Hi all,

I wonder if I've found another, interesting if frustrating, failure

I sorted out the previous s/w read problem by paring the re-
initialisation routine back to the barest necessities and so the
read delay now no longer impacts downstream processing

So I expectantly put the card and application s/w on test. You
may recall this is an 8GB Strontium SDHC and a dsPIC

There are about 60 files, 300MB in total, containg various
sets of data that are retrieved as and when needed

For the purposes of the test I chose two and accessed them
continuously and alternately about 1s apart

Sometime during the night, after probably 12 hours running,
something went wrong. Clk was just going and going when I
got up. "Oh", I thought. What should happen (and was for
several hours before I went to bed) is that the dsPIC holds a
Busy line up whilst reading and processing the file data. It
drops the Busy line, telling the 18F it's OK to try and access
another file. So, when I looked at the system without powering
down, Busy was high and Clk was running. For some reason
it apparently hadn't finished reading the file. It's only 58kB and
is normally read in a fraction of a second. It was probably in
the state I found it in for quite some time

On subsequent re-boots reading that particular file causes the
same incompletion problem. But it fails to complete anywhere
from 1s to 15 minutes, which is from 1 to 900 reads at ~1s
between reads. ie after a re-boot it could fail at any time.

With all the testing taken into consideration, that file has been
access maybe 40,000 times over a couple of weeks, the
majority of them on that one day it failed, perhaps 30,000. As
the FAT is copied into RAM I'm sure it's the file that's broken.
If it wasn't in RAM then the FAT would have been read twice
as often as the file

I checked the board but couldn't see any intermittent electrical
problem. An analyser grab of a failure didn't produce anything
useful, except to show what I already knew. Clk simply ran out
of data to get and didn't turn off as the byte count wasn't finished

What seems to have fixed the problem is re-formatting and re-
loading the card. It's now been running for a day without incident
and I'll leave it going to see if it fails again in the same way

If reading a file is going to cause it to slowly deteriorate then it
seems I'll have to put some sort of block refresh regime in,
otherwise the application is going to fail in months rather than
decades.

Has anyone had experience or some knowledge of what I've
seen and how it appears to have been corrected ?

TIA

Joe


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