The OpenBSD installation guide is well-written and thorough. A few caveats:
- Using HTTP for the file sets is recommended; I was unable to access the file sets on the USB boot media from installer's ramdisk environment.
- For devices like the apu2d4 without a VGA (pc0) port, the installer gets stuck in a boot loop unless the default terminal is re-configured to use the COM port. In short, the following commands must be typed at boot prompt.
boot> stty com0 115200 boot> set tty com0
115200
is the baud rate of the COM port.