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;
volatile SemaphoreHandle_t timerSemaphore;
portMUX_TYPE timerMux = portMUX_INITIALIZER_UNLOCKED;

volatile uint32_t isrCounter = 0;
volatile uint32_t lastIsrAt = 0;

void ARDUINO_ISR_ATTR onTimer() {
  // Increment the counter and set the time of ISR
  portENTER_CRITICAL_ISR(&timerMux);
  isrCounter = isrCounter + 1;
  lastIsrAt = millis();
  portEXIT_CRITICAL_ISR(&timerMux);
  // Give a semaphore that we can check in the loop
  xSemaphoreGiveFromISR(timerSemaphore, NULL);
  // It is safe to use digitalRead/Write here if you want to toggle an output
}

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

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

  // Create semaphore to inform us when the timer has fired
  timerSemaphore = xSemaphoreCreateBinary();

  // Set timer frequency to 1Mhz
  timer = timerBegin(1000000);

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

  // Set alarm to call onTimer function every second (value in microseconds).
  // Repeat the alarm (third parameter) with unlimited count = 0 (fourth parameter).
  timerAlarm(timer, 1000000, true, 0);
}

void loop() {
  // If Timer has fired
  if (xSemaphoreTake(timerSemaphore, 0) == pdTRUE) {
    uint32_t isrCount = 0, isrTime = 0;
    // Read the interrupt count and time
    portENTER_CRITICAL(&timerMux);
    isrCount = isrCounter;
    isrTime = lastIsrAt;
    portEXIT_CRITICAL(&timerMux);
    // Print it
    Serial.print("onTimer no. ");
    Serial.print(isrCount);
    Serial.print(" at ");
    Serial.print(isrTime);
    Serial.println(" ms");
  }
  // 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;
    }
  }
}