digital camera Q

[Gene Heskett]

On Wednesday 25 October 2006 02:02, Tim wrote:
>On Tue, 2006-10-24 at 11:36 -0400, Gene Heskett wrote:
>> That depends.  In my case, swapping memory cards can be dangerous
>> because the credit card thick memory used has open contacts, subject to
>> static damage, I blew the original card that way I believe.
>
>I would have thought they'd design these things to handle users taking
>no anti-static precautions, because that's what most people are going to
>do (rip it out and treat it like just a piece of plastic).
>
>What's clearly obvious to me is that the compact flash cards have
>fragile pins that can bend or break off, and the socket they plug into
>can wear out too.  So I was never keen on taking the card in and out of
>my older digital camera.
>
>My newer one uses MMC/SD cards.  The cards look more robust, but I still
>wonder about how well designed the socket is, with those tongues
>sticking out.
>
>> One thing I did find is an old vfat bug thats never been fixed.  If
>> there are 40 or so pix in the camera, you cannot move them to the
>> computer without losing the last ones as vfat thinks, when the
>> directory sector contains no files, that it has reached the end of the
>> file list.  Not so. So when moving files to the computer, always start
>> at the bottom of the list and work backwards else that bug will grow
>> some awesome teeth and draw blood, requiring the card be formatted to
>> recover.
>
>Why would *reading* some files from the card cause a corruption?
>
Not reading, but moving, which implies deletion of the moved file.  And 
when you have a whole 512 byte sector with no valid files in a vfat 
directory, thats considered to be the end of the directory, so if you 
start such an operation at the begining of the directory, those files 
beyond that empty sector can become inaccessable.  I *think* one coud take 
another pix, which would result in the first available slot in the 
directory being re-used, and that might restore the ability to access the 
other 75 pix on the card, but I haven't tried that due to not having 
thought out the reasoning the first and only time it ever happened to me.  
Fortunately, the lost pix weren't all that precious although I certainly 
was pi$$ed at the time.

So the lesson is to scroll to the bottom of the cameras directory (I use mc 
for this) and start moving the pix to the computer from the bottom of the 
list, which works perfectly now for about 4 years even if there's 80 pix 
on the card.  That way you never self-generate a huge gap in the listing 
that triggers this bug.

It seems to me that this could be fixed if M$ wanted to. I, OTOH, have NDI 
if the msdos and vfat file systems even have a data field to indicate the 
true length of the directory on the disk.  If they don't have this data 
field, I'd be tempted to pay a visit, with a fresh hickory pick handle in 
hand, to the coders responsible for that particular piece of the spec.  
Dumb...

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
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Copyright 2006 by Maurice Eugene Heskett, all rights reserved.