/* Simple joystick test program.  Mappings on my Genius “MaxFighter
 * F-16U” joystick:
 *
 * - Left-right axis is axis 0, from -26688 at the left to +12836 at
 *   the right, with zero at rest position; quantized to units of 337
 *   or 338, giving about 120 distinct positions.
 * - Front-back axis is axis 1, from -21958 full forward to +12836
 *   full back, with zero at rest position; quantized to units of 337
 *   or 338, giving about 100 distinct positions.
 * - Thumbwheel is axis 2, from -32767 full forward to +12836 full
 *   back.  There is some dead space at each end of travel.  Seems to
 *   be quantized to units of 337 or 338, giving about 140 distinct
 *   positions.
 * - Trigger is button 0.
 * - Thumb button on stem is button 1.
 * - When not in autorepeat mode (TA/TB), the C thumb button is button
 *   2 and the D thumb button is button 3.
 *
 * As the docs say, the buttons have value 1 when depressed, 0 when
 * released.
 *
 * Note that, even today, the joystick driver checks to see if you’re
 * doing a 12-byte read() in order to see if it should give you the
 * two-axis, two-button joystick API used before Linux 1.0 with 8-bit
 * resolution.
 */

#include <fcntl.h>
#include <stdint.h>
#include <unistd.h>
#include <stdio.h>

/* From Documentation/input/joystick-api.txt.gz.  This duplicates
 * linux/joystick.h.
 */

struct js_event {
  uint32_t time;
  int16_t value;
  uint8_t type, number;
};

int main(int argc, char **argv)
{
  if (argc == 1) {
    fprintf(stderr, "usage: %s /dev/input/js0 (or similar\n", argv[0]);
    return 1;
  }

  int fd = open(argv[1], O_RDONLY);
  if (fd < 0) {
    perror(argv[1]);
    return 2;
  }

  for (;;) {
    struct js_event e;
    read(fd, &e, sizeof e);
    int type = e.type & 0x7f;
    printf("%10d %6d %d (%s) on axis/button %d\n",
           e.time, e.value, e.type,
           type == 1 ? "button" : type == 2 ? "axis" : "???",
           e.number);
  }

  return 0;
}