ESP32-dualcore-i2s.ino

#include "driver/i2s.h"
#include <WiFi.h>

#define SAMPLE_RATE     44100
#define DMA_BUF_LEN     64
#define DMA_NUM_BUF     2
#define WAVE1_FREQ_HZ    440.0f
#define WAVE2_FREQ_HZ    500.0f
#define TWOPI            (float)(PI*2.0f)
#define PHASE_INC1       (float)(TWOPI * WAVE1_FREQ_HZ / (float)SAMPLE_RATE)
#define PHASE_INC2       (float)(TWOPI * WAVE2_FREQ_HZ / (float)SAMPLE_RATE)
#define I2S_BCLK_PIN     5
#define I2S_WCLK_PIN     19
#define I2S_DOUT_PIN     18

const i2s_port_t i2s_num = I2S_NUM_0; // i2s port number

TaskHandle_t Task1;
TaskHandle_t Task2;
size_t bytes_written;

// Accumulated phase
static float p1 = 0.0f;
static float p2 = 0.0f;

// Output buffers (2ch interleaved)
static uint16_t synth_buf1[DMA_BUF_LEN * 2];
static uint16_t synth_buf2[DMA_BUF_LEN * 2];
static uint16_t out_buf[DMA_BUF_LEN * 2];


static void synth1() {
    float samp = 0.0f;

    for (int i=0; i < DMA_BUF_LEN; i++) {
      samp = (sinf(p1)+1.0f) * 4000; 
      
      // Increment and wrap phase
      p1 += PHASE_INC1;
      if (p1 >= TWOPI) {
          p1 -= TWOPI ;
      }      
      synth_buf1[i*2] = (uint16_t)(samp * 0.8f);
      synth_buf1[i*2+1] = (uint16_t)(samp * 0.2f);
    }
}

static void synth2() {
    float samp = 0.0f;

    for (int i=0; i < DMA_BUF_LEN; i++) {
        samp = (sinf(p2)+1.0f) * 4000; 

        // Increment and wrap phase
        p2 += PHASE_INC2;
        if (p2 >= TWOPI) {
            p2 -= TWOPI ;
        }
        synth_buf2[i*2] = (uint16_t)(samp * 0.2f);
        synth_buf2[i*2+1] = (uint16_t)(samp * 0.8f);
    }
}

static void mixer() { // sum buffers 
    for (int i=0; i < DMA_BUF_LEN; i++) { 
        out_buf[i*2] = synth_buf1[i*2] + synth_buf2[i*2];
        out_buf[i*2+1] = synth_buf1[i*2+1] + synth_buf2[i*2+1] ;
    }
}

// Core0 task
static void audio_task1(void *userData) {
    while(1) {
        // this part of the code never intersects with mixer()
        synth1();
        
        // this part of the code is operating with shared resources, so we should make it safe
        if (ulTaskNotifyTake(pdTRUE, portMAX_DELAY)){
            mixer();
            xTaskNotifyGive(Task2); // if you have glitches, you may place this string in the end of audio_task1
        }
        
        // now out_buf is ready, output
        i2s_write(i2s_num, out_buf, sizeof(out_buf), &bytes_written, portMAX_DELAY);
    }
}

// task for Core1, which tipically runs user's code on ESP32
static void audio_task2(void *userData) {
    while(1) {
        // we can run it together with synth1(), but not with mixer()
        if (ulTaskNotifyTake(pdTRUE, portMAX_DELAY)) {
            synth2();
            xTaskNotifyGive(Task1);
        }
    }
}

void setup(void)
{
  Serial.begin(115200);
  WiFi.mode(WIFI_OFF);
  btStop();
  i2s_config_t i2s_config = {
      .mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_TX ),
      .sample_rate = SAMPLE_RATE,
      .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,
      .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
      .communication_format = (i2s_comm_format_t)(I2S_COMM_FORMAT_STAND_I2S | I2S_COMM_FORMAT_STAND_I2S),
      .intr_alloc_flags = ESP_INTR_FLAG_LEVEL2,
      .dma_buf_count = DMA_NUM_BUF,
      .dma_buf_len = DMA_BUF_LEN,
      .use_apll = false,
  };
  
  i2s_pin_config_t i2s_pin_config = {
      .bck_io_num = I2S_BCLK_PIN,
      .ws_io_num =  I2S_WCLK_PIN,
      .data_out_num = I2S_DOUT_PIN
  };

  i2s_driver_install(i2s_num, &i2s_config, 0, NULL);

  i2s_set_pin(i2s_num, &i2s_pin_config); 

  xTaskCreatePinnedToCore(
                  audio_task1,  // function 
                  "Task1",      // name 
                  1024,         // stack size 
                  NULL,         // params 
                  1,            // priority 
                  &Task1,       // handle 
                  0);           // Core ID 
                      
  xTaskCreatePinnedToCore(
                  audio_task2,  // function 
                  "Task2",      // name 
                  1024,         // stack size 
                  NULL,         // params 
                  1,            // priority 
                  &Task2,       // handle 
                  1);           // Core ID 

  // somehow we should allow tasks to run
  xTaskNotifyGive(Task1);
  xTaskNotifyGive(Task2);
     
}

void loop() {
  // you can still place some of your code here
  // or vTaskDelete();
  taskYIELD();
}