Very laggy input when using 'at_keyboard.mod'

[David]

I use grub 2.04-1ubuntu26.13.

I wanted an localized keyboard layout in Grub so I used this script:

https://gist.github.com/cw2k/5b4d7a1dc3715ce368220b708874ac90#file-01_keyboard_layout-sh

In short at this creates a keyboard layout file (/boot/grub/layouts/de.gkb) that is used in grub like this:
 insmod keylayouts
 keymap de

To finally make it work I need to change the terminal input from 'console' to 'at_keyboard'
 terminal_input at_keyboard
I got the desired German keyboard layout however now the input problem are starting.
I need to hold a key for about 3 seconds until some output is shown. Also it quickly starts to beep on every key press and completely blocks any further input.
That beep is an indication from the bios that whats to say the keyboard buffer is full.
It seem that grub is somehow not correctly getting the 'scan codes' from the keyboard buffer. There seems to be a hidden bug in this.

Well I use an logitech usb-keyboard. On a Dell Optiplex 755 with BIOS A22 release on 04 Jan 2013. However I mostly test my boot config it with Qemu (Phoenix Bios) or Virtual box on some other machine whose CPU as that need VT-support that Virtual box needs.
With the same results.

Okay to the problem when I do.
 terminal_input --append at_keyboard
 terminal_input --append usb_keyboard

and enter 'terminal_input'
it says 'at_keyboard' and 'console' are active. However input is now also wacky.
It JUmpS SPOntaIousLY between upper and lower case. If hold the 'z'-key on a German keyboard
it will look like this 'zZZZZyyyyZZYYYYzz'
It jumps between 'console' and 'at_keyboard'
If I manage it like this the enter
"terminal_input --remove at_keyboard"
it works again normal. However just with the standard us-keyboard.
"terminal_input --remove console"

Will make things worse. Unplugging and plugging back the USB-keyboard helps to clean the buffer and enables me to enter some more chars until it quickly gets jammed again.

Well some idea I just got put have not tested is what will happen if I have two usb keyboards attached...
Anyway if someone likes to have a look at this. Hope you can reproduce this bug.
Got luck and thank ya in advance.