Interest in DOC and YAFFS?

Charles Manning manningc2 at
Tue Sep 24 16:53:57 EDT 2002

> > > How this works with DOC I am unclear as I had noticed a while back that
> > > there was hardware assisted ECC. This might get in the way of YAFFS ECC
> but
> > > maybe this can be circumvented.
> >
> > As far as I can tell, the hardware ECC just makes the DOC faster.
> Umm. It may use some of the oob data area for its own ECC in a YAFFS
> incompatible way. I am not sure of my ground here, only that you need to
> check it out.
> > Also, I think that Microsys has released information about how to use
> > the hardware ECC.
> Ok.

Determining, then straightening out, OOB conflicts is essetially what DOC 
support boils down to.

As far as I am aware, the ECC does not actually impact on the NAND and works 
something like as follows.
* As you write bytes to the NAND buffer, an ECC is calculated on the side in 
the ASIC.
* You can then read ASIC registers to determine the ECC.

Essentially you can just ignore the ECC and see raw NAND chips, ie the ECC is 

Thus, the current YAFFS page programming would change from something like:

* Calculate ecc. + tags and format up OOB (spare)
* Write data + oob
* Program page


* Write data
* Read ECC from ASIC
* Format up and write oob.
* Program page

Essentially, the hw ecc saves the ecc calcs - that's all.

Christian Gan has implemented a hw ecc scheme which I think is like above in 
YAFFS, so I suspect DOC support might almost be done :-).

-- Charles

More information about the linux-mtd mailing list