OpenFirmware and interrupt-map

Eric W. Biederman ebiederman at
Tue Feb 3 13:51:01 CET 2004

There are some interesting points of comparing experience between
Open firmware and LinuxBIOS so I am copying the list.

Tarl Neustaedter <Tarl.Neustaedter at> writes:

> Eric W. Biederman wrote:
> > Tarl Neustaedter <Tarl.Neustaedter at> writes:
> >
> >>If you have any specific questions about OpenFirmware, I'd be
> >>delighted to provide assistance. I've been doing IEEE 1275 since
> >>1996, and was at one time a voting member of that committee (since
> >>pretty much defunct). The specs are engraved upon my skull by now.
> >
> > Cool.  Stefan Reinauer <stepan at> is more likely to ask
> > questions as he is the primary implementor of OpenBIOS.  Which
> > is a payload from the LinuxBIOS context.  As a standard for running
> > code in options roms it does not look too
> > bad.
> The main problem is that cards don't usually come with IEEE 1275 FCode
> on them. We've pretty much had to write all of ours, and have gotten
> tired of it - we're actually looking at LinuxBIOS as a way to get
> out of that business, and just build in the drivers we care to in the
> Linux kernel on the prom. But I can answer questions any questions
> about writing FCode, it's most of what I've done in recent years.

Interesting.   The observation that powerful firmware eventually
becomes an OS so you might as well use an OS, seems true :) 

The one problem with using Linux so far has been size constraints.  
The primary interim solution has been to use etherboot.  You have to
port the Linux drivers to it but it close enough you don't have to
rewrite them from scratch, and it is small. 16K-32K is typical with
one network driver and a IP stack.  128K when you build in all the
network drivers. 

I have recently found some kernel patches that start to shrink the
Linux kernel by allowing you to compile out unnecessary pieces so
I about ready to make a foray into using Linux as our bootloader
again.   But until I have squeezed a lot of the size bloat out I won't
be convinced it is the way to go.

The location where option roms come into play in the pc world are
scsi adapters, raid controllers, and video.  For scsi adapters and
raid controllers every case I have looked at the linux drivers are
good enough that you don't need the option roms.  Video drivers are
still problematic.

How has sun coped with getting video drivers for high end video
cards.  I know Apple seems to have succeeded in working with
NVIDIA.  I suspect that is with open firmware side but I don't know.


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