[SeaBIOS] how sea bios set VGA bar address?

유준봉 mountainlion0523 at gmail.com
Sat Nov 8 09:56:07 CET 2014

Hi SeaBios!!

I'm qemu user and i want to modify qemu vga device to start BAR Address
from 0xE0000000

As you know, Qemu uses SEABIOS as system bios

but when i look into Qemu Debug console, right  using command "info pci"

then it just shows value for PCI BAR address : 0xf0000000

and it seems that VGA PCI BAR address change by the size of VGA RAM(VRAM)
(if VRAM is 128MB, BAR address = 0xf0000000, if it is 256MB, BAR address =

It seems during booting time seabios calculate VGA PCI BAR address as
0xf000000 when its VRAM size is 128MB.

so i wonder where in source code of seabios calculate PCI BAR address?

and also, i wonder why qemu's vga pci bar address is different from
virtualbox's vga pci bar address though
both of devices are classified as same 'vga' device(class id number : 0x30)
(in Virtualbox, VGA PIC BAR ADDRESS always starts from e0000000 and it is
VBE standard)
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