USB driver

[paulwratt]

https://github.com/rsta2/uspi
this project was ported from Circle USB so it may be worth comparing since you are using parts of Circle

also this comment may assist immediately with better usb hub related detection or lack of it:
Chadderz121/csud#10

specifically:

... if you want to connect a USB keyboard, for example, directly to the USB port of RPi model A/A+/Zero/Zero W because they have no on-board USB hub (LAN9512) and their USB port is the port of the root hub.

[kelihlodversson]

The USB code I'm using is currently based on the u-boot DWC2 driver

But I've also been using the two you mention, Circle and Xinu's driver as a reference as well.