Honored Contributor
Honored ContributorUSB is logically (but not quite physically) polled, multi-drop hdlc. The standard requires very tight timing control for the poll loop (so that fixed speed targets can put fixed amounts of data into each poll cycle).
The poll cycle is normally controlled by the uhci hardware module (or maybe the older ocpi??) which is what the linux driver is probably accessing. I've never looked at that hardware interface :-) it may not be that complicated if you have limited requirements. I'd actually guess that most slaves don't actual verify the poll rate, and that, a simple single target host interface could actually be done with a simple hdlc controller....
