## ## This file is part of the sigrok project. ## ## Copyright (C) 2012 Bert Vermeulen ## ## 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 . ## # # DDC protocol decoder # # This decoder extracts a DDC stream from an I2C session between a computer # and a display device. The stream is output as plain bytes. # import sigrokdecode as srd class Decoder(srd.Decoder): id = 'ddc' name = 'DDC' longname = 'Display Data Channel' desc = 'DDC is a protocol for communication between computers and displays.' longdesc = '' author = 'Bert Vermeulen ' license = 'gplv3+' inputs = ['i2c'] outputs = ['ddc'] 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.SRD_OUTPUT_ANN, 'ddc') def decode(self, start_sample, end_sample, i2c_data): try: cmd, data, ack_bit = i2c_data except Exception as e: raise Exception("malformed I2C input: %s" % str(e)) from e if self.state is None: # waiting 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': # back to idle 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(start_sample, end_sample, self.out_ann, [0, ["0x%.2x" % data]])