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Diffstat (limited to 'decoders/usb_signalling/__init__.py')
| -rw-r--r-- | decoders/usb_signalling/__init__.py | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/decoders/usb_signalling/__init__.py b/decoders/usb_signalling/__init__.py new file mode 100644 index 0000000..026875c --- /dev/null +++ b/decoders/usb_signalling/__init__.py @@ -0,0 +1,55 @@ +## +## 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 * + |