[Yaffs] Is YAFFS2 support required in boot loader?

[Charles Manning]

On Tuesday 18 October 2005 02:19, Rakhi Rathi wrote:
> Hi all!
>
> I am having four partiton on NAND flash: boot, environment variable, kernel
> image and root FS ( YAFFS2) and boot loader needs to download kernel image
> and root FS using TFTP / FTP. How kernel image and root FS can be converted
> into YAFFS format and downloaded? What support I need to provide in boot
> loader?


There are really two parts to your question, I think:

1) Is there something like myyaffsimage for YAFFS2?

2) Is there a bootloader for YAFFS2 (ie. some code like yboot that will read a 
boot image from a YAFFS2 partition).

The answer to both of these is currently No, but I can give some guidance on 
these:

1) mkyaffsimage for yaffs1 was pretty straight formward (I wrote it in one 
night), and various patches have been added. It still needs some tinkering 
however. The main reason for this is that mkyaffsimage dumps a binary of the 
file system data + OOB areas. Since this includes ECC etc, this is a bit of a 
problem since mkyaffsimage does not know what ECC strategy you will really be 
using. Thus, if you use mkyaffsimage you really need to fiddle a bit to make 
sure the ECC bytes being put into the image file match what your hardware 
will use.

The above problem is made worse for YAFFS2 because the page size is variable 
and the AUTOPLACE makes the OOB stuff even more variable. Thus, perhaps the 
best that can be offered is something along the lines of mkyaffsimage for 
yaffs1 with even more disclaimers (ie. even more stuff that the system 
integrator must configure. An alternative is to store the image in the 
data+tags form and the mkyaffs or similar process then does the actual OOB 
placement.

There is an alternative process that can be used in the interim to make an 
image by using a target device:
a) Erase the flash on the target.
b) Mount it.
c) Use nfs or whatever to copy the required files onto the fs.
d) Unmount.
e) Use nanddump to suck an image off the nand.
f) Remove all bad blocks and empty blocks from the image.

This should leave an image file that can be sent to a manufacturing house etc 
to load NAND parts for a shipping device.


2)  There is currently no yboot equivalent for YAFFS2 in CVS. However, 
achieving this is not particularly hard (though it is a bit more complex than 
yaffs1).  I see Nick Bane has done something at 
http://husaberg.toby-churchill.com/balloon/releases/development/bootldr/bootldr35/

which might help.

-- Charles