From: wingo@apple.com (Tony Wingo)
Newsgroups: comp.sys.mac.system
Subject: Re: Bad F-line instruction?
Date: 22 Jul 92 18:45:01 GMT
Followup-To: comp.sys.mac.system
Distribution: na
Organization: Apple Computer

In article <1992Jul22.034951.21764@news.stolaf.edu>,
smithc@lars.acc.stolaf.edu (Christopher A. Smith) wrote:

> Tony, let me tell you about my experiences with this Bad F-Line
> instruction, just in case my previous posting from about a month ago
> has scrolled off...
> 
> [Long description of problems with F-Line errors deleted]
> 
> 
> How can a program become corrupted, especially more than once a day,
> under different circumstances (different or no INITs or applications)?

Without being there I can't answer this directly.  One of the weaknesses of
the Mac OS is that memory protection is not built into it, thus allowing an
errant piece of code to do all kinds of random things. (No flames please --
this was a decision made almost a decade ago, and while in retrospect it
might have been made differently, we have to live with it for a bit).

While I can sympathize with your frustration, keep in mind that what you
are seeing is not a system problem. I routinely work on four different
machines (two IIfx, a IIx and a PB 140) running 7.0.1 and 7.1 beta.  My
buddy in the next cube has even more machines including a Quadra 700. 
Since we do software development our machines are always a little flaky,
and neither one of us sees many F-line problems at all.  There is something
about your particular configuration that is causing problems. 
Unfortunately, without being there (fat chance: I grew up in DC, and I
wouldn't go back in July or August if my life depended on it :-) ) there is
not much else I can tell you.  Sometimes these things can only be found
with an intense mixture of TMON and strong black coffee.

However, a couple of things to look at.
1. Are you absolutely sure that the system is installed correctly for the
particular machine?  If you try to run a IIx system on a Classic, all bets
are off.  If you are not sure, drag the system, finder and all the apple
cdevs and extensions to the trash, then carefully use the installer to
re-install the system - never do a system install by dragging the system
files from one machine to another: Always use the installer.  

2. Are all of the applications and extensions you are running up to date? 
Some older versions of software had problems with some aspects of system 7.
 In addition, some older versions didn't get along with 68030's.  There are
still a bunch that don't like 040's.

3. If this is not your own machine, make sure it only has one system
folder.  (use the Find command to make sure there isn't a second one buried
somewhere). I once ran into a machine that had 13 distinct system folders
on it.

4. Do these problems occur primarily on one machine.  If so, what is
different between that machine and machines that don't exhibit the problem.

5. Install MacsBug or TMON.  The F-Line failure will trap into the
Debuegger, and if A5 and A6 are not clobbered, you MAY be able to identify
what is being corrupted.  If you are so lucky, then you can use the
checksumming facility to catch the actual corruption.

6. There is a REMOTE possibility that you have an intermittent hardware
problem, such as a flaky SIMM.  (It would have to be real intermittent for
it to consistently get past the startup diagnostics) The only real way to
test for this is to copy your entire configuration over to another machine
with the same hardware configuration and see if the problem moves with it.

Sorry I couldn't be more help.

-tony

>>usual disclaimers apply<<