#define LED 17
#define C_TIME 1000000
hw_timer_t *My_timer = NULL;

void IRAM_ATTR onTimer(){ //interrupt function
  digitalWrite(LED, !digitalRead(LED));
}

void setup() {
  // put your setup code here, to run once:
  pinMode(LED, OUTPUT);
  Serial.begin(115200);
  
  My_timer = timerBegin(0, 80, true);//timer initialization
  //0: hw timer number (has 4 hw timers available)
  //80: time divider (clk 80MHz so we set every tick to 1 us)
  //true: counter should increment

  timerAttachInterrupt(My_timer, &onTimer, true);//attach interrupt

  timerAlarmWrite(My_timer, C_TIME, true);
  //C_TIME: number of microseconds after which the interrupt should occour
  //true: timer counter will reload after interrupt

  timerAlarmEnable(My_timer);
}

void loop() {
  delay(10);
}