ESP32 DAC square wave

esp32_audio.ino

#include <U8x8lib.h>

U8X8_SSD1306_128X64_NONAME_SW_I2C u8x8(/* clock=*/15, /* data=*/4, /* reset=*/16);

// Timer setup.
volatile int interruptCounter;
volatile int totalInterruptCounter;

hw_timer_t *timer = NULL;
portMUX_TYPE timerMux = portMUX_INITIALIZER_UNLOCKED;

void IRAM_ATTR onTimer()
{
  portENTER_CRITICAL_ISR(&timerMux);
  interruptCounter++;
  portEXIT_CRITICAL_ISR(&timerMux);
}

void setup()
{
  u8x8.begin();
  u8x8.setFont(u8x8_font_chroma48medium8_r);

  u8x8.drawString(0, 0, "square");
  u8x8.setCursor(0, 0);
  // if (totalInterruptCounter % 1000 == 0)
  // {
  //   u8x8.drawString(0, 0, "   ");
  //   u8x8.setCursor(0, 0);
  //   u8x8.print(totalInterruptCounter, DEC);
  // }

  // Setup a timer.
  int prescaler = 80;
  timer = timerBegin(0, prescaler, true); // 80Hz (base frequency) / prescaler (80) = 1,000,000Hz timer.
  timerAttachInterrupt(timer, &onTimer, true);
  timerAlarmWrite(timer, 200, true); // 1,000,000Hz / 50 = 20Khz max frequency
  timerAlarmEnable(timer);
}

void loop()
{
  if (interruptCounter > 0)
  {
    portENTER_CRITICAL(&timerMux);
    interruptCounter = 0;
    totalInterruptCounter++;
    portEXIT_CRITICAL(&timerMux);
  }
  if (totalInterruptCounter % 2 == 0)
  {
    dacWrite(25, 250);
  }
  else
  {
    dacWrite(25, 5);
  }
}