Embedded Multi-core Processors

Designing multi-threaded and multi-core processor architectures has become one of the most challenging projects for computer scientists in the last few years. But not only the design of such architectures for desktop computers, servers, or high performance

EmbeddedMulti-coreProcessors

PhilippZech

Philipp.Zech@student.uibk.ac.at

SeminarEmbeddedSystemDesign,WS2007/08

InstituteofComputerScience,UniversityofInnsbruck

January11,2008

Designingmulti-threadedandmulti-coreprocessorarchitectureshasbecomeoneofthemostchallengingprojectsforcomputerscientistsinthelastfewyears.Butnotonlythedesignofsucharchitecturesfordesktopcomputers,servers,orhighperformancecomputing(HPC)clustershasbeeninvestigatedinasophisticatedmanner,alsointheareaofembeddedsystems,researchershavestartedtoinvestigatethepossibilitiesofusingthenewlyacquiredknowledgetoimplementmulti-coreprocessorsforembeddedsystems.Unfortunately,suchstreamlinedcomputersbringawholelotofconstraintstothedesignofprocessoringeneral.Justtonamesomeofthem,scientistshavetodealwithlessmemoryavailable,lesspossibilitiestocooltheevolvingheat,andlastbutnotleast,themostimportantdesigncriteriameanstobethatembeddedsystemscannotprovidetheintegratedprocessorswiththesameamountofpowerastheabovementionedsystems(likeserversorHPCclusters).Buttheseareonlyafewofthemainproblemsscientistswerefacedwithintheearlydaysofprocessordesign,especiallythedesignofmulti-coreprocessorsforembeddedsystems.

Thispaperwillgivethereaderaprofoundoverviewofthemainarchitecturalapproaches,currentlyusedin eldimplementationsandtheywillalsobediscussed.Furthermorethereaderwillbepresentedsomeoftheavailablereallifeimplementationsofthevariousarchitecturalapproaches,whichwillaswellbediscussedindetailbypointingouttheirassetsanddrawbacks.

Designing multi-threaded and multi-core processor architectures has become one of the most challenging projects for computer scientists in the last few years. But not only the design of such architectures for desktop computers, servers, or high performance

1Motivation

Inthelastdecade,theneedformorepowerful,butatthesametimelesspowerconsumptivemicroproces-sors,especiallyforembeddedsystems,arose.Onecouldforexampleconsideranordinarycellphone.Twentyyearsagoacellphonewasusedforwhatitsnameintendedittobeusedfor:callingotherpeople.Butnowadays,anordinarycellphonemaycontainfourtoeightprocessors,includingRISC(ReducedInstruc-tionSetComputing)foruserinterfaces,DSP(DigitalSignalProcessing)forvoiceencodinganddecoding.Additionallytheymaycontainaudioprocessors,videoprocessors,pictureprocessors,andthelikeforthedi erentmultimediaextensions,allimplementedinanordinarycellphone.Whathastobekeptinmindisthefact,thatacellphoneonlyprovidesalimitedamountofpoweravailabletothedi erentprocessorsandmoreover,limitedmemory,whichinmostcaseshastobesharedamongtheindividualprocessors.

Butnotonlycellphones,alsomoresophisticatedweaponsystemsordailyusedproductslikeDVD-playersordigitalcamerasalreadycontainmorethanoneprocessortoful lltheirtasks.Andallofthemshouldworkwithaslesspoweraspossible.

Onebigadvantageprovidedbymulti-corearchitecturesiscachecoherencybysharingresources(inthiscasethecache).Asaconsequencesignalsbetweenindividualcoreshavetotravellessandthereforealsodegradeless.Furtheron,thisallowsthatmoredatacanbesentaroundinagiventimeperiod,assignalsmaybeshorterandmustnotberepeatedthatoften.

Anotherremarkableadvantageofmulti-coreprocessorarchitecturesisthereducedPrintedCircuitBoard(PCB)spaceneededbysuchdesigns,comparedtomulti-chipSMP(simultaneousmulti-threading)designs.Anothergreatadvantageisthefactthatbecauseofbeingimplementedononedie,multi-coredesignsneedlesspowerthancoupledsingle-coreprocessors,becauseoftheincreasedpowerrequiredtodrivesignalsexternaltothechipandbecausethesmallersiliconprocessgeometryallowsthecorestooperateatlowervoltages;suchreductionreduceslatency.

ByusingtraditionalCPUcorelibrarydesignsitispossibletodevelopmulti-coredesigns,whicharelesserror-proneasinvestigatingnewwidercoredesigns.

Beforenowswitchingontothedi erentarchitecturalapproaches,thereaderwillbegivenashorthistoryofmulti-coreprocessordesignsforembeddedsystems.

2ShortHistory

Theworld’s rstmulti-coreprocessor,realizingtwofullcoresononeprocessorwasIBM’sp960,alsocalledRegatta,whichevolvedfromIBM’sPowerfamily,releasedinOctober2001[Sch].AlthoughIBM’sprocessorwasnotintendedtobeusedinembeddedsystems,anditforsurewasnotarealmulti-coreprocessorasitonlyrealizedtwocoresononeprocessordie,ithastobementionedatthispoint,asitwasthe rstmicroprocessor,realizingatotallynewdesignparadigm.Soon,researchersworkingintheareaonprocessordesignforembeddedsystemsusedthisknowledgetoalsostartdevelopingmulti-coreprocessorsforembeddedsystems.Forsure,thelowpowerresourcemeanttobeahardchallengetobeovercomebytheprocessorarchitects.

Despiteallthechallenges,in2002ARM[ARMa]launcheditsfamousARM11microarchitecture,thebasefordevelopingtheARM11MPCore,aMultiprocessorSystems-On-Chip(MPSoC)microarchitecture,whichwas nallyreleasedinearly2005.Itshouldbementionedthatresearchinghadalreadystartedduringthe rstquarterof1999,whenARMintroducedtheARMv6ISA.Alreadyinthesecondquarterof2004aresearchgroupattheUniversityofBolognapresentedXpipes[PB04],anadvancedNetwork-On-Chip(NoC)architectureforhighlyscalablemultiprocessorembeddedsystems.Itshouldbementionedatthispointthatitwasinthelate1990ies,whenresearchersinventedthetermNetwork-On-Chiptobringanewcommunicationmodeltomicroprocessordesign,asthethenusedcommunicationmodelsdidnotscalewellanymore.

SoonthismodelwasfollowedbytheCortexA9MPCore,alsodevelopedbyARM.AstheARM11MPCore,theCortexalsobuildsupontopoftheARMv6ISA.

ItwasinAugust2007whenTilera[Tilc]announceditsnewTile64,apuremulti-coreprocessorforembeddedsystems,consistingof64coresandusinganon-chipnetworkforcommunicationbetweentheapartcores.

Afterthisbriefoverviewofthemostimportantinnovationsinmulti-coreprocessordesign,wewillnowswitchontothediscussionofth …… 此处隐藏：36143字，全部文档内容请下载后查看。喜欢就下载吧 ……