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DSK6713 BSL Application software limitation - ping pong/EDMA/McBSP issue

Greg D.
Prodigy 20 points

Other Parts Discussed in Thread: CCSTUDIO

I am designing a 38-42 KHz signal, I started with the CCS Studio example (dsp_app) located in directory CCStudio_v3.1\examples\dsk6713\bsl\dsk_app. I used a signal generator to inject a signal to the line-in. From 1KHz to 23.5KHz it works fine. As you increase the frequency, the cycles drop off and eventually the signal is lost while measuring the line-out.  There was another detailed post regarding this issue located at http://www.dsprelated.com/groups/c6x/show/7804.php that went unanswered that describes more detail.

There seems to be a limitation, at this point I do not know if this is a hardware or software architecture limitation. My project requires generating a 38-42 KHz analog signal. If I use a signal generator for the input and apply a fft or a generate a signal from scratch and feed that to the DAC, will I still have my limitations of 23.5 KHz if its a BSL application software limitation? A pointer on how to a get around this issue would be greatly appreciated.

Thanks in advance

Greg

 

  • 0
    TI__Guru**** 171569 points

    Greg,

    Are you sure you set the codec sampling rate correctly? According to section 2.2 of the C6713 DSK Technical Reference guide, the codec built-in to the development kit (TLV320AIC23) has multiple sampling rates. According to the Nyquist theorem, the integrity of the input signal can only be guaranteed up to 1/2 of the sampling rate. If the signal frequency goes beyond that it will suffer severe aliasing, thus compromising its integrity.

    This is the only thing that occurs to me that may be happening in your case, as per your description it seems the system is properly configured and collecting data without issues. This is a very old example originally provided by Spectrum Digital, therefore I don't know if it has any software and/or performance limitations.

    Hope this helps,

    Rafael

     

  • 0 in reply to desouza
    Prodigy 20 points

    Rafael, 

    Cha-ching! You were right on the money with the error. I set the sampling rate to 96 KHz, as you specified with the Nyquist theorem I was able to confirm the output to a maximum of 48 KHz, after that severe aliasing occurred. You have been most helpful; your response is most certainly appreciated.

    Sincerely, 

    Greg D.