Flashing NAND from NAND

[Matthias Huber]

Werner Almesberger schrieb:
> Matthias Huber wrote:
>   
>> Werner Almesberger schrieb:
>>     
>>> # echo -en '\x17' | dd bs=1024 count=1 conv=sync >/dev/mtd4
>>>       
> [...]
>   
>>> Can you tell why it worked ?
>>>       
>
> In the 0x17 case, we're trying to go from 0x0f to 0x17. That's
> one bit set and one bit cleared. Clearing the 0x08 bit can be
> done, and happend when trying to write the 0x17. However, the
> 0x10 bit can't be set (without invoking an erase cycle).
>
> However, since NAND has an ECC, it can still correct a one-bit
> error. As it happens, the ECC pattern that gets written, just
> flips the 0x10 bit, so the byte in NAND is 0x07, but it gets
> corrected to 0x17 - which just happens to be the value we want.
>
>   
>> i can't. it is possible that i flashed my boot with dfu-util and the
>> rootfs directly.
>>     
>
> Yes, DFU follows all the NAND erasing rituals properly. The rootfs
> is very tricky, because there you also have JFFS2 that tries to
> hide problems from you.
>
> For your backup system, you should at least add flash_eraseall
> to the restore procedure. To make things work also for systems
> that have bad NAND blocks, you would have to use nanddump and
> nandwrite. (And you still have to erase explicitly - nandwrite
> won't do it for you.)
>
> - Werner
>   
Thank you for this information about this nand* progs.

I think, this should go into the wiki, if it isn't already.

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