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

#define wait1 350

// Binary values of each digit for 7-segment display
uint8_t seven_seg_digits[10] = { 0xFC,  // = 0
                                 0x60,  // = 1
                                 0xDA,  // = 2
                                 0xF2,  // = 3
                                 0x66,  // = 4
                                 0xB6,  // = 5
                                 0xBE,  // = 6
                                 0xE0,  // = 7
                                 0xFE,  // = 8
                                 0xE6   // = 9
                               };

// Binary values of each individual segment
uint8_t single_seg_digits[8] = {0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01};

// Define pins connected to 74HC595
#define latchPin 3   // ST_CP of 74HC595, latch pin
#define clockPin 4   // SH_CP of 74HC595, clock pin
#define dataPin 2    // DS of 74HC595, serial data

// Setup function to initialize pins as output
void setup() 
{
    // Set latchPin, clockPin, dataPin as output
    DDRD |= (1 << latchPin) | (1 << clockPin) | (1 << dataPin);
}

// Display each individual segment on the display
void singleSegWrite(uint8_t digit) 
{
    // Set latchPin to low voltage before sending
    PORTD &= ~(1 << latchPin);
    
    // Send the bit pattern to the shift register
    shiftOut(dataPin, clockPin, LSBFIRST, single_seg_digits[digit]);
    
    // Set latchPin to high voltage after sending data
    PORTD |= (1 << latchPin);
}

// Display a number on the digital segment display
void sevenSegWrite(uint8_t digit) 
{
    // Set latchPin to low voltage before sending
    PORTD &= ~(1 << latchPin);
    
    // Send the bit pattern to the shift register
    shiftOut(dataPin, clockPin, LSBFIRST, seven_seg_digits[digit]);
    
    // Set latchPin to high voltage after sending data
    PORTD |= (1 << latchPin);
}

int main(void) 
{
    // Initialize ports
    setup();

    while (1) 
    {
        // Count from hexadecimal 0 - 9
        for (uint8_t digit = 0; digit < 10; ++digit) 
        {
            _delay_ms(wait1); // Delay before displaying next digit
            sevenSegWrite(digit); // Display the digit
        }
    }

    return 0;
}