I use the following commands:
$ nbsvm foo newimg
$ nbsvm foo start -cdrom cd63.iso --no-reboot -- serial # Installer
$ nbsvm foo start
$ nbsvm foo serial
or
$ nbsvm foo start -- serial
And in the final openbsd installation:
$ cat /etc/boot.conf
set tty com0
Simple? See https://github.com/ChoHag/nbsvm
Disclaimer - it's mine.
I've also some scripts which take cdXX.iso and/or installXX.iso and inject
an autoinstall.conf into it so that automatic installation is easy without
a PXE setup (or any networking for that matter) but those are still in
~/src somewhere.
Mathew