153 lines
4.0 KiB
C
153 lines
4.0 KiB
C
/**
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* Lab 3
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* To develop a simple stopwatch that measures time intervals between
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* button presses.
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*
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* On pressing the START pseudo-button (GP15),
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* the stopwatch will begin,
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* and the elapsed time will be displayed every second on
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* the Serial Monitor (or equivalent).
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*
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* Releasing the START pseudo-button will stop the timer and
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* reset the elapsed time to zero.
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*
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* The START pseudo-button must incorporate a debouncing algorithm.
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*
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*/
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#include <stdio.h>
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#include "pico/stdlib.h"
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#include "hardware/gpio.h"
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#define PSEUDO_BTN 15 // GPIO 15 is the pseudo-button
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#define TIMER_US 1000000 // 1-second delay for repeating timer
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#define DEBOUNCE_US 100 // 100us debounce time
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struct repeating_timer timer; // Repeating timer
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u_int64_t time = 0; // Elapsed time
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typedef enum btn_state { // Button state
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PRESSED = 0,
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RELEASED = 1
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} btn_state_t;
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struct btn_status { // Button status
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uint btn_pressed;
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uint btn_released;
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} btn_status = {0, 0};
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/**
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* Callback function for repeating timer
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* This function will print the elapsed time every second as required by the
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* lab specification.
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* @param t The timer that triggered the callback
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* @return True to keep the timer running, false to stop it
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*/
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bool elapsed_time_callback (struct repeating_timer *t) {
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time++;
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// Print elapsed time every second
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printf("Elapsed Time: %llus\n", time);
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return true;
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}
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/**
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* Get the state of the pseudo-button (pull-up)
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* This function will implement a debounce algorithm to
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* get the state of the pseudo-button. (With added complexity)
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* @return The state of the pseudo-button
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*/
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btn_state_t get_btn_state () {
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u_int64_t start_time = time_us_64();
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while (time_us_64() - start_time < DEBOUNCE_US)
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{
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if (gpio_get(PSEUDO_BTN))
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{
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btn_status.btn_released += 1;
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}
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else
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{
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btn_status.btn_pressed += 1;
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}
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}
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btn_state_t state = (btn_status.btn_pressed > btn_status.btn_released) ?
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PRESSED : RELEASED;
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// Reset btn_status
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btn_status = (struct btn_status) {0, 0};
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return state;
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}
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/**
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* Interrupt callback function for pseudo-button (pull-up)
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* This function will start the timer on button press (falling edge)
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* and stop the timer on button release. (rising edge)
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* @param gpio The GPIO pin that triggered the interrupt
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* @param events The type of interrupt that triggered the callback
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*/
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void gpio_callback (uint gpio, uint32_t events) {
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btn_state_t btn_state = get_btn_state();
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if (events == GPIO_IRQ_EDGE_FALL && btn_state == PRESSED)
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{
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printf("\n====================================\n");
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printf("Timer Started\n");
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printf("====================================\n");
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add_repeating_timer_us(
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TIMER_US,
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elapsed_time_callback,
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NULL,
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&timer
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);
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}
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if (events == GPIO_IRQ_EDGE_RISE && btn_state == RELEASED)
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{
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cancel_repeating_timer(&timer);
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// Print elapsed time and reset
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printf("\n====================================\n");
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printf("Timer Stopped\n");
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printf("====================================\n");
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printf("Final Elapsed Time: %llus\n", time);
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printf("====================================\n");
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time = 0;
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}
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}
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/**
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* Initialize the pseudo-button (pull-up)
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* The pseudo-button is connected to GPIO 15 and is configured as
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* an input with a pull-up resistor.
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* The interrupt is configured to trigger on both rising and
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* falling edges.
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*/
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static void btn_init () {
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gpio_init(PSEUDO_BTN);
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gpio_set_dir(PSEUDO_BTN, GPIO_IN);
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gpio_set_pulls(PSEUDO_BTN, true, false);
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gpio_set_irq_enabled_with_callback(
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PSEUDO_BTN,
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GPIO_IRQ_EDGE_RISE | GPIO_IRQ_EDGE_FALL,
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true,
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&gpio_callback
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);
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}
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int main () {
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stdio_init_all();
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btn_init();
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while (true)
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{
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tight_loop_contents();
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}
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}
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