This directory provides a bootloader image that loads a Linux initramfs that exports common block devices (EMMC, NVMe) as USB mass storage devices using the Linux gadget-fs drivers.
This allows Raspberry Pi Imager to be run on the host computer and write OS images to the Compute Module block devices.
If secure-boot mode has been locked (via OTP) then both the
bootloader and rpiboot bootcode4.bin will only load boot.img
files signed with the customer's private key. Therefore, access
to rpiboot mass storage mode is disabled.
Mass storage mode can be re-enabled by signing a boot image containing the firmware mass storage drivers.
N.B. The signed image should normally be kept secure because can be used on any device signed with the same customer key.
To sign the mass storage mode boot image run:-
KEY_FILE=$HOME/private.pem
../tools/rpi-eeprom-digest -i boot.img -o boot.sig -k "${KEY_FILE}"To run load the USB MSD device drivers via RPIBOOT run
../rpiboot -d .The activity LED will flash three times once the USB MSD devices have been initialised. A message will also be printed to the HDMI console.
The UART console is also enabled (user 'root' no password) so that the user can login and debug the Compute Module.
N.B. This takes a few seconds longer to initialise than the previous mass storage implementation. However, the write speed should be much faster now that all of the file-system code is running on the ARM processors.