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)
Architecture
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Figure 97. Shared Processing Subframe Segmentation (Example with 5 Subframes)
F: Frame length (number of bits in a frame prior to turbo-encoding)
R: 1/code rate
P: Prolog length (number of symbols to be used in the prolog not taking into account the rate)
The unit is designed so that reliability size ranges from 40 to 128 bits and prolog size ranges from 4 to 48bits. The prolog size is chosen based on whether the code is punctured or non-punctured. The prolog sizecan be programmed from 4 to 48 in the TCP2. If prolog reduction is enabled, the prolog size should rangebetween 4 to16.
Note: In shared-processing mode, the prolog size must be a multiple of 8 due to EDMA3 transfersalignments constraints.
The reliability size is chosen to optimally fill the pipelines; however, there are some limitations. Themaximum size of each sub-block is 256 symbols in which each of the two sliding windows maximumreliability size is 128. The reliability length is computed from the frame length.
Given N the block size, P the prolog length, Nsb the number of sub-blocks, Nsw the number of slidingwindows per sub-block (Nsw =1 or 2), the reliability length R must fill the following properties:
•The last sliding window reliability can be smaller than the others (last beta prolog is not processed, tailsare used to initialize beta states).
•The prolog of the sliding window before the last must point before the end of the frame: for example, N,P, R are such that N = (Nsb * Nsw - 1) * R + P + r; r > 0. The following formula meets the aboveproperties:
TMS320C6457 Turbo-Decoder Coprocessor 262 SPRUGK1 – March 2009Submit Documentation Feedback