Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!usc!snorkelwacker!apple!lsr
From: lsr@Apple.COM (Larry Rosenstein)
Newsgroups: comp.sys.mac.system
Subject: Re: Protected-mode snake oil
Message-ID: <9976@goofy.Apple.COM>
Date: 29 Aug 90 16:44:27 GMT
References: <8919@ur-cc.UUCP> <1990Aug24.180757.3439@Neon.Stanford.EDU> <33355@cup.portal.com>
Organization: Apple Computer, Inc.
Lines: 21

In article <33355@cup.portal.com> ts@cup.portal.com (Tim W Smith) writes:
>In fact, it is trivial to use an MMU with a 68000.  Virtual memory
>is the thing that is not trivial.  Most of the discussion here

>You can even do dynamic stack growth on the 68000.  The trick is
>to get the compiler to generate a "tst.b (a7)" instruction after

The Lisa used a 68000 and had an MMU.  It did the dynamic stack expansion in
the way you describe.  It also handled demand loading of code segments by
limiting the set of instructions used to branch into a segment, and figuring
out how to restart those particular instructions.

It wasn't possible to do this with data segments, because they could be
referenced by almost any instruction.  So the application program had to
explicitly map/unmap the program's data segment(s) in to memory.

-- 
		 Larry Rosenstein,  Object Specialist
 Apple Computer, Inc.  20525 Mariani Ave, MS 46-B  Cupertino, CA 95014
	    AppleLink:Rosenstein1    domain:lsr@Apple.COM
		UUCP:{sun,voder,nsc,decwrl}!apple!lsr