[coreboot] SeaBIOS, serial output, and grub

Ward Vandewege ward at gnu.org
Fri May 1 03:18:45 CEST 2009

On Thu, Apr 30, 2009 at 09:00:59PM -0400, Kevin O'Connor wrote:
> On Wed, Apr 29, 2009 at 11:04:32PM -0400, Ward Vandewege wrote:
> > I tried exactly that today (gmta ;), but that didn't seem to work for me -
> > and SeaBIOS complained about an option rom checksum mismatch on the
> > sgabios.bin option rom.
> That's odd - it works fine for me.  Can you confirm the sgabios build
> and then forward me the SeaBIOS log with it in CBFS?

Will do tomorrow.

> > Since every other component in the boot process already does serial - how
> > hard would it be to make SeaBIOS do serial too?
> Well, SeaBIOS does support serial.  What you're looking for is the
> ability to forward vgabios requests over serial.  SeaBIOS doesn't have
> any vgabios capabilities today, so it would be a bit of work.  Since
> sgabios is already designed to do this, I'm not sure what the value
> would be in duplicating it in SeaBIOS.

So - here's the problem with the sgabios approach. Unless I'm
misunderstanding how this works, using sgabios means that I'd have to disable
serial in any payload started from grub, as well?

I'm trying to get as minimal a changeset as possible between proprietary

> > > >   serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1
> > > >   terminal --timeout=5 serial console
> > > 
> > > The only thing I can think of is that SeaBIOS may be setting the
> > > serial port settings to something that grub doesn't like.  You can try
> > > disabling the code in debug_serial_setup() in src/output.c.  However,
> > > if you've already tried disabling CONFIG_DEBUG_SERIAL, then I don't
> > > think this will do much.  It could be a conflict with coreboot serial
> > > setup and grub I suppose.
> > 
> > Hmm. Suggestions for debugging?
> You could try disabling serial in both coreboot and seabios.  It seems
> like a "long shot" though.
> You could change grub to dump the serial registers and then run it
> from both the proprietary bios and from coreboot/seabios - just to see
> if there is a serial port difference.
> Maybe there is a debugging mode of grub that you could activate?

Will investigate tomorrow...


Ward Vandewege <ward at fsf.org>
Free Software Foundation - Senior Systems Administrator

More information about the coreboot mailing list