sources are defined per board family, in your case sunxi:https://github.com/armbian/build/blob/main/config/sources/families/include/sunxi_common.inc    Before attempting u-boot for a whole family I suggest to do some small scale tests at board level first by setting an override in the board config file. Example for a different board:https://github.com/armbian/build/blob/a7c19f1e35a65daf42f090ecc34ee1151ee6db23/config/boards/orangepi5-plus.conf#L31-L52