#define LED_BUILTIN 25
hw_timer_t *timer = NULL;

volatile bool has_expired = false;
volatile bool led_state = false;
void IRAM_ATTR timerInterrupcion() {
 has_expired = true;
}

void setup() {
  Serial.begin(9600);
  pinMode(LED_BUILTIN, OUTPUT);

  timer = timerBegin(0, 80, true); // Timer 0, clock divider 80
  timerAttachInterrupt(timer, &timerInterrupcion, true); // Attach the interrupt handling function
  timerAlarmWrite(timer, 300000, true); // Interrupt every 1 second
  timerAlarmEnable(timer); // Enable the alarm
}

void loop() {
  if(has_expired)
  {
     // Tasks to perform when the Timer interrupt is triggered
    led_state = !led_state;
    digitalWrite(LED_BUILTIN, led_state);
    char info[255];
    sprintf(info, "Toggle led! -> %X", led_state);
    Serial.println(info);
    has_expired = false; 
  }
  
}