HardenedBSD/share/examples/libusb20

As I dug my own way through the documentation of libusb 2.0 that ships
with FreeBSD 8+ as the OS'es own USB library API, I noticed there are
only few code examples around under /usr/src (namely, usbconfig
itself).

The libusb20(3) man page is a starting point, but it's a reference
manual, nothing less, nothing more.  Using just a reference, it's not
very easy to start writing your own code based on that.

So I started writing my own examples, to "get a feeling" about how to
use the library.  I covered two typical scenarios which are common for
a number of devices.

The first one is called "bulk", and uses bulk output (host to device)
and input transfers to talk to an USB device.

The second one is called "control", and can use both control output
and input transfers, as well as so-called interrupt transfers.  The
latter are used for data that are being reported frequently or
repeatedly, like position updates from a pointing device (mouse).
Despite of its name, the host has to poll devices for their interrupt
transfers on each USB frame (i.e., each 1 ms).

Recommended reading is the USB 3.0 specification (the older 2.0 one
would do as well), to be found under

http://www.usb.org/developers/docs/

as well as documents for individual USB device classes where
appropriate.

Feel free to be liberal in the licensing of these examples: while the
beer-ware license mandates to keep the license notice, this only
applies to modifications of the original examples itself.  For
copy&pasting (even a larger) piece of an example into your own work, I
won't imply you have to reproduce the beer-ware license text there.
Feel free to credit my name in your derived work if you want.

Dresden, July 2012
Joerg Wunsch <joerg@FreeBSD.org>

# $FreeBSD$