[Yaffs-archive] Re: yaffs and ecc

[Nick Bane]

>
> A follow on from my previous comments on this....
>
> > * Unlike NOR, you can attempt to write 1's on top of  0's without the
> > operation failing. The result is the logical AND of the two. ie.
> > programming 0xFE on top of 0x07 should yiled 0x06. Well that's my
current
> > belief anyway (and how I have implemented the writes in the nandemul
> > layer). I will investigate further to check.
> >
>
> Ehem... bitwise AND.
>
> I checked the dox for the Samsumng and Toshiba NAND parts and it looks
like
> this is correct and the NAND parts do not mark these as failures. Indeed
the
> Toshiba docs say that you should not reprogram the same values over
already
> programmed stuff. Instead you should be writing 0xffs. ie. The preferred
way
> to change the sequence 0x01, 0x02, 0xff, 0x04, 0x05 to 0x01, 0x02, 0x03,
> 0x04, 0x05 is to program over 0xff, 0xff, 0x03, 0xff, 0xff. I expect this
all
> ties in with the maximum number of times you can overwrite a page before
an
> erasure.
>
Sounds sane.

> There are however some checks in the nand.c that will fail the write.
These
> checks are enabled by CONFIG_MTD_NAND_VERIFY_WRITE.
> Do you have this enabled?
>
I commented this out for the test that resulted in persistence being
established but zero file length.
I am running a mix of jffs2 and yaffs. As already reported, I found it a
problem to remove all ecc checking as the jffs2 partition did not
mount.Oddly the os didn't report ecc failures though.

> Since YAFFS does its own verification, CONFIG_MTD_NAND_VERIFY_WRITE is not
> required. Maybe this could also become a partition dependent feature?
>
Absolutely.

>
> -- CHarles
>
>
>
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