#define LED 21
hw_timer_t *My_timer = NULL;

void IRAM_ATTR onTimer(){
digitalWrite(LED, !digitalRead(LED));
}
void setup() {
  // put your setup code here, to run once:
pinMode(LED, OUTPUT)
My_timer = timerBegin(0, 80, true);
timerAttachInterrupt(My_timer, &onTimer, true);
timerAlarmWrite(My_timer, 1000000, true);
timerAlarmEnable(My_timer);
  Serial.begin(115200);
  Serial.println("Hello, ESP32!");
}

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