some Uboot commands for ref.

uboot Commands

UBOOT prompt
------------
load mmc 1:2 0x88000000 /boot/am335x-boneblack.dtb  # load dtb to memory
load mmc 1:2 0x82000000 /boot/uImage                # load kernel to memory
  # load: load a file to memory
  # mmc: from MMC
  # 1:2: 1 -> eMMC 2 -> partition 2 
  # 0x82000000: RAM addr to load into
  # /boot/uImage: file name

bootm 0x82000000 - 0x88000000

setenv bootargs console=ttyO0,115200 root=/dev/mmcblk0p2 rw
  # outpul log to console on uart serial connection at baudrate 115200
  # let the root fs be /dev/mmcblk0p2

#to load env variables from memory
loady # to load a file from host using ymodem protocol
env import -t <memory addr> <size in bytes>

uEnv.txt
--------
bootargs=console=ttyO0,115200 root=/dev/mmcblk0p2 rw
bootcmd=echo "**** Booting *****"; load mmc 1:2 0x82000000 /boot/uImage;load mmc 1:2 0x88000000 /boot/am335x-boneblack.dtb;bootm 0x82000000 - 0x88000000