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Re: EFI to grub to DOS?

From: Jake Thomas
Subject: Re: EFI to grub to DOS?
Date: Mon, 23 Jul 2012 20:33:26 -0700

I'd just Google for Linux memory testers and see if any do what you want.

Also, what motherboard do you have?

There's a Dell-specific tool for Linux called syscfg that lets you change Dell BIOS settings from within Linux. And I've heard of an ASUS tool that let's you change ASUS BIOS settings from Windows. There could be a tool to do the switch for your board.

If you know what you're doing, you could use dd to save the  snippet from /dev/mem that is where the system firmware settings are. Save a copy while the setting is "BIOS" and save a copy while the setting is "EFI". Then compare the two. Then you'd know exactly what to write to /dev/mem to do the switch.

Of course, if you mess something up, you might not be able to boot back up until you externally re-flash the chip. But that's worst case scinerio. Many BIOSes nowadays (guessing all) are cut up into sections to protect against this. The idea is that much of the BIOS can be corrupted or missing, but you'll still have just enough functionality to boot into something that can flash the BIOS. Also, if you corrupt only where the firmware saves settings, but not the firmware itself, a simple clear via the password jumper on the motherboard will fix that by putting everything back to default. And no matter how bad you screw up the firmware of an ASUS board that does USB Flashback or whatever it's called, you can flash on a functional firmware simply by holding the power button while a thumb drive is inserted. So if you have one of those, screw around all you want.

I wouldn't be super comfortable doing the above unless I had one of those ASUS boards. If I had one of those ASUS boards I'd be playing with it.

Also, if you have one of those motherboards where the BIOS chip is in a socket rather than soldered on, and you have two motherboards that will take that chip in a socket, then a hotswap flash would be a synch. I'd be playing around with it in that scenario as well.


Sent from my iPhone

On Jul 23, 2012, at 7:41 PM, Greg Grotsky <address@hidden> wrote:

On Mon, Jul 23, 2012 at 11:37 AM, Jake Thomas <address@hidden> wrote:
Ok. A few things:

1. What are you trying to do with the DOS utility? There might be a Linux tool that does the same thing, and Linux can be booted from EFI.

I'm trying to run a memory exerciser that stresses all the DRAM in the system. Something similar to memtest86+ only more rigorous.

2. What would happen if you just left it in BIOS mode all the time?

I'm also trying to run a memory exerciser in that's designed to run from EFI. I want to run one, then the other, automatically. I have one thumb drive that will boot to both DOS and EFI depending on how the BIOS is configured.

3. You might be able to switch the firmware mode from within the operating system, such as by writing to /dev/mem.  If it's possible to do the switch from within an OS, that can be automated.

I thought about this and seems very possible given the thumb drive that I talk about above but I think I'd need some knowledge of the system/BIOS layout in order to hit the correct location which would change the switch.

4. What hardware do you need DOS to access? If you ran DOS in Xen, would PCI passthrough be sufficient?

Mainly direct access to the memory.

I don't think it's gonna happen, no big deal. I think we're just going to have to drop the DOS requirement and build some software to do the DOS-style-memory-testing from Linux. It seems that would make everyone's life easier (I know I dig linux). Thanks for all your help with this Jake.


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