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Path: utzoo!utgpu!water!watmath!clyde!rutgers!ames!oliveb!pyramid!voder!apple!han
From: han@apple.UUCP
Newsgroups: comp.sys.mac
Subject: Re: GetTrapAddress and SetTrapAddress?
Message-ID: <1027@apple.UUCP>
Date: Sat, 13-Jun-87 19:50:37 EDT
Article-I.D.: apple.1027
Posted: Sat Jun 13 19:50:37 1987
Date-Received: Sun, 14-Jun-87 07:38:33 EDT
References: <164500036@uiucdcsb> <164500037@uiucdcsb>
Organization: Apple Computer, Inc., Cupertino, USA
Lines: 44

In article <164500037@uiucdcsb>, kkim@uiucdcsb.cs.uiuc.edu writes:
> 
> > /* Written  6:37 pm  Jun 10, 1987 by han@apple.UUCP */
> 
> > > How can I put my own version in the system heap?
> > > 
> 
> > Traps patches, when done, should be placed in the Application Heap according
> > to current doctrine ... to  maintain compatability with future operating
> > system considerations.
> 
>     Do you mean the LIMIT that the trap dispatch table can address 
> locations within a  range of only 64K bytes from the beginning of the
> system heap has been LIFTED, and that  the format of the trap dispatch 
> table has been changed.
> 

My understanding is that to maintain compatability with 64K ROM machines, one
needs to make sure that the patch is in the first 64K of memory.  According
to Larry Rosenstein, in an internal mail communication with me,

"If you want your program to run on a 64K ROM machine you have to put a jump
vector in the System Heap to ensure that the patch falls within 64K of the
start of RAM."
 
Otherwise, if 64K ROM compatability, one should place patches in the
current application heap, NOT in the system heap.  This has changed
recently so please be aware of it.  You may break in the future if you do not.

Please remember - going patch crazy is uncool and the Apple Thought Police
will get itchy.  One should also try to maintain compatability with old 
ROM's as long as it is practical.  But we are also still working with an
evolving machine, so things are changing.  

=====================================================================
Byron Han            |   UUCP: {sun,voder,nsc,mtxinu,dual}!apple!han
Apple Computer, Inc. |  CSNET: han@apple.csnet 
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All opinions and statements do not necessarily represent those of my
employer, Apple Computer Inc.
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