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