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CF Cards, status register, consequences of CORR bit?

Hi Group

The CompactFlash specification (section 6.1.5.9 in the CF2 specs) denotes the CORR bit in the status register. Acording to the specs, the bit is set "when a Correctable data error has been encountered and the data has been corrected."

A subsequent write to a sector showing this behaviour make the bit go off (seem to correct the "problem").

So far so good, but every now and then I encounter this condition in the field with a smal percentage of installations. This rises the following questions:

- Does this indicate a wear out of the card or is it just something that might happen but otherwise can be ignored?

- What worries me is that if I place a card that showes this bit set with a given sector in a PC CF card reader, the PC seem to look at such sectors as bad and the read operation results in a read error. However, as the specs state, if I read this sector with my embedded system, the sector data is just fine.

- Does the fact that a subsequent write fixes the problem mean that the flash memory area afected was hot swaped by the device?

- I use a FAT filesystem on the card, should I therefore copy the data from the affected cluster to a new one and mark it bad (provied it's a serious issue and the card does not swap it internally)?

- Does the ocurance of this mean a soon to be expected complete failure of the card? That would be odd in that I also experienced this with cards being virtually new...

TIA

Markus

Reply to
Markus Zingg
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Ok group

It seems to be my destiny that whenever I ask a question here I end up answering it by myself....

I contacted the supply channel of the CF's we use and got the reply from their engineers which I embedd within my original text.

--> It's not a WearOut, It just encounter an "ECC correctable error". Some NAND Flash block may happen this kind of error. It's not a bad block, just some bits defective (or charge lose). Controller have to correct it with ECC than reply host the corrected data.

--> The returned data is no problem (correctable). Could you please get more Info about "a given sector in a PC CF card reader"? Is this means "specific LBA"? with a specific CF_Reader?

(to answer this - yes and yes)

--> Yes, we swap blocks for "write operation".....IT's a kind of "WearLeveling". Basically, NAND blocks with "ECC correctable error" are not "bad blocks". They are not perfect but usable. We swap it for "WearLeveling" consideration, not for "ECC correctable error". That "ECC_Correctable" block may allocated to user disk area next time.....

--> NO NEED. don't worry the data integrity. It's not a "wear out" condition, just the characteristic of NAND blocks.

--> No. It's related to NAND block property, not NAND life time. We may say it's some kind of "Initial imperfect" of NAND block......Not perfect but usable.

Actually the answers reflect what I thought by myself already. I just wanted to be sure. I hope this may help others if they stumble about the same thing in the future.

Markus

Reply to
Markus Zingg

Markus,

That happens to me to about half the time... but it's still worth asking. Thanks for posting your findings.

By the way, the world's most complex interface for moving bytes from one place to another place has just got more complex; the CompactFlash 3.0 specification has just been made available for download from

formatting link
It adds Ultra DMA and new PIO modes 5 and 6 to the TrueIDE mode and 80ns cycle times to the memory mode and 'advanced PCMCIA IO' modes (the mode formely known as IO mode).

Tim

Reply to
Tim Clacy

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