SYSRQ...(part2)

[willy tarreau]

Hey mike,

there are lots of keyboards out there which don't
support multiple keys pressed simultaneously. Some
Dell
keyboards I've used are not SysRQ compatible either.
My personnal keyboard works fine, except for the
reboot: I have to press Alt, then SysRQ, then B and
release Alt before the other ones and now the reboot
is
performed. My previous keyboard simply didn't send
anything for Ctrl-Alt-F12.

The problem is due to the fact that keyboards internal
controllers see keys as intersection of columns and
rows. It's not uncommon that multiple rows and cols
connexion collide so that the controller can't
understand what's happening. In your case, I think
you receive the 0xd4 code (SysRQ release) at the
moment
you press the P key, just before it sends 0x19. Your
keyboard simply considers it can't see the SysRQ key
anymore when Alt and P are pressed together.

So the solutions are : 
  - either change your keyboard
  - or replace SysRQ with another key. Common passive
    keys work well (alt, ctrl, shift ...). Why not
    something like Lalt+RCtrl (or even more if you
    agree to modify the sources).

Netware, for example, uses Alt-Lshift-Rshift-Escape to
enter its debugger. I don't know about any keyboard
on which Alt+[LR]Shift don't work together.

Regards,

Willy

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