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4SystemInterconnect
4.1InternalBuses,Bridges,andSwitchFabrics
SM320C6455-EP
FIXED-POINTDIGITALSIGNALPROCESSOR
SPRS462B–SEPTEMBER2007–REVISEDJANUARY2008
OntheC6455device,theC64x+Megamodule,theEDMA3transfercontrollers,andthesystem
peripheralsareinterconnectedthroughtwoswitchfabrics.Theswitchfabricsallowforlow-latency,
concurrentdatatransfersbetweenmasterperipheralsandslaveperipherals.Throughaswitchfabricthe
CPUcansenddatatotheViterbico-processor(VCP2)withoutaffectingadatatransferbetweenthePCI
andtheDDR2memorycontroller.Theswitchfabricsalsoallowforseamlessarbitrationbetweenthe
systemmasterswhenaccessingsystemslaves.
TwotypesofbusesexistintheC6455device:databusesandconfigurationbuses.SomeC6455
peripheralshavebothadatabusandaconfigurationbusinterface,whileothersonlyhaveonetypeof
interface.Furthermore,thebusinterfacewidthandspeedvariesfromperipheraltoperipheral.
Configurationbusesaremainlyusedtoaccesstheregisterspaceofaperipheralandthedatabusesare
usedmainlyfordatatransfers.However,insomecases,theconfigurationbusisalsousedtotransfer
data.Forexample,dataistransferredtotheVCP2andTCP2configurationbus.Similarly,thedatabus
canalsobeusedtoaccesstheregisterspaceofaperipheral.Forexample,theEMIFAandDDR2
memorycontrollerregistersareaccessedthroughtheirdatabusinterface.
TheC64x+Megamodule,theEDMA3trafficcontrollers,andthevarioussystemperipheralscanbe
classifiedintotwocategories:mastersandslaves.Mastersarecapableofinitiatingreadandwrite
transfersinthesystemanddonotrelyontheEDMA3fortheirdatatransfers.Slavesontheotherhand
relyontheEDMA3toperformtransferstoandfromthem.MastersincludetheEDMA3trafficcontrollers,
SRIO,andPCI.SlavesincludetheMcBSP,UTOPIA,andI2C.
TheC6455devicecontainstwoswitchfabricsthroughwhichmastersandslavescommunicate.Thedata
switchfabric,knownasthedataswitchedcentralresource(SCR),isahigh-throughputinterconnect
mainlyusedtomovedataacrossthesystem(formoreinformation,seeSection4.2).ThedataSCR
connectsmasterstoslavesvia128bitdatabusesrunningataSYSCLK2frequency(SYSCLK2is
generatedfromPLL1controller).Peripheralsthathavea128bitdatabusinterfacerunningatthisspeed
canconnectdirectlytothedataSCR;otherperipheralsrequireabridge.
Theconfigurationswitchfabric,alsoknownastheconfigurationswitchcentralresource(SCR)ismainly
usedbytheC64x+Megamoduletoaccessperipheralregisters(formoreinformation,seeSection4.3).
TheconfigurationSCRconnectsC64x+Megamoduletoslavesvia32bitconfigurationbusesrunningata
SYSCLK2frequency(SYSCLK2isgeneratedfromPLL1controller).AswiththedataSCR,some
peripheralsrequiretheuseofabridgetointerfacetotheconfigurationSCR.NotethatthedataSCRalso
connectstotheconfigurationSCR.
Bridgesperformavarietyoffunctions:
•Conversionbetweenconfigurationbusanddatabus.
•WidthconversionbetweenperipheralbuswidthandSCRbuswidth.
•FrequencyconversionbetweenperipheralbusfrequencyandSCRbusfrequency.
Forexample,theEMIFAandDDR2memorycontrollerrequireabridgetoconverttheir64bitdatabus
interfaceintoa128bitinterfacesothattheycanconnecttothedataSCR.InthecaseoftheTCP2and
VCP2,abridgeisrequiredtoconnectthedataSCRtothe64-bitconfigurationbusinterface.
NotethatsomeperipheralscanbeaccessedthroughthedataSCRandalsothroughtheconfiguration
SCR.
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