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+##
+## This file is part of the sigrok project.
+##
+## Copyright (C) 2012 Bert Vermeulen <bert@biot.com>
+##
+## 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 3 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, If not, see <http://www.gnu.org/licenses/>.
+##
+
+'''
+This decoder extracts a DDC stream from an I2C session between a computer
+and a display device. The stream is output as plain bytes.
+
+Details:
+https://en.wikipedia.org/wiki/Display_Data_Channel
+'''
+
+import sigrokdecode as srd
+
+class Decoder(srd.Decoder):
+ id = 'ddc'
+ name = 'DDC'
+ longname = 'Display Data Channel'
+ desc = 'A protocol for communication between computers and displays.'
+ longdesc = ''
+ license = 'gplv3+'
+ inputs = ['i2c']
+ outputs = ['ddc']
+ probes = []
+ options = {}
+ annotations = [
+ ['Byte stream', 'DDC byte stream as read from display.'],
+ ]
+
+ def __init__(self, **kwargs):
+ self.state = None
+
+ def start(self, metadata):
+ self.out_ann = self.add(srd.OUTPUT_ANN, 'ddc')
+
+ def decode(self, ss, es, data):
+ try:
+ cmd, data, ack_bit = data
+ except Exception as e:
+ raise Exception('malformed I2C input: %s' % str(e)) from e
+
+ if self.state is None:
+ # Wait for the DDC session to start.
+ if cmd in ('START', 'START REPEAT'):
+ self.state = 'start'
+ elif self.state == 'start':
+ if cmd == 'ADDRESS READ' and data == 80:
+ # 80 is the I2C slave address of a connected display,
+ # so this marks the start of the DDC data transfer.
+ self.state = 'transfer'
+ elif cmd == 'STOP':
+ # Got back to the idle state.
+ self.state = None
+ elif self.state == 'transfer':
+ if cmd == 'DATA READ':
+ # There shouldn't be anything but data reads on this
+ # address, so ignore everything else.
+ self.put(ss, es, self.out_ann, [0, ['0x%.2x' % data]])
+