Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!mcsun!cernvax!chx400!ugun2b!ugsc2a!fisher
From: fisher@sc2a.unige.ch (Markus Fischer)
Newsgroups: comp.sys.ibm.pc
Subject: Re: System boot and INT 19
Message-ID: <157@sc2a.unige.ch>
Date: 12 Jan 90 12:13:12 GMT
References: <945@excelan.COM> <77@qmsseq.imagen.com> <357@clover.warwick.ac.uk>
Organization: University of Geneva, Switzerland
Lines: 47

In article <357@clover.warwick.ac.uk>, bsrdp@warwick.ac.uk (Hylton Boothroyd) writes:
> [...]
> I wonder how many of those who repeat these recipes have tried them.
> The use of INT 19 is curiously under-documented even in the MSDOS
> interrupt list.
> [...]
> It remains a mystery how to replicate the warm start effect of
> Ctrl-Alt-Del.

It seems the place where to look is in the keyboard driver, as Ctrl-Alt-Del is
after all interpreted by it.  Now I havn't done any hacking in the recent
drivers, but a few years ago, I had to modify the Olivetti MS-DOS 2.11 swiss-
french driver (it was incompatible with the needs of WordPerfect v. 3.21, or
the like - WP used Ctrl- and Alt- Numbers (first row of the keyboard), which
had been remapped in that particular driver...).

Anyway, here is the significant dissasembled code:

	cmp	AH, 05			; Alt-Ctr shift state
	jnz	(further)		; jump to next shift state
	cmp	AL, 53			; Del scan code
	jnz	ACF1			; jump to next function
	;
	; Alt-Ctrl-Del function
	;
	ES:				; is hex 40
	mov	word ptr [0072],1234	; no memory check (but how ?)
	jmp	F000:FFF0		; WARM BOOT !!!
					; (never returns)
ACF1:	cmp	AL, 3B			; F1 scan code
	jnz	ACF2			; jump to next function
	[...]				; Alt-Ctrl-F1 function...

All the variants of `warmboot.com' I have seen use essentially the same idea.
I'm really nothing of an assembler-expert, so I dont know the difference
between
	jmp	F000:FFF0
and
	jmp	FFFF:0000
which is often used instead, it seems that both work (it's the same location
after all).

In any case, this is what you get when you strike Ctrl-Alt-Del...

So long,

Markus Fischer, Dpt. of Anthropology, Geneva