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外文翻译--数字信号处理器重新采纳多核架构.doc

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外文翻译--数字信号处理器重新采纳多核架构.doc

1http//www.eetasia.com/DigitalSignalProcessingChipsreembracemulticorearchitecturePosted03Nov2008Addingcorestoaprocessortogainaperformanceboost,whileloweringpowerdemand,hasbecomestandardpracticeinthecomputingandembeddedprocessorindustries.Whileasimilarevolutionseemsinevitableforalltypesofhighperformanceprocessing,priorexperiencehasmadeDSPvendorsmoreselectiveinapplyingthemulticoreapproach.DSPsarenowbeginningtoreembracemulticorearchitectures,butmainlyforspecificapplicationspossessingwellpartitionedprocessingtasks.PerformpartitioningADSPapplicationoftencomprisesonlyafewhighlycomplextasks,andsystemperformanceimprovementsdependonhasteningtaskexecution,notsimplyrunningmoretasks.Insteadofpartitioningatthetasklevel,thissystemoftenrequirespartitioningatthealgorithmlevel.Theoveralltask,suchascompressingavideostream,mustbebrokenintostepsthatcanruninparallelonseparatecores.ThetaskschedulerorOScannotperformsuchpartitioningitmustcomeduringthesoftwaredesign.ManyDSPapplicationdevelopersavoidthemulticoreapproachbecauseofthedifficultyofalgorithmpartitioning.Atthesametime,sometaskssuchasencryptionarenotsuitabletoparallelization.Homogenousvs.heterogeneousThisdoesntmeanthatthemulticoreapproachhasntbeentriedwithDSPs.PicoChiphaslonghaditspicoArrayarchitecturethatputsmultiple,identicalcorestogetherforhighperformanceDSP.Inmostcases,however,multicoredesignofferingswithDSPhadnotbeenhomogeneoushavingmultiplecopiesofthesamecore.Instead,theyintegratedaDSPcorewithaRISCCPUcore.SuchheterogeneousDSPs,forinstance,havebeenpartofmulticoreprocessordesignsforanumberofyearsinthehandsetsandcommunicationsindustries.TheapplicationstheseprocessorstargetedreadilyseparateintosignalprocessingtasksfortheDSPandcontroltasksfortheRISCCPU,makingpartitioningmoredirect.OneexceptionwastheBlackfinBF561dualcoreDSPfromAnalogDevicesInc.Thedeviceusedcoresthatweredesignedtohandlebothtypesoftaskswell,sotherewasnoneedtopartitionalongtasklines.Instead,developerscouldassigntasksaccordingtotheirpreferencetobalancetheloadamongthecores.Mostdevelopersat2thetime,however,wereinexperiencedatpartitioningsoftwareandautomatedtoolsupportwaslacking,sothehomogeneousmulticoreDSPwasnotquicklyadopted.TheBF561wasanearlyentranttothefield,saidDavidKatz,ADIsBlackfinapplicationsmanager,anditwasaheadofitstime.Ithastakenawhileforpeopletolearnpartitioning.HenotedthatithasnotintroducedahomogeneousmulticoreDSPdesignsincetheBF561,althoughmulticoreisanimportantpartofourroadmapstrategy.OtherDSPvendorsalsoviewmulticoreasaninevitabletrendforDSPs,forthesamereasonitwasadoptedincomputinghigherperformanceatlowerpower.WhatisnowmakinghomogeneousmulticoreDSPchipdesignsappearoncemoreisashiftintheperformanceincreasessomesystemsrequire.Insomeapplications,theneedforperformanceismovingfromperformingasingletaskfastertoperformingmoretasks.ThisshiftissimplifyingDSPtaskpartitioning,makingitmorelikethatofotherembeddedapplications,andDSPvendorsarecreatingproductsthatcapitalizeontheopportunity.ProcessingchangeWiththerisingdemandforVoIPandvideooverIP,mediaprocessinghasbecomeonesuchshiftingapplication.Amediagatewaydesign,forinstance,mustprovideanumberofvoice,audioandvideocodecs,andhandlemultipleindependentchannels.Thisapplicationstructureiseasilypartitionedintoindependenttasks,makingitagoodfitformulticoreDSPdesigns.TheOctasicVocalloaddressesthisapplicationspace.Vocallohas15identicalDSPcores,givingdesignersconsiderableflexibilityincreatingparallelandpipelinedarchitecturesthatstriketherightbalanceofchannelcapacityfordifferentinstallations.AnothermulticoreDSPforcommunicationsisTexasInstrumentsInc.sTNETV3020forhighdensitycorenetworks.Whatwearedoingnowisapplicationspecificmultiprocessing,saidRaySimar,managerofmulticoresolutionsatTI.Ininfrastructureapplicationsyouredoingthesametasks,sodesignscangravitatetomultiplecopiesofthesameprocessor.TheTNETV3020hassixDSPcores,alongwithaswitchfabricandavarietyofserialI/Ochannels,allowingdesignerstoconfigurethedesignfortaskssuchaschannelformatconversion.CommunicationsisnottheonlyDSPapplicationchangingitscharacter.Audioprocessinghasalsogrowntorequirehighperformancehandlingofmultipletasksthatareneededforsimplepartitioningamongmultiplecores.AccordingtoSujataNeidig,audioDSPproductmanageratFreescaleSemiconductorInc.,theadventofhighdefinition,DolbyandBlurayaudioalgorithmshasincreasedperformancedemandsonaudioDSPsasmuchasfivetimes,withrisingcomplexity,dataratesandnumbersofchannels.Further,Neidigsaidmorefeaturessuchasautomaticvolumecontrolarebeingintegratedtoaudio.RecyclingcodesFreescalesSymphonyDSP56724andDSP56725DSPsofferadualcorearchitecturethatallowsdeveloperstosplittheprocessingburdenwhilereusingtheir3existingcode.MulticoreDSPsthattargetvideoormixedaudioandvideoprocessingarealsoappearing.SamplesaretheCT3616fromCradleTechnologiesInc.,theVoyageurfromGennumCorp.andmulticoreDSPsforaudiofromCirrusLogicInc.ThetrendtowardmulticoreDSPchipdesignsmayultimatelymovethepartitioningtaskoutofthedevelopershandsintothechipvendors.AnexampleisthePC302,recentlyintroducedbyPicoChip.ThecompanyuseditsgeneralpurposepicoArrayarchitecturetocreateadevicethatimplementsacompletefemtocellaccesspointonasinglechip.Thecompanyhandledallthepartitioningandputthecoresystemsoftwareinonchipmemory,limitingdeveloperseffortstoaddcustomfunctionality.SuchspecializeddevicesmaybetheneartermfutureformulticoreDSPdesigns,butlongtermthemulticoreapproachwillenvelopegeneralpurposeDSPdesignsaswell.AswelookdowntheroadwecanseethatmulticoreforDSPisnotaonetrickpony,saidSimar.Itwillbecomemorecommon.AlongwiththatshiftwillcomeagrowingneedfordeveloperstolearnhowtopartitiontheirdesignstoeffectivelyutilizehomogenousmulticoreDSPs.Anumberofpeoplewantacompilertohandlethis,saidSimar,butthatsnotgoingtohappenforawhile.Wewillneedtothinkaboutthingsdifferentlyinordertoapplythesedevices.RichardQuinnellEETimes4数字信号处理器重新采纳多核架构为了提升性能同时降低功率要求,在处理器中增加内核已经成为计算和嵌入式处理器产业的标准作法。虽然同样的演变对各种高性能处理来说似乎是不可避免的,以往的经验使得数字信号处理器DSP供应商更愿意选择多核方式。DSP正在开始重新采纳多核架构,不过主要是针对那些处理任务可以得到妥善划分的特殊应用。操作分解DSP应用通常只包含少量高度复杂的任务,系统性能的提升依赖于加快任务执行速度,而不是简单地运行更多的任务。与任务级划分不同,DSP系统通常要求在算法级划分任务。整个任务,比如压缩一个视频流,必须被分解成可以在单独内核上并行运行的多个步骤。任务调度器或操作系统无法完成这种划分,这种划分必须在软件设计过程完成。许多DSP应用开发人员正因为算法划分困难而回避多内核方法。也有一些任务如加密不支持并行运算。比较相同与不同这并不是说多核方法未尝试与DSP亲近过。PicoChip公司很早前推出的picoArray架构就整合了多个相同的内核来支持高性能DSP。然而在大多数情况下,采用DSP的多核设计中的内核不是同一类的。相反,它们采用一个DSP内核和一个RISCCPU内核。多年来这种异质DSP一直被用于蜂窝电话和通信行业中的多核处理器设计。这些处理器的目标应用可以被很好地划分为适合DSP的信号处理任务和适合RISCCPU的控制任务,从而使得划分相当简单。一个例外是ADI的BlackfinBF561双核DSP。该器件使用的内核可以很好地执行两种任务,因此无需对任务组进行划分。相反,开发人员可能随意分配任务来平衡内核之间的负载。不过,大多数开发人员缺少划分软件的经验,而自动化工具支持也非常缺乏,因此同类多核DSP无法得到迅速普及。BF561是较早进入这一领域的产品。ADI公司Blackfin应用经理DavidKatz表示,它是领先于时代的产品。我们需要给开发员一定的时间来学习划分技术。Katz指出,ADI公司在BF561后就没有推出过同类多核DSP设计,虽然多内核是我们发展策略中的重要组成部分。其它DSP供应商也将多核看作是DSP不可避免的发展趋势,这与它被计算应用广泛采纳的理由是相同的以更低的功率提供更高的性能。再次出现同类多核DSP芯片设计的驱动因素,是一些系统要求的性能越来越高。在一些关键应用中,对性能的要求正在从更快地执行单一任务转变为执行更多的任务。这种变化将简化DSP的任务划分,使得它更像是其它嵌入式应用的任务划分,而DSP供应商也在抓住这个难得的机会积极开发产品。

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