SGI O2 unable to boot NetBSD 9.0 through 10.0

[Mike Shields <mike%shieldsworld.com@localhost>]

Hello port-mips folks.
I've been trying to get NetBSD running on a Silicon Graphics O2. I have a
few of these machines, with various complements of memory and CPU. I've
tested on an R5k 180MHz, an R5k 200MHz, and an R12k 400MHz. All the
machines work flawlessly in IRIX and OpenBSD 6.9 so I'm confident  hardware
is not the issue. All exhibit the same results - booting either from CD or
from bootp/tftp.

The kernel loads, and will print between 1 and a few dozen lines before
hard freezing, requiring power plug removal to reboot. Faster CPUs get
farther before freezing (the 400MHz is often able to print out the
copyright message) - one interesting bit is the timestamp on the kernel
messages is always [   1.0000000] - as if it freezes on the first timer
tick.

I've tried booting all versions of 9.x and 10.0 that are available with the
same results

I'd love to help get it working again on this platform, though I'm not
certain where to begin. I was able to install NetBSD 8.3, in the hopes I
could possibly upgrade from there, compile kernels, debug, etc - but I'm
not sure 8.3 is a suitable platform to start with, it being so old.

Is anyone else interested in getting O2s back up to working status in
NetBSD 10.0?