4.4.3 Parameter Termination
4.4.3.1 Maximum Iterations
4.4.3.2 Minimum Iterations
5 Shared-Processing (SP) ModeShared-Processing (SP) Mode
www.ti.com
The CRC will process one sub-block at time using the data stored from the previous sub-block. Thedecision bit will be used by a CRC block. After all sub-blocks have been processed, the CRC bits in theCRC block are checked and compared with the last crc_length bits of the frame. If they all match, then theCRC passes.
The parameters min_iter and max_iter need to be set prior to decode. The decoder must execute min_iternumber of iterations. This parameter can be set from 0 to 31. The decoder will stop executing when theiteration count equals max_iter. Max_iter can be set from 0 to 31 and must be equal or greater thanmin_iter. A zero for max is equal to 32 iterations. A zero for min is equal to 1 iteration.
Turbo decoders execute the MAP decoder twice per iteration. One execution is for non-interleaved dataand the other execution is for interleaved data. This parameter sets the maximum number of decoderiterations for each block of data. Valid sizes are 0 to 31. If either the CRC passed or the SNR stoppingcriteria threshold has been exceeded, then the decoder will stop early. The last iteration will only processthe MAP decoder for the non-interleaved data.
Turbo decoders execute the MAP decoder twice per iteration. One execution is for non-interleaved dataand the other execution is for interleaved data. This parameter sets the minimum number of decoderiterations for each block of data. Valid sizes are 0 to 31 and the min_iter must be less than or equal to themax_iter. The CRC unit will not be enabled until the decoder iteration count is equal or greater than themin_iter parameter. The turbo decoder will not process the CRC, re-encode, or write to the output RAMuntil the minimum number of iterations has been reached.
In shared-processing (SP) mode, the DSP sends systematic and parity data, and a priori data. The TCPperforms one single MAP decode and outputs extrinsic data. A priori data for MAP1 is obtained byde-interleaving the extrinsic data from the previous MAP2, and a priori data for MAP2 is obtained byinterleaving the extrinsics data from the previous MAP1. An overview of the SP mode is shown inFigure 16 . Note that the systematic and parity data to be sent to the TCP has to be demultiplexed from theoriginal flow described in Section 5.1 . The DSP must perform the input data demultiplexing, interleaving,deinterleaving operations, hard decision calculation, and any stopping criteria algorithm.
TMS320C6457 Turbo-Decoder Coprocessor 218 SPRUGK1 – March 2009Submit Documentation Feedback