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-r2.2 (Jan 18 2021 - 15:54:36 +0000)
    DDRINFO: start DRAM init
    DDRINFO: DRAM rate 3000MTS
    DDRINFO:ddrphy calibration done
    DDRINFO: ddrmix config done
    Normal Boot
    Trying to boot from BOOTROM
    image offset 0x0, pagesize 0x200, ivt offset 0x0
    U-Boot dub-2020.04-r2.2 (Jan 18 2021 - 15:54:36 +0000)
    CPU:   i.MX8MNano Quad rev1.0 1400 MHz (running at 1200 MHz)
    CPU:   Industrial temperature grade (-40C to 105C) at 36C
    Reset cause: POR
    DRAM:  1 GiB
    MCA:   HW_VER=1  FW_VER=1.01
    MMC:   FSL_SDHC: 1, FSL_SDHC: 0
    In:    serial
    Out:   serial
    Err:   serial
    Model: Digi ConnectCore 8M Nano Development Kit
    ConnectCore 8M Nano SOM variant 0x01: 1 GiB LPDDR4, Wi-Fi, Bluetooth, MCA, Crypto-auth
      Board version 3, ID undefined
    Boot:  MMC2
      - ATF 9447098
      - U-Boot dub-2020.04-r2.2
    flash target is MMC:0
    Net:   eth0: ethernet@30be0000
    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 and execute the following command:

    ~$ cd tmp/deploy/images/ccimx8mn-dvk/
    ~$ ./
  8. Once the firmware is installed, the device boots automatically. The default username is root with no password.