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From: apratt@atari.UUCP
Newsgroups: comp.sys.atari.st
Subject: Re: RAM locations for safe use
Message-ID: <738@atari.UUCP>
Date: Tue, 26-May-87 16:14:27 EDT
Article-I.D.: atari.738
Posted: Tue May 26 16:14:27 1987
Date-Received: Thu, 28-May-87 05:40:23 EDT
References: <381@uhnix2.UUCP>
Organization: Atari Corp., Sunnyvale CA
Lines: 34

in article <381@uhnix2.UUCP>, uace0@uhnix2.UUCP (Univ ATARI Comp
Enthusiasts) says:
> 
> In response to Moshe Braner's questions concerning a safe place in
> memory, I can only think of one location that is safe.  Actually, it is
> a series of a few longwords that are only safe until the system crashes. 
> That's right, the register save area used after a crash.  As far as I
> know, these memory locations are only used on a system crash, so should
> be free to use while the system is operating normally. 
> 
> - Mike

This turns out not to be the case.

The "bomb handler" gets control from a bus error, address error, etc.
It puts bombs on the screen, DUMPS INFO INTO THE REGISTER SAVE AREA,
then attempts a Pterm0() for the current process.  This often
works: a simple program dereferencing a null (zero) pointer will
give bombs and terminate normally.  

The times when bombs combine with a total system crash are times when a
Pterm0() can't get rid of the offending program: for instance, a rogue
interrupt handler, or trashed internal GEMDOS state. 

In any case, the register save area of memory is overwritten by
any bombs, not just the ones resulting in a total crash.  If you
want a safe place in memory, use your own BSS and execute Ptermres()
to leave your program.  If you want someplace that'll survive a reset,
I can't think of a reliable one.

/----------------------------------------------\
| Opinions expressed above do not necessarily  |  -- Allan Pratt, Atari Corp.
| reflect those of Atari Corp. or anyone else. |     ...lll-lcc!atari!apratt
\----------------------------------------------/