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Keep McASP transmitting without any data?

I know this is a long-shot, but just in case I'm missing some magic setting:

Is it possible to configure a McASP set-up for S/PDIF in a "continuous Tx" mode, so that it will transmit digital silence (0 data) when there is no other data to transmit?

  • The behavior when the McASP experiences an underflow is that it outputs zeros. This is mentioned here:

    processors.wiki.ti.com/.../McASP_Tips

    Admittedly I have not used the S/PDIF mode of the McASP so not sure if there is anything special about that situation. Though I imagine it should not take too much work to simply let it underflow!
  • Thanks Brad - good point.

    For reference the TRM section 22.2.10.4.2 says:

    "In DIT mode, a pair of BMC zeros is shifted out when an underrun occurs (four bit times at 128 × fs). By
    shifting out a pair of zeros, a clock may be recovered on the receiver. To recover, reset the McASP and
    start again with the proper initialization."

    I don't think this helps in my situation as resetting the McASP will likely cause a interruption in the S/PDIF stream.
  • I'm pretty sure you don't need to reset the clock generation. Just put the transmit serializers, frame sync, and state machine into reset, and follow the startup procedure of the transmit section again minus the clock setup (i.e. from step 5 in the procedure in the TRM).

    Alternatively when using EDMA it's easy enough to have it deliver a perpetual stream of zeros.