A round of debugging on the uhci machine check (with key assists from
Jason) led to finding and fixing a flaw in the usb system's handling
of DMA addresses. This problem would affect any system where PCI DMA
addresses are different from memory physical addresses (everything
besides i386?).

Both ohci and uhci controllers seem to work now.

ohci0 at pci0 dev 6 function 0: Opti RM861HA (rev. 0x10)
ohci0: interrupting at eb164 irq 0
ohci0: OHCI version 1.0, legacy support
usb0 at ohci0: USB revision 1.0
uhub0 at usb0
uhub0: Opti OHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub0: 2 ports with 2 removable, self powered
...
ugen0 at uhub0 port 2
ugen0: SanDisk USB SSFDC , rev 1.00/1.00, addr 2

and usbctl shows lots of stuff about it.

uhci0 at pci0 dev 6 function 0: VIA Technologies VT83C572 USB Controller (rev. 0x04)
uhci0: interrupting at eb164 irq 0
usb0 at uhci0: USB revision 1.0
uhub0 at usb0
uhub0: VIA Technologie UHCI root hub, class 9/0, rev 1.00/1.00, addr 1
uhub0: 2 ports with 2 removable, self powered
...
ugen0 at uhub0 port 1
ugen0: KTG CABO II, rev 1.00/20.30, addr 2


usbctl doesn't work quite as well on the uhci; I suspect there may be
some more system-dependant stuff lurking.

I suppose the next step is for me to pick up a USB device that we
actually support...

        - Nathan