[Application] Writing a simple application

#include <fcntl.h
#include <stdio.h
#include <stdlib.h
#include <unistd.h

#define DEFAULT_DEVICE      "/dev/ml0"
#define DEFAULT_DURATION    800

#define ML_STOP         0x00
#define ML_UP           0x01
#define ML_DOWN         0x02
#define ML_LEFT         0x04
#define ML_RIGHT        0x08
#define ML_FIRE         0x10

#define ML_FIRE_DELAY   5000

void send_cmd(int fd, int cmd)
{
    int retval = 0;

    retval = write(fd, &cmd, 1);
    if (retval < 0)
        fprintf(stderr, "an error occured: %d\n", retval);
}

static void usage(char *name)
{
    fprintf(stderr,
            "\nusage: %s [-mslrudfh] [-t msecs]\n\n"
            "  -m      missile launcher [/dev/ml0]\n"
            "  -s      stop\n"
            "  -l      turn left\n"
            "  -r      turn right\n"
            "  -u      turn up\n"
            "  -d      turn down\n"
            "  -f      fire\n"
            "  -t      specify duration in milli seconds\n"
            "  -h      display this help\n\n"
            "notes:\n"
            "* it is possible to combine the directions of the two axes, e.g.\n"
            "  '-lu' send_cmds the missile launcher up and left at the same time.\n"
            "" , name);
    exit(1);
}

int main(int argc, char *argv[])
{
    char c;
    int fd;
    int cmd = ML_STOP;
    int duration = DEFAULT_DURATION;
    char *dev = DEFAULT_DEVICE;

    if (argc < 2)
        usage(argv[0]);

    while ((c = getopt(argc, argv, "mslrudfht:")) != -1)
    {
        switch (c)
        {
            case 'm': dev = optarg;
                      break;
            case 'l': cmd |= ML_LEFT;
                      break;
            case 'r': cmd |= ML_RIGHT;
                      break;
            case 'u': cmd |= ML_UP;
                      break;
            case 'd': cmd |= ML_DOWN;
                      break;
            case 'f': cmd = ML_FIRE;
                      break;
            case 's': cmd = ML_STOP;
                      break;
            case 't': duration = atoi(optarg);
                      break;
            default: usage(argv[0]);
        }
    }

    fd = open(dev, O_RDWR);
    if (fd == -1)
    {
        perror("open");
        exit(1);
    }

    send_cmd(fd, cmd);

    if (cmd & ML_FIRE)
        duration = ML_FIRE_DELAY;
    else if (cmd == ML_UP || cmd == ML_DOWN)
        duration /= 2;
    usleep(duration * 1000);

    send_cmd(fd, ML_STOP);

    close(fd);

    return EXIT_SUCCESS;
}

Reference:

1. Writing a Linux Kernel Driver for an Unknown USB Device