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AppendixAGlossary
AppendixA
BroadcastMACAddress—AspecialEthernetMACaddressusedtosenddatatoallEthernetdevices
onthelocalnetwork.ThebroadcastaddressisFFh-FFh-FFh-FFh-FFh-FFh.TheLSBofthefirst
byteisodd,qualifyingitasagroupaddress;however,itsvalueisreservedforbroadcast.Itis
classifiedseparatelybytheEMAC.
Descriptor(PacketBufferDescriptor)—Asmallmemorystructurethatdescribesalargerblockof
memoryintermsofsize,location,andstate.DescriptorsareusedbytheEMACandapplicationto
describethememorybuffersthatholdEthernetdata.
Device—Inthisdocument,devicereferstotheTMS320C645xprocessor.
EthernetMACAddress(MACAddress)—Aunique6-byteaddressthatidentifiesanEthernetdeviceon
thenetwork.InanEthernetpacket,aMACaddressisusedtwice,firsttoidentifythepacket’s
destination,andsecondtoidentifythepacket’ssenderorsource.AnEthernetMACaddressis
normallyspecifiedinhexadecimal,usingdashestoseparatebytes.Forexample,
08h-00h-28h-32h-17h-42h.
Thefirstthreebytesnormallydesignatethemanufacturerofthedevice.However,whenthefirst
byteoftheaddressisodd(LSBis1),theaddressisagroupaddress(broadcastormulticast).The
secondbitspecifieswhethertheaddressisgloballyorlocallyadministrated(notconsideredinthis
document).
EthernetPacket(Packet)—AnEthernetpacketisthecollectionofbytesthatrepresentsthedataportion
ofasingleEthernetframeonthewire.
FullDuplex—Fullduplexoperationallowssimultaneouscommunicationbetweenapairofstationsusing
point-to-pointmedia(dedicatedchannel).Fullduplexoperationdoesnotrequirethattransmitters
defer,nordotheymonitororreacttoreceiveactivity,asthereisnocontentionforasharedmedium
inthismode.Fullduplexmodecanonlybeusedwhenallofthefollowingaretrue:
•Thephysicalmediumiscapableofsupportingsimultaneoustransmissionandreceptionwithout
interference.
•Thereareexactlytwostationsconnectedwithafullduplexpoint-to-pointlink.Asthereisno
contentionforuseofasharedmedium,themultipleaccess(i.e.,CSMA/CD)algorithmsare
unnecessary.
•BothstationsontheLANarecapableof,andhavebeenconfiguredtouse,fullduplex
operation.
Themostcommonconfigurationenvisionedforfullduplexoperationconsistsofacentralbridge
(alsoknownasaswitch)withadedicatedLANconnectingeachbridgeporttoasingledevice.
FullduplexoperationconstitutesapropersubsetoftheMACfunctionalityrequiredforhalfduplex
operation.
HalfDuplex—Inhalfduplexmode,theCSMA/CDmediaaccessmethodisthemeansbywhichtwoor
morestationsshareacommontransmissionmedium.Totransmit,astationwaits(defers)fora
quietperiodonthemedium,thatis,nootherstationistransmitting.Itthensendstheintended
messageinbit-serialform.If,afterinitiatingatransmission,themessagecollideswiththatof
anotherstation,theneachtransmittingstationintentionallytransmitsforanadditionalpredefined
periodtoensurepropagationofthecollisionthroughoutthesystem.Thestationremainssilentfora
randomamountoftime(backoff)beforeattemptingtotransmitagain.
Host—Thehostisanintelligentsystemresourcethatconfiguresandmanageseachcommunications
controlmodule.Thehostisresponsibleforallocatingmemory,initializingalldatastructures,and
respondingtoport(EMAC)interrupts.Inthisdocument,hostreferstotheTMS320C645xdevice.
Jabber—Aconditionwhereinastationtransmitsforaperiodoftimelongerthanthemaximum
permissiblepacketlength,usuallyduetoafaultcondition.
SPRU975B–August2006Glossary145
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