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Re: GRUB 0.97 stage2/asm.S/prot_to_real undoes Big Real/Flat/Unreal Mode

From: Roger Pao
Subject: Re: GRUB 0.97 stage2/asm.S/prot_to_real undoes Big Real/Flat/Unreal Mode?
Date: Wed, 23 May 2012 11:10:37 -0700

On Wed, May 9, 2012 at 4:01 PM, Jordan Uggla <address@hidden> wrote:
> On Tue, May 8, 2012 at 3:05 PM, Roger C. Pao (Enmotus)
> <address@hidden> wrote:
>> I'm writing an INT 13h Option ROM for an AHCI-like PCIe adapter.  I've
>> noticed that after prot_to_real is called, My INT 13h no longer has
>> access to addresses like es=0:edi=00067BB4.
> Grub 0.97 hasn't had an upstream for over 6 years. If you can
> reproduce this problem with grub2, (meaning grub 1.99 or ideally grub
> 2.0 beta5) then you can try asking about it at address@hidden
> --
> Jordan Uggla (Jordan_U on

As a follow up, I have resolved the problem as follows:

Inside my INT 13h handler, I re-enabled Big Real / Unreal Mode to gain
access to the entire 4 GB range including the AHCI BAR.  I have now
successfully booted GRUB 0.97 and Fedora 14.  GRUB 1.99 and Fedora 16
will be next after I figure out some issues with PMM allocation of
permanent memory.

It seems ASUS P8Z68-V LE BIOS prior to v3702 will allocate permanent
PMM memory per PCI Firmware Specification v3.0; however, BIOS v3702
fails.  So I'm back to allocating from EBDA again.  But this is not a
GRUB issue.

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