Texas Instruments TMS320TCI648x Network Card User Manual


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Switch
Switch
Endpoint
Endpoint
C0
C0
B0
B0
B2
B2
A1
A1
B1
B1
A0
A0
Open
Open
Open
Open
Open
Open
Open
Full
Open
Open
Full
Full
Retry
Retry
Retry
Retry
Retry
Retry
Accept
Retry
Retry
Retry
Action
Action
Retry
Retry
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
Althoughtheswitchfabricdeliversthesegmentsofmulti-packetmessagesintheordertheyweresent,
bufferresourcesatthereceivingendpointmayonlybecomeavailableaftertheinitialsegment(s)ofa
messagehavehadtoberetried.Theperipheralcanacceptout-of-ordersegmentsandtrackcompletionof
theoverallmessage.ScenarioAinFigure20showsthisconcept.
Forapplicationsthataresetupforspecificmessageflowsbetweenasinglesourceanddestination,itmay
requirein-orderdeliveryofmessages.ThisisdescribedinscenarioBofFigure20.Thisscenarioissimilar
toscenarioA,althoughonemessagemayberetriedduetoalackofreceiverresources,subsequent
pipelinedmessagesmayarrivejustasresourcesarefreedup.Thisisaproblemforsystemsrequiring
in-ordermessagedelivery.Inthiscase,theperipheralneedstorecordtheSrc_id/mailbox/letterofthefirst
retriedmessageandretryallsubsequentnewrequestsuntilresourcesareavailableandasegmentfor
thatSrc_id/mailbox/letterisreceived.Aslongasallmessagesarefromthesamesourceandthatsource
sends(andretries)packetsinorder,thenallmessageswillbereceivedinorder.Notethatthissolutionis
lesseffectivewhenmultiplesourcesshareanRXqueue.TheRXCPPIControlregister(Addressoffset
0744h)setsthismodeofoperationonallreceivequeues.Oncethismodeissetandaretryisissued,the
queuewillcontinuetowaitforanincomingmessagethatmatchestheSrc_id/mailbox/lettercombination.If
nosuchpacketarrives,theRXqueueisunusableinalockedstate.Toreenablethequeue,thein-order
bitintheRXCPPIControlregistermustbedisabledbysoftwareforthatqueue,afterwhichitmaybe
enabledagainifdesired.Thein-ordermodeofoperationisonlyvalidonmulti-segmentqueuesbecause
single-segmentmessageswillnevergenerateRETRYresponses.
Figure20.RXCPPIModeExplanation
SPRUE13A–September2006SerialRapidIO(SRIO)49
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