*BSD News Article 19156


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Newsgroups: comp.os.386bsd.development
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From: terry@cs.weber.edu (A Wizard of Earth C)
Subject: Re: Need advice: Which OS to port to?
Message-ID: <1993Aug4.073826.24956@fcom.cc.utah.edu>
Sender: news@fcom.cc.utah.edu
Organization: Weber State University, Ogden, UT
References: <3390@vall.dsv.su.se> <CB11pL.D12@imag.fr> <107181@hydra.gatech.EDU>
Date: Wed, 4 Aug 93 07:38:26 GMT
Lines: 34

In article <107181@hydra.gatech.EDU> gt8134b@prism.gatech.EDU (Howlin' Bob) writes:
>Actually, I'm using the video BIOS just fine under Linux.  All you
>need is a little bit of code to support the 386's virtual-8086 mode
>and access to a BIOS image (/dev/mem does fine under Linux).  Of course,
>I wouldn't recommend this sort of thing for real work, but I
>wouldn't recommend anything else for a DOS emulator.  I decided long
>ago that writing video support code for every card was impossible
>for a lone author, so running the native BIOS seemed the best way.

Item of information: Paradise, ATI, and many other vidoe cards disable all
interrupts other than 2/9 (raster interrupt, don'tcha know) while doing
INT-10 calls.  Therefore it is stupid to do INT-10 calls, even in an emulated
8086 mode unless you are prepared to lose network, serial, mouse, tape, floppy,
and keyboard I/O (and have your clock slip).

If you are so swift as to run KEYBUK.COM or other KEYB*.COM files for local
keyboard layout on British Telecom, Zenith, Toshiba, or Olivetti equipment,
be prepared to lose serial and other low priority interrupts while the
keyboard lookup occurs (during INT-16 instead of during the read from the
queue, like god intended).  Seems that they do their lookup in the interrupt
handler.  This will also blow up a UNIX if an 8086 virtual DOS mode session
is being run.

Yes, BIOS access via VM86 is a good thing(tm) in some cases -- Bill and I
discussed at length implementing a disk driver this way to get around, once
and for all, the drive translation problems, for instance.  But video and
keyboard I/O are not the places that this is good.


					Terry Lambert
					terry@icarus.weber.edu
---
Any opinions in this posting are my own and not those of my present
or previous employers.