#include <avr/io.h>
#include <avr/interrupt.h>

volatile uint8_t state;
volatile uint8_t count;


ISR(TIMER0_OVF_vect)
{
	if(++count == 100){
		count = 0;
		state = (state+1) % 2;
		if(state){
			PORTC &= ~(1<<PC0);
		}
		else{
			PORTC |= (1<<PC0);
		}
	}
}

int main(void) {
	DDRC |= _BV(PC0);
	PORTC &= ~_BV(PORTC0);

	TCCR0A |= (1<<COM0A0);
	TCCR0B |= _BV(CS02) | _BV(CS00);

	TIMSK0 |= _BV(TOIE0);

	sei();

	for(;;);

	return 0;
}