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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):
api_version = 1
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 = []
extra_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 report(self):
pass
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]])
else:
raise Exception('Invalid state: %s' % self.state)
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