It depends on what you're protecting
sizeof (yaffs_PackedTags2) is a full set of tags + ecc on the tags themselves.
if your ecc system is going to cover the spare area too, then youonly need to
store sizeof(yaffs_PackedTags2TagsPart).
You will also need a bad block marker. Say 2 bytes.
-- Charles
On Thursday 12 November 2009 05:28:45 Henri Cloetens wrote:
> Hi,
>
> I am looking at ways to do ECC for MLC nand flash.
> I have a question in this regards on the Yaffs file system:
>
> When used together with a NAND flash with 2kbyte sectors, how many spare
> bytes are needed for the Yaffs headers ?. (#bytes / 2kbyte sector).
>
> I need this number, so I can figure out how many bytes can be used by the
> ECC. I want to design my ECC to use up all spares not needed by Yaffs.
>
> Best Regards,
>
>
> Henri Cloetens.
>
>
> Charles Manning wrote:
> Fixed something...
>
> On Wednesday 11 November 2009 12:59:07 Charles Manning wrote:
>
> Hi Ross
>
> Thanks for that patch.
>
> I had a look and have come up with an alternative solution to the problem:
> instead of trying to unwind a half created object if the string or tnode
> malloc fail it is a lot cleaner to reverse the order of allocation. ie
> forst create the tnode or string, then create the object if that succeeds.
>
> I also had a sniff around and found a few other areas where tnode creation
> failures would cause issues.
>
> The fixed stuff has been running in a stress test for almost 24 hours and
> I've just checked that in.
> http://www.aleph1.co.uk/cgi-bin/viewcvs.cgi/yaffs2/yaffs_guts.c?r1=1.93&r2=
> 1.94
>
> Look at:
>
> http://www.aleph1.co.uk/cgi-bin/viewcvs.cgi/yaffs2/yaffs_guts.c?r1=1.95&r2=
>1.93
>
> I also put a day or so into extending low mem testing and will expand the
> tests more.
>
> Thanks
>
> -- Charles
>
> On Friday 30 October 2009 06:35:32 Ross Younger wrote:
>
> Whilst doing some stress testing on a board with limited RAM, I tripped
> over an assertion failure.
>
> In yaffs_CreateNewObject, YAFFS would sometimes successfully
> AllocateEmptyObject but not be able to allocate a new tnode, so GetTnode
> returned 0. It would then immediately attempt to FreeObject, but the
> freshly allocated object already has a parent so it hits the YBUG trap at
> line 1992 of yaffs_guts.c.
>
> I attach a patch which fixes this assertion (and a similar case I spotted
> in yaffs_MknodObject) by calling DoGenericObjectDeletion instead of
> FreeObject, though it might instead be reasonable for AllocateEmptyObject
> to not try to add the object to the rootDir or lostNFoundDir.
>
>
> Ross
>
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