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SubjectRe: [Linux-fbdev-devel] Re: Generic VESA framebuffer driver and Video card BOOT?
Pavel Machek <pavel@ucw.cz> wrote:

> BTW, does this look like right way to POST VGA BIOS from real
> mode? It is what we currently use... and it works on some
> machines...
>
> movw $0xb800, %ax
> movw %ax,%fs
> movw $0x0e00 + 'L', %fs:(0x10)

What is this for?

> cli
> cld
>
> # setup data segment
> movw %cs, %ax
> movw %ax, %ds # Make ds:0 point to wakeup_start
> movw %ax, %ss
> mov $(wakeup_stack - wakeup_code), %sp # Private stack is needed for ASUS board
> movw $0x0e00 + 'S', %fs:(0x12)

We have never needed to set up a private stack. What ASUS board was it
that you had problems with and needed to do this for?

> pushl $0 # Kill any dangerous flags
> popfl
>
> movl real_magic - wakeup_code, %eax
> cmpl $0x12345678, %eax
> jne bogus_real_magic
>
> testl $1, video_flags - wakeup_code
> jz 1f
> lcall $0xc000,$3

The call to 0xC000:0x0003 is the entry point to POST the card. However
for PCI cards you need to make sure that AX is loaded with the bus, slot
and function for the card that is being POST'ed. It will pass this value
to the PCI BIOS Int 0x1A functions in order to find itself, so if this is
not set many BIOS'es will not work.

The rest of the code you have above seems superfluous to me as we have
never needed to do that. Then again we boot the card using the BIOS
emulator, which is different because it runs within a protected machine
state.

Have you taken a look at the X.org code? They have code in there to POST
the video card also (either using vm86() or the BIOS emulator).

Regards,

---
Kendall Bennett
Chief Executive Officer
SciTech Software, Inc.
Phone: (530) 894 8400
http://www.scitechsoft.com
~ SciTech SNAP - The future of device driver technology! ~


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