src/savemysugar/CallDistanceTransceiver.py

   1 #!/usr/bin/env python3
   2 #
   3 # CallDistanceTransceiver - send and receive Morse using phone calls distance
   4 #
   5 # Copyright (C) 2015  Antonio Ospite <ao2@ao2.it>
   6 #
   7 # This program is free software: you can redistribute it and/or modify
   8 # it under the terms of the GNU General Public License as published by
   9 # the Free Software Foundation, either version 3 of the License, or
  10 # (at your option) any later version.
  11 #
  12 # This program is distributed in the hope that it will be useful,
  13 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 # GNU General Public License for more details.
  16 #
  17 # You should have received a copy of the GNU General Public License
  18 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
  19
  20
  21 # This hack allows MorseTranslator to be imported also when
  22 # __name__ == "__main__"
  23 try:
  24     from .MorseTranslator import MorseTranslator
  25 except SystemError:
  26     from MorseTranslator import MorseTranslator
  27
  28 import logging
  29 import time
  30
  31
  32 class SymbolTime(object):
  33     """
  34     In theory the symbol distance (the distance to discriminate symbols) can
  35     be arbitrary, and it's only bounded below by the stability of the period
  36     time, but in practice it can be necessary to wait a predefined minimum
  37     amount of time between periods because of technological limits of the
  38     transmitting devices, we call this time the "minimum inter-symbol
  39     distance".
  40     """
  41
  42     # pylint: disable=too-few-public-methods
  43     def __init__(self, period_min, period_max, multiplier,
  44                  min_inter_symbol_distance=0.0):
  45         assert multiplier >= 0
  46         if (period_min == period_max) and (min_inter_symbol_distance == 0):
  47             raise ValueError("If (period_min == period_max) a non-zero",
  48                              "inter-symbol distance MUST be specified")
  49
  50         symbol_distance = 2 * (period_max - period_min)
  51         if symbol_distance == 0:
  52             symbol_distance = min_inter_symbol_distance
  53
  54         # The time the transmitter has to wait to disambiguate between this
  55         # symbol and a different one.
  56         self.dist = min_inter_symbol_distance + symbol_distance * multiplier
  57
  58         # The minimum time which represents the symbol at the receiving end.
  59         self.min = min_inter_symbol_distance + period_min + \
  60             symbol_distance * multiplier
  61
  62         # The maximum time which represents the symbol at the receiving end
  63         self.max = min_inter_symbol_distance + period_min + \
  64             symbol_distance * (multiplier + 1)
  65
  66
  67 class MorseDistanceModulator(object):
  68     def __init__(self, period_min, period_max, pulse_min, pulse_max,
  69                  inter_symbol_distance):
  70         self.set_parameters(period_min, period_max,
  71                             pulse_min, pulse_max,
  72                             inter_symbol_distance)
  73
  74     def set_parameters(self, period_min, period_max, pulse_min, pulse_max,
  75                        inter_symbol_distance):
  76         self.period_min = period_min
  77         self.period_max = period_max
  78         self.pulse_min = pulse_min
  79         self.pulse_max = pulse_max
  80         self.inter_symbol_distance = inter_symbol_distance
  81
  82         self.dot_time = SymbolTime(period_min,
  83                                    period_max, 0,
  84                                    inter_symbol_distance)
  85         self.dash_time = SymbolTime(period_min,
  86                                     period_max, 1,
  87                                     inter_symbol_distance)
  88         self.signalspace_time = SymbolTime(period_min,
  89                                            period_max, 2,
  90                                            inter_symbol_distance)
  91         self.wordspace_time = SymbolTime(period_min,
  92                                          period_max, 3,
  93                                          inter_symbol_distance)
  94         self.eom_time = SymbolTime(period_min,
  95                                    period_max, 4,
  96                                    inter_symbol_distance)
  97
  98     def symbol_to_distance(self, symbol):
  99         if symbol == ".":
 100             return self.dot_time.dist
 101         elif symbol == "-":
 102             return self.dash_time.dist
 103         elif symbol == " ":
 104             return self.signalspace_time.dist
 105         elif symbol == "/" or symbol == " / ":
 106             return self.wordspace_time.dist
 107         elif symbol == "EOM":
 108             return self.eom_time.dist
 109
 110         raise ValueError("Unexpected symbol %s" % symbol)
 111
 112     def is_same_period(self, distance):
 113         return distance > self.pulse_min and distance <= self.pulse_max
 114
 115     def distance_to_symbol(self, distance):
 116         if distance > self.dot_time.min and \
 117            distance <= self.dot_time.max:
 118             return "."
 119
 120         if distance > self.dash_time.min and \
 121            distance <= self.dash_time.max:
 122             return "-"
 123
 124         if distance > self.signalspace_time.min and \
 125            distance <= self.signalspace_time.max:
 126             return " "
 127
 128         if distance > self.wordspace_time.min and \
 129            distance <= self.wordspace_time.max:
 130             return "/"
 131
 132         if distance > self.eom_time.min:
 133             return "EOM"
 134
 135         raise ValueError("Unexpected distance %.2f" % distance)
 136
 137     def modulate(self, morse):
 138         signals = morse.split(' ')
 139         distances = []
 140         for i, signal in enumerate(signals):
 141             for symbol in signal:
 142                 distances.append(self.symbol_to_distance(symbol))
 143
 144             # Transmit a signal separator only when strictly necessary.
 145             #
 146             # Avoid it in these cases:
 147             #  - after the last symbol, because EOM is going to ne transmitted
 148             #    anyway and that will mark the end of the last symbol.
 149             #  - between words, because the word separator act as a symbol
 150             #    separator too.
 151             if i != len(signals) - 1 and signals[i + 1] != "/" and signal != "/":
 152                 distances.append(self.symbol_to_distance(" "))
 153
 154         distances.append(self.symbol_to_distance("EOM"))
 155
 156         # Since the Morse signals are encoded in the distance between calls, an
 157         # extra call is needed in order for receiver actually get the EOM and
 158         # see that the transmission has terminated.
 159         distances.append(0)
 160
 161         return distances
 162
 163
 164 class CallDistanceTransceiver(object):
 165     """Transmit Morse messages using the distance between calls.
 166
 167     This is basically a pulse-distance modulation (PDM).
 168
 169     A RING is a pulse and the Morse symbols are encoded in the pause between
 170     the first ring of the previous call and the first ring of a new call.
 171
 172     This strategy is very slow but it can even be used with ancient analog
 173     modems which don't have call progress notifications for outgoing calls, and
 174     make it also hard to count multiple rings in the same call on the receiving
 175     side because there is no explicit notification on the receiving side of
 176     when the caller ends a calls.
 177
 178     For GSM modems, which have a more sophisticate call report signalling,
 179     a more efficient encoding can be used (for example using ring counts to
 180     encode Morse symbols, i.e. a pulse-length modulation), but for
 181     a proof-of-concept, a slow encoding covering the most general setup is
 182     fine.
 183
 184     Plus, supporting communications between analog modems is cool :)
 185     """
 186
 187     def __init__(self, modem,
 188                  call_setup_time_min=7, call_setup_time_max=15,
 189                  ring_time_min=4.8, ring_time_max=5.2,
 190                  add_inter_call_distance=True):
 191         """Encode the Morse symbols using the distance between calls.
 192
 193         Args:
 194
 195             call_setup_time_min: the minimum time between  when the transmitter
 196                 dials the number and the receiver reports RING notifications.
 197             call_setup_time_max: the maximum time between when the transmitter
 198                 dials the number and the receiver reports RING notifications.
 199                 Waiting this time after dialing ensures that the receiver has
 200                 received _at_least_ one ring. The default chosen here have been
 201                 tested to work fine with old analog modems, provided that there
 202                 is some more distance between two calls, and with Android
 203                 receivers.
 204             ring_time_min: the minimum time between two consecutive RINGs
 205                 in the same call.
 206             ring_time_max: the maximum time between two consecutive RINGs
 207                 in the same call, the standard interval is about 5 seconds, but
 208                 line and/or software delays can make it vary.  This is needed
 209                 in order to ignore multiple ring in the same call when multiple
 210                 RING in the same call are notified, and then be able to
 211                 discriminate between two different calls.
 212             add_inter_call_distance: specify if it is needed to wait an extra
 213                 fixed time between calls.
 214             """
 215
 216         self.modem = modem
 217         self.translator = MorseTranslator()
 218
 219         self.destination_number = ""
 220
 221         self.call_setup_time_max = call_setup_time_max
 222
 223         if add_inter_call_distance:
 224             # Analog modems don't like to dial a new call immediately after
 225             # they hung up the previous one; an extra delay of about one
 226             # ring time makes them happy.
 227             inter_symbol_distance = ring_time_max
 228         else:
 229             inter_symbol_distance = 0
 230
 231         self.modulator = MorseDistanceModulator(call_setup_time_min,
 232                                                 call_setup_time_max,
 233                                                 ring_time_min,
 234                                                 ring_time_max,
 235                                                 inter_symbol_distance)
 236
 237         logging.debug("call setup time between %.2f and %.2f "
 238                       "--------- dot transmit time: %.2f + %.2f "
 239                       "receive time: between %.2f and %.2f",
 240                       self.modulator.period_min,
 241                       self.modulator.period_max,
 242                       self.modulator.period_max,
 243                       self.modulator.dot_time.dist,
 244                       self.modulator.dot_time.min,
 245                       self.modulator.dot_time.max)
 246         logging.debug("call setup time between %.2f and %.2f "
 247                       "-------- dash transmit time: %.2f + %.2f "
 248                       "receive time: between %.2f and %.2f",
 249                       self.modulator.period_min,
 250                       self.modulator.period_max,
 251                       self.modulator.period_max,
 252                       self.modulator.dash_time.dist,
 253                       self.modulator.dash_time.min,
 254                       self.modulator.dash_time.max)
 255         logging.debug("call setup time between %.2f and %.2f "
 256                       "- signalspace transmit time: %.2f + %.2f "
 257                       "receive time: between %.2f and %.2f",
 258                       self.modulator.period_min,
 259                       self.modulator.period_max,
 260                       self.modulator.period_max,
 261                       self.modulator.signalspace_time.dist,
 262                       self.modulator.signalspace_time.min,
 263                       self.modulator.signalspace_time.max)
 264         logging.debug("call setup time between %.2f and %.2f "
 265                       "--- wordspace transmit time: %.2f + %.2f "
 266                       "receive time: between %.2f and %.2f",
 267                       self.modulator.period_min,
 268                       self.modulator.period_max,
 269                       self.modulator.period_max,
 270                       self.modulator.wordspace_time.dist,
 271                       self.modulator.wordspace_time.min,
 272                       self.modulator.wordspace_time.max)
 273         logging.debug("call setup time between %.2f and %.2f "
 274                       "--------- EOM transmit time: %.2f + %.2f "
 275                       "receive time: between %.2f and inf",
 276                       self.modulator.period_min,
 277                       self.modulator.period_max,
 278                       self.modulator.period_max,
 279                       self.modulator.eom_time.dist,
 280                       self.modulator.eom_time.min)
 281
 282         self.previous_ring_time = -1
 283         self.previous_call_time = -1
 284
 285         self.morse_message = ""
 286         self.text_message = ""
 287
 288         self.end_of_message = False
 289
 290     def log_symbol(self, distance, symbol, extra_info=""):
 291         logging.info("distance: %.2f Received \"%s\"%s", distance, symbol,
 292                      extra_info)
 293
 294     def receive_character(self):
 295         current_ring_time = time.time()
 296
 297         if self.previous_ring_time == -1:
 298             self.previous_ring_time = current_ring_time
 299             self.previous_call_time = current_ring_time
 300             self.log_symbol(0, "", "(The very first ring)")
 301             return
 302
 303         ring_distance = current_ring_time - self.previous_ring_time
 304         logging.debug("RINGs distance: %.2f", ring_distance)
 305         self.previous_ring_time = current_ring_time
 306
 307         # Ignore multiple rings in the same call
 308         if self.modulator.is_same_period(ring_distance):
 309             logging.debug("multiple rings in the same call, distance: %.2f",
 310                           ring_distance)
 311             return
 312
 313         call_distance = current_ring_time - self.previous_call_time
 314         self.previous_call_time = current_ring_time
 315
 316         try:
 317             symbol = self.modulator.distance_to_symbol(call_distance)
 318         except ValueError as err:
 319             logging.error("%s", err)
 320             logging.error("Check the transmitter and receiver parameters")
 321             return
 322
 323         extra_info = ""
 324         if symbol in [" ", "/", "EOM"]:
 325             signal = self.morse_message.strip().split(' ')[-1]
 326             character = self.translator.signal_to_character(signal)
 327             extra_info = " got \"%s\"" % character
 328
 329         self.log_symbol(call_distance, symbol, extra_info)
 330
 331         if symbol != "EOM":
 332             # Add spaces around the wordspace symbol to make it easier to split
 333             # the Morse message in symbols later on
 334             if symbol == "/":
 335                 symbol = " / "
 336             self.morse_message += symbol
 337         else:
 338             self.end_of_message = True
 339             self.previous_ring_time = -1
 340             self.previous_call_time = -1
 341
 342     def receive_loop(self):
 343         while not self.end_of_message:
 344             self.modem.get_response("RING")
 345             self.receive_character()
 346             logging.debug("Current message: %s", self.morse_message)
 347
 348         self.end_of_message = False
 349         self.text_message = self.translator.morse_to_text(self.morse_message)
 350         self.morse_message = ""
 351
 352     def get_text(self):
 353         return self.text_message
 354
 355     def transmit_symbol(self, symbol, sleep_time):
 356         logging.info("Dial and wait %.2f = %.2f + %.2f seconds "
 357                      "(transmitting '%s')",
 358                      self.call_setup_time_max + sleep_time,
 359                      self.call_setup_time_max,
 360                      sleep_time,
 361                      symbol)
 362
 363         # Dial, then wait self.call_setup_time_max to make sure the receiver
 364         # gets at least one RING, and then hangup and sleep the time needed to
 365         # transmit a symbol.
 366         self.modem.send_command("ATDT" + self.destination_number + ";")
 367         time.sleep(self.call_setup_time_max)
 368         self.modem.send_command("ATH")
 369         self.modem.get_response()
 370         time.sleep(sleep_time)
 371
 372     def transmit(self, message, destination_number):
 373         self.destination_number = destination_number
 374
 375         morse_message = self.translator.text_to_morse(message)
 376         distances = self.modulator.modulate(morse_message)
 377
 378         logging.debug("Starting the transmission")
 379         for i, distance in enumerate(distances):
 380             # Use 'None' for the last call
 381             if i == len(distances) - 1:
 382                 symbol = None
 383             else:
 384                 total_sleep_time = self.call_setup_time_max + distance
 385                 symbol = self.modulator.distance_to_symbol(total_sleep_time)
 386
 387             self.transmit_symbol(symbol, distance)
 388
 389     def estimate_transmit_duration(self, message):
 390         morsemessage = self.translator.text_to_morse(message)
 391         logging.debug(morsemessage)
 392
 393         distances = self.modulator.modulate(morsemessage)
 394
 395         transmitting_time = 0
 396         for distance in distances:
 397             transmitting_time += self.call_setup_time_max
 398             transmitting_time += distance
 399
 400         logging.debug("Estimated transmitting time: %.2f seconds",
 401                       transmitting_time)
 402
 403
 404 def test_send_receive():
 405     logging.basicConfig(level=logging.DEBUG)
 406     call_setup_time_min = 0
 407     call_setup_time_max = 0.01
 408     ring_time_min = 0
 409     ring_time_max = 0
 410
 411     import random
 412
 413     class DummyModem(object):
 414         """Always receive a '.', a '/' and then EOM, which results in 'E '."""
 415
 416         def __init__(self):
 417             self.ring_count = 0
 418
 419             # Take trasmission times from a transceiver
 420             self.transceiver = None
 421
 422             random.seed(None)
 423
 424         def send_command(self, command):
 425             pass
 426
 427         def get_response(self, response=None):
 428             # pylint: disable=unused-argument
 429
 430             setup_time = random.uniform(self.transceiver.modulator.period_min,
 431                                         self.transceiver.modulator.period_max)
 432
 433             if self.ring_count == 0:
 434                 # dummy ring
 435                 pass
 436             elif self.ring_count == 1:
 437                 # received a '.'
 438                 dot_time = self.transceiver.modulator.dot_time.dist
 439                 time.sleep(setup_time + dot_time)
 440             elif self.ring_count == 2:
 441                 # received a '/'
 442                 wordspace_time = self.transceiver.modulator.wordspace_time.dist
 443                 time.sleep(setup_time + wordspace_time)
 444             else:
 445                 # received an 'EOM'
 446                 eom_time = self.transceiver.modulator.eom_time.dist
 447                 time.sleep(setup_time + eom_time)
 448
 449             self.ring_count += 1
 450             self.ring_count %= 4
 451
 452     modem = DummyModem()
 453
 454     xcv = CallDistanceTransceiver(modem,
 455                                   call_setup_time_min, call_setup_time_max,
 456                                   ring_time_min, ring_time_max, True)
 457
 458     modem.transceiver = xcv
 459
 460     xcv.transmit("CODEX PARIS", "0")
 461
 462     while True:
 463         modem.ring_count = 0
 464         xcv.receive_loop()
 465         print()
 466         print("Message received!")
 467         print("\"%s\"" % xcv.get_text(), flush=True)
 468
 469
 470 if __name__ == "__main__":
 471     test_send_receive()