On Mon, 6 Nov 2000, Jeff Wyman wrote:

> I think that in 68k Macs, MacOS plays a large part in hardware
> initialization. PowerPCs use OpenBoot, and I'd imagine it provides a
> pretty clean interface to the hardware. I don't know a whole lot about
> core Mac, so I'm just making a guess here :)

As I understand it, miBoot boots from the Mac ROMs directly, i.e. no
OpenBoot/OpenFirmware/whatever.  I'm almost certain that it works on
non-OF macs (x100 family).

The early PowerMacs gave absolutely no useful information about the
hardware -- they behave just like 68k macs, boot-wise, except for being
able to boot off of HFS+ volumes (which is, as I understand it, strictly a
driver issue).  The ROM has just enough code to read the driver from the
disk, which has enough code to read the system file from the blessed
system folder, and begin execution....

The question was how much of that MacOS initialization is really
necessary?  I don't see all that much of MacOS's effects that carry over
into NetBSD.  I've stared at the SCSI, video, and nubus drivers, and it
looks like they all have enough guts to bring the hardware up cold.

About the only thing I could think of that MacOS really does is give you
32-bit addressing and hand you a few hardware addresses (video, top of
RAM), all of which should be able to be obtained by peeking at the right
addreses.  Of course, this is from the background of somebody who knows a
lot about early PPC Macs, but only enough about the 68k macs to support
the 52/53/62/6300 family of PowerMacs (Quadra 630 with a PPC upgrade
card).  In other words, take my comments with an entire salt flat.  :-)


David

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