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9.3ProgrammingShared-Processing(SP)Mode
Programming
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Theminimumnumberofiterations(MINITbitsinTCPIC3)shouldbeselectedasafunctionoftheoverall
systemperformance(minimumiterations1to31)whenSNRstoppingcriteriaisused.
TheINPUTSIGNbitcanbeenabledordisabledinTCPIC3(0=Usechannelinputdataasis,1=multiply
channelinputdataby-1).
TheOUTORDERbitcanbeenabledordisabledinTCPIC3(0=outputbitorderingfrom0to31,1=
outputbitorderingfrom31to0).
TheEPROREDbitcanbeenabledordisabledinTCPIC3(0=prologreductiondisabled,1=prolog
reductionenabled).
TheCRClengthandCRCiterations(TCPIC4)andCRCPolynbits(TCPIC5)shouldbeselectedasa
functionoftheoverallsystemperformance.Avalue0disablestheCRCstoppingcriteriaalgorithm.
TheTAIL1,TAIL2,TAIL3,TAIL4,TAIL5,andTAIL6bitsshouldbeprogrammedasdescribedin
Section6.8throughSection6.13,respectively.
TheExtrinsicScalingfactorscanbeselectedinregistersTCPIC12,TCPIC13,TCPIC14,andTCPIC15.
Table44.InputConfigurationParametersSettingsinStandalone(SA)Mode
BitFieldRegisterValue
OPMODTCPIC0OPMOD=00:SAMode
INTERTCPIC0INTER=0ifnonewinterleavertableisneeded;otherwise,INTER=1
OUTFTCPIC0OUTF=1ifTCPREVTistobegeneratedfortheoutputparametersload;
otherwise,OUTF=0
Insharedmode,theDSPmustdomoreworkandworkcloselywiththeTCP2.TheDSPbreaksthelarge
frameintosmallerframesof20,480orless.Eachoneoftheseframesiscalledasubframe.Thesizeofall
thesubframes(exceptthelastsubframe)mustbedivisibleby256.Notethattheframe_lengthlistedinthe
shared-processingmodeisthelengthofthesubframesandnotthelengthoftheframe.TheTCPwilltreat
eachsubframeasitsownframeofdata.
Todecodethewholeframe,followthesesteps:
1.DSPsendssubframesystematic,parityandextrinsicdatatoTCP2.
2.TCP2executestwoMAPdecodersforeachiteration.
3.DSPreadstheintermediateresults(extrinsics).
4.DSPinterleavesorde-interleavesdata.
5.Steps1to4arerepeatedforallsubframes.
TheopmodparameterdefineswhichsubframetheTCP2isdecoding.Opmodeissetto1forthefirst
subframe,opmodeissetto2forthemiddlesubframe(s),andopmodeissetto3forthelastsubframe.
Table43highlightstherequiredEDMA3resourcestoperformashared-processing(SP)modedecoding.
Asinstandalone(SA)modedecoding,eachsetofEDMA3parametersusestheEDMA3linking
capabilities.Inaddition,theaprioridatatransferisdoneusingtheEDMA3alternatetransferchaining
capabilities.Section9.3.1detailstheEDMA3transfersprogrammingandSection9.3.2detailstheinput
parametersprogramming.Itshouldbenotedthatanystoppingcriteriaalgorithmhastobeimplementedby
theCPU.
Anynotificationmechanismtoflagthatauser-channelhasjustbeendecodedislefttoyou.Suggested
implementationistousetheEDMA3interruptgenerationcapabilities[seeTMS320C6457DSPEnhanced
DirectMemoryAccess(EDMA3)ControllerReferenceGuide(SPRUGK6)]andprogramtheEDMA3to
generateaninterruptaftertheuser-channel'slastTCPREVTsynchronizedEDMA3transferhas
completed.
70TMS320C6457Turbo-DecoderCoprocessor2SPRUGK1–March2009
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