[coreboot] option roms in SeaBIOS and Coreboot

Kevin O'Connor kevin at koconnor.net
Wed Nov 26 17:58:48 CET 2008

On Wed, Nov 26, 2008 at 08:46:43AM -0800, ron minnich wrote:
> On Wed, Nov 26, 2008 at 8:39 AM, Kevin O'Connor <kevin at koconnor.net> wrote:
> > In order to minimize the number of address decoders needed, a device
> > may share a decoder between the Expansion ROM Base Address register
> > and other Base Address registers. When expansion ROM decode is
> > enabled, the decoder is used for accesses to the expansion ROM and
> > device independent software must not access the device through any
> > other Base Address registers.
> Wow, I hope no hardware ever implemented that bad idea :-)
> Anybody know? how is an expansion rom supposed to actually get to the
> hardware at that point, I wonder. ...

The steps are: enable option rom decode, copy option rom to memory,
disable option rom decode, run option rom.  So, the option rom runs
when it can access the device.

If you're curious - google for "PCI Firmware Specification v3.0
(2005-06-20).pdf" and read section 5.2.


More information about the coreboot mailing list