#include <FreeRTOS.h>

#define LED     12

TimerHandle_t write_timer;
volatile bool state;

void write_callback(TimerHandle_t xTimer) {
  digitalWrite(LED, !digitalRead(LED));
}

void setup() {
  pinMode(LED, OUTPUT);

  digitalWrite(LED, LOW);

  write_timer = xTimerCreate("Blink Timer",
                    pdMS_TO_TICKS(500),
                    pdTRUE,
                    nullptr,
                    write_callback);

  if (write_timer) {
    xTimerStart(write_timer, 0);
  }
}

void loop() {
  //delay(10000); // Nothing to see here
}