Any way to avoid BCK stops on AVRC pause?

[LordManjaca]

I'm currently working on a project in which an ESP32 uses Bluetooth A2DP to transmit music to an STM32. Everything is synchronized by the BCK (ESP master ST slave). I got the clock to work before attaching the Bluetooth.
When Bluetooth is connected, everything works well; but, when the music is paused or stopped, the BCK signal stops after a few seconds.
Is it possible to maintain this clock running regardless of the state of the Bluetooth?

[pschatzmann]

The AudioStream integration is starting and stopping I2S driven by A2DP.

If you do not want I2S to stop, just use the data callback, set up I2S yourself and write to I2S in the callback.

[LordManjaca]

Thanks, I'll try that and paste my code once it's done for future reference!

[LordManjaca]

Something like this, I suppose? (It is currently working).

#include "AudioTools.h"
#include "BluetoothA2DPSink.h"

I2SStream i2s;
BluetoothA2DPSink a2dp_sink;
volatile bool is_playing = false;

void my_stream_reader(const uint8_t* data, uint32_t len) {
  i2s.write(data, len);
}

void bt_audio_state_callback(esp_a2d_audio_state_t state, void*) {
  is_playing = (state == ESP_A2D_AUDIO_STATE_STARTED);
}

void i2s_silence_task(void*) {
  static uint8_t zeros[512] = {0};
  for (;;) {
    if (!is_playing) {
      i2s.write(zeros, sizeof(zeros)); //Fill i2s with zero to keep BCK
    } else {
      vTaskDelay(pdMS_TO_TICKS(10));
    }
  }
}


void setup() {
    auto cfg = i2s.defaultConfig();
    cfg.channels = 2;
    cfg.sample_rate = 44100;
    cfg.bits_per_sample = 16;
    cfg.pin_ws = 25;
    cfg.pin_bck = 26;
    cfg.pin_data = 21;
    cfg.use_apll = true;
    cfg.channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT;
    i2s.begin(cfg);

    a2dp_sink.set_on_audio_state_changed(bt_audio_state_callback);
    a2dp_sink.set_stream_reader(my_stream_reader, false);

    a2dp_sink.start("ESP_BT to STM");
    xTaskCreatePinnedToCore(i2s_silence_task, "i2s_silence", 2048, nullptr, 1, nullptr, 1);
}

void loop() {
}

[pschatzmann]

yes: instead of the separate i2s_silence_task, you could do the writes in the Arduino loop() and instead of writing an empty array you can just call i2s.writeSilence(512)