hw_timer_t *timer = NULL;
volatile uint8_t ledState = 0; // setting initial led state to low
const int ledPin = 16;

void IRAM_ATTR timLed (){ // declaring the interrupt function
  ledState =!ledState; // changing the ledstate in order to toggle the pin
  digitalWrite(ledPin, ledState);
}

void setup() {
  pinMode(ledPin, OUTPUT); // setting led pin to output

  timer = timerBegin(0,160,true); // setting : timer value = 0 , prescaler = 160, counter = Up
  timerAttachInterrupt(timer ,&timLed, true); // attaching interrupt and taking the defined interrupt function
  timerAlarmWrite(timer,2500000,true); // setting Alarm value
  timerAlarmEnable (timer); // enabling alarm
  
}

void loop() {
  // put your main code here, to run repeatedly:
  delay(10); // this speeds up the simulation
}