Path: utzoo!attcan!uunet!know!cs.utexas.edu!swrinde!ucsd!ucbvax!bloom-beacon!eru!hagbard!sunic!mcsun!unido!mpirbn!p554mve
From: p554mve@mpirbn.mpifr-bonn.mpg.de (Michael van Elst)
Newsgroups: comp.sys.amiga.tech
Subject: Re: BB: device
Message-ID: <1324@mpirbn.mpifr-bonn.mpg.de>
Date: 20 Oct 90 00:37:43 GMT
References: <901017.10051766.033595@CMR.CP6> <519@cbmger.UUCP>
Reply-To: p554mve@mpirbn.UUCP (Michael van Elst)
Organization: Max-Planck-Institut fuer Radioastronomie, Bonn
Lines: 25

In article <519@cbmger.UUCP> peterk@cbmger.UUCP (Peter Kittel GERMANY) writes:
>You can't do it from Amiga side because MS-DOS is so stupid.
>Precisely: Most of the MS-DOS functions are not reentrant. So if
>you interrupt from Amiga side you risk to catch the PC side in a
>moment when it must not be interrupted and thus loses or corrupts
>data. As far as I heard from the developers, the first attempts
>for AREAD and AWRITE did things from the Amiga side, but they 
>learnt the hard way that this may cause big trouble on the PC side.
>So they changed to the safe way and invoke these things only from 
>the PC side where they are sure that because of lacking multitasking
>no other process can come in the way.

I don't see a problem, you can trap the MS-DOS syscall. The trap routine
sets a flag if the syscall is busy. Now, when the Amiga side needs
a call to MS-DOS it checks if a syscall is running. If there's none,
then it can call MS-DOS itself, otherwise it has to queue the request
and the trap routine has to poll the queue when the currently running
syscall exits.

Regards,
-- 
Michael van Elst
UUCP:     universe!local-cluster!milky-way!sol!earth!uunet!unido!mpirbn!p554mve
Internet: p554mve@mpirbn.mpifr-bonn.mpg.de
                                "A potential Snark may lurk in every tree."