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 v1.5.182 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:

    U-Boot SPL dub-2024.04-r1.1-git+g93da01eb81e+p0 (Aug 21 2024 - 16:13:01 +0000)
SOC: 0xa0009100
LC: 0x2040010
PMIC: PCA9451A
PMIC: Nominal Voltage Mode
DDR: 3733MTS
Normal Boot
Trying to boot from BOOTROM
Boot Stage: Primary boot
image offset 0x0, pagesize 0x200, ivt offset 0x0
Load image from 0x3d400 by ROM_API
NOTICE:  TRDC init done
NOTICE:  BL31: v2.10.0  (release):android-14.0.0_2.0.0-rc3-0-g9ce177d6d-dirty
NOTICE:  BL31: Built : 10:04:22, May 29 2024

U-Boot dub-2024.04-r1.1-git+g93da01eb81e+p0 (Aug 21 2024 - 16:13:01 +0000)
Reset Status: POR
CPU:   NXP i.MX91(31) Rev1.0 A55 at 1400 MHz
CPU:   Industrial temperature grade  (-40C to 105C) at 31C
DRAM:  480 MiB
Core:  200 devices, 28 uclasses, devicetree: separate
MMC:   FSL_SDHC: 0, FSL_SDHC: 1
In:    serial
Out:   serial
Err:   serial
Model: Digi ConnectCore 91 Development Kit
ConnectCore 91 SOM variant 0x01: 480 MiB LPDDR4, Wi-Fi, Bluetooth
  Board version undefined, ID undefined
Boot:  MMC0
BuildInfo:
  - ELE firmware version 1.1.0-17eafba6
flash target is MMC:0
Net:   eth0: ethernet@428a0000 [PRIME]
Fastboot: Normal
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 1

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

    $ cd tmp/deploy/images/ccimx91-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:
   -b                     Activate bootcount mechanism (3 boot attempts).
   -d                     Install firmware on dualboot partitions (system A and system B).
                          (Implies -b).
   -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 'core-image-base' if not provided.
   -k <dek-filename>      Update includes dek file.
                          (implies -t)."
   -n                     No wait. Skips 10 seconds delay to stop script.
   -t                     Install TrustFence artifacts.
   -u <u-boot-filename>   U-Boot filename.
                          Auto-determined by variant if not provided.

  9. To program the default image files (core-image-base):

    $ ./install_linux_fw_uuu.sh

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