The installXX.img file is typically not used directly on a Raspberry Pi for installation, as the Raspberry Pi Foundation's preferred method for installing operating systems involves writing an image directly to the microSD card.

Instead, the installXX.img file is more commonly used for installing OpenBSD on traditional PC hardware, where you would write it to a USB drive or CD/DVD to boot and install OpenBSD on the target system.

For Raspberry Pi, you generally only need the minirootXX.img file, as it contains the necessary components to boot and install OpenBSD on the Raspberry Pi. You'll write this image to the microSD card using a tool like dd or specialized imaging software.

Once you've written the minirootXX.img file to the microSD card and boot your Raspberry Pi from it, the installation process will guide you through setting up OpenBSD on your Raspberry Pi.

Configure UART/Serial console Before begin the installation, you need to setup boot environment with:

seems not necessary

# echo "enable_uart=1
program_usb_boot_mode=1" >> /SDCARD/BOOT/config.txt

The Raspberry Pi boards require closed but redistributable files on the system disk to load into the VC4 GPU which starts the ARM cores. By default the boot ROM on Raspberry Pi 3 and older versions on Raspberry Pi 4 will only try to load these files off an SD card. To load the firmware off the SD card and have the root disk on USB after installing OpenBSD, reboot and interrupt U-Boot before the timeout expires and instruct U-Boot to prefer USB over the SD card:

Hit any key to stop autoboot: 0 U-Boot> setenv boot_targets usb0 mmc0 pxe dhcp U-Boot> saveenv U-Boot> boot

To install OpenBSD 6.3 on the Raspberry Pi 3 V1.2, I used a 128MB microSD card (to host the installer), a microSD to USB adapter, a no-name 30GB USB stick, a TTL to USB Converter and an RJ45 Ethernet cable.

All was done from a Macbook Pro using macOS 10.13.5. Preparation commands shouldn’t differ that much if using *BSD or Linux.