Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!bellcore!tness7!tness1!uhnix1!uhnix2!uace0
From: uace0@uhnix2.uh.edu (Michael B. Vederman)
Newsgroups: comp.sys.atari.st
Subject: Re: To Fix or Not To Fix (Really: applying patches to OS)
Message-ID: <656@uhnix2.uh.edu>
Date: 27 Aug 88 15:28:29 GMT
References: <635@ihnet.ATT.COM> <383@snjsn1.SJ.ATE.SLB.COM> <1224@netmbx.UUCP> <524@nikhefh.hep.nl> <4582@saturn.ucsc.edu> <530@nikhefh.hep.nl>
Reply-To: uace0@uhnix2.UUCP
Organization: University of Houston
Lines: 24


Perhaps the most confusing point about your posting is calling a LINE A
*exception* a *TRAP* call.  All 680x0 boxes have *TRAP* vectors staring at
HEX $50.  The ST actually uses LINE F for GEM calls, and LINE A for low
level screen BLT routines.

Of course, Motorola specificaaly reserved LINE F for math calls in the 68881
I believe.

But teh original intent of your message, in other words, document location and
a method for returning and changing these locations, would be a nice touch.
I believe tho, if you pass an illegal function number to one of the trap
handlers (1, 13, 14) you get a pointer to the function table in A0.  This is
not documented that I know of, and is more or less a side-effect of passing
an illegal function number.  Of course, it is trivial at this point to get
a pointer to the desired routine, but nothing is standardized then.

- mike

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