'''
USB (low-speed and full-speed) protocol decoder.
+Electrical/signalling layer (USB spec, chapter 7):
+
USB signalling consists of two signal lines, both driven at 3.3V
logic levels. The signals are DP (D+) and DM (D-), and normally operate in
differential mode.
The SE0 transmitted to signal an end-of-packet is two bit intervals long
(low-speed: 1.25uS - 1.50uS, full-speed: 160ns - 175ns).
+Protocol layer (USB spec, chapter 8):
+
Bit/byte ordering: Bits are sent onto the bus LSB-first. Multibyte fields
are transmitted in little-endian order (i.e., LSB to MSB).