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##
## 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[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()
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