Using a foot pedal

Patchbox OS
3

Ask and ye shall receive.

I have cracked reading keypresses from the cheap ($30) three pedal usb keyboard thing…

Stripped of error checking, includes, and such cruft here is how: Three steps:

  1. Wait for a event on the input file handle select
  2. Check what key has been pressed ioctl/EVIOCGKEY
  3. Consume all the data ready to be read from the file handle so next time around the loop select can do its thing.

So simple once you know how…

fd_set rfds;
struct timeval tv;
int retval, res, fd;
unsigned buff_size = 1024;
char buf[buff_size];
unsigned yalv;
uint8_t key_b[KEY_MAX/8 + 1];
fd = open("/dev/input/event0", O_RDONLY);
last_yalv = 0;
while(1){

  // Wait for something to happen on the file                                                                                                                            
  FD_ZERO(&rfds);
  FD_SET(fd, &rfds);
  retval = select(fd+1, &rfds, NULL, NULL, &tv);

  // What key was activated?                                                                                                                                             
  memset(key_b, 0, sizeof(key_b));
  if(ioctl(fd, EVIOCGKEY(sizeof(key_b)), key_b) == -1){
    printf("IOCTL Error %s\n", strerror(errno));
    return -1;
  }
  for (yalv = 0; yalv < KEY_MAX; yalv++) {
    if (test_bit(yalv, key_b)) {
      printf("  This is the key 0x%02x\n", yalv);
    }
  }
  /* Consume what can be read from fd */
  res = read(fd, &buf, buff_size);
 }
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