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#include "driver/i2s.h"
#include "esp_err.h"

void app_main( void )
{
    // configure i2s for internal dac
    static const i2s_config_t i2s_config =
    {
        .mode                   = I2S_MODE_MASTER | I2S_MODE_TX | I2S_MODE_DAC_BUILT_IN,
        .sample_rate            = 48000,
        .bits_per_sample        = 16,
        .channel_format         = I2S_CHANNEL_FMT_RIGHT_LEFT,
        .communication_format   = I2S_COMM_FORMAT_I2S_MSB,
        .intr_alloc_flags       = ESP_INTR_FLAG_LEVEL1,
        .dma_buf_count          = 8,
        .dma_buf_len            = 64,
        .use_apll               = true
    };

    // install i2s driver
    ESP_ERROR_CHECK( i2s_driver_install( I2S_NUM_0, &i2s_config, 0, NULL ) );

    // set pins for internal dac - enable both channels
    ESP_ERROR_CHECK( i2s_set_pin( I2S_NUM_0, NULL ) );

    // enable dac outputs
    ESP_ERROR_CHECK( i2s_set_dac_mode( I2S_DAC_CHANNEL_BOTH_EN ) );

    // I2S log results:
    //-----------------
    // I (325) I2S: DMA Malloc info, datalen=blocksize=256, dma_buf_count=8
    // I (345) I2S: APLL: Req RATE: 48000, real rate: 23999.980, BITS: 16, CLKM: 1, BCK_M: 8, MCLK: 6143995.000, SCLK: 767999.375000, diva: 1, divb: 0

    // memory for i2s write:
    //----------------------
    // 64 samples = 128 bytes at 16bit
    // 8 buffers  = 1024 bytes (  128 x 8 )
    // 2 channels = 2048 bytes ( 1024 x 2 )
    int outBytes  = 2048;

    // allocate output buffer memory
    uint8_t* outBuf = ( uint8_t* )calloc( outBytes, sizeof( uint8_t ) );

    // make spikes
    outBuf[ 0 ] = 255;
    outBuf[ 1 ] = 255;
    outBuf[ 2 ] = 255;
    outBuf[ 3 ] = 255;

    // i2c bytes-written variable
    size_t bytesOut;

    // output the buffer
    while( true )
    {
        ESP_ERROR_CHECK( i2s_write( I2S_NUM_0, outBuf, outBytes, &bytesOut, portMAX_DELAY ) );

        // this results in silence; nothing on either pin 25 or 26; nothing on the scope.
        // ESP_ERROR_CHECK reports nothing
    }
}