Path: utzoo!utgpu!attcan!uunet!seismo!sundc!pitstop!sun!imagen!atari!apratt
From: apratt@atari.UUCP (Allan Pratt)
Newsgroups: comp.sys.atari.st
Subject: Re: NULLFILL
Message-ID: <1260@atari.UUCP>
Date: 14 Dec 88 19:32:07 GMT
References: <8812130704.AA07616@ucbvax.Berkeley.EDU>
Reply-To: apratt@atari.UUCP (Allan Pratt)
Organization: Atari (US) Corporation, Sunnyvale, California
Lines: 43

In article <8812130704.AA07616@ucbvax.Berkeley.EDU> U46050@UICVM.BITNET 
(JOHN ZAFIRIS) writes:
> [...] NULLFILL is not compatible with everything so note which
> programs act up and disable it for them.

Whenever somebody posts a "greatest thing since sliced bread" (or
"breathtaking") program to the net like this, you should be EXTREMELY
CAUTIOUS. 

The poster should at least tell people what this program does, so
they'll know how dangerous it is and that they should think carefully
before using it. 

This program cropped up before, as Mr.  Zafiris points out.  What this
program does is short-circuit the loop in ROM which clears RAM before
launching a program.  It is "not compatible with everything" because
some programs expect RAM to be clear when they start up.  

It is also "not compatible" because if the loop in your set of ROMs is
in a different place (as will be the case for ANY non-USA set of ROMs)
this program will short-circuit some OTHER piece of ROM code.  This is a
crucial bit of information which the poster didn't mention.

Mega ROMs and all future ROMs have a MUCH FASTER loop, so the RAM
clearing doesn't take forever if you have newer ROMs.  Newer ROMs do NOT
have this feature removed: it was not guaranteed, but it has become a
"settled expectation" that RAM from the end of your BSS to the end of
memory you own will be clear when you start up. 

[It *has* been guaranteed that your declared BSS will be clear: does
this program ensure even that?]

If you must use this program, fine.  I don't even blame you: the time
that stupid loop takes to clear most of 1MB really is noticeable.  But
you should be aware of what chances you're taking before installing
something like this in your AUTO folder.  (What chances?  Well, what if
your hard-disk backup program is one which expects RAM to be clear?
What if the non-clear contents of RAM contain a flag which says "format
the hard disk?"  That's what I call taking a chance.)

============================================
Opinions expressed above do not necessarily	-- Allan Pratt, Atari Corp.
reflect those of Atari Corp. or anyone else.	  ...ames!atari!apratt