my system consists of an ADAU1467 and two PCM3168A codecs, for a total of 8 inputs (4 on each codec) and 16 outputs (8 on each codec).
DSP and CODECS receive both the master clock from a 24.576 MHz external oscillator.
The DSP is BCLK and LRCLK master: it receives and transmits digital audio @96kHz in TDM4 format, using Serial Input Port 0 and Serial Output Port 0, using the following audio digital data lines:
|I/O lines||DSP pin||CODEC|
|Input 1 - 4||SDATA_IN0||1|
|Input 5 - 8||SDATAIO0 (input serial port 0)||2|
|Output 1 - 4||SDATA_OUT0||1|
|Output 5 - 8||SDATAIO3 (output serial port 0)||1|
|Output 9 - 12||SDATAIO4 (output serial port 0)||2|
|Output 13 - 16||SDATAIO5 (output serial port 0)||2|
Running a simple DSP application that performs just a input - output routing of the first 8 channels (see the attached project),
- inputs 1 - 4 are faithfully reproduced on the corresponding outputs: if no signal is applied on the input, the outputs are silent and everything works correctly
- inputs 5 - 8 generates the following noise (I took the signal from the analog outputs of the CODEC 1)
I stated it depends on the inputs because if I route input 1 - 4 to output 1 - 4 and 5 - 8 all outputs works fine.
i did a lot of tests before writing here, I'm pretty sure the problem is not in my board layout / schema / power, but it depends on the DSP.
Any suggestion would be really appreciated.