I finally got a chance to try the newest ehci code, and added a
comprehensive note to kern/22325 describing the results. :(

I do not possess ehci clue, so I am not sure what to try next.
I notice there is a lot of heavy, interesting activity in FreeBSD's
cvs involving usb recently.  (It seems they've discovered a scatter/
gather capability in the controller spec, which is the really jihbed
way around the can't-allocate-contiguous-physmem problem we addressed
a while back by reserving memory at boot. Neat, but probably unrelated
to the reliability problems. I'm not sure if something else they've done
could help.)

-Chap