Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucbvax!agate!shelby!neon!torrie From: torrie@Neon.Stanford.EDU (Evan James Torrie) Newsgroups: comp.sys.next Subject: Re: Mac emulator Message-ID: <1990Oct14.185440.23717@Neon.Stanford.EDU> Date: 14 Oct 90 18:54:40 GMT References: Organization: Computer Science Department, Stanford University Lines: 21 aberno@questor.wimsey.bc.ca (Anthony Berno) writes: >Furthermore, the way Mac toolbox calls are executed (direct ROM >addressing to the routines on the ROM chips) makes me doubt that it >would be feasible. I know nothing about emulating other computers, but Actually, Mac Toolbox calls are executed using the 68K's A-line trap mechanism. Every toolbox call has a unique trap number (encoded in the low 9-bits of the trap instruction), which is used to index into a RAM-based table of absolute ROM addresses. Hence, a vendor of an alternative ROM would only have to make sure the RAM-based table pointed to the correct locations in their own ROM. Now, apparently, some Apple OS code checks for absolute ROM addresses, but if a vendor were selling a viable system, they'd have to rewrite that anyway. (This is all assuming that Apple doesn't come round and license its code, which actually looks more and more likely now that Apple management is getting more pragmatic) -- ------------------------------------------------------------------------------ Evan Torrie. Stanford University, Class of 199? torrie@cs.stanford.edu "The All Blacks? Who are they? - some plebian