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August 1st, 2014 07:00
Precision M6700 BIOS/UEFI reset (Clear NVRAM)
The other day I added a new entry to the UEFI on my M6700. There was nothing different than other entries on the device. When I rebooted the laptop got stuck at entering the one-time boot menu. It also gets stuck at trying to enter the BIOS. I'm not sure if removing the CMOS battery actually clears this out on modern machines. I've tried the following:
- Remove CMOS battery and hold the power button for 30-seconds to make sure all capacitors are discharged. No change.
- Tried booting diagnostics by holding END and PWR when plugging in. It gets stuck at entering the diagnostics menu.
Both hard drives are removed during all of this. Does the M6700 have a way to actually clear out the UEFI entries? Is this model known to be overly sensitive to UEFI changes? I'm hoping the solution isn't spending a few hundred dollars on a new motherboard every time this happens.
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ejn63
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August 1st, 2014 07:00
These settings are stored on the hard drive with a UEFI system (that's what the UEFI partition is for). To clear the volatile RAM, unplug, remove (main) battery and hold the power button for 30 sec.
aikidoka69
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August 1st, 2014 07:00
UEFI entries can be manually added and those are not stored on a hard drive. UEFI can also detect media that supports UEFI boot. As I stated, I manually added entries to the UEFI list. The utility I used was efibootmgr. This is what I hope can be cleared. I don't typically like to point at wikipedia but it does describe what I'm referring to.
http://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface
"The UEFI specification defines a "boot manager", a firmware policy engine that is in charge of loading the operating system loader and all necessary drivers. The boot configuration is controlled by a set of global NVRAM variables, including boot variables that indicate the paths to the loaders."
This is Non-Volatile RAM so pulling the battery and discharging capacitors should not be enough to clear it. I need to know how to clear it at boot and start fresh.
EDIT: Just added (Clear NVRAM) to subject.
ejn63
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August 1st, 2014 08:00
Removing the main battery when the system is unplugged and holding the power button for 30 sec will clear the NVRAM.
And UEFI does indeed store boot information in the /efi directory on the hard drive - under Windows, that's edited using bcdedit (presumably that's also what your linux boot manager accessed as well).
aikidoka69
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August 1st, 2014 08:00
Just tried the Diagnostic boot again and this time I got further. I am now back in the BIOS and can see my UEFI entries. This is without the hard drives in the laptop further showing that the entries are in the NVRAM. It is the loaders that reside on the hard drives. I'm deleting the last entry I added and hopefully it will reboot without issue. Ultimately I'm not sure which of the many things I tried that finally got me further.
aikidoka69
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August 1st, 2014 09:00
No, not everything was cleared. BIOS settings were cleared but the UEFI entries were not. There are two things at play with UEFI.
The entries were shown in the BIOS with the hard drives removed. This proved two things.
Microsoft documentation on bcdedit and other utilities also confirms what I am saying. It references the UEFI NVRAM. http://msdn.microsoft.com/en-us/library/windows/hardware/ff543428(v=vs.85).aspx
While I am back up and running I would still like to know if there is a procedure to clear the UEFI NVRAM on the M6700. Chances are there was some other issue causing the hang and not the UEFI entry itself. The newer version of efibootmgr I was using might have done it.