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USB boot code

This is the USB MSD boot code which should work on the Raspberry Pi model A, Compute Module, Compute Module 3, Compute Module 4 and Raspberry Pi Zero.

This version of rpiboot has been modified to work from directories which contain the booting firmware. There is a msd/ directory which contains bootcode.bin and start.elf to turn the Raspberry Pi device into a USB Mass Storage Device (MSD). If run without arguments embedded versions of bootcode.bin and start.elf are used to enable the MSD behaviour.

For more information run 'rpiboot -h'

Building

Ubuntu

Clone this on your Pi or an Ubuntu linux machine

git clone --depth=1 https://github.com/raspberrypi/usbboot
cd usbboot
sudo apt install libusb-1.0-0-dev
make
sudo ./rpiboot

macOS

From a macOS machine, you can also run usbboot, just follow the same steps:

  1. Clone the usbboot repository
  2. Install libusb (brew install libusb)
  3. Build using make
  4. Run the binary
git clone --depth=1 https://github.com/raspberrypi/usbboot
cd usbboot
brew install libusb
make
sudo ./rpiboot

Note: You might see an OS warning message about a new disk that it can't access, click "ignore", this likely means that the storage is empty and has no filesystem. From here I recommend installing an OS using the Raspberry Pi Imager App, or using any other means like dd.

Running your own (not MSD) build

If you would like to boot the Raspberry Pi with a standard build you just need to copy the FAT partition files into a subdirectory (it must have at the minimum bootcode.bin and start.elf). If you take a standard firmware release then this will at the very least boot the linux kernel which will then stop (and possibly crash!) when it looks for a filesystem. To provide a filesystem there are many options, you can build an initramfs into the kernel, add an initramfs to the boot directory or provide some other interface to the filesystem.

sudo ./rpiboot -d boot

This will serve the boot directory to the Raspberry Pi Device.

Compute Module 4

On Compute Module 4 EMMC-DISABLE / nRPIBOOT (GPIO 40) must be fitted to switch the ROM to usbboot mode. Otherwise, the SPI EEPROM bootloader image will be loaded instead.

Secure Boot

TODO - Add link to whitepaper / user-guide

Host setup

Secure boot require a 2048 bit RSA asymettric keypair and the Python pycrytodomex module to sign the EEPROM config and boot image.

Install Python Crypto support (the pycryptodomex module)

python3 -m pip install pycryptodomex
# or
pip install pycryptodomex

Create an RSA key-pair using OpenSSL. Must be 2048 bits

cd $HOME
openssl genrsa 2048 > private.pem

Secure Boot - configuration

Secure Boot - image creation

Secure boot requires a boot.img FAT image to be created. This plus a signature file (boot.sig) must be placed in the boot partition of the Raspberry Pi.

The contents of the boot.img are the files normally present in the Raspberry Pi OS boot partition i.e. firmware, DTBs and kernel image. However, in order to reduce boot time it is advisible to remove unused files e.g. firmware or kernel images for Pi models.

The firmware must be new enough to support secure boot. Either download the latest Raspberry Pi OS Bullseye OS image or alternateively, download the files for the raspberrypi-bootloader APT package directly from Github and use the files in the boot directory.

git clone --depth 1 --branch stable https://github.com/raspberrypi/firmware

A helper script (make-boot-image) is provided to automate the image creation process. This script depends upon the mkfs.fat and udisksctl tools and only runs on Linux.

Clone the Raspberry Pi OS boot files

Copy the contents of /boot to a local directory called secure-boot-files

Set the kernel root device

Verify that cmdline.txt in secure-boot-files points to the correct device for the root file-system. e.g. root=/dev/mmcblk0p2 for the normal partition on CM4 EMMC.

Create the boot image

The -p product argument (pi4,pi400,cm4) tells the script to discard files which are not required by that product. This makes the image smaller and reduces the time taken to calculate the hash of the image file thereby reducing the boot time.

../tools/make-boot-image -d secure-boot-files -o boot.img -p pi4

Sign the boot image

../tools/rpi-eeprom-digest -i boot.img -o boot.sig -k "${KEY_FILE}"

Copy the secure boot image to the device boot filesystem

Copy boot.img and boot.sig to the chosen boot filesystem. Secure boot images can be loaded from any of the normal boot devices (e.g. SD, USB, Network).

Raspberry Pi Imager - BETA

The Raspberry Pi Imager can be run natively on the CM4 providing a GUI for downloading and installing the operating system.

Beta notes:

  • The current version runs rpi-update upon completion in order to update the firwamre and kernel.
  • uart_2ndstage is enabled
  • The HDMI display is limited to 1080p to avoid potential problems with cables etc if a 4K display is attached.

Run Raspberry Pi Imager:

sudo ./rpiboot -d imager

Once the imager is running you will be prompted to remove the micro-usb cable and connect a mouse.