[LinuxBIOS] Question about protect mode?

[Feng, Libo]

I am also confused a little. The propriety BIOS runs in the real mode, how does it test the memory beyond 1MB?

Another question is BIOS ROM can attach to XBUS, LPC, someone told me, even PCI, how dose the address forward to the location?


Best Regards

??? Feng Libo @ AMD  Ext: 20906
Mobile Phone: 13683249071
Office Phone: 0086-010-62801406

-----Original Message-----
From: linuxbios-bounces at linuxbios.org [mailto:linuxbios-bounces at linuxbios.org] On Behalf Of Juergen Beisert
Sent: Wednesday, May 30, 2007 6:09 PM
To: linuxbios at linuxbios.org
Cc: Fu xiayin
Subject: Re: [LinuxBIOS] Question about protect mode?

On Tuesday 29 May 2007 04:50, Fu xiayin wrote:
>  Hello,everyone.
> I'm a student, and now my  task is studying Linuxbios.
>
> I'm not very clear about the difference between the protect mode and 
> the real mode.

Real mode: 16 bit offsets, address space limited to 20 bit.
Protected mode (or "Linear Flat Mode", see below): 32 bit offsets, address space 32 bit

> So I wonder why should Linuxbios turn into protect mode at the very 
> beginning.

Try to access your ROM at physical address 0xFFFF0000 in real mode and you will "feel" the reason. ;-)

> And is there any difference between protect mode in  Linuxbios and in 
> linux kernel.
> If any, what's the main difference?

The mode used in LinuxBIOS is more a 32 bit real mode (called "Linear Flat
Mode") than a protected mode, because there is no protection at all. Also there is no paging and no address translation activated. Every segment starts at physical offset 0x00000000 and has a limit of 4GiB (this means: "no limit").

Juergen

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