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From: toddpw@nntp-server.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple2
Subject: Re: Adding an MMU- the whole hullabaloo
Message-ID: <1990Dec23.054400.10252@nntp-server.caltech.edu>
Date: 23 Dec 90 05:44:00 GMT
References: <311@generic.UUCP>
Organization: California Institute of Technology, Pasadena
Lines: 20

ericmcg@pnet91.cts.com (Eric Mcgillicuddy) writes:

>Perhaps, given that the program counter is saved on /ABORT, it is possible to
>manipulate its value so that it begins the instruction from the start, rather
>than continuing half way through.

Abort is supposed to save the PC of the beginning of the instruction.
one problem solved.

>This brings up another about atomic instructions. Suppose FLAG were is a
>swapped segment, how would ASL FLAG work?                            ^^in

simple, the read cycle traps. abort works fine and the segment is swapped
in before anything nasty has a chance to happen.

the instruction that could give you trouble is an ROL/ROR to a read-only
segment.

Todd Whitesel
toddpw @ tybalt.caltech.edu