NAND Flash

Hello there.

As you remember earlier I have sent a small patch for the NAND portion of u-boot.

This forced me to really take a hard look at the code and really evaluate it.

The big problem with the code as it is its its tendancy not to account properly for errors which are not only probable but certain during the life of the device.

For example the current code cannot boot reliably from NAND and the read and write routines are also unreliable.

It's basic assumption made that you can read/write from the NAND at any position is false. This is impossible because of the bad blocks that may force you to skip a bad sector.

I'm currently in the process of rewritting to actually make it work reliably.

I can keep backwards compatibility with the old code but you can only use it at your own risk.

I'm asking for any people currently working with NAND to comment on the following points:

1. Do you read and write the NAND at arbitrary offsets? That means not in page boundaries.

2. Do you use the NAND boot command? It can be replaced by a copy and bootm sequence.

3. Do you use it as a raw device without employing ECC? Do you understand the implications?

4. What kind of filesystem do you use? JFFS2 & YAFS have different OOB placement of ECC and status bits?

5. What kind of bad block management options would you like? I'm thinking of implementing a bad block detection mechanism which would erase and test the whole chip for any bad blocks.
Another command could also utilise ECC to detect borderline working pages and relocate them to avoid a permanent failure.

Awaiting your input...

Regards

Pantelis

Dear Pantelis,

...

The last message about this topis is more than 6 weeks old. Was there any agreement how to proceed?

Best regards,

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
When properly administered, vacations do not  diminish  productivity:
for every week you're away and get nothing done, there's another when
your boss is away and you get twice as much done.  -- Daniel B. Luten

Hi Wolfgang.

Discussing with the MTD people they appear to be OK with this, and only have some minor things they needed to be addressed.

Unfortunately the patch I last sent is kinda of bit-rotted and have actually re-worked to properly work (and compile for other boards :).

Will post updated patch based on latest cvs tree within the day.

Regards

Pantelis