Energy Efficient Datapath Scheduling using Multipl

EnergyEfficientDatapathSchedulingusingMultipleVoltagesandDynamicClockingSarajuP.MohantyN.RanganathanDept.ofComp.ScienceandEng.Dept.ofComp.ScienceandEng.UniversityofNorthTexas,TX76203.UniversityofSouthFlorida,FL33620.E-mail:[e-mail]-mail:[e-mail],dynamicfrequencyscalinghasbeenexploredattheCPUandsystemlevelsforpoweroptimization.Lowpowerdatapathschedulingusingmultiplesupplyvoltageshasbeenwellresearched.Inthiswork,wedevelopnewdatapathschedulingalgorithmsthatusemultiplesupplyvoltagesanddynamicfrequencyclockinginaco-ordinatedmannerinordertoreduceenergyconsumptionofdatapathcircuits.Indynamicfrequencyclocking,thefunctionalunitscanbeoperatedatdifferentfrequenciesdependingonthecomputationsoccurringwithinthedatapathduringagivenclockcycle.Thestrategyistoschedulehighenergyunits,suchasmultipliersatlowerfrequenciessothattheycanbeoperatedatlowervoltagestoreduceenergyconsumptionandthelowenergyunits,suchasaddersathigherfrequencies,tocompensateforspeed.Theproposedtimeandresourceconstrainedalgorithmshavebeenappliedtovarioushighlevelsynthesisbenchmarkcircuitsunderdifferenttimeandresourceconstraints.Theexperimentalresultsshowsignificantreductioninenergyforboththealgorithms.CategoriesandSubjectDescriptors:B.5.1[Register-Transfer-LevelImplementation]:DatapathDesign;B.5.2[Register-Transfer-LevelImplementation]:AutomaticSynthesis,Optimization;B.7.1[TypesandDesignStyles]:VLSI(verylargescaleintegration)GeneralTerms:Algorithms,Performance,Design,Reliability,Scheduling,TimeComplexityAdditionalKeyWordsandPhrases:High-Levelsynthesis,low-powerdatapathsynthesis,multiplevoltageschedul-ing,timeconstrainedscheduling,resourceconstrainedschedulinganddynamicfrequencyclocking1.INTRODUCTIONWiththeincreaseindemandforpersonalcomputingdevicesandwirelesscommunicationsequipment,thedemandforsynthesizinglowpowerconsumingcircuitshasincreased.Theneedforlowpowersynthesisisdrivenbyseveralfactors,suchas[Pedram1996],demandofportablesystems(batterylife),thermalconsiderations(coolingandpackagingcosts),environmentalconcerns(useofnaturalresources),andreliabilityissues.Whileenergyconsumptionofadevicehastobeminimumtoincreasebatterylife,theenergy-delay-producthastobeminimizedtoincreasebatterylifeandtoreducedelay,simultaneously.LetusconsiderthefollowingequationsforaCMOScircuit[BurdandBrodersen1995;ThisresearchwascarriedoutattheDepartmentofComputerScienceandEngineering,UniversityofSouthFlorida,Tampa,FL33620.Permissiontomakedigital/hardcopyofallorpartofthismaterialwithoutfeeforpersonalorclassroomuseprovidedthatthecopiesarenotmadeordistributedforprofitorcommercialadvantage,theACMcopyright/servernotice,thetitleofthepublication,anditsdateappear,andnoticeisgiventhatcopyingisbypermissionoftheACM,Inc.Tocopyotherwise,torepublish,topostonservers,ortoredistributetolistsrequirespriorspecificpermissionand/orafee.c2004ACM1084-4309/2004/0400-0111$5.00ACMTransactionsonDesignAutomationofElectronicSystems,Vol.V,No.N,August2004,Pages111–133.112MohantyandRanganathanPouwelseetal.2001b]:—Energydissipationperoperationis(1)where,istheeffectiveswitchedcapacitanceandisthesupplyvoltage,—Forfrequency,thepowerdissipationfortheoperationis(2)—Further,thecriticaldelay()inadevicethatdeterminesthemaximumfrequency()isbelow,where,isthethresholdvoltage,!isatechnologydependentfactorandisaconstant.#%$’&)((3)Fromtheabovethreeequations,thefollowingcanbededuced[BurdandBrodersen1995;Pouwelseetal.2001b;Peringetal.2000;MartinandSiewiorek2001]:—Reducingonly,bothenergyandpowercanbesavedatthecostofperformance.—Slowingdownthecircuitbyreducingonlywillsavepowerbutnotenergy.—However,byscalingfrequencyandvoltageinacoordinatedmanner,bothenergyandpowercanbesavedwhilemaintainingperformance.Thethirdfactoraboveformsthemajormotivationforthiswork.Theobjectiveistogener-ateadatapathschedulethatattemptsatenergyandpowerreductionwithoutdegradingtheperformancebyusingmultiplevoltagesanddynamicfrequencyinaco-ordinatedmanner.Inthispaper,weconsidertheuseofdynamicfrequencyclockingorfrequencyscalingalongwithmultiplesupplyvoltagesforsynthesisoflowpowerdatapathcircuitsusefulforsignalprocessingapplications.Indynamicfrequencyclocking(hereto,willbereferredtoasDFC),thefunctionalunitscouldoperateatdifferentspeedsduringeachclockcycledependingontheunitsactiveinthatcycle.Wedeveloptwonewdatapathschedulingalgorithms,onereferredtoasTC-DFC(timeconstrained)andotherreferredtoasRC-DFC(resourceconstrained),bothofwhichaimatreducingenergyconsumption.Theresourceconstraintsconsistofthenumberandtypeofeachfunctionalunit,theallowedvoltagesandfrequencies.Thetimeconstraintisdefinedintermsofmultiplesofthecriticalpathdelayofthedatapathcircuit.RC-DFCminimizesthetotalenergyconsumptionofthedatapathcircuitbymaximizingtheutilizationoflowersupplyvoltageresourcesfromthegivensetsofresourcesoperatingatdifferentsupplyvoltageswhilereducingthetimepenalty.Ontheotherhand,TC-DFCminimizesthetotalenergyconsumptionofthedatapathcircuitwithoutviolatingthetimingconstraintsassumin