microcontrolling/main.c

#define __AVR_ATmega2560__
#define F_CPU 16000000UL

#include <avr/io.h>
#include <util/delay.h>
#include <stdbool.h>
#include "lib/util.h"
#include "lib/7segment.h"
#include "lib/7segment_4digits.h"

/**
 *       O O O O O O O O
 * DDRF  x x x x x x x x
 *       \-\-\-\-\-\-\-\--- 7 segment output
 * 
 *      I I O O O O O O
 * DDRK x x x x x x x x
 *      | |     \-\-\-\--- digit selection output
 *      \-\--------------- Button input
*/

void main() {
    DDRF  = 0b11111111;
    DDRK  = 0b00001111;
    PORTK = 0b11000000; // set pull-up

    uint32_t millis = 0;
    bool counting = false;
    bool pressed_pause = false;
    bool pressed_clear = false;

    while(1) {
        // show_float() doesn't actually print to the display directly, it only updates
        // a variable stored in memory. We call `update_display_all_sync()` periodically,
        // which reads the stored variable and outputs it.
        show_float(millis / 1000.0f);

        // Cycles through all 4 displays, turns them on for a set amount of time
        // while displaying the value set by `show_float()` earlier and returns
        // the total amount waited.
        uint32_t sleep_time = update_display_all_sync();

        if (counting) {
            // We can use the returned sleep_time to (inaccurately) count time.
            millis += sleep_time;
        }

        // If the button connected to PIN7 is pressed, pause or unpause the counter.
        if (!pressed_pause && bit_is_clear(PINK, PINK7)) {
            counting = !counting;
            pressed_pause = true;
        } else if (pressed_pause && bit_is_set(PINK, PINK7)) {
            pressed_pause = false;
        }

        // If the button connected  to PIN6 is pressed, reset and pause the counter.
        if (bit_is_clear(PINK, PINK6)) {
            millis = 0;
            counting = false;

            pressed_clear = true;
        } else pressed_clear = false;
    }
}