My first thought was to install FreeBSD on this Raspberry Pi 3B, unfortunatelly FreeBSD doesn’t support the built-in WiFi, so have moved to OpenBSD 7.8.

This installation instruction mostly comes from mipam007.

Host computer is MacOS.

Update RPI3b firmware

Download Raspberry Pi OS lite and write to SD card, the tool for burning image is Raspberry Imager which can enalbe SSH, set up password even WiFi, recommended.

  1. sudo echo “enable_uart=1” » /Volumes/bootfs/config.txt
  2. sudo touch /Volumes/bootfs/ssh # create this empty file or SSH won’t work
  3. Start RPI & ssh to it
  4. sudo apt update -y
  5. sudo apt full-upgrade -y
  6. sudo reboot
  7. sudo apt autoremove
  8. sudo rpi-update # Update rpi firmware

*Regarding this rpi-update, it requires to download from GitHub and there is problem with the conneciton here, so I chose to Download it in advance and update it locally as below:

curl -L https://codeload.github.com/raspberrypi/rpi-firmware/zip/refs/heads/master -o rpi-firmware-master.zip

#1. 切换到root用户（第一次切到root记得用sudo passwd root**）
su

# 2. 创建一个.rpi-firmware目录，然后进入并解压
mkdir /root/.rpi-firmware
cd /root/.rpi-firmware && unzip /root/rpi-firmware-master.zip

cp -r ./rpi-firmware-master/* ./

# 执行本地更新
UPDATE_SELF=0 SKIP_DOWNLOAD=1 rpi-update

# 重启
reboot

WiFi blocked

Login again and you will see the following error:

Wi-Fi is currently blocked by rfkill.

Use raspi-config to set the country before use.

rfkill = radio frequency kill, is a manage system for WiFi and BulueTooth. Hereby explain what is rfkill:

rfkill is a small userspace tool to query the state of the rfkill switches, buttons and subsystem interfaces. Some devices come with a hard switch that lets you kill different types of RF radios: 802.11 / Bluetooth / NFC / UWB / WAN / WIMAX / FM.

So what need to do is to set the country code through command raspi-config and choose Change wlan country.

Set to boot from USB

sudo echo program_usb_boot_mode=1 | sudo tee -a /boot/config.txti

Then reboot and check the result of following command:

vcgencmd otp_dump | grep 17:

If everything works, it should show you something like below:

17:3020000a

** You can use the following command to reset above.**

sudo sed -i 's/program_usb_boot_mode=1//g' /boot/config.txt

If you need more details, you can check:

  1. How to Boot Raspberry Pi from USB without SD Card
  2. Booting Raspberry Pi 3 B from USB Drive

Connect USB-UART serial cable to PC/MAC

  • USB-UART GND –> RPI GND
  • USB-UART TXD –> RPI RXD
  • USB-UART RXD –> RPI TXD

Raspberry Pi 3B Pin Layout

Find the right tty port in /dev

  • ls -l /dev/tty.usbserial* ## in MacOS
  • ls -l /dev/ttyUSB* ## in Linux
  • ls -l /dev/cu.usbserial* ## in OpenBSD

And two commands to connect rpi to pc/mac as below:

  1. sudo screen /dev/tty.usbserial-1110 115200 # works in Mac
  2. sudo cu -l /dev/cu.usbserial -s 115200 # works in OpenBSD

After above command executed, insert the USB stick and power on the Raspberry Pi and you will see something as below on your Mac screen:


U-Boot 2025.07 (Oct 06 2025 - 07:00:47 -0600)

DRAM:  948 MiB
RPI 3 Model B (0xa22082)
Core:  87 devices, 13 uclasses, devicetree: board
MMC:   mmc@7e202000: 0, mmcnr@7e300000: 1
Loading Environment from FAT... Unable to read "uboot.env" from mmc0:1...
In:    serial,usbkbd
Out:   serial,vidconsole
Err:   serial,vidconsole
Net:   No ethernet found.

starting USB...
USB DWC2
Bus usb@7e980000: 3 USB Device(s) found
       scanning usb for storage devices... 0 Storage Device(s) found
Hit any key to stop autoboot:  0
U-Boot>

Interrupt the boot process and let it boot from USB stick

Just hit any key to stop autoboot and find where is USB stick for booting:

U-boot> ls sd0a:/ or ls sd1a:/

to examine the filesystem before booting. For me, sd0 was the microSD card and sd1 the USB drive.

Then boot from USB as below:

U-boot> boot sd1a:/bsd