#include <avr/wdt.h>
#include <avr/interrupt.h>
#include <util/delay.h>

volatile int f_wdt=0;
int counter=0;

ISR(WDT_vect)
{
    if(f_wdt == 0)
    {
    f_wdt=1;
    }
    else
    {
    }
}
int main(void) {
    DDRB |= (1<<7); //portB.7 output
    DDRA=0xFF;
    /* Clear the reset flag. */
    MCUSR &= ~(1<<WDRF);
    /* In order to change WDE or the prescaler, we need to
    * set WDCE (This will allow updates for 4 clock cycles).
    */
    WDTCSR |= (1<<WDCE) | (1<<WDE);
    /* set new watchdog timeout prescaler value */
    WDTCSR = 1<<WDP2 | 1<<WDP1 | 1<<WDP0; /* 2.0 seconds */
// wdt_enable(WDTO_4S); // don't used, cause system reset.
    /* Enable the WD interrupt (note no reset). */
    WDTCSR |= _BV(WDIE);
    sei(); // don't forget to activate global interrupt
    while(1){
        if(f_wdt == 1)
        {
            /* Toggle the LED */
            PORTB ^=(1<<7);
            /* Don't forget to clear the flag. */
            f_wdt = 0;
            /* Re-enter sleep mode. */
//          enterSleep();
        }
        else
        {
        /* Do nothing. */
        _delay_ms(300);
        PORTA=~counter++;
        }
    }
}