Uinput and Raspberry Pi

Question

I tried to ask this question on the Raspberry Pi forums, but I have received no responses at all. I thought I might query the minds of the StackOverflow community that has been so helpful in the past.

I'm writing a userspace driver for the Raspberry Pi (specifically, may be ported to other platforms later) which makes use of the bcm2835 library (GPIO) and uinput (Linux user-input virtual devices). I need to read GPIO pins and translate their values into simulated keypresses on a virtual keyboard. The GPIO part has been completed, and the translation part is also completed. Unfortunately, the virtual-keyboard part has not been solved. Uinput refuses to cooperate.

Now, the exact same code works perfectly on a Debian desktop machine. The evdev and uinput modules are required, both of which were loaded in all test cases. On the desktop, inputs can be triggered, however, on the Raspberry Pi, I can verify that the GPIO subsystem has registered the input, but the uinput events do not trigger. Does anyone have a lead on what I might do?

Thank you very much, if you need any information, logs, or otherwise, please let me know and I will post them as soon as I can.

Answer 1

This is a complete solution that works for me. I have a custom-made keypad and these are the keys I have defined. Here is the link to original pdf I used. Of course you can define whatever key you want, just add it to the array.

Note: this code only works with elevated permission.

int allowed_keys[allowed_KEYS_size][2] = {0};
void main()
{
   init_keys();
   
   int fd = open_uinput();

   int key_evt = getKeyEVT(49);   // ASCII code for 1
   
   // simulate key press and key release
   emit(fd, EV_KEY, key_evt, 1);
   emit(fd, EV_SYN, SYN_REPORT, 0);
   emit(fd, EV_KEY, key_evt, 0);
   emit(fd, EV_SYN, SYN_REPORT, 0);
}

long int emit(int fd, int type, int code, int val)
{    
    struct input_event ie;

    ie.type = type;
    ie.code = code;
    ie.value = val;
    /* timestamp values below are ignored */
    ie.time.tv_sec = 0;
    ie.time.tv_usec = 0;

    long int y = write(fd, &ie, sizeof(ie));
    return y;
}
int open_uinput()
{
    int fdui = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
    if (fdui < 0)
    {
        printf("uinput fd creation failed!\n");
        exit(EXIT_FAILURE);
    }

    ioctl(fdui, UI_SET_EVBIT, EV_KEY);
    ioctl(fdui, UI_SET_EVBIT, EV_SYN); //added by behzad

    for (int i = 0; i < allowed_KEYS_size; i++)
        ioctl(fdui, UI_SET_KEYBIT, allowed_keys[i][1]);

    struct uinput_setup usetup;
    memset(&usetup, 0, sizeof(usetup));
    usetup.id.bustype = BUS_USB;
    usetup.id.vendor = 0x1234;  /* sample vendor */
    usetup.id.product = 0x5678; /* sample product */
    strcpy(usetup.name, "My Keypad. Ver 1.1");

    ioctl(fdui, UI_DEV_SETUP, &usetup);
    ioctl(fdui, UI_DEV_CREATE);

    sleep(2);
    return fdui;
}

int getKeyEVT(int k)
{
    for (int i = 0; i < allowed_KEYS_size; i++)
    {
        if (allowed_keys[i][0] == k)
            return allowed_keys[i][1];
    }
    return -1;
}
void init_keys()
{
    //   Reference:
    //      https://www.alt-codes.net/arrow_alt_codes.php
    //      /usr/include/linux/input-event-codes.h    

    allowed_keys[0][0] = 48;    //ASCII     ---> 0
    allowed_keys[0][1] = KEY_0; //LINUX

    allowed_keys[1][0] = 49;    //ASCII
    allowed_keys[1][1] = KEY_1; //LINUX

    allowed_keys[2][0] = 50;    //ASCII
    allowed_keys[2][1] = KEY_2; //LINUX

    allowed_keys[3][0] = 51;    //ASCII
    allowed_keys[3][1] = KEY_3; //LINUX
}