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Problem with TX SPORT when using MP3 Decoder library.

Question asked by brizza on Jul 19, 2012
Latest reply on Sep 27, 2012 by brizza

I am having a problem with TX SPORT output when using the ADI MP3 audio decoder library Rel3.1.1 running on a BF512.
I am using the decoder library to process incoming compressed audio packets in a streaming fashion. We receive compressed audio elementary streams via the RX side of a SPORT, decode these streams and then output the audio samples to a DAC via the TX side of the same SPORT (setup in left justified mode with DMA enabled). The receiving and decoding of the compressed audio all seem to work well however I get gaps in L/R clock output of the TX SPORT which obviously causes audio distortion.

To try to isolate the problem I initialized the TX SPORT with two buffers of audio samples that represent a 1KHz tone and set it to run continuously in CHAINED_LOOPBACK mode (DMA enabled, left justified mode). I discard the decoded audio samples so the TX SPORT its only outputting the two buffers it was initialized with. When I run this test without sending the incoming audio samples to the MP3 decoder I get a valid 1Khz tone from the output of the TX SPORT. If I decode the incoming compressed audio then I get the gaps in the L/R clock.

What could the MP3 decoder library be doing to cause the TX SPORT to output a non-continous L/R clock?

Any idea's on how I can debug this problem?