FYI: rudimentary loader for ppcbug-based systems

[Peter Grehan]

Hi Alex,

> >  Clean interfaces would be the best. The ultimate is a single kernel that could
> > run on all combinations of processor and firmware, the true GENERIC, but I'm not
> > sure if that's possible.
> 
> I think this is the wrong way to go.  IMO, NetBSD has the right idea.  Treat each
> PPC platform as a truely independent platform.  They've got sys/arch/powerpc for
> the truly generic stuff.

 Userspace is unnecessarily replicated for each of those platforms. There's
a lot more differences between a lot of FreeBSD/alpha platforms than there is
for the different NetBSD PPC platforms.

 Even properly supporting CPU differences between PPC models on the same h/w platform
is perhaps more work than being able to support h/w differences in the same kernel.

 FreeBSD has a number of features to ease this, such as a common 3rd stage loader,
devfs, etc. As I said, it may not be possible, but there's no point in writing it
off from the start.

> This allows them to support stuff like the BeBox, MacPPC, various IBM boxen, etc.
> 
> This would be, IMO, similar to how FreeBSD handles the pc98 case... and the
> current powerpc stuff would be split up into MI (sys/powerpc) and MD (sys/powermac
> or sys/macppc maybe) portions.

 That's somewhat historical, and there's no need to go down that path unless
necessary.

> Darwin, and perhaps LinuxPPC, apparently handles the device enumeration and such
> without openfirware (actually BootX more or less renders any OF stubs unuseable).
> This is perhaps a nice goal, but IMO, it would be better to at least get
> everything working *with* OFW.  This is of course easier with the new-world
> machines which have reasonable versions of OF.

 Darwin and LinuxPPC still use OpenFirmware - Linux pulls in a copy at boot-time
before blowing it away so the info is still there.

 FWIW, I plan on getting things useable on NewWorld before I start out on my original
goal of getting Free up and running on embedded PPC platforms.

later,

Peter.