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From: dsmall@well.sf.ca.us (David Small)
Newsgroups: comp.sys.atari.st
Subject: Re: Spectre and TOS simultaneously
Message-ID: <22797@well.sf.ca.us>
Date: 22 Jan 91 00:09:56 GMT
References: <14599@milton.u.washington.edu>
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
Lines: 39


(the thread discusses SOFTLINK, Spectre, and basically running Spectre and TOS
at the same time).

	I'm not that familiar with SOFTLINK or what it does.

	The Spectre and TOS have entirely different memory maps, and many things 
would have to be pretty cleverly handled to get them to switch between
modes (say, on a keypress). For instance, the video shifter is pointed to
another place, all the interrupts are reprogrammed, the interrupt vector base
for the MFP is moved, and so forth. 

	We've speculated on whether or not REVOLVER would be able to do this.
In a conversation with its authors, we think it is possible.

	I personally think such a program would have to have one memory
partition active, starting at 0 (interrupt vector area), for the size of the
partition, and the others idle, since none of the low-level critical globals
of either the Mac or GEM/TOS would be available. It could do a block-copy
bankswitch and start running.

	There would be all sorts of interesting things to resolve doing this,
but I think it's technically possiblr.

	With the 68030's onboard MMU, life gets real easy real fast doing this.
With MMU, each partition would think it has its own machine, starting at 0;
the MMU worries about translating what the program thinks into reality.
Hence we could have multiple TOS's and even multu^[ple Spectre's running in
place,
provided there's enough memory to hold them. Oddly enough, we added
the capability of a 12 megabyte ST to our SST board, and this was one
reason why -- the ability to instantly flip from TOS to SuperCharger to
Mac mode is pretty impressive to people.


	Anyway, it's possible, it's FAR easier and more reliabile with a 68030
or other MMU, and we just might add it into a future Spectre for fun.

	-- thanks, Dave / Gadgets