Hi Igor

I don't have any information about error recovery of MMC cards.

I think floppy discs have the same problem; if the user doesnot wait for
write completion, the disc may become corrupted. =20

Perhaps one way to deal with this might be to use the fact that MMC cards
have 2 or more FATs.  MMC cards also have entire 512 byte sectors written
at once. Here is a possible idea...

1. Before you write out a sector of data, first update FAT #2.

2. After writing a sector of data successfully, update FAT #1.

3. In your PC software, compare FAT #1&2. If they are the same, the write
was successful. If they are different, then the data is good up to but not
including the last sector.

I think when MSDOS (Windows, etc.) reads the card, it will read from FAT #1
(I'm guessing here). If the write to the data sector was interrupted (card
pulled out, etc.) the FAT #1 will still show good data up to the corrupted
sector.  (Unless the card was pulled out while writing to the FAT)

I don't think there is *anything* you can do about losing data to a sector
if the user yanks the card out before it's done writing. The only way to
handle this would be to write your own complete card access routines.  Or
have a mechanical lockout to prevent removal of the card if the write is in
progress....???

Good luck!
Tom

At 01:38 AM 6/27/2004 +0200, you wrote:
>Hi friends,=20
>
>I develop a datalogger with a MMC card for our special purpose. There is
>implemented FAT syst=E9m (not fully, but most of it). I am not able to
>solve one problem. When writing operation to root directory is broken
>before finishing and it can hap anytime pulling a card out,  I am not
>able to find a way how to repair the defected sector. Rewriting such
>sector from a PIC ends with endless loop of busy signal. I am not able
>to format the card in a PDA because Windows CE doesn't accept by this
>way damaged card. =20
>I wasn't able to find any appnotes discussed error recovery of MMC cards
>as well as a detailed instructions how to erase a sector or block of
>sectors.=20
>Use SPI mode for communication to MMC/SD card.=20
>I appreciate any help.=20
>
>Thanks=20
>
>Igor=20

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