The USB Driver Technote on how to "Write a USB Driver" is a work-in-progress" document. When it is reasonably complete, the Technote will be made official and included as part of the Macintosh Developer Technical Support (DTS) Technote series.
Please note that this document has not been thoroughly reviewed for accuracy and may contain incorrect information. Some of the hypertext links may also be broken. If you identify incorrect information or broken links, please send a note with the subject field set to "USB Technote correction" to usb@apple.com, and cc me rkubota@apple.com and the matter will be reviewed and corrected.