2 ## This file is part of the sigrok project.
4 ## Copyright (C) 2012 Uwe Hermann <uwe@hermann-uwe.de>
6 ## This program is free software; you can redistribute it and/or modify
7 ## it under the terms of the GNU General Public License as published by
8 ## the Free Software Foundation; either version 2 of the License, or
9 ## (at your option) any later version.
11 ## This program is distributed in the hope that it will be useful,
12 ## but WITHOUT ANY WARRANTY; without even the implied warranty of
13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 ## GNU General Public License for more details.
16 ## You should have received a copy of the GNU General Public License
17 ## along with this program; if not, write to the Free Software
18 ## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
22 USB (low-speed and full-speed) signalling protocol decoder.
24 Electrical/signalling layer (USB spec, chapter 7):
26 USB signalling consists of two signal lines, both driven at 3.3V
27 logic levels. The signals are DP (D+) and DM (D-), and normally operate in
30 Low-speed: The state where DP=1,DM=0 is K, the state DP=0,DM=1 is J.
31 Full-speed: The state where DP=1,DM=0 is J, the state DP=0,DM=1 is K.
33 A state SE0 is defined where DP=DM=0. This common mode signal is used to
34 signal a reset or end of packet (EOP). A state SE1 is defined where DP=DM=1.
36 Data transmitted on the USB is encoded with NRZI. A transition from J to K
37 or vice-versa indicates a logic 0, while no transition indicates a logic 1.
38 If 6 ones are transmitted consecutively, a zero is inserted to force a
39 transition. This is known as bit stuffing.
41 Data is transferred at a rate of 1.5Mbit/s (low-speed) / 12Mbit/s (full-speed).
43 The SE0 transmitted to signal an end-of-packet is two bit intervals long
44 (low-speed: 1.25uS - 1.50uS, full-speed: 160ns - 175ns).
46 Protocol output format:
50 https://en.wikipedia.org/wiki/USB
51 http://www.usb.org/developers/docs/
54 from .usb_signalling import *