[Coco] Simple coco 2 memory test?

[Aaron Wolfe]

On Fri, Apr 8, 2011 at 5:12 PM, Eric Keppel <keppel at earthsounds.com> wrote:
> Hi all,
>
>  I have made progress with my Coco2 here, and just upgraded it to 64k.
> Managed to get GLOVE running using all 64K as well as other games that
> wouldn't run before in 16k, so that is progress. :)
>
> However, I suspect that I may have a bad ram chip, since I can't get
> some things to work reliably.
>
>  For instance, I loaded HDRDOS from the .WAV file included in the
> Drivewire package, and when I typed "DOS" to load Nitros-9 it only very
> rarely (1 in 20 times, perhaps) was able to boot all the way to an OS9
> prompt via Drivewire 3 or Drivewire 4. I tried both versions, hoping one
> would make a difference.  Whenever I do manage to boot fully, the
> machine will lock up sometime shortly after and not respond to commands
> anymore.
>
>  This is a home-made serial cable, so perhaps that is the issue.  I did
> notice CRC errors in the Drivewire logs (error 243 IIRC).  But wouldn't
> I get the same errors if the data is corrupted due to a bad RAM chip and
> thus verifies incorrectly?

It's been a while since I looked at the actual code, but I believe the
checksum is a running sum done on the fly as the bytes are read from
the bitbanger, not something done in a separate pass over the sector
after its been written to memory.  If so, that would pretty much
eliminate ram as the source of the problem.  Maybe someone can verify
or deny this :)

Every CRC error I've seen personally or helped someone else with was
due to a problem with the serial cable (or if you're using a USB
adapter, maybe the serial adapter itself, possibly correctable by
changing the devices settings).  Some CoCos and/or some serial
adapters seem much more picky than others.  Some people report trouble
with cables longer than a couple feet, while others run them 10 feet
or more without any trouble.  Anyway, I've yet to hear of a CRC error
that wasn't connection related.

>
>  Anyway, the bottom line is that I am looking for a small memory test
> program I can run to see if it is working reliably.  Does such a program
> exist, and if so, can someone direct me to it?
>
> Thanks!
>
> --Eric
>
>
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