grub: Vendor power-on keys
10 Using GRUB with vendor power-on keys
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Some laptop vendors provide an additional power-on button which boots
another OS. GRUB supports such buttons with the 'GRUB_TIMEOUT_BUTTON',
'GRUB_TIMEOUT_STYLE_BUTTON', 'GRUB_DEFAULT_BUTTON', and
'GRUB_BUTTON_CMOS_ADDRESS' variables in default/grub (⇒Simple
configuration). 'GRUB_TIMEOUT_BUTTON', 'GRUB_TIMEOUT_STYLE_BUTTON',
and 'GRUB_DEFAULT_BUTTON' are used instead of the corresponding
variables without the '_BUTTON' suffix when powered on using the special
button. 'GRUB_BUTTON_CMOS_ADDRESS' is vendor-specific and partially
model-specific. Values known to the GRUB team are:
<Dell XPS M1330M>
121:3
<Dell XPS M1530>
85:3
<Dell Latitude E4300>
85:3
<Asus EeePC 1005PE>
84:1 (unconfirmed)
<LENOVO ThinkPad T410s (2912W1C)>
101:3
To take full advantage of this function, install GRUB into the MBR
(⇒Installing GRUB using grub-install).
If you have a laptop which has a similar feature and not in the above
list could you figure your address and contribute? To discover the
address do the following:
* boot normally
* sudo modprobe nvram
sudo cat /dev/nvram | xxd > normal_button.txt
* boot using vendor button
* sudo modprobe nvram
sudo cat /dev/nvram | xxd > normal_vendor.txt
Then compare these text files and find where a bit was toggled. E.g.
in case of Dell XPS it was:
byte 0x47: 20 --> 28
It's a bit number 3 as seen from following table:
0 01
1 02
2 04
3 08
4 10
5 20
6 40
7 80
0x47 is decimal 71. Linux nvram implementation cuts first 14 bytes
of CMOS. So the real byte address in CMOS is 71+14=85 So complete
address is 85:3
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