linux-kernel - Re: [PATCH] Use BIOS Keyboard variable to set Numlock

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Date:	Thu, 12 Jul 2007 03:41:03 +0200 (CEST)
From:	Bodo Eggert <7eggert@....de>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Bodo Eggert <7eggert@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] Use BIOS Keyboard variable to set Numlock

On Wed, 11 Jul 2007, H. Peter Anvin wrote:
> Bodo Eggert wrote:

> > Instead of the byte at 0x497 as suggested in that thread, I'm using the 
> > byte at 0x417, which reflects the intended LED state. In order to change 
> > the keyboard LED, DOS programs would change this byte and call INT 5
> > (which is the keyboard software interrupt).
> > 
> 
> 0x417 is actually the current keyboard modifier state, which is the
> right thing to use.

exactly.

> Presumably you meant INT 9 (IRQ 1), not INT 5 which is the print screen
> interrupt (also used by the CPU for BOUND error, which has some amusing
> consequence if anyone ever used the BOUND instruction in DOS.)

I meant int 0x16:
   mem[0x40:0x17] |= 0x20;
   ah = 1;
   int 0x16;

> That being said, one could argue that since this is a BIOS interface it
> should be queried via INT 16h, AH=02h and stuffed in the zeropage
> structure.  This would also solve the issue of it not being supported by
> non-BIOS firmware.

This is an interesting option, but it's more invasive. I'd rather like a 
feedback saying we can depend on that data area to be there.
-- 
Top 100 things you don't want the sysadmin to say:
64. Do you really need your home directory to do any work?
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