The second post in this series just got published at https://ograblog.wordpress.com/2017/06/13/patching-u-boot-for-use-in-an-ubuntu-core-gadget-snap/
It describes how (and why) the uboot.patch file used by Ubuntu Core gadgets snaps is created and uses https://github.com/ogra1/sabrelite-gadget as example code this time.