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2.3.3.4ResetandPowerDownState
2.3.4MessagePassing
SRIOFunctionalDescription
Sothegeneralflowisasfollows:
•Previously,thecontrol/commandregisterswerewrittenandtherequestpacketwassent
•ResponsePacketType13,Trans!=0001barrivesatmoduleinterface,andishandledsequentially(not
basedonpriority)
•TheargetTIDisexaminedtodetermineroutingofaresponsetotheappropriatecore
•ThestatusfieldoftheresponsepacketischeckedforERROR,RETRYorDONE
•IfthefieldisDONE,itsubmitsDMAbusrequestandtransmitsthepayload(ifany)toDSPaddress.If
thefieldisERROR/RETRY,itsetsaninterrupt
•Commandregistersarereleased(BSY=0)
•OptionalInterrupttoCPUnotifyingpacketreception
Uponreset,theLoad/StoremoduleclearsthecommandregisterfieldsandwaitforawritebytheCPU.
TheLoad/StoremodulecanbepowereddownifthedirectI/Oprotocolisnotbeingsupportedinthe
application.Forexample,ifthemessagingprotocolisbeingusedfordatatransfers,poweringdownthe
Load/Storemodulewillsavepower.Inthissituation,thecommandregistersshouldbepowereddownand
inaccessible.Clocksshouldbegatedtotheseblockswhileinthepowerdownstate.
TheCommunicationsPortProgrammingInterface(CPPI)moduleistheincomingandoutgoing
message-passingprotocolengineoftheRapidIOperipheral.Messagescontainapplicationspecificdata
thatispushedtothereceivingdevicecomparabletoastreamingwrite.Messagesdonotcontainread
operations,butdohaveresponsepackets.
Withmessagepassing,adestinationaddressisnotspecified.Instead,amailboxidentifierisusedwithin
theRapidIOpacket.Themailboxiscontrolledandmappedtomemorybythelocal(destination)device.
ForRapidIOmessagepassing,fourmailboxlocationsarespecified.Eachmailboxcancontain4separate
transactions(orletters),effectivelyproviding16messages.Singlepacketmessagesprovide64mailboxes
with4letters,effectivelyproviding256messages.Mailboxescanbedefinedfordifferentdatatypesor
priorities.Theadvantageofmessagepassingisthatthesourcedevicedoesnotrequireanyknowledgeof
thedestinationdevice’smemorymap.TheDSPcontainsbufferdescriptiontablesforeachmailbox.These
tablesdefineamemorymapandpointersforeachmailbox.Messagesaretransferredtotheappropriate
memorylocationsviatheDMA.
ThedatapathforthismoduleusestheDMAbusastheDMAinterface.Theftypeheaderfieldofthe
receivedRapidIOmessagepacketsaredecodedbythelogicallayeroftheperipheral.OnlyType11and
Type13(transactiontype1)packetsareroutedtothismodule.Dataisroutedfromthepriority-basedRX
FIFOstotheCPPImodule’sdatabufferwithinthesharedbufferpool.Thembox(mailbox)headerfields
areexaminedbythemailboxmapperblockoftheCPPImodule.Basedonthemailboxandmessage
length,thedataisassignedmemoryaddresseswithinmemory.DataistransferredviaDMAbus
commandstomemoryfromthebufferspaceoftheperipheral.Themaximumbufferspaceshould
accommodate256bytesofdata,asthatisthemaximumpayloadsizeofaRapidIOpacket.Each
messageinmemorywillberepresentedbyabufferdescriptorinthequeue.
ThefollowingrulesexistforallCPPItraffic:
•Onebufferdescriptorisprovidedpermessage(eachbufferdescriptorconsistsof4wordsor16bytes).
•Contiguousmemoryspaceisrequiredformulti-segmentreadandwriteoperations.
–Therearefixedbuffersizes(configuredtohandletheapplication'smaximummessagesize).
•AnERRORresponseissentiftheRXmessageistoobigfortheallottedbufferspace.
–ERRORresponsesaresentforallsubsequentsegmentsofthatmessage.
•AnERRORresponseissentifthemailboxisnotmapped,orifitismappedtoanon-existentqueue.
•AnERRORresponseissentifthemailboxismappedbutthequeueisnotinitialized(thehead
descriptorpointerisnotwritten),orifthequeueisdisabled(duetoateardown).
•AnERRORresponseissentiftheRXbufferdescriptorqueuehasnoemptybuffers(thereisan
overflow).
SPRUE13A–September2006SerialRapidIO(SRIO)43
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