Re: Extended 80 column card issue

[Linards Ticmanis <ticmanis@gmx.de>]

On 05/23/2011 10:39 PM, Michael J. Mahon wrote:

> But any high address line could be bad and the text and hi-res
> screens would never know about it...

Sure, but a bad buffer chip on the card wouldn't cause such a problem,
right? After all only data is buffered on the card, not addresses, if I
understand the schematic correctly.

Of course there might be a problem with the mainboard as well, but the
OP should be able to rule that out by using a different card in this
board, or this card in a different board.

> Unfortunately, only a real memory test will provide any assurance
> that the memory is functional.  All "use" tests like those above
> are insensitive to a large fraction of problems.  (Though Murphy's
> law pretty much guarantees that if you're actually trying to run an
> important app, a flaky memory chip will stop it in its tracks.  ;-)

That is true if the problem is just one or a few bits, but breakage of
larger memory areas should usually be detectable with "use" tests,
shouldn't it? And if the card isn't even detected as being present by
some software, as reported by the OP... I'd assume that either some key
address (say, 0, $400, $1234, $ffff or one divisible by $1000) happens
to be the one that is bad, or it's a larger area; at least if I were
writing code to merely *detect* the card (rather than to *test* it), I'd
probably test such an address or a few of them, and not $73be or some
other "random" value. Since the chance that some one-bit error happens
to be in such a "nice" location isn't high, I'd assume that it's likely
that a whole block of addresses has failed, which "use" tests SHOULD detect.

Feel free to disagree, though. Maybe my thinking is not correct.

-- 
Linards Ticmanis