAL STANDARD ISO/IEC 14576 First edition 1999-12 Information technology Synchronous split transfer type system bus (STbus) Logical layer Technologies de linformation Bus de systme de transfert de fente synchrone (STbus) Couche logique Reference number ISO/IEC 14576:1999(E)INTERNATIONAL STA
2、NDARD ISO/IEC 14576 First edition 1999-12 Information technology Synchronous split transfer type system bus (STbus) Logical layer Technologies de linformation Bus de systme de transfert de fente synchrone (STbus) Couche logique PRICE CODE ISO/IEC 1999 All rights reserved. Unless otherwise specified,
3、 no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. ISO/IEC Copyright Office Case postale 56 CH-1211 Genve 20 Switzerland X For price, see current cat
4、alogueii 14576ISO/IEC:1999(E) Contents 1. Overview1 1.1 Scope. 1 1.2 Applicability1 2. Definitions. .3 2.1 ExplanationofTerms 3 2.2 Notation.5 3. InterfaceSpecifications 6 3.1 InterfaceSignals 6 4. BusOperations .11 4.1 ProtocolforBasicOperations11 4.2 TransferProtocol .16 4.2.1 Busoperationtypes.16
5、 4.2.2 Commandformat 16 4.2.3 Transfersequence .25 4.3 Arbitration.27 4.4 StatusReports27 4.5 DataTransfer .29 4.5.1 Memoryaccess(write)29 4.5.2 Memoryaccess(read) .35 4.5.3 Controlspaceaccess(write) .38 4.5.4 Controlspaceaccess(read).40 4.5.5 Messagetransfer 42 4.5.6 Controlregisteraccess(write) 44
6、 4.5.7 Controlregisteraccess(read)46 4.6 LockOperations 48 4.7 CacherelatedOperations.50 4.7.1 Cacheinvalidation 50 4.7.2 Retryindication.53 4.7.3 Copybackandstealoperationsafterretryindication55 4.7.4 Stealinhibitoperation.57 4.8 ErrorHandling.59 4.8.1 Handlingerrorsnotifiedinanswer .59 4.8.2 Other
7、errordetection .6114576ISO/IEC:1999(E) iii 5. CacheCoherencyControl 62 5.1 CacheControlMethods.62 5.2 CacheBlockAttributes62 5.3 OperationsonSystemBus.63 5.4 RetryIndication .65 5.5 StealOperation 66 5.6 CacheDataManagementandStateTransition67 5.6.1 Writethroughcache67 5.6.2 Copybackcache 70 5.7 Not
8、esonMemoryAccess75 6. FunctionsforEnhancedReliability76 6.1 Redundancy.76 6.2 DetectingFaults.77 6.3 PreventingFaultsfromSpreading .77 6.4 SupportingFaultHandlingandDiagnosis 78 AnnexA(informative) Performance(Estimated) 79 AnnexB(informative) Returnofanswerinalocktransfer .80 AnnexC(informative) Lo
9、cktransferandwritebackofcopybackcache 81iv 14576ISO/IEC:1999(E) Figures Figure1STbusApplications .2 Figure2Connectioninterfacebetweenfunctionunits(basicpattern) 7 Figure3Conceptofbusoperationprotocol(for1cycleor2cycletransfer: 8bytebuswidthspecification,writeoperation) 11 Figure4Conceptofbusoperatio
10、nprotocol(fortransferof3cyclesormore: 8bytebuswidthspecification,readoperation)13 Figure5Conceptofbusoperationprotocol(for1cycleor2cycletransfer: 4bytebuswidthspecification,writeoperation) 15 Figure6Pipelineoperation20 Figure7BCTfield.21 Figure8RAandbytealignment23 Figure9a)Onewordmemorywrite(noansw
11、ertransaction) 31 Figure9b)Onewordmemorywrite(basictransaction).32 Figure9c)nwordmemorywrite(noanswertransaction) .33 Figure9d)nwordmemorywrite(basictransaction) .34 Figure10a)Onewordmemoryread.36 Figure10b)nwordmemoryread.37 Figure11nwordwrite:controlspaceaccess39 Figure12nwordread:controlspaceacce
12、ss .41 Figure13nwordmessagetransfer43 Figure14Onewordwrite:controlregisteraccess 45 Figure15Onewordread:controlregisteraccess .47 Figure16Buslocktransfer49 Figure17Cacheinvalidation.52 Figure18Retryindication .54 Figure19Copybackandstealoperationsafterretryindication 56 Figure20Stealinhibitoperation
13、 .58 Figure21ErrorreportinanswertransactionwhenDUTdetectserror .60 Figure22Whenfunctionunit(0#)detectstimeout61 Figure23RelationbetweenCPUoperationandcommandsonsystembus .64 Figure24STbuswritethroughcachecoherencycontrolprotocol69 Figure25STbuscopybackcachecoherencycontrolprotocol 74 FigureA.1STbusp
14、erformance(in8bytebuswidthand32bitaddressingmode)79 FigureB.1Exampleofdeadlockproblem 80 FigureC.1ExampleoflocktransfertoEMcachedata.8114576ISO/IEC:1999(E) v Tables Table1BasicInterfaceSignals(functionunitinterfacesotherthanbushandler) .6 Table2OptionalInterfaceSignals(functionunitinterfacesothertha
15、nbushandler) .6 Table3CommandFormatforInformationTransferBus17 Table4OPTCodeDefinitions 18 Table5MBitDefinition .19 Table6MessageSequence 22 Table7AnswerCodeDefinition .28 Table8SystemBusCommandTypes.63 Table9SemanticsofDiscrepancybetweenBaseandSpareSignals76vi 14576ISO/IEC:1999(E) INFORMATIONTECHNO
16、LOGY SYNCHRONOUSSPLITTRANSFERTYPE SYSTEMBUS(STbus) LOGICALLAYER FOREWORD ISO(theInternationalOrganizationforStandardization)andIEC(theInternational ElectrotechnicalCommission)formthespecializedsystemforworldwide standardization.NationalbodiesthataremembersofISOorIECparticipateinthe developmentofInte
17、rnationalStandardsthroughtechnicalcommitteesestablishedby therespectiveorganizationtodealwithparticularfieldsoftechnicalactivity.ISOand IECtechnicalcommitteescollaborateinfieldsofmutualinterest.Otherinternational organizations,governmentalandnongovernmental,inliaisonwithISOandIEC,also takepartinthew
18、ork. Inthefieldofinformationtechnology,ISOandIEChaveestablishedajointtechnical committee,ISO/IEC JTC 1.DraftInternationalStandardsadoptedbythejoint technicalcommitteearecirculatedtonationalbodiesforvoting.Publicationasan InternationalStandardrequiresapprovalbyatleast75%ofthenationalbodiescasting avo
19、te. InternationalStandardISO/IEC14576waspreparedbysubcommittee26: Microprocessorsystems,ofISO/IECjointtechnicalcommittee1:Information technology. InternationalStandardsaredraftedinaccordancewiththerulesgivenintheISO/IEC Directives,Part3. AnnexesA,BandCareforinformationonly.14576ISO/IEC:1999(E) 1 INF
20、ORMATIONTECHNOLOGY SYNCHRONOUSSPLITTRANSFERTYPE SYSTEMBUS(STbus) LOGICALLAYER 1. Overview 1.1Scope ThisInternationalStandardspecifiesthelogicalspecificationsofSTbuswhichisahigh performanceandhighlyreliablesystembus.STbusadoptsasynchronoustransfermethodwitha highspeedclockandasplittransfermethodenabl
21、ingtominimizebusholdingtimeduringone busoperationandtouseabusefficiently. Thecontentsgiveninthisspecificationsareasfollows: a)Systembusinterfacesignalprovisions; b)Busoperationsandtransferprotocolforeachbusoperation; c)Copybackcachecoherencycontrolformaintainingconsistencybetweenasharedmemoryand aca
22、chememoryofeachprocessorinamultiprocessorsystem; d)Faultdetectionfunctionusingparitycheckandduplexconfigurationforcontrolsignals. 1.2Applicability ThisInternationalStandardisApplicabletoahighperformancesystembusoranI/Obusina multiprocessorsystem.TypicalSTbusapplicationsareindicatedinFigure1: a)ASyst
23、embusandanI/ObusinaTCMPsystem; b)ASystembusinanLCMPsystem. TCMP:tightlycoupledmultiprocessorsystem (Asystemconsistingoftwoormoreprocessorssharingthesamememory,withthe entiresystemcontrolledbyoneOS.) LCMP:looselycoupledmultiprocessorsystem (Asysteminwhicheachprocessorisconnectedbyasharedmemoryorother
24、medium, witheachprocessoroperatedbyanindividualOS.)2 14576ISO/IEC:1999(E) Figure1STbusApplications CPU CPU Shared memory System bus I/Obus I/O I/O TCMP system Processor Localmemory LCMP system Localmemory CPU CPU LocalI/O LocalI/O Systembus Processor Processor Processor . . .14576ISO/IEC:1999(E) 3 2
25、. Definitions 2.1 ExplanationofTerms ForthepurposesofthisInternationalStandard,thefollowingtermsanddefinitionsapply. 1) Answertransaction Aninformationtransferoperationbywhichafunctionunitreceivingacommandreturns answerinformation,tonotifytheunitissuingthecommandthatthecommandhasbeen completed(insom
26、ecasestherequesteddataisappended)andtoindicatestatusinformation. 2) Basicsignal ThosebusinterfacesignalsthatmustbeimplementedineverySTbussystem,andthusfor whichcompatibilityisassuredamongdifferentsystems. 3) Block Theminimumunitregisteredincachememory.InSTbusthisislimitedto32bytes. 4) Bushandler(BH)
27、 Aconcentratedbuscontrolmechanismforsortingoutcompetingbusrequestsfromdifferent functionunits,selectingoneoftherequests,andgrantingthebusrighttothatfunctionunit. 5) Busmaster Afunctionunitthathasthebusright(agrantsignalhasbeenasserted)andistransferring informationonthebus. 6) Busslave Afunctionunitt
28、owhichinformationisbeingtransferredbythebusmaster. 7) Bussnoop Monitoringofthebusforreadoperationsfromexternalmemoryandwriteoperationsto externalmemory. 8) Cacheinvalidation Arequesttoinvalidateablockincachememory.Forexample,whenawriteaccessismade toaShared&Unmodified(SU)area,thisisusedtoinvalidatet
29、hesameareainanother cache. 9) CPU Acentralprocessingelementwithfunctionsforinterpretingandexecutinginstructions.In thesespecifications,cachememoryisincludedwiththeCPU. 10)Copybackscheme Acacheupdatingmethodinwhichdatawrittenbytheprocessororinstructionexecution partisupdatedonlyinthecache,withoutbein
30、greflecteddirectlyinmemory.Thecopyback4 14576ISO/IEC:1999(E) cachesupportedinSTbushasthefollowingthreeinternalstates:Invalidstate(I),Shared& Unmodifiedstate(SU),Exclusive&Modifiedstate(EM). 11)DUT(DestinationUnit) Afunctionunitperformingananswertransaction. 12)Exclusive&Modifiedstate(EM) Aninternals
31、tateinacopybackcache,wherebytheonlyplaceinthesystemanaccessareais registeredisincachememory,andthecontentsarenotthesameassharedmemory.Inthis state,onlythecachehasbeenupdated. 13)Functionunit Ahardwareunitconnectedtothebusandhavingamechanismforbusinterfacecontrol. Normallyonefunctionunitconsistsofone
32、board. 14)I/Oadapter AfunctionunitthatcontrolsI/Odevicesundercontrolofaprocessor. 15)Invalidstate(I) Astateinwhichanareaaccessedbytheprocessorisnotregisteredincachememory. 16)Modifiedreadcommand Acommandissuedtothesystembusbyacopybackcachememorywhenawriteaccessby theprocessorresultsinawritemiss. 17)
33、Optionalsignal Thosebusinterfacesignalsthatusersarefreetoadoptornotinsystemimplementation. 18)Ordertransaction Aninformationtransferoperationforsendingacommandandrequestingprocessingby anotherfunctionunit. 19)Parity Whennototherwisenotedinthesespecifications,parityisalwaysodd.Hereoddparity meansthat
34、whenagivensignal(e.g.,8bits)isaugmentedbyaparitybit(e.g.,8+1=9 bits),thenifthesumof1bitsintheaugmentedsetisanevennumber(including0)anerror isdetected. 20)Processor AfunctionunitwiththecapabilityofexecutinginstructionsandcontrollingthevariousI/O adapters.ProcessorconsistsofCPUandmemoryingeneral. 21)R
35、eadhit/readmiss Whenaninstructionoroperandtobereadbytheprocessorisregisteredincachememory, thisiscalledareadhit.Ifnot,itisareadmiss.14576ISO/IEC:1999(E) 5 Inthecaseofareadmiss,iftheobjectofthereadiscacheable,oneblockcontainingthe objectisnewlyregisteredinthecache. 22)Retryindication Thetemporarysusp
36、ensionofaccessbyexternaldevicestoacopybackcacheareathathas beenupdatedwithoutthechangehavingbeenreflectedinmainmemory. 23)Shared&Unmodifiedstate(SU) Aninternalstateinawritethroughorcopybackcache,wherebyanaccessareaisregistered inacacheandhasthesamecontentsassharedmemory.Sharingbymorethanonecacheis p
37、ossible. 24)SUT(SourceUnit) Afunctionunitperforminganordertransaction. 25)Writehit/writemiss Ifanareatobewrittenbytheprocessorisregisteredincachememory,thisiscalledawrite hit.Ifnot,itisawritemiss. Inthecaseofawritethroughcache,thewritedataisimmediatelyreflectedinshared memory. Ifacopybackcachescheme
38、isused,inthecaseofawritehitthewritedataisreflectedinthe cacheonly.Ifawritemissoccurs,oneblockofthewriteareaisreadfromsharedmemory andnewlyregistered,thenthewritedataiswrittenoverthatareainthecacheonly. 26)Writethroughscheme Acacheupdatingmethodinwhichdatawrittenbytheprocessororinstructionexecution p
39、artisreflecteddirectlyinmemory.Theinternalstatesare:Invalidstate(I),Shared& Unmodifiedstate(SU). 2.2 Notation Thefollowingsymbolsandothernotationareusedinthesespecifications. Functionunitnumbersareindicatedby(#n),andcontrolsignalstoeachunitarewrittenas signallinename+(functionunitnumber),e.g.,RQL*(#
40、n),GR*(#n). Whenthevaluesofcontrolsignalsareindicated,thefollowingnotationisused. Whenindicatingthelogicalvalueofasignalline:1and0areused,with1meaningassert and0meaningnegate. Whenindicatingtheactualvalueonasignalline:“H“and“L“areused,with“H“ meaninghighand“L“meaninglowsignalpotential. Hexadecimalno
41、tationinthesespecificationsisindicatedbyH#(e.g.,HFF,H00).6 14576ISO/IEC:1999(E) 3. InterfaceSpecifications 3.1 InterfaceSignals TheSTbusbasicinterfacesignalsarelistedinTable1,asseenfromonefunctionunit. Inthistable,RQL*,RQH*,GR*,andET*aresignalsconnectedindividuallytoeachfunction unit. Table1BasicInt
42、erfaceSignals(functionunitinterfacesotherthanbushandler) No. Signalname Count Functionalcategory Connectiontype 1R Q L * (Request low) 1 2R Q H * (Requesthigh) 1 Arbitrationcontrol Individually 3G R * (Grant) 1 connected 4ET * (Endofbustransaction) 1 5B S * (Bustransactionstart) 1 6B U R * (Burst) 1 Transfercontrol 7C S P * (Control signal parity) 1 8L C K * (Lock) 1 Bus connection 9 AD0063 * (Command/address/data) 64 Command/address/data 10 ADP07 * (ADparity) 8 11 RTY * (Retry) 1 Cachecoherencycontrol 12 RST * (Reset) 1 Resetsignal 13 CK (Clock) 1 Clock SeeNote2. Totalnumberofsignals 83 Note
