[openfirmware] On Raspberry Pi
Mark Morgan Lloyd
markMLl.openfirmware at telemetry.co.uk
Mon Jan 5 09:34:45 CET 2015
James Cameron wrote:
> For interest, a port of a Forth to Raspberry Pi happened in the last
> couple of months. There's enough working code there to make a port of
> Open Firmware slightly less effort.
I think the problem here is that for OpenFirmware to really be useful,
i.e. to the same extent that it is on Sun systems, it needs to take
control as early as possible and in particular shouldn't be loaded from
a filesystem which can be screwed. On a Raspberry Pi, that raises two
i) The (originally undocumented) Broadcom SoC contains firmware or
equivalent hardware to pull a first-stage loader off the SD card. So the
SD card is always needed, even though the mechanical connector is known
to be one of the less-reliable components and the card itself will,
ultimately, have a limited life.
ii) If one grits ones teeth and subverts that mechanism, one ends up in
control of the SoC rather than in control of the application processer
that normally runs Linux.
If one instead tolerates the existing multi-stage loader, then one
should be able to boot Forth onto the application processor in lieu of
Linux. But this breaks the Sun model of "Open Boot in ROM, everything
else on disc", and loses the desirable characteristic that any media or
controller problem returns you to the "ok" prompt with diagnostic
capabilities, and as such I'm not sure it's worth the effort.
I'd be interested to know of any low-cost boards which could have
OpenFirmware grafted in sufficiently early. A colleague is trying to
build some router systems which, as a prerequisite, must have a serial
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
More information about the openfirmware