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Quick Guide to U-Boot Modes & Customisation

Entering Loader / Recovery Mode​

Loader Mode Image

To access the Loader Mode on your Fydetab Duo, follow these steps:

  1. Shut down the Device

    • Ensure your Fydetab Duo is completely powered off.
  2. Connect USB Cable

    • Insert a USB cable into the Fydetab Duo and the host device.
  3. Activate Loader Mode

    • Press and hold both the Volume Up button and the Power button simultaneously.
  4. Confirm Loader Mode

    • The Fydetab Duo will boot into Loader Mode, allowing firmware updates and other maintenance tasks.

Entering USB Mass Storage(UMS) Mode​

UMS Image

To put your Fydetab Duo into UMS Mode, proceed with the following:

  1. Shut down the Device

    • Ensure the Fydetab Duo is turned off.
  2. Prepare for UMS Mode

    • Press and hold the Volume Down button and the Power button simultaneously.
  3. Connect USB Cable

    • Plug in a USB cable to the Fydetab Duo and the host device.
  4. Confirm UMS Mode

    • The device will enter UMS Mode, acting as a USB disk that can be accessed by the host computer.

Low Power Charge Mode​

Understanding the low power charging behaviour in U-Boot:

  1. Critical Battery Level <3%

    • If the battery capacity falls below 3% and the device is not connected to a charger, U-Boot will automatically shut down the system to protect the battery and your data.
  2. Low Battery Level <8% Low Battery Image

    • If the battery capacity is below 8%, U-Boot will remain on the charging screen until the battery charges to at least 8%, preventing the device from booting until it reaches a safer charge level.

Compiling and Replacing U-Boot​

Follow these instructions to compile U-Boot and replace the original firmware on your Fydetab Duo:

  1. Update Overlay

  2. Compile U-Boot

    • Enter the cros_sdk environment.
    • Execute the following command:
      emerge-${your_board} virtual/u-boot
  3. Locate Compiled Files

    • If the compilation is successful, uboot.img and resource.img will be created in /build/${your_board}/boot.
  4. Transfer Files to Device

    • Copy the uboot.img and resource.img files to your Fydetab Duo.
  5. Flash Images to eMMC

    • Use the following commands to flash the images:
      dd if=uboot.img of=/dev/mmcblk0p11 conv=fsync
      dd if=resource.img of=/dev/mmcblk0p10 conv=fsync

Customising U-Boot Display Images​

To personalise the splash images (they are exported as bitmap images in the file system) used in U-Boot, follow these steps:

  1. Replace BMP Files

  2. Rebuild U-Boot Resource

    • Enter the cros_sdk environment.
    • Run the following command:
      emerge-${your_board} rk-uboot-resource
  3. Transfer New Resource Image

    • Copy the newly created resource.img from /build/${your_board}/boot to your Fydetab Duo.
  4. Flash New Resource Image

    • Use the following command to replace the original resource image on partition 10:
      dd if=resource.img of=/dev/mmcblk0p10 conv=fsync

The following is our design file for the BMP images. Please note that there is a 90-degree rotation in the design file to fit the screen.