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2.10.4HardwareReceiveQOSSupport
2.10.5HostFreeBufferTracking
2.10.6ReceiveChannelTeardown
PeripheralArchitecture
Hardwarereceivequalityofservice(QOS)issupported,whenenabled,bytheTagProtocolIdentifier
formatandtheassociatedTagControlInformation(TCI)formatpriorityfield.Whentheincomingframe
length/typevalueisequalto81.00h,theEMACrecognizestheframeasanEthernetEncodedTag
ProtocolType.Thetwooctetsimmediatelyfollowingtheprotocoltypecontainthe16-bitTCIfield.Bits
15-13oftheTCIfieldcontainthereceivedframespriority(0to7).Thereceivedframeisalow-priority
frame,ifthepriorityvalueis0to3;thereceivedframeisahigh-priorityframe,ifthepriorityvalueis4to7.
Allframesthathavealength/typefieldvaluenotequalto81.00harelow-priorityframes.Receivedframes
thatcontainpriorityinformationaredeterminedbytheEMACas:
•A48-bit(6bytes)destinationaddressequalto:
–Thedestinationstation'sindividualunicastaddress.
–Thedestinationstation'smulticastaddress(MACHASH1andMACHASH2).
–Thebroadcastaddressofallones.
•A48-byte(6bytes)sourceaddress.
•The16-bit(2bytes)length/typefieldcontainingthevalue81.00h.
•The16-bit(2bytes)TCIfieldwiththepriorityfieldintheupper3bits.
•Databytes
•The4bytesCRC.
Thereceivefilterlowpriorityframethresholdregister(RXFILTERLOWTHRESH)andthereceivechannel
nfreebuffercountregisters(RXnFREEBUFFER)areusedinconjunctionwiththepriorityinformationto
implementreceivehardwareQOS.Low-priorityframesarefilteredifthenumberoffreebuffers
(RXnFREEBUFFER)fortheframechannelislessthanorequaltothefilterlowthreshold
(RXFILTERLOWTHRESH)value.HardwareQOSisenabledbytheRXQOSENbitinthereceive
multicast/broadcast/promiscuouschannelenableregister(RXMBPENABLE).
Thehostmusttrackfreebuffersforeachenabledchannel(includingunicast,multicast,broadcast,and
promiscuous),ifreceiveQOSorreceiveflowcontrolisused.Disabledchannelfreebuffervaluesaredo
notcares.Duringinitialization,thehostshouldwritethenumberoffreebuffersforeachenabledchannel
totheappropriatereceivechannelnfreebuffercountregisters(RXnFREEBUFFER).TheEMAC
decrementstheappropriatechannel’sfreebuffervalueforeachbufferused.Whenthehostreclaimsthe
framebuffers,thehostshouldwritethechannelfreebufferregisterwiththenumberofreclaimedbuffers
(writetoincrement).Thereareamaximumof65,535freebuffersavailable.RXnFREEBUFFERonly
needstobeupdatedbythehostifreceiveQOSorflowcontrolisused.
Thehostcommandsareceivechannelteardownbywritingthechannelnumbertothereceiveteardown
register(RXTEARDOWN).Whenateardowncommandisissuedtoanenabledreceivechannel,the
followingoccurs:
•Anycurrentframeinreceptioncompletesnormally.
•TheTDOWNCMPLTflagissetinthenextbufferdescriptorinthechain,ifthereisone.
•Thechannelheaddescriptorpointerisclearedto0.
•Areceiveinterruptforthechannelisissuedtothehost.
•Thecorrespondingreceivechannelncompletionpointerregister(RXnCP)containsthevalueFFFF
FFCh.
Channelteardownmaybecommandedonanychannelatanytime.Thehostisinformedoftheteardown
completionbythesetteardowncomplete(TDOWNCMPLT)bufferdescriptorbit.TheEMACdoesnot
clearanychannelenablesduetoateardowncommand.Ateardowncommandtoaninactivechannel
issuesaninterruptthatsoftwareshouldacknowledgewithanFFFFFFFChacknowledgevaluetoRXnCP
(notethatthereisnobufferdescriptorinthiscase).SoftwaremayreadRXnCPtodetermineifthe
interruptwasduetoacommandedteardown.ThereadvalueisFFFFFFFCh,iftheinterruptwasduetoa
teardowncommand.
40EthernetMediaAccessController(EMAC)/SPRU941A–April2007
ManagementDataInput/Output(MDIO)
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