Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!amdahl!nsc!voder!apple!dan
From: dan@Apple.COM (Dan Allen)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Knowing Machine Code
Keywords: 68881 emulator.
Message-ID: <12256@apple.Apple.COM>
Date: 16 Jun 88 04:32:25 GMT
References: <13735@comp.vuw.ac.nz> <104700032@uiucdcsp> <4760@husc6.harvard.edu> <13542@shemp.CS.UCLA.EDU> <12217@apple.Apple.COM> <8915@dartvax.Dartmouth.EDU>
Reply-To: dan@apple.apple.com.UUCP (Dan Allen)
Organization: Apple Computer Inc, Cupertino, CA
Lines: 20

In article <8915@dartvax.Dartmouth.EDU> earleh@eleazar.dartmouth.edu (Earle R. Horton) writes:
>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.

The Mac Plus with its 128K of ROM space has virtually NO unused space in
it.  We squeezed in every bit of functionality we could into that 128KB.

The Mac SE is a different story.  Its 256KB ROMs do have a lot of wasted
space, hence the pictures of the team in ROM.  We really should have
used it better, but there was no time to write, test, debug, and hone
the code that would have filled up the ROM, so a two day hack of the
photos was done.  (Ever been under the pressure of getting a ROM burned
months before the machine is supposed to ship???)

One final thought on emulating the 68881: since the 881 uses a lot of
the same addressing modes that the rest of the 68xxx family does, an
emulator would have to disassemble or correctly emulate ALL of the 68xxx
addressing modes, something that takes LOTS of code to do. 

Dan Allen
Apple Computer