#include <avr/io.h>
void TimerInit();
unsigned char periode;

int main (void)
{
  DDRB |= _BV(PB7);
  TimerInit();
  while(1)
  {
    if(TIFR0&(1<<TOV0))
    {
      TCNT0= (unsigned char)-250;
      TIFR0 |= (1<<TOV0);
      PORTB ^= (1<<PB7);
    }
  }
}

void TimerInit(void)
{
  TCNT0= (unsigned char) -250;
  TCCR0B= (1<<CS01);
}