[OpenBIOS] Beginners How-To for DTS and OpenFirmware?

[Michael]

Hello list and G 3,

thanks for your time and for the OpenBIOS implementation (btw)!

On Mon, Nov 21, 2016 at 11:11:37AM -0500, G 3 wrote:
> ...
> The website does have several pages that supply information. If you feel
> there
> should be more added, I will be glad to do so.

I have read them first. But for ma as a new arriving person it is a mixture
between outdated (examples with old qemu, with svn repo, ...) and new stuff
and so I did not know exactly what information is relevant.

More structured information I found on the OLPC websites and from a few
companies.

> ...
> The git repo is what we are using now. I would chose that.
> ...

Thanks for confirmation. I looked at the patches (the dates) and convinced
me to use the git repo. For a short time I was on the wrong track because
the (oler) code from the svn repo did compile with ppc, when the newer code
from git did not. Just a lot try-and-error for me for a certain time :-)

> ...
> We use OpenBIOS as the project's name. Open Firmware is a standard OpenBIOS
> follows.
> ...

One example which confused me: If you follow the link "Implementations / Open
Firmware" from the main site (https://www.openfirmware.info/Open_Firmware),
then you see the site "https://www.openfirmware.info/Open_Firmware" and
there I was told to use the svn repo...

> ...
> I don't think Linux touches the OpenBIOS device tree. It likes to discover
> things for itself.

There is no plug-n-play in our hardware. We have to tell the OpenBIOS and
the linux exactly every detail about the hardware. That is, about the
memory (ranges & capabilities), about the busses, the interfaces, the CPUs
etc.
In my understanding we do the basic inits in powerpc assemblercode, so
that the right flags are set and the RAM is able to work and then we call
OpenBIOS from this assemblercode and give it our devicetree with the whole
information about the hardware.
The OpenBIOS then initialises serial & network and gives us the opportunity
to debug some stuff and to boot in different ways.

> ...
> Being a BIOS, I would think about anything could run OpenBIOS. I think any
> computer made in the last 20 years should work.
> ...

That would be nice :-)
But our hardware is challenging.

Thanks for your time and greetings!
Michael