Second link seems ok, I would like to use it to restore backups made by ReaR (https://github.com/rear/rear) made on an orangepipc+ (For some reason rear backup only support the PXE output on arm)
I have a TFTP server set up on a windows computer on the network (with Tftpd64) serving the ReaR backup folder (containing: orangepipcplus.initrd.gz, orangepipcplus.kernel, orangepipcplus.message, rear-orangepipcplus, backup.tar.gz)
What command to use in uboot to load the image on armbian? Would need similar process indicated from https://docs.armbian.com/User-Guide_Recovery/ not sure how to make it match the example above