When ConnectCore 8X boots from the eMMC the U-Boot environment is read from eMMC boot partition 2 (device
/dev/mmcblk0boot1 in Linux).
See Environment variables.
A closed device with a RPMB authentication key programmed sets boot partition 2 as read only. This means the U-Boot environment cannot be overwritten.
To be able to modify the U-Boot environment, you can boot from USB using a signed bootloader image without Trusty and then make your changes.
Follow the steps at 5. Sign the bootloader images to get a
uuuto boot from USB. See Boot U-Boot in USB debug mode.
Add, remove, or modify U-Boot variables.
For example, create a new variable:
=> env set test "This is a test variable"
Save the environment.
=> env save Saving Environment to MMC... Writing to MMC(0)... OK => env save Saving Environment to MMC... Writing to redundant MMC(0)... OK