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You can pass the main partition of the eMMC to the computer via USB OTG by executing the following command in U-Boot:
run update_blums 0 mmc 0
A “Linux UMS Disk” storage device should show up in the USB Image Tool and an Image can be applied to it.Note: The “run update_bl”-command is for SD-Card images that contain the bootloader. If you are using the bootloader on the eMMCs boot partition you can use the following command to deploy a new OS image (without bootloader) to the eMMCs main partition:ums 0 mmc 0