4.4.3ParameterTermination
4.4.3.1MaximumIterations
4.4.3.2MinimumIterations
5Shared-Processing(SP)Mode
Shared-Processing(SP)Mode
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TheCRCwillprocessonesub-blockattimeusingthedatastoredfromtheprevioussub-block.The
decisionbitwillbeusedbyaCRCblock.Afterallsub-blockshavebeenprocessed,theCRCbitsinthe
CRCblockarecheckedandcomparedwiththelastcrc_lengthbitsoftheframe.Iftheyallmatch,thenthe
CRCpasses.
Theparametersmin_iterandmax_iterneedtobesetpriortodecode.Thedecodermustexecutemin_iter
numberofiterations.Thisparametercanbesetfrom0to31.Thedecoderwillstopexecutingwhenthe
iterationcountequalsmax_iter.Max_itercanbesetfrom0to31andmustbeequalorgreaterthan
min_iter.Azeroformaxisequalto32iterations.Azeroforminisequalto1iteration.
TurbodecodersexecutetheMAPdecodertwiceperiteration.Oneexecutionisfornon-interleaveddata
andtheotherexecutionisforinterleaveddata.Thisparametersetsthemaximumnumberofdecoder
iterationsforeachblockofdata.Validsizesare0to31.IfeithertheCRCpassedortheSNRstopping
criteriathresholdhasbeenexceeded,thenthedecoderwillstopearly.Thelastiterationwillonlyprocess
theMAPdecoderforthenon-interleaveddata.
TurbodecodersexecutetheMAPdecodertwiceperiteration.Oneexecutionisfornon-interleaveddata
andtheotherexecutionisforinterleaveddata.Thisparametersetstheminimumnumberofdecoder
iterationsforeachblockofdata.Validsizesare0to31andthemin_itermustbelessthanorequaltothe
max_iter.TheCRCunitwillnotbeenableduntilthedecoderiterationcountisequalorgreaterthanthe
min_iterparameter.TheturbodecoderwillnotprocesstheCRC,re-encode,orwritetotheoutputRAM
untiltheminimumnumberofiterationshasbeenreached.
Inshared-processing(SP)mode,theDSPsendssystematicandparitydata,andaprioridata.TheTCP
performsonesingleMAPdecodeandoutputsextrinsicdata.AprioridataforMAP1isobtainedby
de-interleavingtheextrinsicdatafromthepreviousMAP2,andaprioridataforMAP2isobtainedby
interleavingtheextrinsicsdatafromthepreviousMAP1.AnoverviewoftheSPmodeisshownin
Figure16.NotethatthesystematicandparitydatatobesenttotheTCPhastobedemultiplexedfromthe
originalflowdescribedinSection5.1.TheDSPmustperformtheinputdatademultiplexing,interleaving,
deinterleavingoperations,harddecisioncalculation,andanystoppingcriteriaalgorithm.
TMS320C6457Turbo-DecoderCoprocessor2 18SPRUGK1–March2009
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