Creating an image of an emmc OS installed on a S905X


I do have a handful of AML-s905x-cc boards with emmc - and I want to use one board as ‘master’, take a copy of the emmc and flash that to all others.
I’m currently using Raspberry Pi OS; I’ve used dd to flash the emmc.
That all worked out quite smoothly thanks to the documentation.
But once the emmc is flashed I haven’t figured out if its possible to mount it again as USB drive. So all my attempt typically wiped the bootloader (I believe).
Is there a way to create a backup from an existing emmc based S905X?


Stop at the u-boot prompt. Run ums 0 mmc 0. Then plug in the top USB port next to Ethernet into a computer. Your eMMC will appear as a flash drive to the computer with your board as the reader.

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silly question - how do I enter the u-boot prompt?
Default start gets me intro GRUB, pressing the u-boot button basically shows an empty screen. Or did I miss something there?
Last time I had to work on a u-boot prompt I needed to attach stuff to the UART (RX, TX) - thats not the case here, right?

Thanks in advance

Before it gets to u-boot. It asks you to Press any key to stop on our images.

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Another way:

  1. echo "boot_targets=usb mmc1 mmc0" > /boot/efi/boot.ini to set boot into USB/uSD before eMMC
  2. write OS of choice to uSD card larger than eMMC
  3. boot into uSD OS
  4. dd if=/dev/mmcblk0 of=/emmc.ddimg
  5. shutdown, move uSD over to new host with blank eMMC
  6. boot into uSD OS
  7. dd if=/emmc.ddimg of=/dev/mmcblk0