I got the firmware for the xhci controller in the b350 loaded correctly now (huge thanks to himko9)! Turns out, python is maybe not a great choice for mmio.
Oh well, the board has a few extra wires on it now (from debugging attempts).
only usb full-speed for now though
@coreforge Let us know of your progress :)
@Foxarc I usually post it in the github issue. high-speed now works too though