void setup(void)
{
  pinMode(LED_BUILTIN, OUTPUT);
}

/****************************************************************/
void delay_and_poll(long microseconds)
{
  unsigned long last_update_clock = micros();
  
  while (microseconds > 0) {
    unsigned long now = micros();
    unsigned long interval = now - last_update_clock;
    last_update_clock = now;
    microseconds -= interval;

    static long led_blink_timer = 0;
    static bool led_blink_state = false;
    const long led_blink_interval = 500000;

    led_blink_timer -= interval;
    if (led_blink_timer <= 0) {
      led_blink_timer += led_blink_interval;
      led_blink_state = !led_blink_state;
      digitalWrite(LED_BUILTIN, led_blink_state);
    }
  }
}

/****************************************************************/
void loop(void)
{
  // entering state 0
  delay_and_poll(1000000);

  // entering state 1
  delay_and_poll(1000000);

  // entering state 2
  delay_and_poll(1000000);

  // entering state 3
  while (true) delay_and_poll(1000000);
}