2 ## This file is part of the sigrok project.
4 ## Copyright (C) 2012 Bert Vermeulen <bert@biot.com>
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 3 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, If not, see <http://www.gnu.org/licenses/>.
21 This decoder extracts a DDC stream from an I2C session between a computer
22 and a display device. The stream is output as plain bytes.
25 https://en.wikipedia.org/wiki/Display_Data_Channel
28 import sigrokdecode as srd
30 class Decoder(srd.Decoder):
33 longname = 'Display Data Channel'
34 desc = 'A protocol for communication between computers and displays.'
42 ['Byte stream', 'DDC byte stream as read from display.'],
45 def __init__(self, **kwargs):
48 def start(self, metadata):
49 self.out_ann = self.add(srd.OUTPUT_ANN, 'ddc')
51 def decode(self, ss, es, data):
53 cmd, data, ack_bit = data
54 except Exception as e:
55 raise Exception('malformed I2C input: %s' % str(e)) from e
57 if self.state is None:
58 # Wait for the DDC session to start.
59 if cmd in ('START', 'START REPEAT'):
61 elif self.state == 'start':
62 if cmd == 'ADDRESS READ' and data == 80:
63 # 80 is the I2C slave address of a connected display,
64 # so this marks the start of the DDC data transfer.
65 self.state = 'transfer'
67 # Got back to the idle state.
69 elif self.state == 'transfer':
70 if cmd == 'DATA READ':
71 # There shouldn't be anything but data reads on this
72 # address, so ignore everything else.
73 self.put(ss, es, self.out_ann, [0, ['0x%.2x' % data]])