Filter
Top Products
Parity A
Parity A’
Parity B
Parity B’
Void input
I
I
I
−1
Apriori 1
Apriori 2
Systematic
Stop?
(stopping
criterion
algo)
New
apriori
Previous apriori
Yes
Systematic
No
Slicer
Create hard
decisions
End
MAP
decoder
unit
Extrinsic
saved
as new
apriori
Keep on iterations
Enable next log−map
by switching the
switches
4.1InputDataFormat
4.1.1SystematicandParityData
www.ti.com
Standalone(SA)Mode
Oneiterationofturbodecodingconsistsof2MAPsprocessing,thefirstMAPwiththeinitialswitchposition
(asshowninFigure4),thesecondMAPwiththeotherpositionoftheswitch.AftereachMAP,astopping
testcanbeperformedbasedonthefollowingmethods.Thesetestsareuserconfigurable.
•ComparingtheextrinsicSNRestimatetoaSNRthreshold(userdefined)
•CRCpatternmatch
•Maxiterations
Whenstartingadecoding,youmustsupplyamaximumnumberofiterationsandoptionallyanSNR
thresholdratio(orCRC)forthestoppingtest.Ifthestoppingtestispositiveorthemaximumnumberof
iterationsisreached,thedecodingstops,theharddecisionsarecomputed(frombothextrinsicand
systematicdata),andthenthecoprocessornotifiesEDMA3thattheprocessingiscomplete.InFigure4,
switchpositionsareforMAP0andoppositepositionsareforMAP1.
Figure4.Standalone(SA)ModeBlockDiagram
Symbols(data)havetobequantizedon6bitsas(4,2)bitnumbers,thatis,SIII.FF(whereS=signbit,I=
integerbit,F=fractionalbit).Dependingontherate,Figure6throughFigure16showhowdatamustbe
organizedintheDSPmemorytoconformtoaratethatis1/5oftheinputdatastream,whichTCP2
requires.Thebaseaddressmustbedouble-wordaligned.Forbig-endianconfiguration,seetheTCP2
endianregister(TCPEND)inSection6.22.Alsonotethatinterleavedparitiesmustbede-interleavedprior
tobeingsenttoTCP2.
SPRUGK1–March2009TMS320C6457Turbo-DecoderCoprocessor213
SubmitDocumentationFeedback