TS-7840 u-boot environment

The U-Boot environment on the TS-7840 is stored in the on-board eMMC flash in the /dev/mmcblk0boot0 partition.

# Print all environment variables
env print -a

# Sets the variable bootdelay to 5 seconds
env set bootdelay 5

# Variables can also contain commands
env set hellocmd 'led red on; echo Hello world; led green on;'

# Execute commands saved in a variable
env run hellocmd

# Commit env changes to the spi flash
# Otherwise changes are lost
env save

# Restore env to default
env default -a

# Remove a variable
env delete emmcboot