Arch Linux

Wowitscow

Member

Registered: 2025-06-28

Posts: 3

Keyboard locking up on FN key usage

I have a bit of an obscure keyboard that uses some odd windows only firmware (its called LDN i cant find much about it anywhere other than a help guide on github written almost exclusively in Chinese. here's the download if anyone's curious https://d-r.works/pages/daringrun-70f-software-guide). I've not had any trouble with it while setting up the keyboard in a windows 10 VM using USB pass through on virtualbox but when i shut down the VM and try to use the keyboard on Linux any time i try and access a function layer the keyboard crashes(freezes?) and has to be unplugged and plugged back in. The only thread I've found on this matter is in the Mint forum and there was no real fix found (https://forums.linuxmint.com/viewtopic.php?t=373521). I followed the advice and tried the FN key with xev open but it registers nothing. the key itself works fine, ive tried mapping multiple keys that all have worked to function and they all behave the same. wondering if anyone knew anything about this? I forgot to mention earlier but i just updated my entire machine so all my packages are up to date as of this post, and i've tried the keyboard on my pop!OS laptop and had the same result.

cryptearth

Member

Registered: 2024-02-03

Posts: 1,809

Re: Keyboard locking up on FN key usage

according to https://mekibo.com/pages/software (btw: your link is broken) the LDN is just a pcb (likely with a microcontroller) to be used with DYI or in OEM products
also this looks related: https://github.com/lswhome/C3_LDN_DRIVERS_Source_Code
guess the simplest options are:
- use windows
- don't use the Fn keys
- buy a cheap office keyboard like the Logitech K120 or similar cheap office keyboards from m$, hp or others ... I mean they cost 20bucks and you get them in pretty much any store that sells anything computer related

Wowitscow

Member

Registered: 2025-06-28

Posts: 3

Re: Keyboard locking up on FN key usage

Thanks for the github link, i hadn't seen that. welp guess im just not using my function layers unless i feel like porting the driver? maybe rebind the function key to something that i can have the computer intercept and fake a function layer that way? who knows. thank you either way.

Last edited by Wowitscow (2025-06-28 12:15:22)

cryptearth

Member

Registered: 2024-02-03

Posts: 1,809

Re: Keyboard locking up on FN key usage

well - don't give up that easy
as the device works it obviously uses at least some parts of the HID standard
the main question is: is the Fn handling done on the microcontroller which due to some bug hangs/crashes and no longer responds to the polls from the computer - or is the Fn just transmitted with a special keycode the driver listens for and the interpretation is done in the driver?
for the latter: why does this cause the issue? it could be the keyboards firmware waits for some acknowledge from the driver that the Fn is pressed, held and released - but doesn't handle the error properly not receiving any because the computer uses standard HID only
although in that case it would happen even on windows when the driver is not installed - unless windows does handle the Fn way different overall than Linux

so, you see - the issue isn't just as simple as "it stops working on use of Fn" but without help of its original designer it's likely hard to fix even with a public driver repo

hope you (or anyone) can get this working - good luck

Wowitscow

Member

Registered: 2025-06-28

Posts: 3

Re: Keyboard locking up on FN key usage

Yeah after some further experimenting the keyboard sends NOTHING when the function layer is triggered (either successfully on windows or unsuccessfully on linux) so i think it is truly hopeless without help from someone involved in making the thing. that is unless there's a lower level to monitor than /dev/input/event*. thanks either way

cryptearth

Member

Registered: 2024-02-03

Posts: 1,809

Re: Keyboard locking up on FN key usage

well - hooking up an oscilloscope or digital analyzer to the data pins of the usb connection aand what it replies
USB works by polling: the computer has to ask the keyboard: do you have anything for me? - and keyboard then usually replies with:
- no change
- key X pressed
- key X held
- key X released
- on more advanced stuff with several other reply codes
now it could be that pressing the Fn key generates not a regular HID key event bit some lower response the special driver listens for and if it gets triggered responding with some more stuff
but I don't know if either the linux kernel or the windows kernel for that matter allows such a deep dive that low-level from the os or if this is something hardware based one really needs physical hooking the cables