RepeatTimer.ino

/*
 Repeat timer example

 This example shows how to use hardware timer in ESP32. The timer calls onTimer
 function every second. The timer can be stopped with button attached to PIN 0
 (IO0).

 This example code is in the public domain.
 */

// Stop button is attached to PIN 0 (IO0)
#define BTN_STOP_ALARM    0

hw_timer_t * timer = NULL;

void onTimer(){
  static unsigned int counter = 1;

  Serial.print("onTimer no. ");
  Serial.print(counter);
  Serial.print(" at ");
  Serial.print(millis());
  Serial.println(" ms");

  counter++;
}

void setup() {
  Serial.begin(115200);

  // Set BTN_STOP_ALARM to input mode
  pinMode(BTN_STOP_ALARM, INPUT);

  // Use 1st timer of 4 (counted from zero).
  // Set 80 divider for prescaler (see ESP32 Technical Reference Manual for more
  // info).
  timer = timerBegin(0, 80, true);

  // Attach onTimer function to our timer.
  timerAttachInterrupt(timer, &onTimer, true);

  // Set alarm to call onTimer function every second (value in microseconds).
  // Repeat the alarm (third parameter)
  timerAlarmWrite(timer, 1000000, true);

  // Start an alarm
  timerAlarmEnable(timer);
}

void loop() {
  // If button is pressed
  if (digitalRead(BTN_STOP_ALARM) == LOW) {
    // If timer is still running
    if (timer) {
      // Stop and free timer
      timerEnd(timer);
      timer = NULL;
    }
  }
}