##
'''
-USB (low-speed and full-speed) packet protocol decoder.
+This decoder stacks on top of the 'usb_signalling' PD and decodes the USB
+(low-speed and full-speed) packet protocol.
Protocol layer (USB spec, chapter 8):
consists of a 4-bit packet type field, and a 4 bit check field.
The check field is the one's complement of the packet type field.
-Protocol output format:
-TODO
-
Details:
https://en.wikipedia.org/wiki/USB
http://www.usb.org/developers/docs/