Multiple writes to NAND OOB...

Multiple writes to NAND OOB...

[Siddharth Choudhuri]

Hi,

I have the following question regarding multiple writes to OOB data:

Is it possible to write to the OOB data of the same page multiple times ?
If so, does it mean that the bytes being written are to different
locations(offsets) of the OOB because a byte cannot be rewritten in NAND
unless its block is erased ?

thanks,
-siddharth

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     Unix is user friendly - its just picky about its friends.
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Re: Multiple writes to NAND OOB...

[Charles Manning]

On Thursday 21 September 2006 04:30, Siddharth Choudhuri wrote:
> Hi,
>
> I have the following question regarding multiple writes to OOB data:
>
> Is it possible to write to the OOB data of the same page multiple times ?
Yes it is **possible**, but be be careful. If you do too many writes without 
an erase you can cause corruptions due to "write disturb".

> If so, does it mean that the bytes being written are to different
> locations(offsets) of the OOB because a byte cannot be rewritten in NAND
> unless its block is erased ?

If you write to NAND, then what you get is the ANDing of the pattern you write 
against what was already there.

If a byte had 0011-0101 and you program 1101-0011 nto it you'll end up with 
0001-0001.

Thus, if you want to program a new pattern into some bytes, you use 0xff for 
any bytes you don't want to change.

You need to do an erase to change bits back to 1.

Note a subtle difference. Most NOR writes will fail if you write a pattern 
that tries to set a bit from 0 to a 1.  On NAND, the bit will not change, but 
it is not an error to try to do this.

-- CHarles