Question: Would like to use the TDM port on the C542 as a bi-directional bus to transfer data between two DSPs.

Answer: The TDM will look bi-directional, since each DSP can be set up to both transmit and receive in different time slots. You can speed up the process by configuring the TRTA and TCSR registers to allow DSP1 to talk on channels 0 through 3 and listen on channels 4 through 7. Conversely, set DSP2 to talk on channels 4 through 7 and listen on channels 0 through 3.

This will give you a 4x increase in throughput. Of course, if one DSP is doing most of the talking, DSP1 can talk on 7 channels and DSP2 on 1 channel.