*BSD News Article 8429


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Newsgroups: comp.unix.bsd
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From: gerhard@netmbx.netmbx.de (Gerhard Hoffmann)
Subject: Re: [386BSD] 16550 Not Resetting.
Organization: netmbx, Berlin, Germany
Date: Wed, 2 Dec 1992 01:39:24 GMT
Message-ID: <SJF9YPB@netmbx.netmbx.de>
References: <1992Nov28.115716.8219@runx.oz.au> <CGD.92Nov28202543@eden.CS.Berkeley.EDU> <1992Nov30.131213.18948@runx.oz.au>
Lines: 25

Bruce Evans  (bde@runx.oz.au)  wrote:
>Blame the hardware.  After the software has put the h/w in a weird state,
>it is often too difficult, and sometimes impossible, to recover without a
>full h/w reset.  Yet the h/w doesn't provide any (standard?) way to force
>a h/w reset from s/w.  386BSD shuts down by causing a triple fault.  My
>understanding is that this doesn't reset the h/w, it just shuts down the
>cpu, then on most systems the motherboard h/w detects the shutdown and
>causes some sort of reset.  I wonder why the reset isn't full?  Perhaps
>so that it can be used to switch 286's out of protected mode.

The triple fault doesn't reset anything but the cpu. It is a bug ( too 
difficult to handle) declared a feature and has been used by DOS ex-
tenders to leave protected mode for a moment in order to do a syscall.
Not much of a system reset.

If you want to do a REAL RESET, ask the keyboard controller to do it:

		outb ( 0x64, 0xf0 );

 a triple fault  --- aaarggh!
-- 
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