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2.2EnhancedC67x+CPU
.D1 .M1 .S1 .L1
Register File A
Data Path A
Cross
Paths
.D2 .M2 .S2 .L2
Register File B
Data Path B
TMS320C6727,TMS320C6726,TMS320C6722
Floating-PointDigitalSignalProcessors
SPRS268E–MAY2005–REVISEDJANUARY2007
TheTMS320C672xfloating-pointdigitalsignalprocessorsarebasedonthenewC67x+CPU.Thiscoreis
code-compatiblewiththeC67xCPUcoreusedontheTMS320C671xDSPs,butwithsignificant
enhancementsincludinganincreaseincoreoperatingfrequencyfrom225MHzto300MHz
(2)
while
operatingat1.2V.
TheCPUfetches256-bit-wideadvancedvery-longinstructionword(VLIW)fetchpacketsthatare
composedofvariable-lengthexecutepackets.Theexecutepacketscansupplyfromonetoeight32-bit
instructionstotheeightfunctionalunitsduringeveryclockcycle.Thevariable-lengthexecutepacketsare
akeymemory-savingfeature,distinguishingtheC67xCPUfromotherVLIWarchitectures.Additionally,
executepacketscannowspanfetchpackets,providingacodesizeimprovementovertheC67xCPU
core.
TheCPUfeaturestwodatapaths,showninFigure2-1,eachcomposedoffourfunctionalunits(.D,.M,.S,
and.L)andaregisterfile.The.Dunitineachdatapathisadata-addressingunitthatisresponsibleforall
datatransfersbetweentheregisterfilesandthememory.The.Mfunctionalunitsarededicatedfor
multiplies,andthe.Sand.Lfunctionalunitsperformageneralsetofarithmetic,logical,andbranch
functions.Allinstructionsoperateonregistersasopposedtodatainmemory,butresultsstoredinthe
32-bitregisterscanbesubsequentlymovedtomemoryasbytes,half-words,orwords.
Figure2-1.CPUDataPaths
Theregisterfileineachdatapathcontains3232-bitregistersforatotalof64general-purposeregisters.
ThisdoublesthenumberofregistersfoundontheC67xCPUcore,allowingtheoptimizingCcompilerto
pipelinemorecomplexloopsbydecreasingregisterpressuresignificantly.
ThefourfunctionalunitsineachdatapathoftheCPUcanfreelysharethe32registersbelongingtothat
datapath.Eachdatapathalsofeaturesasinglecrosspathconnectedtotheregisterfileontheopposing
datapath.Thisallowseachdatapathtosourceonecross-pathoperandpercyclefromtheopposing
registerfile.OntheC67x+CPU,thissinglecross-pathoperandcanbeusedbytwofunctionalunitsper
cycle,animprovementovertheC67xCPUinwhichonlyonefunctionalunitcouldusethecross-path
operand.Inaddition,thecross-pathregisterread(s)arenotcountedaspartofthelimitoffourreadsofthe
sameregisterinasinglecycle.
TheC67x+CPUexecutesallC67xinstructionsplusnewfloating-pointinstructionstoimprove
performancespecificallyduringaudioprocessing.ThesenewinstructionsarelistedinTable2-2.
(2)CPUspeedisdevice-dependent.SeeTable2-1.
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