Path: utzoo!attcan!uunet!husc6!mailrus!ames!amdahl!pyramid!voder!apple!darin
From: darin@Apple.COM (Darin Adler)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Fake Color Quickdraw (was Re: a whole bunch of things)
Message-ID: <14545@apple.Apple.COM>
Date: 23 Jul 88 11:26:01 GMT
References: <467@hodge.UUCP>
Reply-To: darin@apple.apple.com.UUCP (Darin Adler)
Organization: Apple
Lines: 20

In article <467@hodge.UUCP> adail@pnet06.cts.com (Alan Dail) writes:
> Rather than rewriting color QD, would it be possible to write an INIT that
> would patch the 68000 instruction set to emulate the 68020?

Unfortunately, this is difficult, if not impossible, due to the fact that
the 68000 does not fully decode the effective address word for indexed
instructions. This is discussed in Appendix D.3 of the 68020 User's Manual.

> Does the trap for unimplemented instructions allow you to determine what
> instruction was executed similar to the way the A traps work? This seemingly
> minor patch could help simplify software development without the major work
> it would take to try to patch for the 881.

This is the technique David G. was referring to earlier when he mentioned that
Apple considered emulation the 68881 and Motorola "tried it and gave up."
"Seemingly minor" is definitely *not* the right adjective.
--
Darin Adler					       AppleLink: Adler4
UUCP: {sun,voder,nsc,mtxinu,dual}!apple!darin	  CSNET: darin@Apple.com