Troubleshooting netboot on a PowerMac G4 Cube

For lack of a working CD drive, I've been trying to install NetBSD 9.3
on my ancient Cube using netboot.  I seem to have the bootp and tftp
stages working, but I can't get it to load the installation kernel
from NFS.

I spent a fair amount of hair-tearing before realizing that there
seems to be a typo in the INSTALL instructions.  They recommend
(for Open Firmware >= 3) a boot command like

	boot enet:0,ofwboot.xcf enet:0,/netbsd-GENERIC_MD.gz

For me, with Open Firmware 4.1.8f5, the "0" after "enet:" has to be
left off.  I didn't have too much trouble guessing that, because the
command is also shown without "0" for older OF versions.  But what
I did not find out except by accident is that *it's wrong to use a
comma in the kernel file specification*.  The syntax that works
for me is

	boot enet:,ofwboot.xcf enet:/netbsd-GENERIC_MD.gz

(and you can't leave out the "/").  Is this specific to my Open
Firmware version?  It seems like it ought to be mostly a function
of ofwboot not OF proper.

Anyway, using that syntax, I get plausible-looking messages
including a cursor that spins for a plausible amount of time,
but then:

>> NetBSD/macppc OpenFirmware Boot, Revision 1.13 (Thu Aug  4 15:30:37 UTC 2022)
14050212\
DEFAULT CATCH!, code=300 at   %SRR0: 00e006d8  %SRR1: 00083030

I'm encouraged by the fact that it reports the correct decompressed
kernel size, so that at least some data is getting transferred
correctly.  It seems like it's fetching the whole kernel and then
messing up at the point of launching the kernel.

I get the same results with compressed or decompressed kernels,
except that I see "code=900" with a decompressed kernel.

I also tried ofwboot.xcf from the 9.2 distribution, and also
netbsd-GENERIC_MD.gz from the 9.2 distribution, with no changes
except for the reported kernel size.  So whatever this is, it's
not a very new problem.

Any suggestions?

			regards, tom lane