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

H. Peter Anvin
2007-07-12T00:59:43Z

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.

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.)

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.

-hpa