[ECOS] JFFS2 for NAND flash file system

[ECOS] JFFS2 for NAND flash file system

[Paul MAILLET]

Hi,

I am currently working on adding JFFS2 component to my eCos
configuration but I am still not sure if the dev on this module is
complete.
As I can read in some TODOs or readme found in the JFFS2 package from
the repository of my devkit, NAND support is not yet implemented in
the module.
Does this functionality has been completed today, or is it still on progress?
However, if it's not implemented yet, what solution can I use to add a
NAND Flash file system?


Best regards,
Paul

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Re: [ECOS] JFFS2 for NAND flash file system

[Ross Younger]

On 16/05/11 13:05, Paul MAILLET wrote:
> Does this functionality has been completed today, or is it still on progress?
> However, if it's not implemented yet, what solution can I use to add a
> NAND Flash file system?

There's a YAFFS port for eCos, which is targetted specifically for NAND 
parts.

At the moment, NAND support is not in the eCos trunk, so to get it 
working you'd have to start with the public trunk, then pull from the 
nand-ecoscentric repository on http://hg-pub.ecoscentric.com/. YAFFS has 
its own license so is in a separate repository named 
yaffs-ecoscentric-gpl. You haven't said which board you're using, so 
it's likely that you will also need to add NAND support to the board HAL 
(and possibly a chip driver for whatever is on that board).


Ross

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Re: [ECOS] JFFS2 for NAND flash file system

[Stanislav Meduna]

On 01.06.2011 11:23, Paul MAILLET wrote:

> For me it is clear that the FS has nothing to do with all the NAND
> drawbacks, it's the job of the NAND support layer, isn't it?

If I understand it correctly, unfotunately that's not the case -
the NAND layer does not implement an abstraction of linear
error-free blocks, rotated and refreshed according to the
hardware needs. The filesystem still needs to know what
it is allowed to do - see e.g.
http://www.kernel.org/doc/htmldocs/mtdnand.html

  Filesystems must be aware of the NAND pecularities
  and restrictions. One major restrictions of NAND Flash
  is, that you cannot write as often as you want to a page.
  The consecutive writes to a page, before erasing it again,
  are restricted to 1-3 writes, depending on
  the manufacturers specifications. This applies similar
  to the spare area.

My question is: would it be possible/desirable to implement
an abstraction layer similar to e.g. a controller in
a SD-Card or a SSD flash drive? Then it would be possible
to use just about any fs, including FAT and similar beasts.

Regards
-- 
                                  Stano

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Re: [ECOS] JFFS2 for NAND flash file system

[Stanislav Meduna]

On 31.05.2011 17:42, Ross Younger wrote:

> Running a non-NAND-aware filesystem on NAND is a very bad idea.

Is there any NAND-aware filesystem with eCos-compatible license?
I only know of jffs2 - yaffs2 is GPL or (a lot of) $$$ and ubifs
is also GPL.

Actually I am seeing this situation as a major drawback to eCos -
nowadays just about any device uses NAND for larger storage...

> Even reading a NAND page can, once in a while, cause a bit in-flash to
> flip (the "read disturb" effect). If your filesystem doesn't periodically
> refresh its contents, files and/or filesystem metadata which is frequently
> read but never changed will gradually rot.

Hmm, does jffs2 handle this? I don't remember seeing something like this
in the code, but maybe I did not look at recent enough one.

> Now, the public JFFS2 tree has had support for NAND flash since 2003.
> It looks like the version in eCos dates from around that time, though
> has its NAND support disabled; there's an argument to be made that this
> perhaps ought to be put right some time.

AFAIK when this was discussed there was some architectural problem -
Linux's jffs2 uses mtd layer and that code is GPL, so it needs
to be written from scratch:
http://www.cygwin.com/ml/ecos-discuss/2008-07/msg00055.html

-- 
                                           Stano

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