INF2004_Labs/lab_3/lab_3.c

/**
 * Lab 3
 *
 * This is my solution to the lab 3 assignment.
 * There are multiple structs and enums defined in this file.
 *
 * time_struct is used to store the start time and current time for
 * time calculations.
 *
 * btn_status struct is used to keep track of the number of times the
 * button is pressed and released. This is used to implement a debounce
 * algorithm.
 *
 * btn_state enum is used to return the states of the button, used to check
 * for errors and to return the state of the button.
 *
 * This firmware will use GPIO 15 as a pseudo-button (pull-up) and
 * will start a timer on button press (falling edge) and stop the timer
 * on button release (rising edge).
 *
 * The Timer will print the elapsed time every second as required by the
 * lab specification.
 *
 * The DEBOUNCE_US macro is used to set the debounce delay to 20ms, the value
 * can be refined to get more accurate results.
 *
 * This is made more complex with the use of interrupts, timers and a debounce
 * algorithm.
 *
 */

#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/gpio.h"

#define PSEUDO_BTN  15          // GPIO 15 is the pseudo-button
#define TIMER_US    1000000     // 1-second delay for repeating timer
#define DEBOUNCE_US 20000       // 20ms debounce delay

struct repeating_timer timer;   // Repeating timer

struct time_struct {
    uint64_t start_time;
    uint64_t current_time;
} time_struct = {0, 0};

struct btn_status {             // Button status (Used to implement debounce)
    uint btn_pressed;
    uint btn_released;
} btn_status = {0, 0};

typedef enum btn_state {        // Button state (Used as return value)
    PRESSED = 0,
    RELEASED = 1,
    ERROR = -1
} btn_state_t;

/**
 * Callback function for repeating timer
 * This function will print the elapsed time every second as required by the
 * lab specification.
 * @param t    The timer that triggered the callback
 * @return     True to keep the timer running, false to stop it
 */
bool elapsed_time_callback (struct repeating_timer *t) {
    time_struct.start_time = (time_struct.start_time == 0) ?
                             time_us_64() : time_struct.start_time;

    time_struct.current_time = time_us_64();

    printf("%llus\n",
           (time_struct.current_time - time_struct.start_time) / 1000000);

    return true;
}

/**
 * Get the state of the pseudo-button (pull-up)
 * This function will implement a debounce algorithm to
 * get the state of the pseudo-button. (With added complexity)
 * @return The state of the pseudo-button
 */
btn_state_t get_btn_state () {
    if (btn_status.btn_pressed != 0 || btn_status.btn_released != 0)
    {
        return ERROR;
    }

    u_int64_t start_time = time_us_64();

    while (time_us_64() - start_time < DEBOUNCE_US)
    {
        if (gpio_get(PSEUDO_BTN))
        {
            btn_status.btn_released += 1;
        }
        else
        {
            btn_status.btn_pressed += 1;
        }
    }

    btn_state_t state = (btn_status.btn_pressed > btn_status.btn_released) ?
                        PRESSED : RELEASED;

    // Reset btn_status
    btn_status = (struct btn_status) {0, 0};

    return state;
}

/**
 * Interrupt callback function for pseudo-button (pull-up)
 * This function will start the timer on button press (falling edge)
 * and stop the timer on button release. (rising edge)
 * @param gpio      The GPIO pin that triggered the interrupt
 * @param events    The type of interrupt that triggered the callback
 */
void gpio_callback (uint gpio, uint32_t events) {
    btn_state_t btn_state = get_btn_state();

    if (btn_state == ERROR)
    {
        printf("Error: Button is bouncing\n");
        return;
    }

    if (events == GPIO_IRQ_EDGE_FALL && btn_state == PRESSED)
    {
        printf("Timer Started\n");

        add_repeating_timer_us(
                TIMER_US,
                elapsed_time_callback,
                NULL,
                &timer
        );
    }

    if (events == GPIO_IRQ_EDGE_RISE && btn_state == RELEASED)
    {
        if (cancel_repeating_timer(&timer))
        {
            printf("Timer Stopped\n");
            printf("Final Elapsed Time: %llus\n",
                   (time_struct.current_time - time_struct.start_time) /
                   1000000);
        }

        time_struct = (struct time_struct) {0, 0};
    }
}

/**
 * Initialize the pseudo-button (pull-up)
 * The pseudo-button is connected to GPIO 15 and
 * is configured as an input with a pull-up resistor.
 *
 * The interrupt is configured to trigger on both
 * rising and falling edges.
 */
static void btn_init () {
    gpio_init(PSEUDO_BTN);
    gpio_set_dir(PSEUDO_BTN, GPIO_IN);
    gpio_set_pulls(PSEUDO_BTN, true, false);

    gpio_set_irq_enabled_with_callback(
            PSEUDO_BTN,
            GPIO_IRQ_EDGE_RISE | GPIO_IRQ_EDGE_FALL,
            true,
            &gpio_callback
    );
}

int main () {
    stdio_init_all();
    btn_init();

    while (true)
    {
        tight_loop_contents();
    }

}