Thanks everyone.

It took me several days to find out the solution, finally, I found the right way.

Reference

Map scancodes to keycodes

Background

Version 11 of the X protocol only supports single-byte key codes. So key codes above 255 are ignored. Ubuntu 20.04 LTS, so far, still uses version 11 of X protocol.

My G7BTS remote keyboard has a “OK” button. This button has a key code of 353. Within “xev”, nothing happens when this button is pressed.

Solution

By brief, the solution is to create a hwdb configuration file, which is used to remap certain keys to other keys.

udev

udev provides a builtin function called hwdb to maintain the hardware database index in /etc/udev/hwdb.bin. The database is compiled from files with .hwdb extension located in directories /usr/lib/udev/hwdb.d/, /run/udev/hwdb.d/ and /etc/udev/hwdb.d/. The default scancodes-to-keycodes mapping file is /usr/lib/udev/hwdb.d/60-keyboard.hwdb.

Generic input devices (also USB keyboards) identified by the usb kernel modalias:

evdev:input:b<bus_id>v<vendor_id>p<product_id>e<version_id>-<modalias>

where <bus_id>, <vendor_id> and <version_id> are the 4-digit hex uppercase vendor, product and version IDs

How to find those ids above is the key

install hardinfo

sudo apt install hardinfo

software – System Profiler – Input Devices – G7BTS Comsumer Control

Device Information

 Name       G7BTS Comsumer Control

 Type       keyboard

 Bus        0x0005

 Vender     0x045e

 Product    0x0041

 Version    0x0300

Another import thing is to get the scan code of the “OK” button.

install evtest

sudo apt-get install evtest

sudo evtest

No device specified, trying to scan all of /dev/input/event*

Available devices:

/dev/input/event0:    Lid Switch

/dev/input/event1:    Sleep Button

/dev/input/event2:    Power Button

/dev/input/event3:    AT Translated Set 2 keyboard

/dev/input/event4:    SynPS/2 Synaptics TouchPad

/dev/input/event5:    TPPS/2 IBM TrackPoint

/dev/input/event6:    ThinkPad Extra Buttons

/dev/input/event7:    Video Bus

/dev/input/event8:    Integrated Camera: Integrated C

/dev/input/event9:    G7BTS Keyboard

/dev/input/event10:    G7BTS Mouse

/dev/input/event11:    G7BTS Consumer Control

/dev/input/event12:    G7BTS System Control

/dev/input/event13:    HDA Intel PCH Mic

/dev/input/event14:    HDA Intel PCH Dock Mic

/dev/input/event15:    HDA Intel PCH Headphone

/dev/input/event16:    HDA Intel PCH Dock Headphone

/dev/input/event17:    HDA Intel PCH HDMI/DP,pcm=3

/dev/input/event11:    HDA Intel PCH HDMI/DP,pcm=7

/dev/input/event19:    HDA Intel PCH HDMI/DP,pcm=8

Select the device event number [0-19]: ^C

Pay attention to “/dev/input/event11”

sudo evtest /dev/input/event11

Then press “OK” button, and the output is below

Event: time 1640238746.775220, type 4 (EV_MSC), code 4 (MSC_SCAN), value c0041

Event: time 1640238746.775220, type 1 (EV_KEY), code 353 (KEY_SELECT), value 0

Event: time 1640238746.775220, -------------- SYN_REPORT ------------

Pay attention to “value c0041“. This value c0041 is the scan code of “OK” button.

Make the hwdb file

Now, we have the ids and the scan code we need. Put them into the “Generic input devices (also USB keyboards) identified by the usb kernel modalias” above, and finally we have the configuration file G7BTS.hwdb below:

evdev:input:b0005v045Ep0041e0300*

 KEYBOARD_KEY_c0041=enter

In the context, the “OK” button is mapped into “enter” key. You can map it into any key you want.

Put file to destination

sudo mv G7BTS.hwdb /etc/udev/hwdb.d/

Update

sudo udevadm hwdb --update

sudo udevadm trigger --verbose 

Test

sudo udevadm hwdb --test='evdev:input:b0005v045Ep0041e0300*'

result is

KEYBOARD_KEY_c0041=enter

The End

That is all the steps to remap keys. Those remapping still work after reboot.