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feat(lab03): add trigger on button 1 with epoll

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This commit is contained in:
fastium
2026-04-18 16:07:19 +02:00
parent 6fc8edfd66
commit a9a5ecd4c7
2 changed files with 139 additions and 131 deletions
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195
src/03-led-controller/main.c
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@@ -33,13 +33,15 @@
#include <time.h>
#include <unistd.h>
#include <sys/epoll.h>
#include <sys/inotify.h>
#include "setup.c"
/*
* status led - gpioa.10 --> gpio10
* power led - gpiol.10 --> gpio362
*/
#define GPIO_EXPORT "/sys/class/gpio/export"
#define GPIO_UNEXPORT "/sys/class/gpio/unexport"
#define GPIO_LED "/sys/class/gpio/gpio10"
#define LED "10"
@@ -51,139 +53,70 @@
#define BTN3 "3"
static int open_led(char* gpio_path, char* pin)
int main(void)
{
// unexport pin out of sysfs (reinitialization)
int f = open(GPIO_UNEXPORT, O_WRONLY);
write(f, pin, strlen(pin));
close(f);
// export pin to sysfs
f = open(GPIO_EXPORT, O_WRONLY);
write(f, pin, strlen(pin));
close(f);
// config pin
char direction_path[100];
strcpy(direction_path, gpio_path);
strcat(direction_path, "/direction");
f = open(direction_path, O_WRONLY);
write(f, "out", 3);
close(f);
// open gpio value attribute
char value_path[100];
strcpy(value_path, gpio_path);
strcat(value_path, "/value");
f = open(value_path, O_RDWR);
return f;
}
static int open_btn(char* gpio_path, char* pin) {
int f = open(GPIO_UNEXPORT, O_WRONLY);
write(f, pin, strlen(pin));
close(f);
f = open(GPIO_EXPORT, O_WRONLY);
write(f, pin, strlen(pin));
close(f);
char direction_path[100];
strcpy(direction_path, gpio_path);
strcat(direction_path, "/direction");
f = open(direction_path, O_WRONLY);
write(f, "in", 2);
close(f);
char edge_path[100];
strcpy(edge_path, gpio_path);
strcat(edge_path, "/edge");
f = open(edge_path, O_WRONLY);
write(f, "both", 4); close(f);
char value_path[100];
strcpy(value_path, gpio_path);
strcat(value_path, "/value");
f = open(value_path, O_RDONLY);
return f;
}
int main(int argc, char* argv[])
{
long duty = 2; // %
long period = 1000; // ms
if (argc >= 2) period = atoi(argv[1]);
period *= 1000000; // in ns
// compute duty period...
long p1 = period / 100 * duty;
long p2 = period - p1;
int led = open_led(GPIO_LED, LED);
pwrite(led, "1", sizeof("1"), 0);
printf("Starting Button 1 Test...\n");
int btn1 = open_btn(GPIO_BTN1, BTN1);
int btn2 = open_btn(GPIO_BTN2, BTN2);
int btn3 = open_btn(GPIO_BTN3, BTN3);
// epoll
int epfd = epoll_create1(0);
struct epoll_event ev;
ev.events = EPOLLIN;
ev.data.fd = btn1;
epoll_ctl(epfd, EPOLL_CTL_ADD, btn1, &ev);
ev.data.fd = btn2;
epoll_ctl(epfd, EPOLL_CTL_ADD, btn2, &ev);
ev.data.fd = btn3;
epoll_ctl(epfd, EPOLL_CTL_ADD, btn3, &ev);
struct timespec t1;
clock_gettime(CLOCK_MONOTONIC, &t1);
int k = 0;
while (1) {
struct timespec t2;
clock_gettime(CLOCK_MONOTONIC, &t2);
long delta =
(t2.tv_sec - t1.tv_sec) * 1000000000 + (t2.tv_nsec - t1.tv_nsec);
int toggle = ((k == 0) && (delta >= p1)) | ((k == 1) && (delta >= p2));
if (toggle) {
t1 = t2;
k = (k + 1) % 2;
if (k == 0)
pwrite(led, "1", sizeof("1"), 0);
else
pwrite(led, "0", sizeof("0"), 0);
}
struct epoll_event events[3];
int n = epoll_wait(epfd, events, 3, 0);
// printf("epoll_wait returned %d events\n", n);
char buf[2];
for (int i = 0; i < n; i++) {
// printf ("event=%d on fd=%d\n", events[i].events, events[i].data.fd);
if (events[i].data.fd == btn1) {
pread(btn1, buf, sizeof(buf), 0);
if (buf[0] == '1') {
printf("btn1 activated\n");
}
} else if (events[i].data.fd == btn2) {
// printf("btn2 pressed\n");
} else if (events[i].data.fd == btn3) {
// printf("btn3 pressed\n");
}
}
if (btn1 < 0) {
perror("Failed to open button");
return 1;
}
// 1. Create epoll instance
int epfd = epoll_create1(0);
if (epfd < 0) {
perror("Failed to create epoll");
return 1;
}
// 2. Add button to epoll
struct epoll_event ev;
// CRITICAL: Sysfs GPIOs use EPOLLPRI (priority data) and EPOLLERR, not EPOLLIN!
ev.events = EPOLLPRI | EPOLLERR | EPOLLET;
ev.data.fd = btn1;
if (epoll_ctl(epfd, EPOLL_CTL_ADD, btn1, &ev) < 0) {
perror("Failed to add btn1 to epoll");
return 1;
}
// 3. Dummy read to clear initial state before waiting
char buf[2];
pread(btn1, buf, sizeof(buf), 0);
printf("Waiting for button presses (CPU should be at 0%%)...\n");
// 4. Event loop
while (1) {
struct epoll_event events[1]; // We only care about 1 event for now
// Timeout is -1: Block infinitely until an event occurs!
int n = epoll_wait(epfd, events, 1, -1);
if (n < 0) {
perror("epoll_wait error");
break;
}
for (int i = 0; i < n; i++) {
if (events[i].data.fd == btn1) {
// Read the new value. pread uses offset 0 so we don't need lseek()
pread(btn1, buf, sizeof(buf), 0);
// Print the result. '1' or '0' depends on your hardware pull-up/down resistors
if (buf[0] == '1') {
printf("Button 1 State: HIGH (1)\n");
} else {
printf("Button 1 State: LOW (0)\n");
}
}
}
}
close(btn1);
close(epfd);
return 0;
}

75
src/03-led-controller/setup.c Normal file
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@@ -0,0 +1,75 @@
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>
#include <sys/epoll.h>
#define GPIO_EXPORT "/sys/class/gpio/export"
#define GPIO_UNEXPORT "/sys/class/gpio/unexport"
static int open_led(char* gpio_path, char* pin) {
// unexport pin out of sysfs (reinitialization)
int f = open(GPIO_UNEXPORT, O_WRONLY);
write(f, pin, strlen(pin));
close(f);
// export pin to sysfs
f = open(GPIO_EXPORT, O_WRONLY);
write(f, pin, strlen(pin));
close(f);
// config pin
char direction_path[100];
strcpy(direction_path, gpio_path);
strcat(direction_path, "/direction");
f = open(direction_path, O_WRONLY);
write(f, "out", 3);
close(f);
// open gpio value attribute
char value_path[100];
strcpy(value_path, gpio_path);
strcat(value_path, "/value");
f = open(value_path, O_RDWR);
return f;
}
static int open_btn(char* gpio_path, char* pin) {
int f = open(GPIO_UNEXPORT, O_WRONLY);
write(f, pin, strlen(pin));
close(f);
f = open(GPIO_EXPORT, O_WRONLY);
write(f, pin, strlen(pin));
close(f);
char direction_path[100];
strcpy(direction_path, gpio_path);
strcat(direction_path, "/direction");
f = open(direction_path, O_WRONLY);
write(f, "in", 2);
close(f);
char edge_path[100];
strcpy(edge_path, gpio_path);
strcat(edge_path, "/edge");
f = open(edge_path, O_WRONLY);
write(f, "both", 4); // "both" means it triggers on press AND release
close(f);
char value_path[100];
strcpy(value_path, gpio_path);
strcat(value_path, "/value");
f = open(value_path, O_RDONLY);
return f;
}