OpenBSD on BeagleBone Black Revision C

$ ftp https://ftp.openbsd.org/pub/OpenBSD/7.0/armv7/miniroot-am335x-70.img
$ ftp https://ftp.openbsd.org/pub/OpenBSD/7.0/armv7/SHA256.sig
$ signify -C -p /etc/signify/openbsd-70-base.pub -x SHA256.sig miniroot-am335x-70.img
$ doas dd if=./miniroot-am335x-70.img of=/dev/rsdXc

Replace rsdXc with your actual disk.

You'll want to flash the image onto the microSD card.

Plug the USB to TTL cable to a computer. The black wire in the USB to TTL cable must be facing the ethernet port (near the letter J1 on the board), while the green wire must be facing the USB port.

See: https://miro.medium.com/max/615/1*mElf7VvdGpcCuwV0uhEvAQ.png

Plug in the mini-USB(?) to USB cable. The mini-USB end should be plugged into the BeagleBone and the USB side to the PC. This will power on the system.

Press and hold the black button near the microSD card, then unplug the mini-USB to USB cable, then plug it back in. This will cause the BeagleBone Black to boot from the micro SD card.

To connect to the serial console with OpenBSD, run:

$ doas cu -l /dev/cuaU0 -s 115200

To connect to the serial console with Debian, run:

$ sudo screen /dev/ttyUSB0 115200