void timer_init(void)
{
	ICR1 = (1 << 11) - 1;/* 11 bit pwm */
	OCR1A = 0;
	TCCR1A = (1 << COM1A1) | (1 << CS10) | (1 << WGM11);/* fast pwm, non inverted, top in ICR1 */
	TCCR1B = (1 << WGM13) | (1 << WGM12) | (1 << CS10);/* fast pwm, top in ICR1,  */
	DDRD |= (1 << PD5);/* set pwm pin as output */
	TIMSK = 1 << TOIE1;/* interrupt at top */
}