This technique involves you have a small (1~2MiB is sufficient)
HFS partition which you will use to start the bootloader. On that
partition you will add the ofwboot.xcf and create a file called
bootbsd.of and include the following in it:
---bootbsd.of----------
\ netbsd open-firmware boot command
." hello1" cr
" screen" output
." hello2" cr
boot hd:,\ofwboot.xcf hd:9,/netbsd
----------------------------------
Replace the last line with your boot command. This will usually
create enough of a delay to wait for the drives to spin up. If the
delay is not long enough, you'll be able to play with the script to
make it wait a little longer. This is what worked on my PM9600 and
my PM G4 Digital Audio (the former needed disk spin time and the
latter video startup time). Later on to setup auto boot use "setenv
boot-command boot hd:,\bootbsd.of".