Re: Apple 1 CFFA1 AND FORTH +

[David Schmenk <dschmenk@gmail.com>]

On Nov 2, 4:25 pm, mwillegal <m...@willegal.net> wrote:
> On Nov 2, 12:53 pm, David Schmenk <dschm...@gmail.com> wrote:
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> > On Nov 2, 4:03 am, mwillegal <m...@willegal.net> wrote:
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> > > DRAM refresh suspends the CPU clock, so should have no effect on reads
> > > or writes on a real Apple 1, Obtronix or Mimeo.
> > > I'm heavily engaged in another project at this time, but I'll try this
> > > Forth port on a Mimeo, as soon as I get a chance.
> > > In the meantime, a while back, I have put up a page with a memory test
> > > that could be used to test the memory on any of these systems.
>
> > >http://www.willegal.net/appleii/6502mem.htm
>
> > > Regards,
> > > Mike Willegal
>
> > HI Mike-
>
> > I did use your memory test on my Obtronix.  It passed (actually it did
> > fail once, but ran for a day afterward).  However, I wouldn't put too
> > much faith in the test.  It checks to see if the value written is the
> > one read back, but there aren't any checks for secondary effects such
> > as other memory locations being affected by the one being tested (at
> > least that I could find).  I'm not saying that the refresh is
> > definitely the culprit.  I have no real diagnostic tools so I'm just
> > speculating as I can't think of any other differences in the way the
> > CPU, memory, and code interact at this point.  Rich and I went back
> > and forth (ha) over the best way to track down the failure.  He wanted
> > me to probe the address the CPU was at after it locked up and I wanted
> > to run the trace code to see *why* it failed.   The age old hardware
> > guy vs software guy debugging argument.  I would love to hear your
> > results on the Mimeo.  More data is good.  If it works, save me a
> > Mimeo and I'll order one ;-)
>
> > Dave...
>
> Actually checking that writing one location doesn't affect another
> location
> is exactly what the address in address tests do.  I believe I pulled
> up an address pin on a ram chip  at one point during development
> of this test tool to make sure the test would properly find the fault,
> which it did.
>

OK, good.  I mustn't have looked hard enough.

> Trying this software out is pretty high on the list of things to do.
> I really
> don't expect different results from the Obtronix, but maybe I'll be
> able
> to find root cause of the problem.
>

Thanks.  I can't completely rule out a software bug - I've been burned
by that before.  As a friend of mine once said: "the logic analyzer
doesn't lie" after he tracked down a software bug of mine in an IRQ
handler that I swore was hardware.

> Regards,
> Mike W.

Dave...