[Coco] [Color Computer] 1M simms in Cloud9 SIMM upgrade kit

[deleted2006]

--- In ColorComputer at yahoogroups.com, "Paul T. Barton" 
<idezilla at y...> wrote:
> Mike,
> 
> Just let it sit for a minute or so,
> doing nothing, it may crash. My experience.


Sorry to just jump into the discussion, but you are right...

Way back when I did my 512k upgrade for my brand new CC3, I too had a 
refresh problem.

It'd work okay as long as I ran it hard (doing memory tests etc.), 
but it'd fail if I let it sit doing nothing.

(Long story, but the solution was to leave a long jumper hooked up.  
It left enough capacitance or provided enough delay that the memory 
upgrade worked.)


Testing memory involves three distinct aspects, each with several 
phases and their own requirements.  Testing for refresh problems, 
testing for path errors (shorted or opened paths, etc.) and actually 
testing the memory itself (usually in such a way that certain types 
of problems show up more easily.)

Most memory tests do little more than a few flavors of checkerboards 
etc.  The results are rarely useful beyond saying you have a 
problem.  And most of the checks wont even detect some sorts of 
problems.

And the way they work can often hide a refresh issue because the test 
itself will provide enough memory accesses to refresh the memory.  
(Just like in the old days of the CC1/2 where you'd POKE it to 
increase the speed.  Then you had to do your own memory refreshes.)


A good memory test is very hard to write.  Most get it wrong.  And 
will usually take advantage of the memory type / organization to 
better test it wihout having to spend hours doing a single pass.

Still, a decent test can detect most errors.  They just may not be 
able to say exactly what the cause is.









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