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From: captkidd@athena.mit.edu (Ivan Cavero Belaunde)
Newsgroups: comp.sys.mac.programmer
Subject: Re: What's System Error 12, exactly?
Message-ID: <1991Apr9.162026.3819@athena.mit.edu>
Date: 9 Apr 91 16:20:26 GMT
References: <670554754.1@mmug.fidonet.org> <1991Apr5.011516.23646@athena.mit.edu> <16299@reed.UUCP>
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In article <16299@reed.UUCP> bowman@reed.UUCP (Eric Bowman) writes:
>This was the problem...which raises another question?: Why doesn't a _Debugger
>trap bring up the funky old debugger in rom?

In the Mac you break into the debugger in one of a number of ways. You press
the NMI switch, you cause a system error, or you issue a debugger trap. The
NMI switch is tied (via the NMI vector) to the ROM Debugger. The _Debugger
trap, however, does not exist until it is installed by Macsbug/TMON/Whatever
using SetTrapAddress. When it's installed, the debugger will also reroute the
NMI vector to itself so that pressing the switch will take you to itself
instead of giving you the '>' prompt (shades of MessyDOS ;-). I pressume
that the System Error Handler checks for the existence of the Debugger
trap before giving you the bomb alert and breaks into it.

-Ivan Cavero Belaunde
Visualist
Digital Video Applications Corp. (DiVA)
Internet: captkidd@ATHENA.MIT.EDU