# evdev (/integration/embedded_linux/drivers/evdev)



Overview [#overview]

The Linux event device (evdev) is a hardware-independent API that gives access to input events from,
for example, a mouse or touchscreen. It is exposed via the Linux device file system interface.

Prerequisites [#prerequisites]

Your system has an input device configured (usually under `/dev/input/` such as `/dev/input/event0`).

Configuring the driver [#configuring-the-driver]

Enable the Linux LVGL evdev driver support in `lv_conf.h`.

```c title=" " lineNumbers=1
#define LV_USE_EVDEV 1
```

Usage [#usage]

To set up an event input, first create an input device with `lv_edev_create` setting it to the correct Linux event device.
Then link this to the LVGL display with `lv_indev_set_display`.

```c title=" " lineNumbers=1
lv_indev_t *touch = lv_evdev_create(LV_INDEV_TYPE_POINTER, "/dev/input/event0");
lv_indev_set_display(touch, disp);
```

Ensure that an `lv_display_t` object is already created for `disp`. An example for this is shown below, using the Linux framebuffer driver.

```c title=" " lineNumbers=1
lv_display_t * disp = lv_linux_fbdev_create();
lv_linux_fbdev_set_file(disp, "/dev/fb0");
```

Locating your input device [#locating-your-input-device]

If you can't determine your input device, first run

`$cat /proc/bus/input/devices`

This should show input devices and there will be entries with the word `event` which give a clue as to the device to use eg. `event1` would be `/dev/input/event1`.

You can use `evtest` to show data from that event source to see if it is actually the one you want.

Try:

`$evtest /dev/input/event1` replacing `eventX` with your event device from above.

Automatic input device discovery [#automatic-input-device-discovery]

There is support for automatically finding and adding input devices in `/dev/input/`. New devices will automatically be added
when they are connected. To enable this feature, you can simply call <ApiLink name="lv_evdev_discovery_start" display="lv_evdev_discovery_start(NULL, NULL)" />.

You may want to react to a new device being added so that a cursor image can be applied, for example. You can provide a callback
function which will be called when a new device is added.

```c title=" " lineNumbers=1
#include "lvgl/src/core/lv_global.h"

static void indev_deleted_cb(lv_event_t * e)
{
    if(LV_GLOBAL_DEFAULT()->deinit_in_progress) return;
    lv_obj_t * cursor_obj = lv_event_get_user_data(e)
    lv_obj_delete(cursor_obj);
}

static void discovery_cb(lv_indev_t * indev, lv_evdev_type_t type, void * user_data)
{
    LV_LOG_USER("new '%s' device discovered", type == LV_EVDEV_TYPE_REL ? "REL" :
                                              type == LV_EVDEV_TYPE_ABS ? "ABS" :
                                              type == LV_EVDEV_TYPE_KEY ? "KEY" :
                                              "unknown");

    if(type == LV_EVDEV_TYPE_REL) {
        LV_IMAGE_DECLARE(mouse_cursor_icon);
        lv_obj_t * cursor_obj = lv_image_create(lv_screen_active());
        lv_image_set_src(cursor_obj, &mouse_cursor_icon);
        lv_indev_set_cursor(indev, cursor_obj);
        lv_indev_add_event_cb(indev, indev_deleted_cb, LV_EVENT_DELETE, cursor_obj);
    }
}

int main()
{
    /* ... */
    lv_evdev_discovery_start(discovery_cb, NULL);
    /* ... */
}
```

At the time of writing, this feature is not supported in BSD.