Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!cs.utexas.edu!usc!ucsd!hub!6600sirt
From: 6600sirt@hub.UUCP (Mike O'Brien)
Newsgroups: comp.sys.ibm.pc.programmer
Subject: Re: cold/warm boots with TASM
Message-ID: <4339@hub.UUCP>
Date: 16 Mar 90 01:42:38 GMT
References: <3015@uudell.dell.com>
Sender: news@hub.UUCP
Distribution: usa
Lines: 29

From article <3015@uudell.dell.com>, by jrh@mustang.dell.com (James R. Howard):
> How about this???
[...]
> 	mov	ax, 0feh		; load mask into AX
> 	out     64h, ax			; write reset mask value to kbd controller 
[...]


I have used this method before, but it is not at all reliable.  I
know of at least two computers at my work that this method will not
work on, and they are both true-blue IBM's.

What you are doing here is telling the keyboard controller to wait
three microseconds and then reset the processor.  The problem with
this, as I understand it, is that on a 286 there is no way to get
out of protected mode without resetting the processor.  So programs
that need to switch into and out of protected mode set a flag
telling the processor where to jump after a memory reset.  Not only
are you not guaranteed that this flag will point to the boot code
in ROM at any given time, you are not even guaranteed it will point
there when the computer is first turned on.

So, while this solution doesn't work in general, it might be the
beginnings of a good solution.  Hopefully someone reading this will
point me to a book that explains in detail the flag I have referred
to, so I can set it myself to the boot code.

Michael O'Brien
6600sirt@ucsbuxa.ucsb.edu