As seen on OSnews: "The ins and outs of USB".  

http://www-128.ibm.com/developerworks/power/library/pa-spec7.html?ca=dgr-lnxw07InOutUSB

This article mentions NetBSD and its very early & very stable USB stack.  

"Particular credit goes to Lennart Augustsson's work on the NetBSD USB
implementation which is quite frankly awe-inspiring (see Resources). The
NetBSD implementation was unusually complete and stable back when USB
devices were still fairly experimental to many users. The net result is
a huge base of code under flexible and open licensing terms (providing a
way to sanity-check implementation questions) and also a lot of
practical information about device quirks."

Credit where credit is due. :-)  

GH

-- 
:wq