Newsgroups: comp.sys.apple2
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From: bazyar@ernie (Jawaid Bazyar)
Subject: Re: Multitasking programs
Message-ID: <1991Apr3.230600.538@m.cs.uiuc.edu>
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Reply-To: bazyar@cs.uiuc.edu (Jawaid Bazyar)
Organization: Mutation Testing Facility, University of Illinois
References: <28671.apple.net@pro-avalon> <51124@apple.Apple.COM>
Date: Wed, 3 Apr 91 23:06:00 GMT
Lines: 29

In article <51124@apple.Apple.COM> dlyons@Apple.COM (David A. Lyons) writes:
>A P8 emulator is a very interesting idea; it could actually work, although I
>don't see how it can be *guaranteed* to work, since P8 programs will wind
>up doing device access behind the back of loaded GS/OS device drivers, and
>this could cause major problems (the GS/OS rule is never to make SmartPort
>calls behind a device driver's back).

   I can see how that would cause a problem, with GS/OS drivers caching
and all. Maybe during the duration of the P8 program they just tell the
drivers to flush their caches. No problem then.  

>I also wonder whether they're switching the bank 0 portion of GS/OS in and
>out all the time, which would be tricky (for one thing, there's a heartbeat
>interrupt down there that dispatches SIGNALs).

  Wouldn't it be possible to just have the P8 program somewhere in regular,
fast memory, since no P8 programs use long addressing (none should, although
I'm sure naughties like ProTerm do)?  All the short address references
would refer to the particular bank the program was in, and they could easily
hook their emulator into the MLI vector.  Doesn't seem to hard to me.

  This multiswitch appears to be real- most excellent.  We may order a copy
soon- if/when we (too poor to buy it alone) get it, we'll let ya know how
it is.
--
Jawaid Bazyar               |"I'm sure K&R have never heard of Mike." 
Senior/Computer Engineering |
bazyar@cs.uiuc.edu          |"That's okay. I'm sure Mike's never heard of K&R".
   Apple II Forever!        |  (discussion about Orca/C)