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VESA VBE always failed
Posted: Mon Oct 10, 2011 1:27 am
by 0x3D5
I am trying to use the int 0x10(VIDEO BIOS) but it always returns al != 0x4f(VBE Function failed). This is the code that I write in a driver:
Code: Select all
USHORT GetVbeMode()
{
__asm
{
cli
mov eax,cr0
mov Cr0Reg,eax
and eax,0xffffffff
mov cr0,eax
mov eax,0x4F03 ;VESA VBE Function
INT 0x10 ;VIDEO BIOS
cmp al,0x4F
jnz falhou ;always al != 4f
mov Resultado,bx
mov eax,Cr0Reg
mov cr0,eax
sti
jmp final
falhou
mov Resultado,0
mov eax,Cr0Reg
mov cr0,eax
sti
jmp final
final:
}
return Resultado;
}
What is wrong at this code that I write???
Re: VESA VBE always failed
Posted: Mon Oct 10, 2011 1:46 am
by Combuster
Code: Select all
mov eax,cr0
mov Cr0Reg,eax
and eax,0xffffffff
mov cr0,eax
(...)
mov eax,Cr0Reg
mov cr0,eax
nop
nop
nop
nop
Re: VESA VBE always failed
Posted: Mon Oct 10, 2011 1:46 am
by gerryg400
Code: Select all
mov eax,cr0
mov Cr0Reg,eax
and eax,0xffffffff
mov cr0,eax
What is this supposed to do ? Are you trying to get from 32bit protected mode to real mode ? That's not how to do it.
Even if you fix the obvious bug in your code, it still won't do what you want it to do.
Re: VESA VBE always failed
Posted: Mon Oct 10, 2011 2:00 am
by 0x3D5
I am trying to switch to real mode to call the INT 0x10
Re: VESA VBE always failed
Posted: Mon Oct 10, 2011 2:07 am
by gerryg400
0x3D5 wrote:I am trying to switch to real mode to call the INT 0x10
Switching to real mode requires a lot more than simply changing a bit in CR0. (and your code does not modify CR0). You need to restore the entire real mode environment that the BIOS expects. You need to reverse all the operations that you performed to go from real mode to protected mode.