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2SRIOFunctionalDescription
2.1Overview
2.1.1PeripheralDataFlow
SRIOFunctionalDescription
Thisperipheralisdesignedtobeanexternallydrivenslavemodulethatiscapableofactingasamasterin
theDSPsystem.Thismeansthatanexternaldevicecanpush(burstwrite)datatotheDSPasneeded,
withouthavingtogenerateaninterrupttotheCPUorwithoutrelyingontheDSPEDMA.Thishasseveral
benefits.Itcutsdownonthetotalnumberofinterrupts,itreduceshandshaking(latency)associatedwith
read-onlyperipherals,anditfreesuptheEDMAforothertasks.
SRIOspecifiesdatapacketswithpayloadsupto256bytes.Manytimes,transactionswillspanacross
multiplepackets.RapidIOspecifiesamaximumof16transactionspermessage.Althougharequestis
generatedforeachpackettransactionsothattheDMAcantransferthedatatoL2memory,aninterruptis
onlygeneratedafterthefinalpacketofthemessage.ThisinterruptnotifiestheCPUthatdataisavailable
inL2Memoryforprocessing.
Asanendpointdevice,theperipheralacceptspacketsbasedonthedestinationID.Twooptionsexistfor
packetacceptanceandaremodeselectable.ThefirstoptionistoonlyacceptpacketswhoseDestIDs
matchthelocaldeviceIDin0x0080.Thisprovidesalevelofsecurity.Thesecondoptionisissystem
multicastoperation.WhenmulticastisenabledinSP_IP_MODE(offset12004h)bit5,incomingpackets
matchingthedeviceIDintheregistersshowninareaccepted.
Table2.RegistersCheckedforMulticastDeviceID
RegistersCheckedForMulticastDeviceID
DeviceNameAddressOffset
TMS320TCI6482LocalDeviceIDRegister0080h
MulticastDeviceIDRegister0084h
Dataflowthroughtheperipheralcanbeexplainedusingthehigh-levelblockdiagramshowninFigure4.
High-speeddataentersfromthedevicepinsintotheRXblockoftheSERDESmacro.TheRXblockisa
differentialreceiverexpectingaminimumof175mVpeak-to-peakdifferentialinputvoltage(Vid).Level
shiftingisperformedintheRXblock,suchthattheoutputissingleendedCMOS.Theserialdataisthen
fedtotheSERDESclockrecoveryblock.Thesolepurposeofthisblockistoextractaclocksignalfrom
thedatastream.Todothis,alow-frequencyreferenceclockisrequired.Typically,thisclockcomesfrom
anoff-chipstablecrystaloscillatorandisaLVDSdeviceinputseparatetotheSERDES.Thisclockis
distributedtotheSERDESPLLblockwhichmultipliesthatfrequencyuptothatofthedatarate.Multiple
high-speedclockphasesarecreatedandroutedtotheclockrecoveryblocks.Theclockrecoveryblocks
furtherinterpolatebetweentheseclockstoprovidemaximumUnitInterval(UI)resolutionontherecovered
clock.Theclockrecoveryblocksamplestheincomingdataandmonitorstherelativepositionsofthedata
edges.Withthisinformation,itcanprovidethedataandacenter-alignedclocktotheS2Pblock.TheS2P
blockusesthenewlyrecoveredclocktode-multiplexthedatainto10-bitwords.Atthispoint,thedata
leavestheSERDESmacroat1/10ththepindatarate,accompaniedbyanalignedbyteclock.
SPRUE13A–September2006SerialRapidIO(SRIO)21
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