+To use a device tree file that you have compiled yourself, pass
+EXT_DTB=<filename> to 'make', as in:
+
+ make EXT_DTB=boot/am335x-boneblack-pubkey.dtb
+
+Then U-Boot will copy that file to u-boot.dtb, put it in the .img file
+if used, and u-boot-dtb.bin.
+