setenv get_usbstart usb start
setenv get_usbboot_enable fatload usb 0:1 ${loadaddr} usbboot_enable
 
if run get_usbstart; then
 if run get_usbboot_enable; then
  echo try USB boot...
  usb stop
  run usbboot
 else
  echo try MMC boot...
  usb stop
  setenv boot_cmd "run setup_mmcargs; ext4load mmc 0:2 ${loadaddr} /boot/uImage; ext4load mmc 0:2 0x83000000 /boot/a640.dtb; bootm ${loadaddr} - 0x83000000;"
  boot
 fi
else
 echo try MMC boot...
 setenv boot_cmd "run setup_mmcargs; ext4load mmc 0:2 ${loadaddr} /boot/uImage; ext4load mmc 0:2 0x83000000 /boot/a640.dtb; bootm ${loadaddr} - 0x83000000;"
 boot
fi