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31
0
1
2
1523
7
27 11
19
3
29
O
W
N
E
R
S
H
I
P
T
E
A
R
D
O
W
N
E
O
P
E
O
Q
S
O
P
3
Reserved
Retry_count
cc
Message Length
13
21
5
25
9
17 1
30
1422
626 10
18
2
28
12
20
424
8
16 0
Bit Fields
Next Descriptor Pointer
Buffer Pointer
Dest_ID PRI tt SSIZE Mailbox
Port_ID
Word
Offset
SRIOFunctionalDescription
2.3.4.2TXOperation
Outgoingmessagesarehandledsimilarly,withbufferdescriptorqueuesthatareassignedbytheCPUs.
Thequeuesareconfiguredandinitializeduponreset.WhenaCPUwantstosendamessagetoan
externalRapidIOdevice,itwritesthebufferdescriptorinformationviatheconfigurationbusintothe
SRAM.Again,thereisasinglebufferdescriptorperRapidIOmessage.Uponcompletionofwritingthe
bufferdescriptor,theOWNERSHIPbitissettogivecontroltotheperipheral.TheCPUthenwritestheTX
DMAStateHDPregistertoinitiatethequeuetransmit.ForTXoperation,PortIDisspecifiedtodirectthe
outgoingpackettotheappropriateport.Table18andTable19showtheTXDMAstateregisters.
Figure22showstheTXbufferdescriptorfields.ATXbufferdescriptorisacontiguousblockoffour32-bit
datawordsalignedona32-bitboundary.
Table18.TXDMAStateHeadDescriptorPointer(HDP)(AddressOffset0x500–0x53C)
BitNameDescription
31:0TXQueueHeadTxQueueHeadDescriptorPointer:Thisfieldisthehostmemoryaddressforthefirstbuffer
DescriptorPointerdescriptorinthetransmitqueue.Thisfieldiswrittenbythehosttoinitiatequeuetransmit
operationsandiszeroedbytheportwhenallpacketsinthequeuehavebeentransmitted.Anerror
conditionresultsifthehostwritesthisfieldwhenthecurrentfieldvalueisnonzero.Theaddress
mustbe32-bitwordaligned.
Table19.TXDMAStateCompletionPointer(CP)(AddressOffset0x580–0x5BC)
BitNameDescription
31:0TXQueueTxQueueCompletionPointer:Thisfieldisthehostmemoryaddressforthetransmitqueue
CompletionPointercompletionpointer.Thisregisteriswrittenbythehostwiththebufferdescriptoraddressforthelast
bufferprocessedbythehostduringinterruptprocessing.Theportusesthevaluewrittento
determineiftheinterruptshouldbedeasserted.
Figure22.TXBufferDescriptorFields
Table20.TXBufferDescriptorFieldDefinitions
FieldDescription
next_descriptor_pointerNextDescriptorPointer:The32-bitwordalignedmemoryaddressofthenextbuffer
descriptorintheTXqueue.Thisisthemechanismusedtoreferencethenextbuffer
descriptorfromthecurrentbufferdescriptor.Ifthevalueofthispointeriszerothenthe
currentbufferisthelastbufferinthequeue.Thehostsetsthenext_descriptor_pointer.
buffer_pointerBufferPointer:Thebytealignedmemoryaddressofthebufferassociatedwiththe
bufferdescriptor.Thehostsetsthebuffer_pointer.
sop=1StartofMessage:Indicatesthatthedescriptorbufferisthefirstbufferinthemessage.
•Thisbitwillalwaysbesetasthisdeviceonlysupportsonebufferpermessage.
eop=1EndofMessage:Indicatesthatthedescriptorbufferisthelastbufferinthemessage.
•Thisbitwillalwaysbesetasthisdeviceonlysupportsonebufferpermessage.
SPRU976–March2006SerialRapidIO(SRIO)49
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