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

#define BLINK_DELAY_MS 500

ISR (INT0_vect){
	// switch pin 0 of PORTB while leaving the rest as is
	PORTB ^= (1 << PORTB5);
}
int main (void){
	DDRB |= (1 << DDB5);
	DDRD &= ~(1 << DDD2);
	PORTD |= (1 << PORTD2);

	//set INT0 to trigger on falling edge
	EICRA |= (1 << ISC01);
	//Turns on INT0
	EIMSK |= (1 << INT0);
	//SEt Interrupts
	sei();
	while(1) {
		PORTB ^= 1 << PORTB5;
		_delay_ms(BLINK_DELAY_MS);
	}
}