#include <avr/wdt.h>

#define LED_WDT 12

const unsigned long BLINK_HALF_PERIOD = 500;
const unsigned long WDT_RESET_PERIOD = 1000;
const unsigned long SKIP_WDT_RESET_AFTER_MS = 10000;

unsigned long blink_time;
unsigned long wdt_reset_time;
unsigned long wdt_enable_reset_time;

void setup() {
	wdt_reset();
	wdt_enable(WDTO_8S);

  pinMode(LED_BUILTIN, OUTPUT);
  pinMode(LED_WDT, OUTPUT);
  digitalWrite(LED_BUILTIN, LOW);
  digitalWrite(LED_WDT, LOW);

  if ((MCUSR) & (1<<(WDRF))) {
    // utolso reset WDT miatt volt
    digitalWrite(LED_WDT, HIGH);
  }
  MCUSR = 0;
}

void loop() {
  const unsigned long time = millis();

  if ((time - blink_time) >= BLINK_HALF_PERIOD) {
    blink_time = time;
		digitalWrite(LED_BUILTIN,!digitalRead(LED_BUILTIN));
  }

  if (((time - wdt_enable_reset_time) <= SKIP_WDT_RESET_AFTER_MS) 
      && ((time - wdt_reset_time) >= WDT_RESET_PERIOD))
  {
    wdt_reset_time = time;
    wdt_reset();
  }
}