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From: ralphw@ius3.ius.cs.cmu.edu (Ralph Hyre)
Newsgroups: comp.sys.apple
Subject: Re: multitasking, softswitch, etc.
Message-ID: <4655@pt.cs.cmu.edu>
Date: 5 Apr 89 21:38:56 GMT
References: <8903181259.aa27052@SMOKE.BRL.MIL> <10183@bloom-beacon.MIT.EDU> <9949@smoke.BRL.MIL>
Organization: Carnegie-Mellon University, CS/RI
Lines: 30

In article <9949@smoke.BRL.MIL> gwyn@brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>) writes:
>In article <10183@bloom-beacon.MIT.EDU> dcw@athena.mit.edu (David C. Whitney) writes:
>>multitasking environment on my //GS, I *know* that it can't be done within
>>any reasonable degree of efficiency.
>[followed by stuff about the Mac II PMMU]
>
>The only serious problem with multitasking the IIGS (in 16-bit mode)
>is that a context switch involves saving quite a bit of state, for
>example the direct page.

I thought the 65816 would allow you could change the direct page pointer.
If so, then you don't need to save stuff, just have your interrupt handler
create/switch to a new one for the next task.

I know that the '816 stack pointer is changeable, so you don't have to
worry about stack management if you don't want to.

On the //e, you can change memory spaces with bank-switching, so
you can avoid the problem here as well.

For a Unix clone on the GS, my understanding of Unix philosophy
suggests that none of the applications need to be > 64K anyway, so
8-bit mode should mostly suffice.

disclaimer: I could be wrong.
-- 
					- Ralph W. Hyre, Jr.
Internet: ralphw@{ius{3,2,1}.,}cs.cmu.edu    Phone:(412) CMU-BUGS
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"You can do what you want with my computer, but leave me alone!8-)"
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