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SRIOFunctionalDescription
TX_Queue_MaphasbeenprogrammedtosendtwomessagesfromQueue0beforemovingtoQueue1,
itwillre-attempttosendthesamemessagefromQueue0beforemovingon.Whetheritissuccessfulor
not,thenextattemptwillcomefromQueue1.Withinagivenqueue,thehardwarewillalwaystrytosend
theheadbufferdescriptorandcannotmovetothenextbufferdescriptorinthequeueuntilacompletion
codeiswritten.Theweightedroundrobincontroladvocates,thatstatisticallyovermanytransmissions,the
messageswillbetransmittedinaccordancewiththepercentagesprogrammedintotheregisters.
Networktrafficcanalsoaffectthepacketdeliveryorder.ThephysicallayeroftheRapidIOperipheralcan
re-orderpacketsofdifferentprioritieswhenfabriccongestionoccurs.
Ifmessageorderingisneeded,thefollowingmustbeobeyed:
•MultiSegmentedMessages
–IfthereareonlytwodevicesAsendingtoBwhereorderinghastobeguaranteed:
•-UseoneTXqueue
•-Usethesamepriority
•-MapallmessagestothesameRXqueue
–IftherearemultipledevicesAandBbothsendingtoC,andorderinghastobeguaranteedfor
both:
•-UseoneTXqueueineachsendingdevice
•-UsethesameprioritywithineachTXqueue
•-MapallAmessagestothesameRXqueueandallBmessagestoanotherqueuebydisabling
thepromiscuousmodeandprogrammingallowablesourceIDs.
•SingleSegmentedMessages
–Therewillneverbearetrysoeveniftherearemultiplesenders:
•-UseoneTXqueueineachsendingdevice
•-UsethesameprioritywithineachTXqueue
•-MapallmessagestothesameRXqueue
SPRUE13A–September2006SerialRapidIO(SRIO)55
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