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 micro USB cable to your development PC and the other end to the target USB OTG 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 dub-2020.04-r6.1 (Sep 19 2023 - 07:12:31 +0000)

CPU:   i.MX6UL rev1.2 528 MHz (running at 396 MHz)
CPU:   Industrial temperature grade (-40C to 105C) at 32C
Reset cause: POR
I2C:   ready
DRAM:  256 MiB
MCA:   HW_VER=1  FW_VER=1.19
PMIC:  PFUZE3000 DEV_ID=0x30 REV_ID=0x11
NAND:  256 MiB
MMC:   FSL_SDHC: 0
In:    serial
Out:   serial
Err:   serial
Model: Digi International ConnectCore 6UL SBC.
ConnectCore 6UL SOM variant 0x06: Industrial Ultralite 528MHz, 256MB NAND, 256MB DDR3, -40/+85C, Wireless, Bluetooth
  Board version 3, ID 135
Boot device:  NAND
Net:   FEC0 [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 0

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

    $ cd tmp/deploy/images/ccimx6ulsbc/

  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 'dey-image-qt' 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 (dey-image-qt):

    $ ./install_linux_fw_uuu.sh

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