There is one mini system that you can use to make one bootable TF card. You can find it here:
https://chipsee-tmp.s3.amazonaws.com/mksdcardfiles/IMX6UL/7/prebuilt-cs10600u070v1-mini-sd-20190603.tar.gz
Change the boot mode to SD ( 0 0 1 0) on PCB, then boot this mini system. You can use it to compress the rootfs in eMMC. Once you are in the mini system, run the following command:
# mkdir /mnt/rootfs
# mount /dev/mmcblk1p2 /mnt/rootfs // mmcblk1p2 is the second partition of your eMMC
# cd /mnt/rootfs/
# tar zcvf rootfs.tar.gz *
# sync
Once you get the rootfs.tar.gz, copy it to a USB storage or TF card.
# mkdir /mnt/tf
# mount /dev/mmcblk0p2 /mnt/tf
# cp /mnt/rootfs/rootfs.tar.gz /mnt/tf
Use this rootfs.tar.gz to replace the default one in prebuilt-xxx/emmc-flash/emmc/rootfs.tar.gz. (The prebuilt-xxx is our released system package.)
Use the new prebuilt-xxx to make one bootable SD card and use the SD card to flash other boards.