I2S input to PICO - 4x32 (2x64) channels - I think there might be an issue with the audio buffer or dma

[johnofleek]

I'm experiencing an issue where the audio data is occasionally being corrupted - around once a second at 8KHz frame rate.

Whilst investigating this I notice that the i2s0.read() is blocking for longer than I would expect

The blocked time seems to increase with the size of the buffer

// I2S i2s0(OUTPUT);
#define I2S0_DATA                 0 // GPIO0
#define I2S0_BCLK                 1 // GPIO1 LRCLK = I2C0_BCLK + 1
//      Due to PIO structure      2 // GPIO2  I2C0_LRCLK

#define I2S0_BUFFERS              4 
#define I2S0_BUFFERS_WORDS        0x1000
#define I2S0_SILENCE_SAMPLE       0xE5E5E5E5
#define I2S0_FREQUENCY            8000   // Hz This is the L/R CLK FREQUENCY

static void pico_i2s0_setup(void){
  i2s0.setDATA(I2S0_DATA);
  i2s0.setBCLK(I2S0_BCLK); 
  i2s0.setBitsPerSample(64);      // in this cases uses pio_i2s_in64_program_init(PIO pio, uint sm, uint offset, uint data_pin, uint clock_pin_base, uint bits)
  //i2s0.setBitsPerSample(32);
  i2s0.setBuffers(I2S0_BUFFERS, I2S0_BUFFERS_WORDS, I2S0_SILENCE_SAMPLE);
  i2s0.setFrequency(I2S0_FREQUENCY);
  
  i2s0.begin();
}

Any ideas what is happening?