[U-Boot] Use U-Boot command to reload image file and reboot

The following step is about the U-Boot to reboot your machine:

U-Boot>printenv

• You can find the image address and bootm address.

U-Boot>setenv ipaddr 192.168.4.40
U-Boot>setenv serverip 192.168.4.26
U-Boot>setenv ethaddr 00:01:02:03:04:05
U-Boot>setenv netmask 255.255.255.0
U-Boot>saveenv
U-Boot>tftpboot 0xA800000040000000 <<your image file>>
U-Boot>bootm 0xA800000040000074