Note: It is very unlikely that reinstalling the Home Assistant OS is necessary. Before going through this procedure, make sure to use the built-in device wipe mechanism.

To reinstall Home Assistant OS, the Home Assistant OS Installer for Yellow flashed on a USB flash drive needs to be used. However, the Raspberry Pi Compute Module 4 has a fixed boot order: eMMC -> NVMe SSD -> USB flash drive.

Option 1 disables booting of Home Assistant OS (from eMMC or NVMe SSD), which makes it possible to start the Installer again from a USB flash drive. This option only works if you currently have Home Assistant OS installed!

Option 1 (recommended): Reinstall Home Assistant OS using Red + Blue button

  1. Make sure no USB device is plugged into the device. Remove power from your system.
  2. Power up the system.
  3. Within 3 s (or from start), press and hold the red and blue button on the backside of the device simultaneously.
  4. Hold the two buttons for approximately 10 s. The Yellow LED should not start blinking!
  5. Remove power from your system.
  6. Follow the instructions to install Home Assistant OS using the Home Assistant OS Installer for Yellow from a USB flash drive.

Option 2: Reinstall Home Assistant OS using rpiboot

  1. Install rpiboot onto your computer.
    • Using Windows Installer here
    • From source code here
  1. Open the Home Assistant Yellow enclosure to access jumpers on the PCB.
  2. Set JP1 to USB.
  3. Plug-in a USB-C cable to Home Assistant Yellow and connect it to your PC.
  4. Press and hold the USB-C Recvry push button. Older Home Assistant Yellow versions: Bridge JP2 (USB-C Rcvry).
  5. Power up the board. Only the red LED should be on at this point (solid, not blinking).
  6. Release the USB-C Recvry push button. Older Home Assistant Yellow versions: Un-bridge JP2.
  7. Run rpiboot on your PC and let it run through.
    • If you are on a Windows, it might ask you if you want to reformat the disk. Select Cancel each time.
    • Afterwards, the green LED should be on.
  8. To flash the Home Assistant OS Installer for Yellow onto the eMMC ("RPi-MSD"), run the Raspberry Pi Imager. Refer to Step 1 through 5 from the Installing Home Assistant Software on Kit procedure for the exact steps.
    • Windows might bring up a message asking to insert a disk. Close this message.
    • Ignore the Raspberry Pi Imager prompt to remove the SD card.
    • Select Continue and close the Raspberry Pi Installer.
  9. Remove power from the board.
  10. Set JP1 to UART.
  11. Follow the instructions here. Note that because the installer is now installed to the eMMC, no USB flash drive is required.

Resources:

Raspberry Pi Steps to Flash eMMC

Home Assistant Yellow   –   Support   –   GitHub   –   Discord#yellow   –   home-assistant.io   –   Nabu Casa