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[C6745] sample delay between stereo audio (McASP) input

yl
Expert 1215 points

Hi,

My application is based on the audio example that comes with the C6747 biosPSP. I believe the same would happen when running the audio example on EVMC6747.

When feeding both left and right channels with the same signal, sometimes there is one sample delay between the channels, and sometimes there is none. The delay remains consistent until next power cycle or restart.

Is this a known issue? Has it been fixed? It seems that the support packages for L137/C6747/45 has not been updated for well over a year.

Thanks

  • 0
    TI__Genius 14545 points

    Yan,

    Yan said:
    Is this a known issue?

    Seeing that it is inconsistent, I would look into it a little more to determine why it sometimes works and sometimes doesn't. It might be related to timing,

  • 0 in reply to dabuan
    Expert 1215 points

    thanks for the tip.

    after some digging, all evidence pointed to the PSP and driver. You can probably repro this with your EVM.

    It is now TI's responsibility. I'd avoid looking into the huge pile of OS and driver code.

  • 0 in reply to yl
    TI__Genius 14545 points

    Yan,

       What evidence lead to the conclusion that it is a driver issue?

  • 0 in reply to dabuan
    Expert 1215 points

    It is certainly not my application because it happened with a simple pass thru. It is not likely caused by the the audio codec (we have the same on other products). The only thing I can think of is something between the I2S reaching the DSP and fetching data from the streaming IO. Where else could it be?

    The inconsistency between power cycles suggests something odd happened during initialization.

    Did you try on the EVM? A simple test of one sample delay is to feed the system with white noise, sum the two channel together and look at the output spectrum. If the spectrum is more or less flat, there is no delay. If the spectrum starts to roll off around half of the Nyquist, you got a one sample delay.

  • 0 in reply to yl
    TI__Genius 14545 points

    Yan,

       Thanks for the additional information. I wasn't suggesting it was your application, rather just wanted to get some additional details from your observations. Sorry if it came across that way.

    I haven't had a chance to try it on an EVM.

     

    Yan said:
    The only thing I can think of is something between the I2S reaching the DSP and fetching data from the streaming IO. Where else could it be?

    I agree it's probably not the Codec that is causing the inadvertent delays, however there is a lot of setup from a DSP point of view that is required for the driver to run.

     

    In your simple loopback program, do you have anything else that utilizes the EDMA3 as a DMA?

    Have you tried to use the example program located in the path below?

     

    C:\Program Files\Texas Instruments\pspdrivers_02_10_01\packages\ti\psp\examples\evmDA830\audio?

    It should work fine on the C6745 EVM as well.