5.39BackOffTestRegister(BOFFTEST)
5.40TransmitPacingAlgorithmTestRegister(TPACETEST)
EthernetMediaAccessController(EMAC)Registers
Thebackofftestregister(BOFFTEST)isshowninFigure79anddescribedinTable78.
Figure79.BackOffRandomNumberGeneratorTestRegister(BOFFTEST)
31262516
ReservedRNDNUM
R-0R-0
1512111090
COLLCOUNTReservedTXBACKOFF
R-0R-0R-0
LEGEND:R=Readonly;-n=valueafterreset
Table78.BackOffTestRegister(BOFFTEST)FieldDescriptions
BitFieldValueDescription
31-26Reserved0Reserved
25-16RNDNUM0-3FFhBackoffrandomnumbergenerator.ThisfieldallowstheBackoffRandomNumberGeneratortobe
read.Readingthisfieldreturnsthegenerator'scurrentvalue.Thevalueisresetto0andbegins
countingontheclockafterthedeassertionofreset.
15-12COLLCOUNT0-FhCollisioncount.Thesebitsindicatethenumberofcollisionsthecurrentframehasexperienced.
11-10Reserved0Reserved
9-0TXBACKOFF0-3FFhBackoffcount.Thisfieldallowsthecurrentvalueofthebackoffcountertobeobservedfortest
purposes.Thisfieldisloadedautomaticallyaccordingtothebackoffalgorithm,andisdecremented
byoneforeachslottimeafterthecollision.
Thetransmitpacingalgorithmtestregister(TPACETEST)isshowninFigure80anddescribedin
Table79.
Figure80.TransmitPacingAlgorithmTestRegister(TPACETEST)
3116
Reserved
R-0
15540
ReservedPACEVAL
R-0R-0
LEGEND:R=Readonly;-n=valueafterreset
Table79.TransmitPacingAlgorithmTestRegister(TPACETEST)FieldDescriptions
BitFieldValueDescription
31-5Reserved0Reserved
4-0PACEVAL0-1FhPacingregistercurrentvalue.Anonzerovalueinthisfieldindicatesthattransmitpacingisactive.A
transmitframecollisionordeferralcausesPACEVALtobeloadedwith1Fh(31);goodframe
transmissions(withnocollisionsordeferrals)causePACEVALtobedecrementeddownto0.When
PACEVALisnonzero,thetransmitterdelaysfourInterPacketGapsbetweennewframetransmissions
aftereachsuccessfullytransmittedframethathadnodeferralsorcollisions.Ifatransmitframeis
deferredorsuffersacollision,theIPGtimeisnotstretchedtofourtimesthenormalvalue.Transmit
pacinghelpsreducecaptureeffects,whichimprovesoverallnetworkbandwidth.
EthernetMediaAccessController(EMAC)/ManagementDataInput/Output(MDIO) 118SPRUEQ6–December2007
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