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51 lines
1.9 KiB
Python
51 lines
1.9 KiB
Python
##
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## This file is part of the libsigrokdecode project.
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##
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## Copyright (C) 2012 Uwe Hermann <uwe@hermann-uwe.de>
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##
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## This program is free software; you can redistribute it and/or modify
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## it under the terms of the GNU General Public License as published by
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## the Free Software Foundation; either version 2 of the License, or
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## (at your option) any later version.
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##
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## This program is distributed in the hope that it will be useful,
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## but WITHOUT ANY WARRANTY; without even the implied warranty of
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## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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## GNU General Public License for more details.
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##
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## You should have received a copy of the GNU General Public License
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## along with this program; if not, see <http://www.gnu.org/licenses/>.
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##
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'''
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This PD decodes the USB (low-speed and full-speed) signalling protocol.
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Electrical/signalling layer (USB spec, chapter 7):
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USB signalling consists of two signal lines, both driven at 3.3V
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logic levels. The signals are DP (D+) and DM (D-), and normally operate in
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differential mode.
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Low-speed: The state where DP=1,DM=0 is K, the state DP=0,DM=1 is J.
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Full-speed: The state where DP=1,DM=0 is J, the state DP=0,DM=1 is K.
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A state SE0 is defined where DP=DM=0. This common mode signal is used to
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signal a reset or end of packet (EOP). A state SE1 is defined where DP=DM=1.
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Data transmitted on the USB is encoded with NRZI. A transition from J to K
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or vice-versa indicates a logic 0, while no transition indicates a logic 1.
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If 6 ones are transmitted consecutively, a zero is inserted to force a
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transition. This is known as bit stuffing.
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Data is transferred at a rate of 1.5Mbit/s (low-speed) / 12Mbit/s (full-speed).
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The SE0 transmitted to signal an end-of-packet is two bit intervals long
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(low-speed: 1.25uS - 1.50uS, full-speed: 160ns - 175ns).
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Details:
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https://en.wikipedia.org/wiki/USB
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http://www.usb.org/developers/docs/
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'''
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from .pd import Decoder
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