C code for Griffin Technology PowerMate USB Knob

/*
 * Copyright (c) 2017 Kris Occhipint.
 * http://filmsbykris.com
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, version 3.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <linux/input.h>
#include <string.h>
#include <stdio.h>

static const char *const evval[2] = {
  "RELEASED",
  "PRESSED "
};

int main(void){
  //get input device
  const char *dev = "/dev/input/by-id/usb-Griffin_Technology__Inc._Griffin_PowerMate-event-if00";
  struct input_event ev;
  ssize_t n;
  int fd;

  //open device for reading
  fd = open(dev, O_RDONLY);
  //exit on error opening device
  if (fd == -1) {
    fprintf(stderr, "Cannot open %s: %s.\n", dev, strerror(errno));
    return -1;
  }
  while (1) {
    n = read(fd, &ev, sizeof ev);
    //printf("%d\n",ev.type);
    //printf("%d\n",(int)ev.value);
    if(ev.type == 2 && (int)ev.value == 1){
      printf("Clock Wise\n");
    }else if(ev.type == 2 && (int)ev.value == -1){
      printf("Counter Clock Wise\n");
    }
    if (ev.type == EV_KEY && ev.value >= 0 && ev.value <= 2){
      printf("%s 0x%04x (%d)\n", evval[ev.value], (int)ev.code, (int)ev.code);
    }
  }

  return 0;
}