Install/boot panic on PowerPC

[j proctor <jproctor_(_at_)_oit_(_dot_)_umass_(_dot_)_edu>]

I'm not a total newbie to OpenBSD, but I've never tried it on a PowerPC
before.  I encounter the error below on the initial boot (before
installation); is there anything I can tweak to get around it (options to
bsd.rd, etc.?), or am I pretty much stuck?

The machine is a B&W G3, factory config for initial OS X server release 
(~2 years ago), including extra 4-port 10/100 ethernet card.  Using
OpenFirmware 3.1.1, booting from OpenBSD 2.8 CD:

[ can't get entire dmesg, for obvious reasons ... ]

ofbus1 at ofroot0 (pci)
ofbus2 at ofbus1 (pci-bridge)
ofbus3 at ofbus2 (mac-io)
ofbus4 at ofbus3 (scsi)
ofbus5 at ofbus3 (escc-legacy)
ofbus6 at ofbus3 (escc)
ofbus7 at ofbus3 (davbus)
ofbus8 at ofbus3 (fdc)
ofbus9 at ofbus3 (via-cuda)
ofrtc0 at ofbus9 (rtc): rtc
ofbus10 at ofbus9 (adb)
ofbus11 at ofbus3 (ata-3)
ofbus12 at ofbus2 (pci-ata)
ofbus13 at ofbus2 (pci-bridge)
ofbus14 at ofbus2 (ADPT,2940U2B)
ofbus15 at ofbus2 (usb)
ofbus16 at ofbus15 (hub)
ofcons0 at ofbus1 (ATY,Rage128y)
mpcpcibr0 at mainbus0: grackle, Revision 0x40
pci0 at mpcpcibr0 bus 0
pchb0 at pci0 dev 0 function 0 "Motorola MPC106 Host-PCI" rev 0x40
ppb0 at pci0 dev 13 function 0 "DEC DECchip 21154 PCI-PCI" rev 0x02
pci1 at ppb0 bus 1
vendor "Texas Instruments", unknown product 0x8000 (class serial bus,
subclass Firewire, rev 0x02) at pci1 dev 0 function 0 not configured
"CMD Technology PCI0646" rev 0x07 at pci1 dev 1 function 0 not configured
panic: trap type 200 at 1b8eb4 lr 2b8de0

Stopped at      0x1a12dc:       rw 0, r2, r2,
ddb>