Fastboot is a protocol for communication between your device and a computer. It allows you to modify file system images over a USB connection, which is a quick way to update firmware during development. Fastboot requires the USB interface to work as 'device'.

Although it was originally developed for Android images, its implementation on the NXP UUU (Universal Update Utility) tool extends the functionality to any file type.

To update U-Boot via USB OTG using uuu and the Fastboot protocol:

  1. Download the latest Universal Update Utility (UUU), a software tool from NXP.

    UUU version should be v1.5.11 or higher.

  2. Place the uuu executable in a directory in your PATH, such as /usr/bin.

  3. Install udev rules to allow any user to run uuu to access the USB port:

    $ sudo sh -c "uuu -udev >> /etc/udev/rules.d/70-uuu.rules"
$ sudo udevadm control --reload

  4. Connect a USB type-C cable to your development PC and the other end to the target USB type-C connector.

  5. Reset the device by pressing the reset button on the board and immediately press any key in the serial terminal to stop the auto-boot process. The U-Boot bootloader prompt displays:

    NOTICE:  CPU: STM32MP257F?? Rev.B
NOTICE:  Model: Digi International ConnectCore MP25 Development Kit
NOTICE:  BL2: v2.8-stm32mp2-beta-r1.0(release):65cda4fe7(65cda4fe)
NOTICE:  BL2: Built : 08:14:45, Jul 12 2024
NOTICE:  BL2: Booting BL31
NOTICE:  BL31: v2.8-stm32mp2-beta-r1.0(release):65cda4fe7(65cda4fe)
NOTICE:  BL31: Built : 08:14:50, Jul 12 2024

U-Boot 2022.10-stm32mp25-beta-r1-gc5d85ac8567-dirty (Jul 12 2024 - 11:27:03 +0200)
CPU: STM32MP257F?? Rev.B
Model: Digi International ConnectCore MP25 Development Kit
ConnectCore MP25 SOM variant 0x01: 0 Bytes DDR4, Wi-Fi, Bluetooth
  Board version 1
Boot:  MMC
DRAM:  1 GiB
optee optee: OP-TEE: revision 3.19 (e66a2a51)
Core:  374 devices, 31 uclasses, devicetree: board
WDT:   Started watchdog with servicing (32s timeout)
MMC:   STM32 SD/MMC: 0, STM32 SD/MMC: 2
Loading Environment from MMC... OK
In:    serial
Out:   serial
Err:   serial
Net:   eth0: eth2@482d0000
Normal Boot
Hit any key to stop autoboot:  0
=>
    Information in the console log may vary.

  6. On the target, in U-Boot, execute the following command:

    => fastboot 0

  7. On your development PC, change to your Digi Embedded Yocto project’s deploy images folder:

    $ cd tmp/deploy/images/ccmp25-dvk/

  8. Run the install_linux_fw_uuu.sh script with -h parameter to check the syntax:

    $ ./install_linux_fw_uuu.sh -h
############################################################
#           Linux firmware install through USB OTG         #
############################################################
Usage: ./install_linux_fw_uuu.sh [options]

  Options:
   -a <atf-filename>      Arm-trusted-firmware filename.
                          Auto-determined by variant if not provided.
   -b                     Activate bootcount mechanism (3 boot attempts).
   -d                     Install firmware on dualboot partitions (system A and system B).
                          (Implies -b).
   -f <fip-filename>      FIP filename.
                          Auto-determined by variant if not provided.
   -h                     Show this help.
   -i <dey-image-name>    Image name that prefixes the image filenames, such as 'dey-image-qt',
                          'dey-image-webkit', 'core-image-base'...
                          Defaults to 'dey-image-webkit' if not provided.
   -n                     No wait. Skips 10 seconds delay to stop script.
   -t                     Install TrustFence artifacts.

  9. To program the default image files (dey-image-webkit):

    $ ./install_linux_fw_uuu.sh

  10. Once the firmware is installed, the device boots automatically. The default username is root with no password.