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Shared-processing frame (length > 20730)
First subframe
Middle subframe
Middle subframe
Middle subframe
Last subframe
Prolog
Must point to
valid address
Tail
Subframe (length ≤ 20480)
8.3ReliabilityandPrologLengthCalculation
Architecture
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Figure97.SharedProcessingSubframeSegmentation(Examplewith5Subframes)
F:Framelength(numberofbitsinaframepriortoturbo-encoding)
R:1/coderate
P:Prologlength(numberofsymbolstobeusedintheprolognottakingintoaccounttherate)
Theunitisdesignedsothatreliabilitysizerangesfrom40to128bitsandprologsizerangesfrom4to48
bits.Theprologsizeischosenbasedonwhetherthecodeispuncturedornon-punctured.Theprologsize
canbeprogrammedfrom4to48intheTCP2.Ifprologreductionisenabled,theprologsizeshouldrange
between4to16.
Note:Inshared-processingmode,theprologsizemustbeamultipleof8duetoEDMA3transfers
alignmentsconstraints.
Thereliabilitysizeischosentooptimallyfillthepipelines;however,therearesomelimitations.The
maximumsizeofeachsub-blockis256symbolsinwhicheachofthetwoslidingwindowsmaximum
reliabilitysizeis128.Thereliabilitylengthiscomputedfromtheframelength.
GivenNtheblocksize,Ptheprologlength,Nsbthenumberofsub-blocks,Nswthenumberofsliding
windowspersub-block(Nsw=1or2),thereliabilitylengthRmustfillthefollowingproperties:
•Thelastslidingwindowreliabilitycanbesmallerthantheothers(lastbetaprologisnotprocessed,tails
areusedtoinitializebetastates).
•Theprologoftheslidingwindowbeforethelastmustpointbeforetheendoftheframe:forexample,N,
P,RaresuchthatN=(Nsb*Nsw-1)*R+P+r;r>0.Thefollowingformulameetstheabove
properties:
TMS320C6457Turbo-DecoderCoprocessor2 62SPRUGK1–March2009
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