On Thu, 3 Oct 2002, John M McIntosh wrote:

> I recall at last year's OOPSLA Ian was showing off a squeak image that
> he was booting via open firmware.  Basically he was using open
> firmware on an apple powerbook to load a VM and an image instead of a
> commerical/opensource Operating system. I believe by use of some of
> the open firmware drives (disk/network/video) he was able to manage
> quite a bit without having to write drivers etc.

OF gives you very limited functionality: just enough disk i/o to boot a
kernel and just enough console/keyboard to ask the uer where to look for
that kernel.  After that you're pretty much on your own for mapping memory
and doing anything other than text console and keyboard -- there's no
mouse, for example, or graphics driver.  OF's only really contribution to
your running kerner is that it has laready probed the hardware and built
you a device tree describing what's there.  Configuring, enabling and then
using the devices is clearly the responsibility of your kernel not OF.

For Squeak I had to write my own mouse driver, the image was compressed
and placed in its own segment of `VM kernel' (no sources/changes) and I
almost got enough of the colourmap initialised to display the screen
correctly (although console framebuffers have a hard time with the notion
of `transparency' ;).  But anyone who was there will remember the video
projector not wanting to display anything coming out of the vga connector.

> If someone really really needs this they should ask Ian for a copy I'd
> guess.  Looked like a good way to do kioks software and not worry
> about OS issues.

You can only not worry up to the point where OF hands control to your
`kernel'.  From that point on you're expected to do pretty much
everything, starting with mapping yourself some real memory and deciding
how you're going to deal with (raw!) interrupts, etc...

Ian