Clock frequency

Introduction

Inelectronictechnology,apulsesignalisapulsesignalthatiscontinuouslyemittedaccordingtoacertainvoltageamplitudeandacertaintimeinterval.Thetimeintervalbetweenpulsesignalsiscalledperiod;andthenumberofpulsesgeneratedinaunittime(suchas1second)iscalledfrequency.Frequencyisameasurementnamethatdescribesthenumberofpulsesthatoccurinaperiodiccyclesignal(includingpulsesignals)inaunittime;thestandardmeasurementunitoffrequencyisHz(Hertz).Thesystemclockinacomputerisatypicalpulsesignalgeneratorwithafairlyaccurateandstablefrequency.Frequencyisrepresentedby"f"inmathematicalexpressions,anditscorrespondingunitsare:Hz(hertz),kHz(kilohertz),MHz(megahertz),GHz[Gigahertz(1Gigahertz=1000000000)].

Amongthem,1GHz=1000MHz,1MHz=1000kHz,1kHz=1000Hz.Thetimeunitforcalculatingthepulsesignalperiodandthecorrespondingconversionrelationshipare:s(seconds),ms(milliseconds),μs(microseconds),ns(nanoseconds),amongwhich:1s=1000ms,1ms=1000μs,1μs=1000ns.TheclockfrequencyofthetransmissioncodeisshowninFigure1.

CPUclockspeed

CPUclockspeed,thatis,theclockfrequencyoftheCPUcore(CPUClockSpeed).Generallyspeaking,howmanyGHzdoesacertainCPUhave,andthisnumberofGHzisthe"CPU'smainfrequency".ManypeoplethinkthatthemainfrequencyoftheCPUisitsoperatingspeed,butitisnot.ThemainfrequencyoftheCPUrepresentsthespeedatwhichthedigitalpulsesignaloscillatesintheCPU,andisnotdirectlyrelatedtotheactualcomputingpoweroftheCPU.Thereisacertainrelationshipbetweenthemainfrequencyandtheactualcomputingspeed,butsofarthereisnodefiniteformulathatcanquantifythenumericalrelationshipbetweenthetwo,becausethecomputingspeedoftheCPUdependsontheperformanceindicatorsofallaspectsoftheCPU'spipeline(cache,instructionset),ThenumberofCPUbits,etc.).Sincethemainfrequencydoesnotdirectlyrepresentthecalculationspeed,undercertaincircumstances,theactualcalculationspeedoftheCPUwithahighermainfrequencyislikelytobelower.

Forexample,mostofAMD’sAthlonXPseriesCPUscanachievethehigherCPUperformanceofIntel’sPentium4seriesCPUsatalowerfrequency,sotheAthlonXPseriesCPUsarebasedonthePRvalue.Tonameit.Therefore,themainfrequencyisonlyanaspectofCPUperformance,anddoesnotrepresenttheoverallperformanceoftheCPU.ThemainfrequencyoftheCPUdoesnotrepresentthespeedoftheCPU,butincreasingthemainfrequencyisessentialtoincreasetheCPU'scomputingspeed.Forexample,supposeacertainCPUexecutesanarithmeticinstructioninoneclockcycle,thenwhentheCPUrunsat100MHz,itwillbetwiceasfastasitrunsat50MHz.Becausethe100MHzclockcycletakeshalfthetimecomparedtothe50MHzclockcycle,thatis,thetimerequiredforaCPUworkingat100MHztoexecuteanoperationinstructionisonly10nsshorterthan20nswhenworkingat50MHz,whichisnaturaloperation.Thespeedisalsodoubled.It'sjustthattheoveralloperatingspeedofthecomputerdependsnotonlyonthecomputingspeedoftheCPU,butalsoontheoperatingconditionsofothersub-systems.Onlywhenthemainfrequencyisincreased,theoperatingspeedofeachsub-systemandthedatatransmissionspeedbetweeneachsub-systemcanbeAfterbeingimproved,theoveralloperatingspeedofthecomputercanbetrulyimproved.

Restrictions

IncreasingtheCPUfrequencyismainlyrestrictedbytheproductionprocess.BecausetheCPUismanufacturedonasemiconductorsiliconchip,wiresarerequiredtoconnectbetweenthecomponentsonthesiliconchip.Becausethewiresarerequiredtobeasthinaspossibleunderhighfrequencyconditions,soastoreducestrayinterferencesuchaswiredistributedcapacitanceInordertoensurethecorrectoperationoftheCPU.Therefore,thelimitationofthemanufacturingprocessisoneofthebiggestobstaclestothedevelopmentofCPUfrequency.

Abriefhistoryofdevelopment

Theclockfrequencyismeasuredin"severalcyclespersecond",usingtheinternationalstandardunitHertz(Hz).Thecomputerperformsitsmostbasicactionssuchasaddingtwonumbersortransferringvalues​​fromoneregistertoanother.Differentchipsmayhavedifferentclockfrequenciesonthesamecomputermotherboard.Usuallywhenreferringtoacomputer,itisstipulatedthatthe"clockfrequency"usesthespeedoftheCPU.TheclockfrequencyoftheCPUisusuallydeterminedbythefrequencyoftheoscillatorcrystal.TheoriginalIBMpersonalcomputer,circa1981,hadaclockfrequencyof4.77MHz(4,770,000cycles/second).In1995,Intel'sPentiumchipranat100MHz(100millioncycles/second),andin2002,theIntelPentium4modelwasintroducedasthefirstCPUwithaclockfrequencyof3gigahertz(3billioncycles/second).

Clockfrequencyistheonlywaytocomparetheperformanceofchipsinthesamefamily.AnIBMpersonalcomputerwithanIntel486CPUrunningat50MHzwillbetwiceasfastasonerunningat25MHzwiththesameCPU,memory,anddisplay.However,therearemanyotherfactorstoconsiderwhencomparingthespeedoftheentirecomputer,suchastheclockfrequencyofthecomputer'sfrontbus,theclockfrequencyofthememorychip,thewidthofthebitsontheCPU'sbus,andtheamountoflevel1and2caches.

Clockfrequencyshouldnotbeusedwhencomparingdifferentcomputersordifferentprocessorfamilies.Instead,acertainsoftwarebenchmarkshouldbeused.Theclockfrequencycanbeverymisleading,becausedifferentcomputerchipsmaychangeaconsiderableamountofworkinonecycle.Forexample,RISCCPUstendtohavesimplerinstructionCPUs(buthigherclockfrequencies)thanCISC,andpipelinedprocessorsperformmorethanoneinstructionpercycle.

Intheearly1990s,mostcomputercompaniesprimarilyadvertisedthespeedoftheircomputersbyreferringtotheirCPUs'clockfrequencies.Thishasledtovariousmarketingcompetitions,suchasApple’sdecisiontocreateandselltheMacintosh8100/110ataclockfrequencyof110MHzsothatApplecanadvertisethatitscomputershavethefastestclockspeedavailable-themostFastIntelprocessorscanbeutilizedatthetimerunningat100MHz.Thisadvantageisinclockspeed,however,ismeaningless;PowerPCandPentiumCPUarchitecturesarecompletelydifferent.PowerPCisfasterinsometasks,butslowerinothers.

Inthe2000s,Intel’scompetitorAMDbegantousemodelnumbersinsteadofclockfrequenciestosellitsCPUs,sayingthatthe"megahertzmyth"didnotexplainthepowerofitsCPUs.In2004,Intelannouncedthatitwoulddothesame,presumablyduetoconsumerconfusioninitsPentiumMmobileCPU,whichreportedlyranatapproximatelyhalftheclockfrequencyofthePentium4CPU.

Frequencyandspeed

Therelationshipbetweenfrequencyandspeed:Generallyspeaking,thenumberofinstructionscompletedinoneclockcycleisfixed,sothehigherthefrequency,ThefastertheCPUspeed.However,becausetheinternalstructureofvariousCPUsisnotthesame,themainfrequencycannotbeusedtosummarizetheperformanceoftheCPU.ButtheCPUfrequencycandeterminethegradeandpricelevelofthecomputer.TakePentium42.0asanexample.Itsmainfrequencyis2.0GHz.Whatdoesthisshow?

Specifically,2.0GHzmeansthatitgenerates2billionclockpulsesignalspersecond,andeachclocksignalperiodis0.5nanoseconds.ThePentium4CPUhas4pipelineoperationunits.Iftheloadiseven,theCPUcanperform4binaryadditionoperationsin1clockcycle.

ThismeansthatthePentium4CPUcanperform8billionbinaryadditionoperationspersecond.Butsuchanamazingcomputingspeedcannotfullyserveusers,andthecomputerhardwareandoperatingsystemitselfconsumeCPUresources.However,theAthlonXPprocessoradoptsthePRnominalmethod.TheconversioncalculationformulabetweenthenominalfrequencyandtheactualfrequencyoftheAthlonXPprocessorwitha266MHzfront-sidebusfrequencydisclosedbyAMDisasfollows:nominalfrequency=3×actualfrequency/2-500actualfrequency=2×nominalfrequency/3+333Forexample,theactualfrequencyofAthlonXP2100+is1733MHz=2×2100/3+333

Conceptinterpretation

AbeautifulpieceofmusicTherewillbeamaintheme,andthemainthemeofthecomputeristheclockfrequencyoftheCPU.Mainfrequency,FSBandmultiplier,wheredotheycomefrom?Whatisgoingonwithfrequencylockingandoverclocking?

Therearemanysemiconductorchipsinacomputer,andeachchipworksataspecificclockfrequency.Theclocksignalprovidedbytheclockgeneratortothechipisacontinuouspulsesignal,andthepulseisequivalenttothepulseofthechip.Eachtimeapulsearrives,thetransistorinthechipchangesstateonce,allowingtheentirechiptocompleteacertaintask.

Mostofthechipsinthecomputeraredigitallogicchips.Manytransistorsinthedigitalchipareallintheon-offstate,andtheirturn-onandturn-offactionsareallcarriedoutinaccordancewiththerhythmoftheclocksignal.Iftheclockfrequencyistoohigh,thestateofthetransistormaynotbechangedintime,resultingindeadlockorrandommisoperation.Therefore,eachchiphasitsownfrequencylimit.

Whatisthefrequency?

Frequencyisrepresentedbyf,andthebasicunitis"1time/second",whichisrecordedasHz(hertz).1Hzmeansoncepersecond,and10Hzmeans10timespersecond.However,theunitofHzistoosmallincomputers,sothesignalfrequencyisusuallyexpressedinKHz,MHz,orGHz.Asthefrequencyrises,IamafraidthatTHzwillneedtobeusedastheunitoffrequencyinafewyears(Table1).

1.Periodandfrequency

Incomputertechnology,acommontermcorrespondingtofrequencyisperiod.Theperiodisthereciprocalofthefrequency,thehigherthefrequency,theshortertheperiod.Forexample,whentheclockfrequencyis1GHz,theclockperiodis1nanosecond.

2.Bandwidthfrequency

AnotherparameterrelatedtofrequencyisdatatransmissionRate,alsoknownas"bandwidth",isusedtomeasurethespeedofdatacommunication.Undernormalcircumstances,bandwidth=clockfrequency×(bitwidth÷8).Forexample,theclockfrequencyofthePCIbusis33.33MHz,andbecauseitsbitwidthis32bit,itsbandwidthis33.33×(32÷8)=133MB/s.

3.CPUfrequency:In286andearliercomputers,theCPUfrequencyisthesameasthefrequencyoftheexternalbus.TheIntel386computerusesaclockfrequencydivisionmethod.TheclockcircuitprovidesaclocksignaltotheCPUatafrequencyof33MHz,whiletheCPUinternallyworksatafrequencyof66MHz.Intel80486DX2usesfrequencymultiplication,whichallowstheCPUtorunat2or3timesthespeedoftheexternalbus,butstillcommunicateswiththeoutsideworldattheoriginalclockfrequency.AfterenteringthePentiumera,frequencymultiplicationtechnologyhasbeenwidelyused,andthefrequencymultiplicationoftheprocessorhasreached20times.

Systemclockfrequency:Usuallyalsocalled"externalfrequency"-theclockfrequencyoftheCPUexternalbus.Theexternalfrequencyisprovidedbythefrequencysynthesizerchip,andthefrequencysynthesizerchipwillbeintroducedindetaillater.Mainfrequency:ThemainfrequencyistheactualoperatingfrequencyoftheCPUcore(integerandfloating-pointarithmeticunit)circuit,whichisdeterminedbytheFSB(orfrontsidebusfrequency)andthemultiplier,thatis:mainfrequency=FSB×multiplier.

FrontSideBusFrequency:TheFrontSideBus(FSB)frequencyisthefrequencyofdataexchangebetweentheCPUandtheNorthBridgechip.ItisrelatedtotheFSBandhasthedifference.FSBisthefrequencyofthefrontsidebusclocksignal,andthefrontsidebusfrequencyreferstothefrequencyofdatatransmission.ForthePentium4processor,duetotheQDR(QuadDataRate,4timesdatarate)technology,datacanbetransmitted4timesinoneclockcycle,sothefront-sidebusfrequencyisequivalentto4timestheFSB:FSB800MHzTheprocessor,theFSBisonly200MHz.

Whoisgeneratingthefrequency

Wecanregardtheclocksignalgeneratorasthefrequencysourceastheheartofthecomputer.Thecomputercanonlyworkiftheheartbeats.

1.Oscillationsource:crystaloscillator

Thechipitselfdoesnotusuallyhaveaclocksignalsource,soadedicatedclockcircuitmustprovidetheclocksignal.OSC)isoneofthemostcommonlyusedclocksignaloscillationsources.

Quartzcrystalispuresilicondioxide,asinglecrystalofsilicondioxide,whichiswhatweoftencallcrystal.Therearetwotypesofquartzcrystals:natural(Crude)crystalsandsynthetic(synthetic)crystals.Theimpuritycontentandmorphologyofnaturalquartzcrystalsaremostlynotuniform,sothecrystaloscillatorsinelectroniccircuitsmostlyuseartificialquartzcrystals.

Athinslice(calleda"wafer")iscutfromacrystalatacertainazimuthangle,andathinsilverlayerisappliedtothetwosurfacesofthewaferandthenapairofmetalplatesareattached.Solderingthepinsandencapsulatingitwithametalshellconstitutesaquartzcrystaloscillator.

Thereasonwhyaquartzwafercanbeusedasanoscillatorisbasedonitspiezoelectriceffect:addinganelectricfieldtothetwopolesofthewaferwillcausemechanicaldeformationofthecrystal;addingonthequartzwaferWithalternatingvoltage,thecrystalwillproducemechanicalvibration,andatthesametime,mechanicaldeformationandvibrationwillproduceanalternatingelectricfield.Althoughthevoltageofthisalternatingelectricfieldisextremelyweak,itsvibrationfrequencyisverystable.Whenthefrequencyoftheappliedalternatingvoltageisequaltothenaturalfrequencyofthewafer(determinedbythesizeandshapeofthewafer),theamplitudeofmechanicalvibrationwillincreasesharply.Thisphenomenoniscalled"piezoelectricresonance."

Theestablishmentandmaintenanceofthepiezoelectricresonancestatemustberealizedwiththeaidofanoscillatorcircuit.Aseriesoscillator,two-stageamplifiercomposedoftransistorsT1andT2,quartzcrystalXTandcapacitorC2formanLCcircuit.Inthiscircuit,thequartzcrystalisequivalenttoaninductance,andC2isavariablecapacitor.Adjustingitscapacitycanmakethecircuitenteraresonancestate.Thepowersupplyvoltageofthisoscillatoris5V,andtheoutputwaveformisasquarewave.

Thefrequencystabilityofthequartzcrystaloscillatorcanreach10^-9/day,even10^-11.Forexample,fora10MHzoscillator,thefrequencychangewithinadayisgenerallynotmorethan0.1Hz.Therefore,thecrystaloscillatorcanberegardedasaconstantreferencefrequencysource(quartzwatchesandelectronicwatchesallusequartzcrystalsfortimingreferencefrequencies).SincethebirthofthePC,a14.318MHzquartzcrystaloscillatorhasbeenusedasareferencefrequencysourceonthemotherboard.Asforthereasonforalwaysusingthefrequencyof14.318MHz,perhapsitistheneedtomaintaincompatibility.However,Ialsofound14.318MHzcrystaloscillatorsingraphicscards,flashdrivesandmobilephones,soIdon’tknowwhy.

Inadditiontothis14.318MHzcrystalonthemotherboard,youcanalsofinda32.768KHzcrystal,whichisusedinthereal-timeclock(RTC)circuittodisplayaccuratetimeanddate.

2.Frequencydividerandfrequencymultiplier

Reducethepulsefrequencybyntimes.Thisisthefunctionofthefrequencydivider.InthefirstgenerationofPCs,theoutputfrequencyofthequartzcrystaloscillatorwas14.318MHz,whilethemainfrequencyoftheIntel8086processorwas4.77MHz,whichwasexactly1/3oftheformer.ThefrequencyconversionisdoneinIntel8284(clockgenerator/driver),becausetheIntel8284chipintegratesathree-frequencydividercircuit,whichcanreducethepulsesignalgeneratedbythecrystaloscillatorby3timesandprovideittotheCPUandexternalSuppose

AstheCPUfrequencyincreases,thecrystaloscillatorneedstobeincreasedseveraltimestomeettheneedsoftheCPU,sothefrequencymultiplierreplacesthepositionofthefrequencydividerintheclockcircuit.Ifthefrequencydividerperformsadivisionoperation,thefrequencymultiplierperformsamultiplicationoperation,whichincreasesthefrequencyofthecrystaloscillatorbyntimes.

Clockchip:Programmablefrequencysynthesizer

Theintegratedclockcircuitisasignoftheadvancementofhardwaretechnology.Differentdevicesinthecomputerhavedifferentrequirementsfortheclockfrequency.Ifyoufinda286motherboardfromthewastebin,youcanseethatthereareseveralcrystaloscillatorsarrangedtogether.TheCPU,AGPslot,PCIslot,harddiskinterface,USBportandPS/2portinthecomputerhaveverydifferentcommunicationspeeds,sodifferentclockfrequenciesneedtobeprovided,forexample,PCIrequires33MHz,USBis48MHz,etc..However,aquartzoscillatorcanonlyprovideonefrequency,somotherboardmanufacturersusuallyintegratetheseoscillatorcircuitsthatwereoriginallyscatteredonthemotherboardintoa"FrequencySynthesizer"chip.Thegeneratedpulsesignalisdivided(ormultiplied)inordertoprovidetherequiredclockfrequencyforchips(ordevices)ofdifferentoperatingspeeds.

Ordinaryfrequencydividerisanintegerfrequencydivider,andtherelationshipbetweentheoutputfrequencyandtheinputfrequencyisanintegermultiple,andthefrequencycanonlybeadjustedinsections,whichcannotmeettherequirementsofpreciseadjustment.Thefrequencysynthesizerisa"fractionaldivider"thatcanfine-tunetheoutputfrequency.R&Dengineerscanfreelydesignvariousfrequenciesinthecircuit,andarenolongerlimitedbythefixedfrequencyspecificationsofthequartzoscillator.Theclockchipinthecomputergenerallyhasthe"fractionalfrequencydivision"capability,andtheadjustmentsteplengthcanbedesignedto1%oreven0.1%asneeded.Inordertoguideandstandardizethedesignandapplicationoffrequencysynthesizers,Intelhasformulatedfrequencysynthesizerdesignguidelines,suchasCK97,CK40X,etc.ThespecificationforthelatestPentium4processorisCK410.

1.Principleoffrequencyadjustment

Frequencysynthesizerisaclocksignalsystemwithfrequencynegativefeedback,whichusestwofrequencydividers,Mpisusedtoreducethereferencefrequency,NpItisusedtodividetheVCO.Thefrequencyfigeneratedbythecrystaloscillator(OSC)getsthereferencefrequencyfrefaftertheMfrequencydivider,whichandthefeedbackfrequencyffdarerespectivelysenttothetworeverseinputterminalsofthefrequencydetector(FrequencyDetector,FD),andthefrequencydiscriminatoroutputADCvoltagereflectingthequotientofthetwoisfilteredbyalowpassfilter(LPF)toremovetheACcomponent,andthenprovidedtoaVoltageControlledOscillator(VCO)tooutputthefrequencysignalfout.

Therelationshipbetweentheoutputfrequencyfoutofthefrequencysynthesizerandtheinputfrequencyfincanbeexpressedbytheformulafout=fin×(N+k/M),whereN,MandKareallintegers,KItcanbeanyintegerbetween0andM.Thenon-integervalueN+k/MisusuallywrittenasN.F,wherethedotrepresentsthedecimalpoint,Nrepresentstheintegerpartofthefrequency,andF=k/Mrepresentsthefractionalpartofthefrequency.Undertheconditionthattheinputfrequencyfin,N,andMarenotchanged,therequiredfrequencyvaluefoutcanbeobtainedbymodifyingthevalueofk.

Inthefrequencysynthesizerchip,thereisaspecialSMBusinterfacecircuit,whichisawayforthechip'sregisterstocommunicatewiththeoutside.Withit,theregisterscanberewrittenthroughBIOSorsoftware.Therearetwopossibilitiesforeachbitofdatainthefrequencyregister,"0"or"1",thenwhenthesebitsarecombinedindifferentstates,avarietyofexternalfrequencyoutputscanbeobtained.

Thefrequencyadjustmentaccuracyofthefrequencysynthesizerisrelatedtothenumberofbitsinthefrequencyregister.Forexample,ifthefrequencyregisteris5bits,theadjustmentstepsizeis1MHz.Themorethenumber,thehighertheadjustmentaccuracy.Inapracticalfrequencysynthesizer,thetwofrequencydividersMpandNpareprogrammable.Aslongastheusersetsthecorrespondingfoutvalue,theBIOScanautomaticallygivethevalues​​ofN,MandK,andwritethemthroughtheSMBusbus.Intothecorrespondingregister.

2.PLLrealizestheautomaticcontrolprincipleofphasesynchronization

Theclockchipistheheartofthecomputer,anditsperformanceandstabilitydirectlydeterminetheperformanceoftheentirehardwaresystem.Ontheonehand,thefrequencysynthesizercansavecostandmotherboardspace,andthemoreimportantpurposeistomaintainastrictsynchronizationrelationshipbetweentheclocksignalsofthemotherboardchipsandperipheraldevicesandtheclocksignalsoftheCPUtoensurecorrectdataexchange.TheFSchipnotonlyhasafrequencymultiplication/frequencydivisionfunction,butalsohasaphaselockfunction-thephaseoftheoutputsignalisforcedtobeconsistentwiththephaseofthereferencesignal.Therefore,althoughthefrequenciesofthevariousclocksignalsoutputbythefrequencysynthesizeraredifferent,theyarecompletelyconsistentinphase,andtheyallmaintainphasesynchronizationwiththereferencesignalsource.

Inordertoachievephaselock,theclocksignaloutputbytheVCOiscomparedwiththereferencefrequencysignalinthephasedetector.Ifthetwophasesaredifferent,anerrorvoltageproportionaltothephasedifferencewillbeoutput;Thepolarityoftheerrorvoltagedetermineswhetherthecurrentsourceinthechargepumpabsorbsorsendscurrent,sothechargewillflowintooroutofthecapacitorinthefilter,andtheamountofchargeflowingisproportionaltothesizeofthephasedifference.Thevoltage-controlledoscillatorisavoltage-controlledoscillator.Whenthevoltageacrosstheinternalvaractordiodechanges,itscapacitancewillchangeaccordingly,therebychangingthefrequencyoftheoscillator.

Thevoltage-controlledoscillatoristhecoreunitofthePLLcircuit.Thephasecontrolprocessisachievedbychangingtheinputvoltageofthevoltage-controlledoscillator(iethetuningvoltage).ThesizeandpolarityofthetuningvoltagedeterminethephaseadjustmentIsitlaggingorleadingsothatthephaseerrorcanbecorrected.

3.Otherfunctionsofthefrequencysynthesizer

Usingthefrequencysynthesizerchipinthemotherboarddesigncaneasilyrealizetheadjustmentoftheclockfrequencyandphaselock.Inadditiontothesefunctions,thefrequencysynthesizeralsoallowsmotherboarddesignengineerstofine-tunetheclockdelaybetweenthevariousinterfaceclockstokeepthecomponentsofvariousrelatedinterfacessynchronized,whichfacilitatesthedesignanddebuggingwork.

Inaddition,thefrequencysynthesizerchipcanalsomakeadifferenceintermsofsystemstabilityandsecurity.Ontheonehand,itcanlockthefrequencythatdoesnotneedtobeadjustedtopreventotherdevicesfromfailingduetooverclockingoftheCPU;ontheotherhand,somefrequencysynthesizerchipsarealsodesignedwitha"watchdog"function,whichwillcauseacrashifoverclockingfails.Atthistime,thisfunctioncanclearthefrequencyregistertomakethesystemstartnormallyaccordingtothedefaultfrequencyoftheCPU.

Nowadays,theapplicationoffrequencysynthesizerchipsisverycommon.CommonbrandsincludeICS,Cypress,IDT,RealtekandWinbond.However,inthenForce2motherboard,nofrequencysynthesizercanbefound,becausethefrequencysynthesisfunctionhasbeenintegratedintotheIGP/SPPchip.

TheworkingprocessofthefrequencymultipliersignalofAMDAthlonseriesprocessors.WhentheRESET#signalarrives,theprocessorsendstheFIDsignaltothelogicsignalconversionchip,andthechipgeneratesSIP(SerializationInitializationPacket,serialInitializationdatapacket)toinitializeandsetthesystembus.

TherearesomeconnectinglinescalledgoldenbridgesontheCPU.TheleveloftheFIDsignalcanbesetbychangingtheon-offofthegoldenbridge.Whenthegoldenbridgeison,itislowandwhenitisoff,itishigh.Level.TheFIDsignalisgeneratedinthebuilt-infrequencymultipliercontrolunit,andafterthesignalisamplifiedbythebuilt-inFIDdrivecircuit,itissentfromtheFIDpintothelogicsignalconversionchip,andthegeneratedSIPdatapacketisreturnedtotheCPUfromtheBP_FIDpin.Inthisway,thefrequencysynthesiscircuitinsidetheCPUcansynthesizethecorefrequencyoftheCPUtogetherwiththetwosignalsofthefrequencymultiplierandtheexternalfrequency.

3.Memoryfrequencysetting

Thememorybusclocksignalontheearlymotherboardswasalsogeneratedbythefrequencysynthesizer,butthenewermotherboardshaveleftthefrequencysynthesizerchiponthemotherboardaside,AndtheclockfrequencyofthememorybusissetbytheNorthbridgechip,whichiscalled"memoryasynchronous"intheindustry.

SimilartotheprincipleofautomaticsettingofCPUfrequency,thefrequencysynthesizerintheNorthbridgechipalsorealizesautomaticsettingoffrequencythroughcertainmeans.ThefrequencyofthememoryisprovidedbytheSPD(SerialPresenceDetectmemoryserialstoragechip)onthememorystick.SPDissimilartotheBIOSonthemotherboard.Itstoresthememorycapacity,operatingfrequency,delaytime(CAS,tRCD,tRP,tCA),operatingvoltageandmanufacturerinformationofthememorychip.TheNorthbridgechipreadseachmemorychipthroughtheSDApinoftheSMBusbus.FortheparametersintheSPDofaDIMM,theinformationoftheSPDchipwillberecordedintheregisterofthePLLcircuitintheNorthbridgechip.

Thefrequencyofthememorybusclockandthesystemclockisoftendifferent.Forexample,whenthesystemclockis133MHzandthefrequencyofthememoryclockis200MHz,thereisa67MHzdifferencebetweenthetwo.ThisdifferenceinfrequencyItiscalled"memoryasynchronous".However,inordertoachievesynchronouscommunicationbetweenthememoryandtheCPU,thetwobusesstillneedtobesynchronizedinphase.Itisnottechnicallydifficulttoachievephasesynchronization,aslongasthePLLcircuitintheNorthbridgechipandthePLLcircuitinthefrequencysynthesizerusethesamereferencefrequencyfref.

Infact,thefrequencysettingofplug-and-playexternaldevicesisbasicallythesameastheautomaticsettingofmemoryfrequency.ThehostreadsthecharacteristicparametersincludingfrequencyintheROMchipinthedevice,andthenautomaticallyassignsit.Systemresources,automaticallyconfigurethedriver,sothatthedevicecanworknormally.

Getthepulseofthecomputer

1.Checktheactualfrequencyandreleasethepotentialofthedevice

IntelProcessorFrequencyIDUtilityistheCPUdetectionsoftwarereleasedbyIntel.Thesoftwareliststwodata,"reportfrequency"and"expectedfrequency".ThefirstitemrepresentsthecurrentoperatingspeedofthetestedCPU,andthelatterrepresentsthehighestoperatingspeeddesignedbythetestedCPUwhenitleavesthefactory.Ifthetwodataarethesame,itmeansthattheCPUisnotoverclocked.Ifthereportedfrequencyislowerthantheexpectedfrequency,itmeansthattheprocessor'scapabilitiesarenotbeingused.

Usingthetestsoftwarecanroughlyunderstandtheworkingstatusofeachdevice,whichisveryimportantforoptimizingsystemperformance.Therearemanysimilartotheabovedetectionsoftware,andallthefrequenciesthatneedtobetestedcanbedisplayedthroughthetestingsoftware.However,someadvancedplayersdoubtwhetherthefrequencymeasuredbythesoftwareisaccurate.Thissuspicionisnotunfounded,becausetheplatformonwhichthedetectionsoftwarerunsisbasedonthereferencefrequencyfref.Ifthereferencefrequencyitselfisnotaccurate,thefrequencyvaluemeasuredbythesoftwareisdifficulttoguarantee.However,toaccuratelymeasurethefrequencyoftheclocksignal,youcanuseanoscilloscope.

Thereisacloserelationshipbetweentheperformanceofexternalequipmentandtheoperatingfrequencyoftheinterfacecircuit.Taketheharddiskasanexample,ifyouuseAIDA32andothersoftwaretomeasurethehighestUDMAtransmissionmodeoftheharddiskasUDMA6(ATA-133),butthecurrentUDMAtransmissionmodeisUDMA1(ATA-33).Thatis,theharddiskcanworkatafrequencyof133MHz,buttheinterfaceonlyexchangesdataatafrequencyof33MHz.Thenitwillgreatlyreducetheharddiskperformance.Inthiscase,itmeansthatthepotentialofthedevicehasnotbeenfullyutilized.YoushouldcheckwhethertheinterfacemodeselectionintheBIOSiscorrectorsolveitbyinstallingtherelevantIDEdriver.

2.Preventheartbeatrate

Ifthefrequencyistoolow,theperformanceoftheequipmentwillbelow.Onthecontrary,ifthefrequencyistoohigh,itwillcausetheequipmenttoworkunstableandevenstrikeoutcompletely.Usually,afterweoverclockthedisplaychipandvideomemory,thedisplayscreenisatypicalcase.Theinabilityofthedevicetoworkduetoafastheartrateoccupiesaconsiderableproportionofcomputerfailures.Forvariousreasons,theoperatingfrequencyofsomeequipmentisactuallynotuptothenominalfrequency.Forthetreatmentofsuchproblems,theauthorhasintroducedindetailinthearticle"ComputerFailureFrequencyReductionDiagnosis"("Microcomputer"2003Issue17).ItshouldbeaddedherethatiftheCPUfailstostartduetooverclockingfailure,dischargetheCMOSandtheBIOSwillstartinthesafemodeof100MHzFSB,whichwillnotcauseseriousconsequences.