USB keyboard not responding in GRUB-PC when Legacy USB is disabled

[Ian Brown]

GRUB is not responding to a USB keyboard, whereas the same keyboard does
respond in the UEFI and also responds in Linux (and an RTOS called "SLRT").

The setup:
 - Advantech AIMB-707G2 motherboard
 - GRUB 2.06 or GRUB 2.12 (GRUB-PC, which is required for SLRT)
 - CSM enabled in the BIOS (this is required for SLRT)
 - Legacy USB Disabled (this is required for SLRT)
 - XHCI Hand-off enabled OR disabled (i.e. I tested both options)
 - Keyboard plugged into USB2 or USB 3 port (i.e. I tested both options)
     - Note: there are no PS2 ports on this motherboard

Background:
We are attempting to dual boot to Linux and a rather old RTOS (Simulink
Real-time R2019b). Because SLRT is an RTOS we need to have Legacy USB
disabled in the UEFI. Because it is an older RTOS we need have CSM enabled
in the UEFI and we need to use GRUB-PC.

Question(s)

1) Am I correct that GRUB does not yet natively support XHCI?

2) Should GRUB be able to respond when XHCI Hand-off is disabled? In other
words, is it possible that the UEFI has a bug and is not supporting this
feature correctly? My naive understanding of XHCI hand-off is that when
disabled, the UEFI is supposed to "handle" the USB. But I am not confident
I am understanding this setting correctly.

3) Any other suggestions on how to get a USB keyboard to work with GRUB
when legacy USB is disabled?

Thanks,

Ian


*Ian Brown, Ph.D., P.Eng.*

Vice-president

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