03-11-2017, 09:02 AM
Let's say that u-boot provide a kernel argument called "root=<something>" and that "something" could be either a partition device such as "/dev/mmcblk0p2" for the partition #2 of an sdcard, or such as "/dev/sda1" for partition #1 of an USB HDD. Only changing that should be enough for you to be able to have your rootfs on external drive, although you will still need the sdcard inserted for u-boot itself been executed.
