Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!mailrus!husc6!bloom-beacon!bu-cs!dartvax!eleazar.dartmouth.edu!earleh
From: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Knowing Machine Code
Summary: I know I'm dreaming, but...
Keywords: 68881 emulator.
Message-ID: <8915@dartvax.Dartmouth.EDU>
Date: 15 Jun 88 23:17:19 GMT
References: <13735@comp.vuw.ac.nz> <104700032@uiucdcsp> <4760@husc6.harvard.edu> <13542@shemp.CS.UCLA.EDU> <12217@apple.Apple.COM>
Sender: news@dartvax.Dartmouth.EDU
Reply-To: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Organization: Dartmouth College, Hanover, NH
Lines: 42

In article <12217@apple.Apple.COM> dan@apple.apple.com.UUCP (Dan Allen) writes:
>In article <13542@shemp.CS.UCLA.EDU> kennel@minnie.UUCP 
	(Matthew Kennel) writes:
...
>>Then why doesn't the trap handler call the SANE 
	package for '881 instructions?
>>ISN'T THAT WHY MOTOROLA PUT THOSE TRAPS IN THERE IN THE FIRST PLACE????!!????
...
>Unfortunately, this has been considered but rejected.  I am not sure why
>it was rejected, but it does sound like the slick solution.
...
>It could be done, and may be a neat solution, but has not been done.
>
>Dan Allen

SANE can't emulate the 68881 now, I think Dan explained that pretty
well.  However, although the 68881 is a powerful processor, it should
be possible to build a software emulator for it which runs on the
68000.  I am not talking about traps to SANE here, I am proposing a
full-blown 68881 emulator, and I have a suggestion about where to put
it.

There is 128k of useable ROM space on my Mac Plus, according to IM IV.
There is also a pretty big chunk available on the SE, if you take out
the pictures of the design team (sorry guys).  Put the 68881 emulator
code in the unused ROM space, along with some code to initialize it.
Package the thing as "super-enhanced Macintosh FP emulator ROMs" and
sell the thing for a fair, but still large profit, plus requiring
dealer installation.  Furthermore, tell all developers that they can
assume a 68881 is always present.

Everybody wins with this idea.  Apple gets to sell a required upgrade
to all 68000-Macintosh owners, developers don't have to worry about
checking for a coprocessor, Plus/SE users get to stay in the game
a little longer, and dealers get to charge whatever they want for
plugging in two chips.

Please do it?


Earle R. Horton, Thayer School of Engineering, Hanover, NH
  I wouldn't mind dying -- it's that business of having to stay dead that
  scares the sh*t out of me.  -- R. Geis