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The VCU-II is the second-generation Viterbi, Complex Math, and CRC extension to the C28x CPU. The VCU-II extends the capabilities of the C28x CPU by adding registers and instructions to accelerate the performance of FFTs and communications-based algorithms. The C28x+VCU-II supports the following algorithm types:
Viterbi decoding is commonly used in baseband communications applications. The Viterbi decode algorithm consists of three main parts: branch metric calculations, compare-select (Viterbi butterfly), and a traceback operation. Table 6-12 shows a summary of the VCU performance for each of these operations.
|VITERBI OPERATION||VCU CYCLES|
|Branch Metric Calculation (code rate = 1/2)||1|
|Branch Metric Calculation (code rate = 1/3)||2p|
|Viterbi Butterfly (add-compare-select)||2(1)|
|Traceback per Stage||3(2)|
Cyclic redundancy check (CRC) algorithms provide a straightforward method for verifying data integrity over large data blocks, communication packets, or code sections. The C28x+VCU can perform 8-bit, 16-bit, 24-bit, and 32-bit CRCs. For example, the VCU can compute the CRC for a block length of 10 bytes in 10 cycles. A CRC result register contains the current CRC, which is updated whenever a CRC instruction is executed.
Complex math is used in many applications, a few of which are:
The complex FFT is used in spread spectrum communications, as well as in many signal processing algorithms.
Complex filters improve data reliability, transmission distance, and power efficiency. The C28x+VCU can perform a complex I and Q multiply with coefficients (four multiplies) in a single cycle. In addition, the C28x+VCU can read/write the real and imaginary parts of 16-bit complex data to memory in a single cycle.
Table 6-13 shows a summary of the VCU operations enabled by the VCU.
|COMPLEX MATH OPERATION||VCU CYCLES||NOTES|
|Add or Subtract||1||32 +/- 32 = 32-bit (Useful for filters)|
|Add or Subtract||1||16 +/- 32 = 15-bit (Useful for FFT)|
|Multiply||2p||16 x 16 = 32-bit|
|Multiply and Accumulate (MAC)||2p||32 + 32 = 32-bit, 16 x 16 = 32-bit|
|RPT MAC||2p+N||Repeat MAC. Single cycle after the first operation.|
For more information, see the TMS320C28x Extended Instruction Sets Technical Reference Manual.