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2.10.9ReceiveOverrun
PeripheralArchitecture
Thetypesofreceiveoverrunare:
•FIFOstartofframeoverrun(FIFO_SOF)
•FIFOmiddleofframeoverrun(FIFO_MOF)
•DMAstartofframeoverrun(DMA_SOF)
•DMAmiddleofframeoverrun(DMA_MOF)
Thestatisticscountersusedtotrackthesetypesofreceiveoverrunare:
•Receivestartofframeoverrunsregister(RXSOFOVERRUNS)
•Receivemiddleofframeoverrunsregister(RXMOFOVERRUNS)
•ReceiveDMAoverrunsregister(RXDMAOVERRUNS)
Startofframeoverrunshappenwhentherearenoresourcesavailablewhenframereceptionbegins.Start
offrameoverrunsincrementtheappropriateoverrunstatistic(s)andtheframeisfiltered.
Middleofframeoverrunshappenwhentherearesomeresourcestostarttheframereception,butthe
resourcesrunoutduringframereception.Innormaloperation,aframethatoverrunsafterstartingthe
framereceptionisfilteredandtheappropriatestatistic(s)areincremented;however,theRXCEFENbitin
thereceivemulticast/broadcast/promiscuouschannelenableregister(RXMBPENABLE)affectsoverrun
frametreatment.Table5showshowtheoverrunconditionishandledforthemiddleofframeoverrun.
Table5.MiddleofFrameOverrunTreatment
AddressMatchRXCAFENRXCEFENMiddleofFrameOverrunTreatment
00XOverrunframefiltered.
010Overrunframefiltered.
011Asmuchframedataaspossibleistransferredtothepromiscuouschannel
untiloverrun.Theappropriateoverrunstatistic(s)isincrementedandthe
OVERRUNandNOMATCHflagsaresetintheSOPbufferdescriptor.Note
thattheRXMAXLENnumberofbytescannotbereachedforanoverrunto
occur(itwouldbetruncatedandbeajabberoroversize).
1X0Overrunframefilteredwiththeappropriateoverrunstatistic(s)incremented.
1X1Asmuchframedataaspossibleistransferredtotheaddressmatch
channeluntiloverrun.Theappropriateoverrunstatistic(s)isincremented
andtheOVERRUNflagissetintheSOPbufferdescriptor.Notethatthe
RXMAXLENnumberofbytescannotbereachedforanoverruntooccur(it
wouldbetruncated).
SPRU941A–April2007EthernetMediaAccessController(EMAC)/43
ManagementDataInput/Output(MDIO)
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