/* Name: main.c
 * Author: Nathan Williams
 * 2011
 */

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


#define CLOCK_DIV8      TCCR0B = _BV(CS01);
#define CLOCK_DIV64     TCCR0B = _BV(CS01) | _BV(CS00);
#define CLOCK_DIV256    TCCR0B = _BV(CS02);
#define CLOCK_DIV1024 TCCR0B = _BV(CS02) | _BV(CS00);
#define TIMER TCNT0
#define TIMER_CLEAR  TIMER = 0;   

#define LED_ON  PORTB |= _BV(PB0);
#define LED_OFF PORTB &= ~(_BV(PB0));
#define TOGGLE_LED PORTB ^= _BV(PB0);

uint8_t overflow_count;

void start_timer()
{
    CLOCK_DIV1024;
    TIMSK |= (1<<TOIE0);
    overflow_count = 0;
    TIMER_CLEAR;
}

ISR(TIMER0_OVF_vect)
{
    if(overflow_count >= 114) //about 30 seconds
    {
        TIMSK &= ~(1<<TOIE0); //disable the overflow interrupt
        LED_OFF;
    }
    else
        overflow_count++;
}

int main(void)
{
    DDRB = (1<<PB0);
    PORTB |= (1<<PB1);
    LED_OFF;
    sei(); //don't forget to enable interrupts!
    for(;;){
        if( !(PINB & (1<<PB1)))
        {
            LED_ON;
            start_timer();
        }
    }
    return 0;   /* never reached */
}