DSView/libsigrokdecode4DSL/decoders/miller/pd.py

##
## This file is part of the libsigrokdecode project.
##
## Copyright (C) 2017 Christoph Rackwitz <christoph.rackwitz@rwth-aachen.de>
##
## 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 2 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/>.
##

# http://www.gorferay.com/type-a-communications-interface/
# https://resources.infosecinstitute.com/introduction-rfid-security/
# https://www.radio-electronics.com/info/wireless/nfc/near-field-communications-modulation-rf-signal-interface.php
# https://www.researchgate.net/figure/Modified-Miller-Code_fig16_283498836

# Miller: either edge
# modified Miller: falling edge

import sigrokdecode as srd

def roundto(x, k=1.0):
    return round(x / k) * k

class Decoder(srd.Decoder):
    api_version = 3
    id = 'miller'
    name = 'Miller'
    longname = 'Miller encoding'
    desc = 'Miller encoding protocol.'
    license = 'gplv2+'
    inputs = ['logic']
    outputs = []
    tags = ['Encoding']
    channels = (
        {'id': 'data', 'name': 'Data', 'desc': 'Data signal'},
    )
    options = (
        {'id': 'baudrate', 'desc': 'Baud rate', 'default': 106000},
        {'id': 'edge', 'desc': 'Edge', 'default': 'falling', 'values': ('rising', 'falling', 'either')},
    )
    annotations = (
        ('bit', 'Bit'),
        ('bitstring', 'Bitstring'),
    )
    annotation_rows = tuple((u, v, (i,)) for i, (u, v) in enumerate(annotations))
    binary = (
        ('raw', 'Raw binary'),
    )

    def __init__(self):
        self.reset()

    def reset(self):
        self.samplerate = None

    def metadata(self, key, value):
        if key == srd.SRD_CONF_SAMPLERATE:
            self.samplerate = value

    def start(self):
        self.out_ann = self.register(srd.OUTPUT_ANN)
        self.out_binary = self.register(srd.OUTPUT_BINARY)

    def decode_bits(self):
        timeunit = self.samplerate / self.options['baudrate']
        edgetype = self.options['edge'][0]

        self.wait({0: edgetype}) # first symbol, beginning of unit
        prevedge = self.samplenum

        # start of message: '0'
        prevbit = 0
        yield (0, prevedge, prevedge + timeunit)
        expectedstart = self.samplenum + timeunit

        # end of message: '0' followed by one idle symbol

        while True:
            self.wait([{0: edgetype}, {'skip': int(3 * timeunit)}])
            got_timeout = (self.matched & (0b1 << 1))
            sampledelta = (self.samplenum - prevedge)
            prevedge = self.samplenum
            timedelta = roundto(sampledelta / timeunit, 0.5)

            # a mark stands for a 1 bit
            # a mark has an edge in the middle

            # a space stands for a 0 bit
            # a space either has an edge at the beginning or no edge at all
            # after a mark, a space is edge-less
            # after a space, a space has an edge

            # we get 1.0, 1.5, 2.0 times between edges

            # end of transmission is always a space, either edged or edge-less

            if prevbit == 0: # space -> ???
                if timedelta == 1.0: # 1.0 units -> space
                    yield (0, self.samplenum, self.samplenum + timeunit)
                    prevbit = 0
                    expectedstart = self.samplenum + timeunit
                elif timedelta == 1.5: # 1.5 units -> mark
                    yield (1, expectedstart, self.samplenum + 0.5*timeunit)
                    prevbit = 1
                    expectedstart = self.samplenum + timeunit*0.5
                elif timedelta >= 2.0:
                    # idle symbol (end of message)
                    yield None
                else:
                    # assert timedelta >= 2.0
                    yield (False, self.samplenum - sampledelta, self.samplenum)
                    break
            else: # mark -> ???
                if timedelta <= 0.5:
                    yield (False, self.samplenum - sampledelta, self.samplenum)
                    break
                if timedelta == 1.0: # 1.0 units -> mark again (1.5 from start)
                    yield (1, expectedstart, self.samplenum + 0.5*timeunit)
                    prevbit = 1
                    expectedstart = self.samplenum + 0.5*timeunit
                elif timedelta == 1.5: # 1.5 units -> space (no pulse) and space (pulse)
                    yield (0, expectedstart, self.samplenum)
                    yield (0, self.samplenum, self.samplenum + timeunit)
                    prevbit = 0
                    expectedstart = self.samplenum + timeunit
                elif timedelta == 2.0: # 2.0 units -> space (no pulse) and mark (pulse)
                    yield (0, expectedstart, expectedstart + timeunit)
                    yield (1, self.samplenum - 0.5*timeunit, self.samplenum + 0.5*timeunit)
                    prevbit = 1
                    expectedstart = self.samplenum + timeunit*0.5
                else: # longer -> space and end of message
                    yield (0, expectedstart, expectedstart + timeunit)
                    yield None
                    break

    def decode_run(self):
        numbits = 0
        bitvalue = 0
        bitstring = ''
        stringstart = None
        stringend = None

        for bit in self.decode_bits():
            if bit is None:
                break

            (value, ss, es) = bit

            if value is False:
                self.put(int(ss), int(es), self.out_ann, [1, ['ERROR']])
            else:
                self.put(int(ss), int(es), self.out_ann, [0, ['{}'.format(value)]])

            if value is False:
                numbits = 0
                break

            if stringstart is None:
                stringstart = ss

            stringend = es

            bitvalue |= value << numbits
            numbits += 1

            bitstring += '{}'.format(value)
            if numbits % 4 == 0:
                bitstring += ' '

        if not numbits:
            return

        self.put(int(stringstart), int(stringend), self.out_ann, [1, ['{}'.format(bitstring)]])

        numbytes = numbits // 8 + (numbits % 8 > 0)
        bytestring = bitvalue.to_bytes(numbytes, 'little')
        self.put(int(stringstart), int(stringend), self.out_binary, [0, bytestring])

    def decode(self):
        while True:
            self.decode_run()