Booting from USB on RPI3

[Georg Lindenberg]

Hey,
These are the steps I took to boot my RPI3B from usb.

1. Put the .img file on both the usb device and the SD Card (e.g. with dd).
2. Plug in everything. RPI starts uboot from the SD Card.
3.  Type any key to enter the U-Boot prompt. Then type "run usb_boot".

You can see all the uboot variables with "env print". Maybe it is possible to add "boot_cmd=run usb_boot" to one of the config files, but I was too scared to try it.