[coreboot] re-enabling boot for ChromeOS

[Matthias Apitz]

Hello,

I've switched my Acer C720 years ago to legacy boot mode (SeaBIOS) to be
able to install another OS (FreeBSD). This required, after removing the
write protection screw, the following commands:

Disable the software write protection.

# flashrom --wp-disable

Run set_gbb_flags.sh with no parameters.

# set_gbb_flags.sh
GBB_FLAG_DEV_SCREEN_SHORT_DELAY 0x00000001
GBB_FLAG_FORCE_DEV_SWITCH_ON 0x00000008
GBB_FLAG_FORCE_DEV_BOOT_LEGACY 0x00000080
GBB_FLAG_DEFAULT_DEV_BOOT_LEGACY 0x00000400

Now set SeaBIOS as default.

# set_gbb_flags.sh 0x489

Enable back the software write protection.

# flashrom --wp-enable

This work fine and FreeBSD which I installed on a replaced SSD runs
fine on the hardware. The original SSD still contains the ChromeOS.

Now I want to switch back to boot a few times ChromeOS from this SSD to see
something in the boot messages of this and compare it with the sources.
I doubt that the replace SSD will boot due to the changed gbb_flags and
of course FreeBSD has no support for this tool. How I could change them
back, for example, booting some Ubuntu version? Or is there any other
standalone bootable tool to do so?

Thanks
Matthias
-- 
Matthias Apitz, ✉ guru at unixarea.de, ⌂ http://www.unixarea.de/  ☎ +49-176-38902045
"Wer übersieht, dass wir uns den anderen weggenommen haben und sie uns wiederhaben wollen,
kann von den Kämpfen der letzten Tage keinen verstehen. Und kann natürlich auch keinen
dieser Kämpfe bestehen." Hermann Kant in jW 1.10.1989