Re: Re: Generic VESA framebuffer driver and Video card BOOT?

Pavel Machek [off-list ref] wrote:

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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?

Debugging.

Ok ;-)

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        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?

This is running at system resume, so it is not normal boot. Some
ASUS Athlon 900MHz machine needed this; I'm no longer using this
one. 

Ok. For the BIOS emulator the code always has it's own local stack anyway 
so I assume the problme you had may have been that the BIOS on the board 
was using too much stack space, so setting up a local stack that is big 
enough is probably a good idea.

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        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.

Ok, this one is bad... ... In case of just one vga adapter, we
should be able to store its parameters in some well-known place.
For more than one adapter, we'll definitely need to run BIOS in
emulator. 

Yes. If you are running this in real mode you don't have any option but 
to use the BIOS emulator. If you are running in protected mode and using 
vm86() style service, the 0xC0000 memory is just memory and can be re-
written. For instance on Linux you can map 0xC0000 into your process 
address space as copy on write, which then allows you to re-write the 
BIOS image for a secondary controller and then restore it when you are 
done.

But you will also need to make sure you can hook the Int 0x1A interrupt 
to hide any other graphics cards on the bus as some BIOS'es are pretty 
stupid and will find the first card on the bus that matches their 
Vendor/Device ID's. So if you have two of the same card, it will find th 
wrong one ;-)

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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