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2.5.4.7EndofPacket(EOP)Flag
2.5.4.8Ownership(OWNER)Flag
2.5.4.9EndofQueue(EOQ)Flag
2.5.4.10TeardownComplete(TDOWNCMPLT)Flag
2.5.4.11PassCRC(PASSCRC)Flag
EMACFunctionalArchitecture
Whenset,thisflagindicatesthatthedescriptorpointstothelastpacketbufferforagivenpacket.Fora
singlefragmentpacket,boththestartofpacket(SOP)andEOPflagsareset.Otherwise,thedescriptor
pointingtothelastpacketbufferforthepacketsetstheEOPflag.Thisbitissetbythesoftware
applicationandisnotalteredbytheEMAC.
Whenset,thisflagindicatesthatallthedescriptorsforthegivenpacket(fromSOPtoEOP)arecurrently
ownedbytheEMAC.ThisflagissetbythesoftwareapplicationontheSOPpacketdescriptorbefore
addingthedescriptortothetransmitdescriptorqueue.Forasinglefragmentpacket,theSOP,EOP,and
OWNERflagsareallset.TheOWNERflagisclearedbytheEMAConceitisfinishedwithallthe
descriptorsforthegivenpacket.NotethatthisflagisvalidonSOPdescriptorsonly.
Whenset,thisflagindicatesthatthedescriptorinquestionwasthelastdescriptorinthetransmitqueue
foragiventransmitchannel,andthatthetransmitterhashalted.Thisflagisinitiallyclearedbythe
softwareapplicationpriortoaddingthedescriptortothetransmitqueue.ThisbitissetbytheEMACwhen
theEMACidentifiesthatadescriptoristhelastforagivenpacket(theEOPflagisset),andthereareno
moredescriptorsinthetransmitlist(nextdescriptorpointerisNULL).
ThesoftwareapplicationcanusethisbittodetectwhentheEMACtransmitterforthecorresponding
channelhashalted.Thisisusefulwhentheapplicationappendsadditionalpacketdescriptorstoatransmit
queuelistthatisalreadyownedbytheEMAC.NotethatthisflagisvalidonEOPdescriptorsonly.
Thisflagisusedwhenatransmitqueueisbeingtorndown,oraborted,insteadofallowingtransmission,
suchasduringdevicedriverresetorshutdownconditions.TheEMACsetsthisbitintheSOPdescriptor
ofeachpacketasitisabortedfromtransmission.
NotethatthisflagisvalidonSOPdescriptorsonly.Alsonotethatonlythefirstpacketinanunsentlisthas
theTDOWNCMPLTflagset.TheEMACdoesnotprocesssubsequentdescriptors.
ThesoftwareapplicationsetsthisflagintheSOPpacketdescriptorbeforeitaddsthedescriptortothe
transmitqueue.SettingthisbitindicatestotheEMACthatthe4-byteEthernetCRCisalreadypresentin
thepacketdata,andthattheEMACshouldnotgenerateitsownversionoftheCRC.
WhentheCRCflagiscleared,theEMACgeneratesandappendsthe4-byteCRC.Thebufferlengthand
packetlengthfieldsdonotincludetheCRCbytes.WhentheCRCflagisset,the4-byteCRCissupplied
bythesoftwareapplicationandisappendedtotheendofthepacketdata.Thebufferlengthandpacket
lengthfieldsincludetheCRCbytes,astheyarepartofthevalidpacketdata.Notethatthisflagisvalidon
SOPdescriptorsonly.
EthernetMediaAccessController(EMAC)/ManagementDataInput/Output(MDIO) 32SPRU975B–August2006
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