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From: koreth@ssyx.ucsc.edu (Steven Grimm)
Newsgroups: comp.sys.atari.st
Subject: Re: RTE causing bus error
Message-ID: <1139@saturn.ucsc.edu>
Date: Mon, 16-Nov-87 15:27:32 EST
Article-I.D.: saturn.1139
Posted: Mon Nov 16 15:27:32 1987
Date-Received: Sat, 21-Nov-87 00:48:40 EST
References: <1498@ihlpm.ATT.COM>
Sender: usenet@saturn.ucsc.edu
Reply-To: koreth@ssyx.ucsc.edu (Steven Grimm)
Organization: University of California, Santa Cruz
Lines: 34
Keywords: bus error, rte

In article <1498@ihlpm.ATT.COM> nicholso@ihlpm.ATT.COM (B E Nicholson) writes:
>[ Line eater, come and get it]
>
>
>I've recently been developing some code which installs it's own interrupt,
>and trap handlers.  Unfortunately, whenever the code tries to return to 
>the original code a bus error results.  For example, if the routine 
>_clock_int is installed as either a trap, timer interrupt, or any other
>exception handler by the main routine when the rte instruction is executed 
>at the end of the _restart routine a bus error will result.  I'm a little 
>lost as to why.  
>
> (assembly code follows)

What is that routine supposed to do?  Knowing that makes debugging it a lot
easier.  At first glance, it looks like it could be a task-switcher for a
multitasking kernel; is that it?  It looks like you aren't doing the same
number of pushes and pops to the stack.  That could be intentional (if you're
doing multitasking), but is a pretty sure way to get a bus error.  My advice
to you is to trace your code on paper, keeping track of exactly what's on
the user and supervisor stacks.  Remember that exceptions push the status
register and return address to the supervisor stack before running the
exception code; make sure you know in what order those are pushed, as that
can mess you up too.

Hope that helps.

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