Raspberry Pi LED blink test.

wink.c

// wink.c
// LED blink test
// hardware: LED with resistor shall be connected to GPIOxx
// compile: cc wink.c -o wink
// execute: sudo ./wink xx

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>

int main (int argc, char *argv[]){
  char buf[40];
  int port;
  int fd;
  int ret;
  int i;

  if(argc != 2){
    printf("Useage\n");
    printf("wink gpio_number\n");
    return 0;
  }
  port = atoi(argv[1]);

  if(port == 0){
    fprintf(stderr, "invalid GPIO number.\n");
    return -1;
  }

  // enable port
  fd = open("/sys/class/gpio/export", O_WRONLY);
  if(fd < 0){
    fprintf(stderr, "fail to open GPIO. %s\n", strerror(errno));
    return -1;
  }
  sprintf(buf, "%d", port);
  write(fd, buf, strlen(buf));
  close(fd);

  // set port as output
  sprintf(buf, "/sys/class/gpio/gpio%d/direction", port);
  fd = open(buf, O_WRONLY);
  write(fd, "out", 3);
  close(fd);

  // open port for output
  sprintf(buf, "/sys/class/gpio/gpio%d/value", port);
  fd = open(buf, O_WRONLY);

  //printf("%s\n", buf);
  //return 0;

  for(i = 0; i < 10; i++){
    printf("count%d: on", i);
    //lseek(fd, 0, SEEK_SET);
    write(fd, "1", 2);
    sleep(5);
    printf("->off\n");
    //lseek(fd, 0, SEEK_SET);
    write(fd, "0", 2);
    sleep(5);
  }

  // disable port
  fd = open("/sys/class/gpio/unexport", O_WRONLY);
  sprintf(buf, "%d", port);
  write(fd, buf, strlen(buf));
  close(fd);

  return 0;
}