Timer

Timer

Example: RepeatTimer

The program uses Timer 0 for timing and prints the timing results to the serial monitor. The timing stops when the user button on P38 is pressed.

Hardware Required:

• ESP32 IoT Programmable Controller (SKU: DFR0886)×1

Example Code:

/*
 * Repeat Timer Example
 * This example demonstrates how to use a hardware timer on the ESP32.
 * The timer calls the onTimer function once per second.
 * The timer can be stopped using a button connected to PIN 38 (IO38).
 * This example code is in the public domain.
 */

// Stop button connected to PIN 38 (IO38)
#define BTN_STOP_ALARM    38

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 counter and record interrupt occurrence time
  portENTER_CRITICAL_ISR(&timerMux);
  isrCounter++;
  lastIsrAt = millis();
  portEXIT_CRITICAL_ISR(&timerMux);
  // Release semaphore to notify loop of the trigger
  xSemaphoreGiveFromISR(timerSemaphore, NULL);
  // It is safe to use digitalRead/Write here if an output state switch is needed
}

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

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

  // Create a semaphore to notify when the timer triggers
  timerSemaphore = xSemaphoreCreateBinary();

  // Use the first of the four available timers (index starts at 0)
  // Set prescaler value to 80
  // The board's clock frequency is currently 80MHz, with 80 prescaler, the count unit is microseconds
  timer = timerBegin(0, 80, true);

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

  // Set timer alarm to trigger onTimer function every second (value in microseconds)
  // Enable repeated alarm (third parameter)
  timerAlarmWrite(timer, 1000000, true);

  // Start the timer alarm
  timerAlarmEnable(timer);
}

void loop() {
  // If the timer has triggered
  if (xSemaphoreTake(timerSemaphore, 0) == pdTRUE){
    uint32_t isrCount = 0, isrTime = 0;
    // Read interrupt count and time
    portENTER_CRITICAL(&timerMux);
    isrCount = isrCounter;
    isrTime = lastIsrAt;
    portEXIT_CRITICAL(&timerMux);
    // Print output
    Serial.print("onTimer Trigger Count: ");
    Serial.print(isrCount);
    Serial.print(" Time: ");
    Serial.print(isrTime);
    Serial.println(" ms");
  }
  // If the button is pressed
  if (digitalRead(BTN_STOP_ALARM) == LOW) {
    // If the timer is still running
    if (timer) {
      // Stop and release the timer
      timerEnd(timer);
      timer = NULL;
    }
  }
}

Result: The serial monitor prints the timer data. When the user button on the board is pressed, the timer stops counting.!