srd: clear objects after final decref, so it doesn't happen twice

[libsigrokdecode.git] / decoders / ddc / ddc.py

##
## 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, 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 = 'DDC2'
    longname = 'Display Data Channel'
    desc = 'A protocol for communication between computers and displays.'
    longdesc = ''
    license = 'gplv3+'
    inputs = ['i2c']
    outputs = ['ddc2']
    options = {}
    annotations = [
        ['Byte stream', 'DDC2B byte stream as read from display.'],
    ]

    def __init__(self, **kwargs):
        self.state = None

    def start(self, metadata):
        self.out_proto = self.add(srd.OUTPUT_PROTO, 'ddc2')
        self.out_ann = self.add(srd.OUTPUT_ANN, 'ddc2')

    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_proto, data)
                self.put(ss, es, self.out_ann, [0, ['0x%.2x' % data]])
        else:
            raise Exception('Invalid state: %s' % self.state)