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) tool, a software tool from NXP.

  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 the uuu for accessing the USB port:

    ~$ sudo sh -c "uuu -udev >> /etc/udev/rules.d/99-uuu.rules"
~$ sudo udevadm control --reload-rules

  4. Connect a micro USB cable to your development PC and the other end to the target USB recovery 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-2020.04-r3.1-git-00114-g909871f6fff7-dirty (Feb 11 2021 - 16:54:47 +0100)
DDRINFO: start DRAM init
DDRINFO: DRAM rate 3000MTS
DDRINFO:ddrphy calibration done
DDRINFO: ddrmix config done
Normal Boot
Trying to boot from MMC2


U-Boot dub-2020.04-r3.1-git-00114-g909871f6fff7-dirty (Feb 11 2021 - 16:54:47 +0100)

CPU:   i.MX8MMQ rev1.0 1600 MHz (running at 1200 MHz)
CPU:   Industrial temperature grade (-40C to 105C) at 32C
Reset cause: POR
DRAM:  2 GiB
MCA:   HW_VER=1  FW_VER=1.00
MMC:   FSL_SDHC: 1, FSL_SDHC: 0
In:    serial
Out:   serial
Err:   serial
Model: Digi ConnectCore 8M Mini Development Kit
ConnectCore 8M Mini SOM variant 0x03: 2 GiB LPDDR4, Wi-Fi, Bluetooth, MCA, Crypto-auth
  Board version 3, ID undefined
Boot:  MMC2

 BuildInfo:
  - ATF a7f57f3
  - U-Boot dub-2020.04-r3.1-git-00114-g909871f6fff7-dirty

flash target is MMC:0
Net:   eth0: ethernet@30be0000
Fastboot: Normal
Normal Boot
Hit any key to stop autoboot:  0
{pu}
    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 and execute the following command:

    ~$ cd tmp/deploy/images/ccimx8mm-dvk/
~$ ./install_linux_fw_uuu.sh

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