#include <stdint.h>
#define F_CPU 8000000UL // 8 MHz

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

#define SN74_SER (1 << PC6)
#define SN74_RCLK (1 << PB5)
#define SN74_SRCLK (1 << PE6)

#define SEG_DIG1 (1 << PF6)
#define SEG_DIG2 (1 << PF5)
#define SEG_DIG3 (1 << PF4)
#define SEG_DIG4 (1 << PF1)

void init_3461BS() {
    DDRF |= SEG_DIG1 | SEG_DIG2 | SEG_DIG3 | SEG_DIG4;

    PORTF &= ~(SEG_DIG1 | SEG_DIG2 | SEG_DIG3 | SEG_DIG4);
}

void init_74HC595() {
    DDRC |= SN74_SER;
    DDRB |= SN74_RCLK;
    DDRE |= SN74_SRCLK;

    PORTB &= ~SN74_RCLK;
    PORTE &= ~SN74_SRCLK;
}

const uint8_t digit_segments[] = {
    0b11111110, // 0
    0b11001111, // 1
    0b10010010, // 2
    0b10000110, // 3
    0b11001100, // 4
    0b10100100, // 5
    0b10100000, // 6
    0b10001101, // 7
    0b10000000, // 8
    0b10000100, // 9
};

void send_serial_byte(uint8_t n) {
    for (int i = 7; i > 0; i--) {
        if (n & (1 << i)) {
            PORTC |= SN74_SER;
        }
        else {
            PORTC &= ~SN74_SER;
        }
        PORTE |= SN74_SRCLK;
        _delay_ms(100);
        PORTE &= ~SN74_SRCLK;
        PORTC &= ~SN74_SER;
        _delay_ms(100);
    }

    PORTB |= SN74_RCLK;
    _delay_ms(100);
    PORTB &= ~SN74_RCLK;
}

int main() {
    init_74HC595();
    init_3461BS();

    while (1) {
        for (int i = 0; i < 255; i++) {
            for(int j = 0; j < 100; j++) {
                PORTF |= SEG_DIG1;
                send_serial_byte(digit_segments[i / 1000]);
                _delay_ms(2);
                PORTF &= ~SEG_DIG1;

                PORTF |= SEG_DIG2;
                send_serial_byte(digit_segments[(i / 100) % 10]);
                _delay_ms(2);
                PORTF &= ~SEG_DIG2;

                PORTF |= SEG_DIG3;
                send_serial_byte(digit_segments[(i / 10) % 10]);
                _delay_ms(2);
                PORTF &= ~SEG_DIG3;

                PORTF |= SEG_DIG4;
                send_serial_byte(digit_segments[i % 10]);
                _delay_ms(2);
                PORTF &= ~SEG_DIG4;
            }
        }
    }
}