Identifying bad RAM on Amiga 1000 WCS board

[Ethan Dicks]

On Mon, Apr 30, 2018 at 10:07 AM, Geoffrey Oltmans <oltmansg at gmail.com> wrote:
> On Sat, Apr 28, 2018 at 6:34 PM, Ethan Dicks via cctalk
> <cctalk at classiccmp.org> wrote:
>>
>> Hi, All,
>>
>> I've been doing component-level diagnosis of a bad Amiga 1000 WCS
>> board and since I was unable to find this information anywhere, I
>> thought I'd post it to the list so that it's in the hands of more than
>> one person.
>
>
> I wonder if one might be able to use the excellent Diagrom in place of the
> A1000 ROMs to do some testing.

When I started debugging these dead A1000s, I took a look at Diagrom...

https://github.com/ChuckyGang/DiagROM/blob/master/DiagROM.s

There's code in there to handle the A1000 as a separate case, but it
seems only to remove features to make it fit in smaller EPROMs, and
that is a recent update.  The original DiagROM was written for all
later machines, without a WCS board.

> At least then you might be able to put some known patterns into the WCS to
> read back and see if they make sense.

One could use the DiagROM as a starting point and _add_ those tests
in.  I haven't gone over the specifics, but there is some code in the
real A1000 ROMs to write enable the WCS board before reading in the
Kickstart disk.  The exact value to write to which address is
documented somewhere but I haven't done any digging to find it.  I've
just been using the Fluke and running the processor for a few seconds
(UUT button) to let the ROMs do their thing, _then_ using the Fluke
for RAM tests at $FC0000-$FFFFFF.

If I hadn't had the Fluke handy, I'd probably have taken the route of
writing some new ROM code to test WCS RAM.  Fortunately I also have an
old Grammar Engine PromICE so I could plug that into the ROM sockets
and do some quick turnover on the code development before burning real
EPROMs.

-ethan