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1、BranchtargetbufferdesignforembeddedprocessorsNadavLevison,ShlomoWeiss*Dept.ofElectricalEngineering–Systems,TelAvivUniversity,TelAviv69978,IsraelThedemandforembeddedapplicationprocessorsthatsupportmulti-taskingoperatingsystemandcanexecutecomplexapplicationsbringthemclosertogeneralpurposeprocess
2、ors.ThesestrongprocessorshavealimitedpowersourcebecausetheyareusuallyfoundinportabledevicessuchassmartphonesandotherPDAs,andarepoweredbybatteries.TheBranchTargetBuffer(BTB),whichiscommonlyusedingeneralpurposeprocessors,isbecomingprevalentinhigh-endembeddedprocessorsinordertosupportlongpipeline
3、sandmitigatehighmisspenalties.However,theBTBisamajorpowerconsumerbecauseitisalargeSRAMstructurethatisaccessedalmosteverycycle.WeproposetwoBTBdesignsthatfitthetightpowerbudgetsofembeddedprocessors.Inthefirstdesign,thepowerconsumptionofasingleBTBaccessisreducedbyreadingonlythelowerpartofthepredi
4、ctedtargetaddressbits.Thisdesignhaspowersavingsofupto25%dynamicpower,witheffectivelynoperformancedegradation.Intheseconddesign,weavoidredundantBTBaccessestothesamesetbyusingasmallbufferthatholdsthemostrecentlyaccessedset.Thisdesignresultsin75%dynamicpowersavingsatthecostofupto0.64%systemslowdo
5、wnina2-wayBTB,and80%dynamicpowersavingsatthecostofupto0.58%systemslowdownina4-wayBTB.2010ElsevierB.V.Allrightsreserved.1.IntroductionIn1994IBMandBellSouthlaunchedanewmobilephonecalledSimonPersonalCommunicator.Apartfromthecommonmobilephonecapabilities,theSimonhadadditionalfeaturessuchasacalend
6、ar,sendingandreceivingE-mailsandfaxes,games,andanaddressbook.Althoughitwasbig,heavy,andcostly,theSimonisconsideredtobethefirstsmartphone.Sincethensmartphoneshavebecomepowerful,easytouse,populardevicesthatsupportawiderangeoffunctionsandreplaceseveralspecial-purposegadgetswithasinglehighlyintegr
7、ateddevice.Asmartphoneisusuallydefinedasacommonmobilephonethatcanalsofunctionasapersonaldigitalassistant(PDA).Thefeatures[8]thatmightbeexpectedinamodernsmartphoneincludetheabilitytorunamulti-taskingoperatingsystem,alargedisplay,internet
