AppendixAGlossary
AppendixA
BroadcastMACAddress—AspecialEthernetMACaddressusedtosenddatatoallEthernetdevices
onthelocalnetwork.ThebroadcastaddressisFFh-FFh-FFh-FFh-FFh-FFh.TheLSBofthefirst
byteisodd,qualifyingitasagroupaddress;however,itsvalueisreservedforbroadcast.Itis
classifiedseparatelybytheEMAC.
Descriptor(PacketBufferDescriptor)—Asmallmemorystructurethatdescribesalargerblockof
memoryintermsofsize,location,andstate.DescriptorsareusedbytheEMACandapplication
todescribethememorybuffersthatholdEthernetdata.
Device—Inthisdocument,devicereferstotheTMS320DM646xprocessor.
EthernetMACAddress(MACAddress)—Aunique6-byteaddressthatidentifiesanEthernetdevice
onthenetwork.InanEthernetpacket,aMACaddressisusedtwice,firsttoidentifythepacket’s
destination,andsecondtoidentifythepacket’ssenderorsource.AnEthernetMACaddressis
normallyspecifiedinhexadecimal,usingdashestoseparatebytes.Forexample,
08h-00h-28h-32h-17h-42h.
Thefirstthreebytesnormallydesignatethemanufacturerofthedevice.However,whenthefirst
byteoftheaddressisodd(LSBis1),theaddressisagroupaddress(broadcastormulticast).
Thesecondbitspecifieswhethertheaddressisgloballyorlocallyadministrated(notconsidered
inthisdocument).
EthernetPacket(Packet)—AnEthernetpacketisthecollectionofbytesthatrepresentsthedata
portionofasingleEthernetframeonthewire.
FullDuplex—Full-duplexoperationallowssimultaneouscommunicationbetweenapairofstations
usingpoint-to-pointmedia(dedicatedchannel).Full-duplexoperationdoesnotrequirethat
transmittersdefer,nordotheymonitororreacttoreceiveactivity,asthereisnocontentionfora
sharedmediuminthismode.Full-duplexmodecanonlybeusedwhenallofthefollowingare
true:
•Thephysicalmediumiscapableofsupportingsimultaneoustransmissionandreception
withoutinterference.
•Thereareexactlytwostationsconnectedwithafullduplexpoint-to-pointlink.Asthereisno
contentionforuseofasharedmedium,themultipleaccess(thatis,CSMA/CD)algorithms
areunnecessary.
•BothstationsontheLANarecapableof,andhavebeenconfiguredtouse,full-duplex
operation.
Themostcommonconfigurationenvisionedforfull-duplexoperationconsistsofacentralbridge
(alsoknownasaswitch)withadedicatedLANconnectingeachbridgeporttoasingledevice.
Full-duplexoperationconstitutesapropersubsetoftheMACfunctionalityrequiredfor
half-duplexoperation.
HalfDuplex—Inhalf-duplexmode,theCSMA/CDmediaaccessmethodisthemeansbywhichtwoor
morestationsshareacommontransmissionmedium.Totransmit,astationwaits(defers)fora
quietperiodonthemedium,thatis,nootherstationistransmitting.Itthensendstheintended
messageinbit-serialform.If,afterinitiatingatransmission,themessagecollideswiththatof
anotherstation,theneachtransmittingstationintentionallytransmitsforanadditionalpredefined
periodtoensurepropagationofthecollisionthroughoutthesystem.Thestationremainssilent
forarandomamountoftime(backoff)beforeattemptingtotransmitagain.
Host—Thehostisanintelligentsystemresourcethatconfiguresandmanageseachcommunications
controlmodule.Thehostisresponsibleforallocatingmemory,initializingalldatastructures,and
respondingtoport(EMAC)interrupts.Inthisdocument,hostreferstotheTMS320DM646x
device.
Jabber—Aconditionwhereinastationtransmitsforaperiodoftimelongerthanthemaximum
permissiblepacketlength,usuallyduetoafaultcondition.
SPRUEQ6–December2007Glossary133
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