p1load/gpio_sysfs.c

198 lines
3.8 KiB
C

/*
* gpio_sysfs.c
*
* Raspberry Pi GPIO handling using sysfs interface.
* Guillermo A. Amaral B. <g@maral.me>
*
*/
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include "gpio_sysfs.h"
#define IN 0
#define OUT 1
#define LOW 0
#define HIGH 1
#define PIN 24 /* P1-18 */
#define POUT 4 /* P1-07 */
/**
* Export GPIO pin for use.
* @param pin - The pin number to be used.
* @returns Zero on success -1 on failure.
*/
int gpio_export(int pin)
{
#define BUFFER_MAX 3
char buffer[BUFFER_MAX];
ssize_t bytes_written;
int fd;
fd = open("/sys/class/gpio/export", O_WRONLY);
if (-1 == fd) {
fprintf(stderr, "Failed to open export for writing!\n");
return(-1);
}
bytes_written = snprintf(buffer, BUFFER_MAX, "%d", pin);
write(fd, buffer, bytes_written);
close(fd);
return(0);
}
/**
* Unexport GPIO pin for use.
* @param pin - The pin number to be used.
* @returns Zero on success -1 on failure.
*/
int gpio_unexport(int pin)
{
char buffer[BUFFER_MAX];
ssize_t bytes_written;
int fd;
fd = open("/sys/class/gpio/unexport", O_WRONLY);
if (-1 == fd) {
fprintf(stderr, "Failed to open unexport for writing!\n");
return(-1);
}
bytes_written = snprintf(buffer, BUFFER_MAX, "%d", pin);
write(fd, buffer, bytes_written);
close(fd);
return(0);
}
/**
* Set GPIO pin direction.
* @param pin - The pin number to be used.
* @param dir - The desired pin directio, 1 = out, 0 = in.
* @returns Zero on success -1 on failure.
*/
int gpio_direction(int pin, int dir)
{
static const char s_directions_str[] = "in\0out";
#define DIRECTION_MAX 35
char path[DIRECTION_MAX];
int fd;
snprintf(path, DIRECTION_MAX, "/sys/class/gpio/gpio%d/direction", pin);
fd = open(path, O_WRONLY);
if (-1 == fd) {
fprintf(stderr, "Failed to open gpio direction for writing!\n");
return(-1);
}
if (-1 == write(fd, &s_directions_str[IN == dir ? 0 : 3], IN == dir ? 2 : 3)) {
fprintf(stderr, "Failed to set direction!\n");
return(-1);
}
close(fd);
return(0);
}
/**
* Read GPIO pin state.
* @param pin - The pin number to be read.
* @returns The pin state 0 or 1.
*/
int gpio_read(int pin)
{
#define VALUE_MAX 30
char path[VALUE_MAX];
char value_str[3];
int fd;
snprintf(path, VALUE_MAX, "/sys/class/gpio/gpio%d/value", pin);
fd = open(path, O_RDONLY);
if (-1 == fd) {
fprintf(stderr, "Failed to open gpio value for reading!\n");
return(-1);
}
if (-1 == read(fd, value_str, 3)) {
fprintf(stderr, "Failed to read value!\n");
return(-1);
}
close(fd);
return(atoi(value_str));
}
/**
* Write GPIO pin state.
* @param pin - The pin number to be written to.
* @returns The desired pin state 0 or 1.
*/
int gpio_write(int pin, int value)
{
static const char s_values_str[] = "01";
char path[VALUE_MAX];
int fd;
snprintf(path, VALUE_MAX, "/sys/class/gpio/gpio%d/value", pin);
fd = open(path, O_WRONLY);
if (-1 == fd) {
fprintf(stderr, "Failed to open gpio value for writing!\n");
return(-1);
}
if (1 != write(fd, &s_values_str[LOW == value ? 0 : 1], 1)) {
fprintf(stderr, "Failed to write value!\n");
return(-1);
}
close(fd);
return(0);
}
#ifdef TEST_GPIO_SYSFS
/* This test blinks GPIO 4 (P1-07) while reading GPIO 24 (P1_18) */
int main(int argc, char *argv[])
{
int repeat = 10;
// Enable GPIO pins
if (-1 == gpio_export(POUT) || -1 == gpio_export(PIN))
return(1);
// Set GPIO directions
if (-1 == gpio_direction(POUT, OUT) || -1 == gpio_direction(PIN, IN))
return(2);
do {
// Write GPIO value
if (-1 == gpio_write(POUT, repeat % 2))
return(3);
// Read GPIO value
printf("I'm reading %d in GPIO %d\n", gpio_read(PIN), PIN);
usleep(500 * 1000);
}
while (repeat--);
// Disable GPIO pins
if (-1 == gpio_unexport(POUT) || -1 == gpio_unexport(PIN))
return(4);
return(0);
}
#endif // TEST_GPIO_SYSFS