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From: hyc@math.lsa.umich.edu (Howard Chu)
Newsgroups: comp.sys.atari.st.tech
Subject: idle rambling
Message-ID: <1990Aug30.225713.24233@math.lsa.umich.edu>
Date: 30 Aug 90 22:57:13 GMT
Sender: usenet@math.lsa.umich.edu
Reply-To: hyc@math.lsa.umich.edu (Howard Chu)
Organization: University of Michigan Math Dept., Ann Arbor
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Uucp-Path: {mailrus,umix}!um-math!hyc

Why is it that every time someone comes along to patch one of the TOS
functions, they have to intercept the trap handler? I've been thinking
about writing an AUTO folder program that basically copies all the BIOS,
XBIOS, etc. jump tables to RAM, so you don't have to duplicate all the
effort of intercepting the call, testing the function number, etc.
(i.e., the program has a functional duplicate of the current BIOS/XBIOS
trap handler, but it uses a jump table in RAM. When you want to replace
a function with your own, you just need to change the jump table, not
install a brand new trap handler.)

Why didn't anyone ever do this before? 

The program could be very stupid, and just have the jump tables for each
version (1.0, 1.2, 1.4) of TOS hard coded, or it could be very incredibly
smart, and walk thru the existing trap handler until it encounters the
magic jump instruction, and duplicate things that way. Either way it would
make later changes much more convenient, no?
--
  -- Howard Chu @ University of Michigan
  one million data bits stored on a chip, one million bits per chip
	if one of those data bits happens to flip,
		one million data bits stored on the chip...