srd: Split USB decoder in two PDs (which stack).

[libsigrokdecode.git] / decoders / usb_signalling / __init__.py

diff --git a/decoders/usb_signalling/__init__.py b/decoders/usb_signalling/__init__.py
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+##
+## This file is part of the sigrok project.
+##
+## Copyright (C) 2012 Uwe Hermann <uwe@hermann-uwe.de>
+##
+## This program is free software; you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 2 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program; if not, write to the Free Software
+## Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+##
+
+'''
+USB (low-speed and full-speed) signalling 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.
+
+Low-speed: The state where DP=1,DM=0 is K, the state DP=0,DM=1 is J.
+Full-speed: The state where DP=1,DM=0 is J, the state DP=0,DM=1 is K.
+
+A state SE0 is defined where DP=DM=0. This common mode signal is used to
+signal a reset or end of packet (EOP). A state SE1 is defined where DP=DM=1.
+
+Data transmitted on the USB is encoded with NRZI. A transition from J to K
+or vice-versa indicates a logic 0, while no transition indicates a logic 1.
+If 6 ones are transmitted consecutively, a zero is inserted to force a
+transition. This is known as bit stuffing.
+
+Data is transferred at a rate of 1.5Mbit/s (low-speed) / 12Mbit/s (full-speed).
+
+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 output format:
+TODO
+
+Details:
+https://en.wikipedia.org/wiki/USB
+http://www.usb.org/developers/docs/
+'''
+
+from .usb_signalling import *
+