Back up of the "Factory Bad Block Table" BBT, needed or a waste of time?

[Harald Welte]

On Sat, Jul 28, 2007 at 02:46:24PM +0200, Visti Andresen wrote:
> I'm probably going to receive my Neo next Monday (the joy).

good luck.

> The gpsd should be backed up by the procedure in:
> http://wiki.openmoko.org/wiki/Getting_Started_with_your_Neo1973#Initial_backup

this is not present on phase-1 handsets and only accidentially ended up
on the GTA01Bv4 that were sent to phase-0 developers before.  I've
updated the wiki accordingly.

> and inside the bad block table (BBT), I guess that the BBT isn't located 
> inside the 4. partition and therefor not backed up?
> http://wiki.openmoko.org/wiki/NAND_bad_blocks#Bad_Block_Table_.28BBT.29

well, technically it is in the rootfs partition... but in blocks that
are marked as bad blocks ;) so depending on the method of your backup,
you will either have it or not.

> QUESTIONS:
> ==========
> Is it necessary to back up the BBT alt all?

Depends on what you want to do.  It makes sense.  In fact, I have asked
our production software team multiple times to store the bad-block
information at the factory for each device, so we can theoretically
restore that information for any given device.  I don't know the status
of it, though.

> Can the "factory BBT" be recreated using JTAG?

not if you erase all inline and OOB data by something like 'nand scrub'
of u-boot.  This will erase everything!

> or has the factory used a special kind of "magic" when
> establishing the BBT?

no.  it just scans the nand flash for factory bad block markers (see
nand data sheet) and creates its own table (for faster access and as a
backup copy).

-- 
- Harald Welte <laforge at openmoko.org>          	        http://openmoko.org/
============================================================================
Software for the world's first truly open Free Software mobile phone