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

// GLOBAL VARIABLES

	volatile unsigned int seconds = 3000;

// MAIN

int main (void)
{
	wdt_disable(); // disable watchdog

	// port initialization
	DDRB = 0xFF; // portb = output
	PORTB = 0xFF; // all leds off

	DDRC = 0x00; // portd = input
	PINC = 0xFF; // all buttons off
	
	// button interrupt initialization
	PCICR |= (1 << PCIE1); // enable PORTC interrupts
	PCMSK1 |= 0x3F; // enable PCINT8 - PCINT13
	sei(); // enable global interrupts

	// SLEEP
	sleep_enable(); // enable sleep
	set_sleep_mode(SLEEP_MODE_PWR_DOWN);
	sleep_mode();
	cli(); // disable global interrupts

	// START BUTTON
	while(PINC & (1 << 1));

	PORTB = 0x00;
	// timer interrupt initialization
	// count = (1 / target freq) / (prescale / frequency)
	TCCR1B |= (1 << CS12); // prescale = 256
	TCCR1B |= (1 << WGM12); // enable clear on timer compare
	TIMSK1 |= (1 << OCIE1A); // output compare A match interrupt enabled
	OCR1A = 31250; // compare value A. 31250 equals 1Hz at 8Mhz with prescaler at 256

	// watchdog timer initialization
	wdt_enable(WDTO_8S); // watchdog timeout = 8 seconds
	WDTCSR |= (1 << WDE); // timeout action = reset

	sei(); // reenable global interrupts

	while(1);

}

// TIMER INTERRUPT
ISR(TIMER1_COMPA_vect)
{
	//PORTB = ~(seconds % 60); // seconds
	PORTB = ~(seconds / 60); // minutes

	// conditional prevents underflow 
	if(seconds > 0) {
		seconds--;
		wdt_reset(); // kick the dog
	}
	else {
		PORTB = 0x00; // toggle all leds
		PRR |= (1 << PRTIM1); // power reduction timer/counter1 (turn off timer)
	}
}

// BUTTON INTERRUPT
ISR(PCINT1_vect)
{
	PORTB = PINC;
}