[flashrom] JIDA CMOS

Carl-Daniel Hailfinger c-d.hailfinger.devel.2006 at gmx.net
Thu Apr 8 04:20:07 CEST 2010


On 08.04.2010 01:11, Bill Flanders (wtflanders) wrote:
> I ran into the same problem when I automated flashing the BIOS followed
> by running nvramtool to set the CMOS values.
> The settings do not hold if you power down the system, however, they do
> hold when you reboot the system via the "reboot" command.

So unless I'm misunderstanding you, the BIOS performs some "magic" on a
warm reboot which causes the effect of nvramtool to become permanent.

I see two ways to achieve this:
1. Update/change/... some stuff in CMOS/NVRAM which marks the changes as
OK. This makes sense because the settings might be erroneous and you
generally only want to keep settings if the machine can still boot with
the new settings.
2. Copy/merge/transform NVRAM contents to flash.

If hypothesis 1 is correct, you'll see that NVRAM content change from
after the nvramtool write to after the warm reboot. This should be
easily verifiable by dumping NVRAM contents after writing the new
settings but before warm reboot and after warm reboot.

If hypothesis 2 is correct, dumping flash with flashrom after changing
NVRAM values with nvramtool and after the successive warm reboot should
get you two different flash dumps (they may differ anyway, but the
difference shouldn't only be in the "last boot time/date" field).

You'll probably see a mix of both methods. Once you know where to look,
it should be possible to write the desired configuration settings in a
way that allows you to set them reliably with flashrom and/or nvramtool.



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