ESP32 Forum

Posted: **Wed Dec 23, 2020 1:47 pm**

Dear all,

I am building a kind of Bluetooth audio extender. The setup includes two ESP32. The idea is to receive
an a2dp audio stream with ESP32#1, send it via i2s to ESP32#2 and from there via Bluetooth to a Bluetooth speaker.

ESP32 #1 (Audio Sink):

A classical A2DP audio sink. Receiving audio data via Bluetooth and sends the audio via I2S

Configuration:

Code: Select all

 i2s_config_t i2s_config = {

        .mode = I2S_MODE_MASTER | I2S_MODE_TX,                                  // Only TX
        .sample_rate = 44100,
        .bits_per_sample = 16,
        .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,                           //2-channels
        .communication_format = I2S_COMM_FORMAT_I2S_MSB,
        .dma_buf_count = 6,
        .dma_buf_len = 60,
        .intr_alloc_flags = 0,                                                  //Default interrupt priority
        .tx_desc_auto_clear = true                                              //Auto clear tx descriptor on underflow
    };

    i2s_driver_install(0, &i2s_config, 0, NULL);
    i2s_pin_config_t pin_config = {
        .bck_io_num = CONFIG_EXAMPLE_I2S_BCK_PIN,
        .ws_io_num = CONFIG_EXAMPLE_I2S_LRCK_PIN,
        .data_out_num = CONFIG_EXAMPLE_I2S_DATA_PIN,
        .data_in_num = -1                                                       //Not used
    };

    i2s_set_pin(0, &pin_config);

This works and I can also listen to the audio when connecting a PCM5102 DA converter.

ESP32 #2 (Audio Source):

This ESP32 is connected to the I2S bus as SLAVE. The goal is to receive the audio stream from ESP32#1 and send it to a Bluetooth speaker.
I can see that there are many examples where the source of the I2S signal is a microphone or SD Cards, but I could not find an example
which takes a I2S signal and sends it via Bluetooth A2DP to a speaker. I was experimenting a lot and since I was not successful I thought
I post here and see if someone can point me into the right direction. Here is what I have done so far w/o success:

Configuration:

Code: Select all

 static const int i2s_num = 0; // i2s port number

    static const i2s_config_t i2s_config = {
        .mode = I2S_MODE_SLAVE | I2S_MODE_RX,
        .sample_rate = 44100,
        .bits_per_sample = 16,
        .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
        .communication_format = I2S_COMM_FORMAT_I2S,
        .intr_alloc_flags = 0, // default interrupt priority
        .dma_buf_count = 8,
        .dma_buf_len = 64,
        .use_apll = false
    };


    static const i2s_pin_config_t pin_config = {
        .bck_io_num = 26,
        .ws_io_num = 22,
        .data_out_num = -1,
        .data_in_num = 25
    };

    i2s_driver_install(i2s_num, &i2s_config, 0, NULL);   //install and start i2s driver
    i2s_set_pin(i2s_num, &pin_config);

The pin_config is correct and corresponds to the I2S pins of module #1

I assume the magic has to happen here:

Code: Select all

static int32_t bt_app_a2d_data_cb(uint8_t *data, int32_t len)
{
    if (len < 0 || data == NULL) {
        return 0;
    }

    size_t bytes_read = 0;
    //int a = bytes_read;
    //int b = (int)data;
    
    i2s_read(0, data, SIZE???, &bytes_read, portMAX_DELAY);
    //ESP_LOGI(BT_AV_TAG, "bytes read: %d ", a);
    //ESP_LOGI(BT_AV_TAG, "data:%d ",b);
    return len;
}

I do have several problems here:

1. I am not sure if I can directly handover the I2S data w/o putting it into a buffer
2. I could not find a good documentation about the parameters of i2s_read and so I am lost on what to put there for e.g. SIZE
3. The return value is int32_t len. Where do I get this from? Maybe sizeof(data)?
4. I have problems to understand the bytes_read variable. Seems like that there is not usage for it.

Can anybody kindly help me out here?
Thank you very much in advance
Mike

Posted: **Sat Nov 19, 2022 11:19 pm**

Hi did you manage to make it works ?
I'm trying to do an A2DP source from I2S/ADC too but the sound is or very noisy, "chunked" (like if you keep turning on and off)...
I presume there is an endiannes correction to do, it looks like the data format is very important... (but changing "communication_format" in i2s setup changes nothing at all...)
Also it looks like the audio frequencies are shifted up (about 2 tones upper)...

here is my data reading plus sending to ringbuffer

Code: Select all

	size_t bytes_read;
	char* i2s_read_buff[ADC_BUF_LEN];
	
	while (1) {
		i2s_read(0, (void*)i2s_read_buff, ADC_BUF_LEN, &bytes_read, portMAX_DELAY);
		// send to ring buffer
		if (xRingbufferSend(buf_handle, i2s_read_buff, bytes_read, pdMS_TO_TICKS(1000)) != pdTRUE) {
			printf("ERROR WRITING\n");
		}
	}

and here is the A2DP callback

Code: Select all

	size_t item_size = 0;
	char *buffer = (char *)xRingbufferReceiveUpTo(buf_handle, &item_size, pdMS_TO_TICKS(1000), len / 2);
	if (item_size == 0 || buffer == NULL) {
		return 0;
	}
	// copy data over
	for (int i = 0; i < item_size; i++)
	{
		char v1 = buffer[2 * i];
		char v2 = buffer[2 * i + 1];
		data[4 * i] = v1;
		data[4 * i + 1] = v2;
		data[4 * i + 2] = v1;
		data[4 * i + 3] = v2;
	}
	// remove buffer
	vRingbufferReturnItem(buf_handle, (void *)buffer);

This code works but gives a very bad sound...

ESP32 Forum

Send I2S audio from A2DP sink to A2DP Source and then to Bluetooth Speaker

Send I2S audio from A2DP sink to A2DP Source and then to Bluetooth Speaker

Re: Send I2S audio from A2DP sink to A2DP Source and then to Bluetooth Speaker