--- /dev/null
+##
+## 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 decoder for NFC'
+ desc = 'Decodes (modified) Miller encoding as used in NFC communication.'
+ license = 'gplv2+'
+ inputs = ['logic']
+ outputs = ['miller']
+ 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))
+
+ def __init__(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[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, [1, bytestring])
+
+ def decode(self):
+ while True:
+ self.decode_run()
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