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From: olson@endor.harvard.edu (Eric Olson)
Newsgroups: comp.sys.mac
Subject: Re: GetTrapAddress and SetTrapAddress?
Message-ID: <2277@husc6.UUCP>
Date: Thu, 11-Jun-87 12:01:55 EDT
Article-I.D.: husc6.2277
Posted: Thu Jun 11 12:01:55 1987
Date-Received: Sat, 20-Jun-87 09:45:05 EDT
References: <164500036@uiucdcsb> <986@apple.UUCP>
Sender: news@husc6.UUCP
Reply-To: olson@endor.UUCP (Eric Olson)
Organization: Aiken Computation Lab Harvard, Cambridge, MA
Lines: 22

In article <986@apple.UUCP> han@apple.UUCP (Byron Han) writes:
>Traps patches, when done, should be placed in the Application Heap according
>to current doctrine.  This is to maintain compatability with future operating
>system considerations.
>

Note that in order to maintain compatibility with 64K ROMs (for which the
jump table can only reach 64K into memory), a jump to the patch should be
installed in the System Heap, and the TrapAddress set to that jump.  On
128K ROMs (and, presumably, SE and Mac II ROMs), the jump table is able
to reference anywhere in memory.

Be sure to deinstall your patch before ExitToShell, otherwise, the trap will
point to the jump (in System Heap), which will point to garbage.

-Eric
Eric K. Olson	olson@harvard.harvard.edu	harvard!olson
"If the War were fought today, most Americans doubt that we could defeat the
new Japan.  Its atom bombs would be cleaner than ours and come equipped with
"How Did You Like Our Product" postcards that would drop from the sky and
ask questions like "Where did you hear about us?" and "How many in your
family died?"	-John Dvorak