Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!apple!portal!cup.portal.com!ts
From: ts@cup.portal.com (Tim W Smith)
Newsgroups: comp.sys.mac.system
Subject: Re: Protected-mode snake oil
Message-ID: <33355@cup.portal.com>
Date: 29 Aug 90 08:01:44 GMT
References: <33164@cup.portal.com> <1204.26c2fb48@waikato.ac.nz>
  <8919@ur-cc.UUCP> <1990Aug24.180757.3439@Neon.Stanford.EDU>
Organization: The Portal System (TM)
Lines: 15

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
about the possible need for an MMU was related to protection
issues, which are independent of virtual memory.

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 link instruction in function headers.  The bus error handler
can without too much work detect this and grow the stack.

In summary, a plain 68000 can easily support an MMU for protection.
With a slight amount of work in the OS and the compiler, it can also
support dynamic allocation of stack space.  You need gross hacks,
however, to get full virtual memory.
						Tim Smith