GPIO IRQ Usage

Switch to root user

Only root user can control GPIO, you need to switch to root user before testing.

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$ khadas@Khadas:~$ su
Password:
root@Khadas:/home/khadas#

GPIO Pin Control Setting

  • Check the pins you need to use, take VIM3 as an example:
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root@Khadas:/home/khadas# gpio readall
+------+-----+----------+------+---+----+---- Model Khadas VIM3 --+----+---+------+----------+-----+------+
| GPIO | wPi | Name | Mode | V | DS | PU/PD | Physical | PU/PD | DS | V | Mode | Name | wPi | GPIO |
+------+-----+----------+------+---+----+-------+----++----+-------+----+---+------+----------+-----+------+
| | | 5V | | | | | 1 || 21 | | | | | GND | | |
| | | 5V | | | | | 2 || 22 | P/U | | 1 | ALT1 | PIN.A15 | 6 | 475 |
| | | USB_DM | | | | | 3 || 23 | P/U | | 1 | ALT1 | PIN.A14 | 7 | 474 |
| | | USB_DP | | | | | 4 || 24 | | | | | GND | | |
| | | GND | | | | | 5 || 25 | P/U | | 1 | ALT0 | PIN.AO2 | 8 | 498 |
| | | MCU3V3 | | | | | 6 || 26 | P/U | | 1 | ALT0 | PIN.AO3 | 9 | 499 |
| | | MCUNRST | | | | | 7 || 27 | | | | | 3V3 | | |
| | | MCUSWIM | | | | | 8 || 28 | | | | | GND | | |
| | | GND | | | | | 9 || 29 | P/D | | 0 | ALT0 | PIN.A1 | 10 | 461 |
| | | ADC0 | | | | | 10 || 30 | P/D | | 0 | ALT0 | PIN.A0 | 11 | 460 |
| | | 1V8 | | | | | 11 || 31 | P/D | | 0 | ALT0 | PIN.A3 | 12 | 463 |
| | | ADC1 | | | | | 12 || 32 | P/D | | 0 | ALT0 | PIN.A2 | 13 | 462 |
| 506 | 1 | PIN.H5 | ALT3 | 0 | | P/U | 13 || 33 | P/D | | 0 | ALT1 | PIN.A4 | 14 | 464 |
| | | GND3 | | | | | 14 || 34 | | | | | GND | | |
| 433 | 2 | PIN.H6 | IN | 0 | | P/D | 15 || 35 | P/D | | 0 | ALT3 | PWM-F | 15 | 432 |
| 434 | 3 | PIN.H7 | IN | 0 | | P/D | 16 || 36 | | | | | RTC | | |
| | | GND | | | | | 17 || 37 | P/D | | 0 | IN | PIN.H4 | 16 | 431 |
| 497 | 4 | PIN.AO1 | ALT0 | 1 | | P/U | 18 || 38 | | | | | MCU-FA1 | | |
| 496 | 5 | PIN.AO0 | ALT0 | 1 | | P/U | 19 || 39 | P/D | | 0 | IN | PIN.Z15 | 17 | 426 |
| | | 3V3 | | | | | 20 || 40 | | | | | GND | | |
+------+-----+----------+------+---+----+-------+----++----+-------+----+---+------+----------+-----+------+

Select the GPIO you need to use, and confirm the corresponding physical pin and GPIO value. Taking GPIOH6 as an example here, the related GPIO value is 433, and the physical pin is PIN15.

  • Export GPIO
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root@Khadas:/home/khadas# echo 433 > /sys/class/gpio/export
  • Source code for gpio-irq.c
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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <poll.h>

#define SYSFS_GPIO_DIR "/sys/class/gpio"
#define MAX_BUF 255

int gpio_export(unsigned int gpio)
{
int fd, len;
char buf[MAX_BUF];

fd = open(SYSFS_GPIO_DIR "/export", O_WRONLY);

if (fd < 0) {
fprintf(stderr, "Can't export GPIO %d pin: %s\n", gpio, strerror(errno));
return fd;
}

len = snprintf(buf, sizeof(buf), "%d", gpio);
write(fd, buf, len);
close(fd);

return 0;
}

int gpio_unexport(unsigned int gpio)
{
int fd, len;
char buf[MAX_BUF];

fd = open(SYSFS_GPIO_DIR "/unexport", O_WRONLY);

if (fd < 0) {
fprintf(stderr, "Can't unexport GPIO %d pin: %s\n", gpio, strerror(errno));
return fd;
}

len = snprintf(buf, sizeof(buf), "%d", gpio);
write(fd, buf, len);
close(fd);

return 0;
}

int gpio_set_edge(unsigned int gpio, char *edge)
{
int fd, len;
char buf[MAX_BUF];

len = snprintf(buf, sizeof(buf), SYSFS_GPIO_DIR "/gpio%d/edge", gpio);

fd = open(buf, O_WRONLY);

if (fd < 0) {
fprintf(stderr, "Can't set GPIO %d pin edge: %s\n", gpio, strerror(errno));
return fd;
}

write(fd, edge, strlen(edge)+1);
close(fd);

return 0;
}

int gpio_set_pull(unsigned int gpio, char *pull)
{
int fd, len;
char buf[MAX_BUF];

len = snprintf(buf, sizeof(buf), SYSFS_GPIO_DIR "/gpio%d/pull", gpio);

fd = open(buf, O_WRONLY);

if (fd < 0) {
fprintf(stderr, "Can't set GPIO %d pin pull: %s\n", gpio, strerror(errno));
return fd;
}

write(fd, pull, strlen(pull)+1);
close(fd);

return 0;
}

int main(int argc, char *argv[])
{
struct pollfd fdset[2];
int fd, ret, gpio;
char buf[MAX_BUF];

if (argc < 3 || argc > 4) {
fprintf(stdout, "usage : sudo sysfs_irq_test <gpio> <edge> [pull]\n");
fflush(stdout);
return -1;
}

gpio = atoi(argv[1]);
if (gpio_export(gpio)) {
fprintf(stdout, "error : export %d\n", gpio);
fflush(stdout);
return -1;
}

if (gpio_set_edge(gpio, argv[2])) {
fprintf(stdout, "error : edge %s\n", argv[2]);
fflush(stdout);
return -1;
}

if (argv[3] && gpio_set_pull(gpio, argv[3])) {
fprintf(stdout, "error : pull %s\n", argv[3]);
fflush(stdout);
return -1;
}

snprintf(buf, sizeof(buf), SYSFS_GPIO_DIR "/gpio%d/value", gpio);
fd = open(buf, O_RDWR);
if (fd < 0)
goto out;

while (1) {
memset(fdset, 0, sizeof(fdset));
fdset[0].fd = STDIN_FILENO;
fdset[0].events = POLLIN;
fdset[1].fd = fd;
fdset[1].events = POLLPRI;
ret = poll(fdset, 2, 3*1000);

if (ret < 0) {
perror("poll");
break;
}

fprintf(stderr, ".");

if (fdset[1].revents & POLLPRI) {
char c;
(void)read (fd, &c, 1) ;
lseek (fd, 0, SEEK_SET) ;
fprintf(stderr, "\nGPIO %d interrupt occurred!\n", gpio);
}

if (fdset[0].revents & POLLIN)
break;

fflush(stdout);
}

close(fd);
out:
if (gpio_unexport(gpio)) {
fprintf(stdout, "error : unexport %d\n", gpio);
fflush(stdout);
}

return 0;
}

  • Compile the source code
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root@Khadas:/home/khadas# gcc -o gpio-irq gpio-irq.c
  • Check
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./gpio-irq 433 rising down
.
GPIO 433 interrupt occurred!
..........

Connect the PIN20 and PIN15 of the physical PIN via the DuPont line to trigger the interrupt. The phenomenon is as follows:

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root@Khadas:/home/khadas# ./gpio-irq 433 rising down
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GPIO 433 interrupt occurred!
..
GPIO 433 interrupt occurred!
.
GPIO 433 interrupt occurred!
.
GPIO 433 interrupt occurred!
  • Test Program Introduce

The running format is as follows:

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root@Khadas:/home/khadas# ./gpio-irq <edge> [pull]

<edge> can be set to rising or failing, [pull] is an optional parameter, set to up or down.