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Switch
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C0
C0
B0
B0
B2
B2
A1
A1
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B1
A0
A0
Open
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Open
Open
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Full
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Scenario A - Default
Scenario B - In order mode
Data flow destined for the
same Rx Queue
Rx Queue Status when
packet arrives
Rx Queue Status when
packet arrives
Records SourceID/letter of
first retry packet
SRIOFunctionalDescription
Figure20.RXCPPIModeExplanation
Inaddition,multiplemessagescanbeinterleavedatthereceiveportduetoorderingwithinaconnected
switch’soutputqueue.Thiscanoccurwhenusingasingleormultiplepriorities.TheRXCPPIblockmust
handlesimultaneousinterleavedmulti-segmentmessages.Thisimpliesthatstateinformation(write
pointersandsrcID)mustbemaintainedoneachsimultaneousmessagetoproperlystorethesegmentsin
memory.Thenumberofsimultaneoustransactionssupporteddirectlyimpactsthenumberofstatestobe
stored,andthesizeofthebufferdescriptormemoryoutsidetheperipheral.Withthisinmind,the
peripheral’ssupportedbufferdescriptorSRAMisparameterizable.Aminimumsizeof1.25KBis
recommended,whichwillallowupto64bufferdescriptorstobestoredatanygiventimeforonecore.
Thesebufferdescriptorscanbeconfiguredtosupportanycombinationofsingleandmulti-segment
messages.Forexample,iftheapplicationonlyhandlessingle-segmentmessages,all64bufferscanbe
allottedtothatqueue.NotethatagivenRXqueuecancontainpacketsofallprioritieswhichhavebeen
directedfromanyofthereceiveports.
ACPUmaywishtostopreceivingmessagesandreclaimbuffersbelongingtoaspecificqueue.Thisis
calledqueueteardown.TheCPUinitiatesaRXqueueteardownbywritingtotheRXQueueTeardown
commandregister.
SPRU976–March2006SerialRapidIO(SRIO)47
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