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

#define SETBIT(ADDRESS,BIT) (ADDRESS |= (1<<BIT))
#define CLEARBIT(ADDRESS,BIT) (ADDRESS &= ~(1<<BIT))
#define FLIPBIT(ADDRESS,BIT) (ADDRESS ^= (1<<BIT))
#define CHECKBIT(ADDRESS,BIT) (ADDRESS & (1<<BIT))

volatile int counter;

void set_digit(int digit) {
    if (digit == 0) {
        PORTB = 0b00001110;
        PORTD = 0b11100000;
    } else if (digit == 1) {
        PORTD = 0b10000000;
        PORTB = 0b00001000;
    } else if (digit == 2) {
        PORTB = 0b00001101;
        PORTD = 0b01100000;
    } else if (digit == 3) {
        PORTB = 0b00001101;
        PORTD = 0b11000000;
    } else if (digit == 4) {
        PORTB = 0b00001011;
        PORTD = 0b10000000;
    } else if (digit == 5) {
        PORTB = 0b00000111;
        PORTD = 0b11000000;
    } else if (digit == 6) {
        PORTB = 0b00000111;
        PORTD = 0b11100000;
    } else if (digit == 7) {
        PORTB = 0b00001100;
        PORTD = 0b10000000;
    } else if (digit == 8) {
        PORTB = 0b00001111;
        PORTD = 0b11100000;
    } else if (digit == 9) {
        PORTB = 0b00001111;
        PORTD = 0b11000000;
    }
}

ISR(INT0_vect) {
    counter = (counter + 1) % 10;
    set_digit(counter);
}

int main()
{
    int i;
    DDRD = PORTD = DDRB = PORTB = 0;
    for (i = 5; i < 8; i++) {
        DDRD |= (1 << i);
    }
    for (i = 0; i < 4; i++) {
        DDRB |= (1 << i);
    }
    PORTD |= 1 << 2;
    counter = 0;

    CLEARBIT(EICRA, ISC01);
    SETBIT(EICRA, ISC00);
    sei(); // allow interrupts
    SETBIT(EIMSK, 0);

    set_digit(counter);
    while(1) { }
    return 0;
}