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

uint8_t font[] = {
    0xEE,
    0x82,
    0xDC,
    0xD6,
    0xB2,
    0x76,
    0x7E,
    0xC2,
    0xFE,
    0xF6,
};

uint8_t display[4];

void timer0_init()
{
    TCCR0 = (1<<WGM01); //TIMER0 SET-UP: CTC MODE
    TCCR0 = (1<<CS01)|(1<<CS00); // PS 1:64
    OCR0 = 249; // 1ms reach for clear (16mz:64=>250kHz:250-=>1kHz)
    TIMSK |= 1<<OCIE0;     //IRQ on TIMER0 output compareA
}

int main(void){
    DDRB |= _BV(3) | _BV(2) | _BV(1) | _BV(0);
    DDRD = 0xFC;
    DDRA = 0x03 << 4;
    DDRC = 0xFE;

    display[3] = font[1];
    display[2] = font[3];
    display[1] = font[3];
    display[0] = font[7];

    timer0_init();
    sei();

    while(1){
    }

}

ISR(TIMER0_COMP_vect)                             
{
    if(PORTB & 0x01){
        PORTB = 1<<1 | 1<<3;
        PORTD = display[3] & 0xFC;
        PORTA = (display[3] & 0x03) << 4;
        PORTC = display[1];
    }
    else{
        PORTB = 1<<0 | 1<<2;
        PORTD = display[2] & 0xFC;
        PORTA = (display[2] & 0x03) << 4;
        PORTC = display[0];
    }
}