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blink.c
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blink.c
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/*
* Blinks a LED forever (until Ctrl+C)
*/
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#define IN 0
#define OUT 1
#define LOW 0
#define HIGH 1
#define POUT 11
static int GPIOExport(int pin);
static int GPIOUnexport(int pin);
static int GPIODirection(int pin, int dir);
static int GPIORead(int pin);
static int GPIOWrite(int pin, int value);
volatile int done = 0;
void term(int signum)
{
done = 1;
}
int main(int argc, char *argv[]) {
printf("START...\n");
//catch SIGTERM for graceful exit
struct sigaction action;
memset(&action, 0, sizeof(struct sigaction));
action.sa_handler = term;
sigaction(SIGTERM, &action, NULL);
printf("INIT GPIO\n");
//Enable GPIO pins
if (-1 == GPIOExport(POUT))
return(1);
//Set GPIO directions
if (-1 == GPIODirection(POUT, OUT))
return(2);
while(done == 0) {//while not done...
//Write GPIO value
printf("ON\n");
if (-1 == GPIOWrite(POUT, HIGH))
return(3);
usleep(1000 * 1000);
printf("OFF\n");
if (-1 == GPIOWrite(POUT, LOW))
return(3);
usleep(1000 * 1000);
}
//Disable GPIO pins
if (-1 == GPIOUnexport(POUT))
return(4);
return(0);
}
int GPIOExport(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);
}
int GPIOUnexport(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);
}
int GPIODirection(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);
}
int GPIORead(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));
}
int GPIOWrite(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);
}