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 pulse
  36     time, but in practice it can be necessary to wait a predefined minimum
  37     amount of time between pulses 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, pulse_min, pulse_max, multiplier,
  44                  min_inter_symbol_distance=0.0):
  45         assert multiplier >= 0
  46         if (pulse_min == pulse_max) and (min_inter_symbol_distance == 0):
  47             raise ValueError("If (pulse_min == pulse_max) a non-zero",
  48                              "inter-symbol distance MUST be specified")
  49
  50         symbol_distance = 2 * (pulse_max - pulse_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 + pulse_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 + pulse_min + \
  64             symbol_distance * (multiplier + 1)
  65
  66
  67 class CallDistanceTransceiver(object):
  68     """Transmit Morse messages using the distance between calls.
  69
  70     This is basically a pulse-distance modulation (PDM).
  71
  72     A RING is a pulse and the Morse symbols are encoded in the pause between
  73     the first ring of the previous call and the first ring of a new call.
  74
  75     This strategy is very slow but it can even be used with ancient analog
  76     modems which don't have call progress notifications for outgoing calls, and
  77     make it also hard to count multiple rings in the same call on the receiving
  78     side because there is no explicit notification on the receiving side of
  79     when the caller ends a calls.
  80
  81     For GSM modems, which have a more sophisticate call report signalling,
  82     a more efficient encoding can be used (for example using ring counts to
  83     encode Morse symbols, i.e. a pulse-length modulation), but for
  84     a proof-of-concept, a slow encoding covering the most general setup is
  85     fine.
  86
  87     Plus, supporting communications between analog modems is cool :)
  88     """
  89
  90     def __init__(self, modem,
  91                  call_setup_time_min=7, call_setup_time_max=15,
  92                  ring_time_min=4.8, ring_time_max=5.2,
  93                  add_inter_call_distance=True):
  94         """Encode the Morse symbols using the distance between calls.
  95
  96         Args:
  97
  98             call_setup_time_min: the minimum time between  when the transmitter
  99                 dials the number and the receiver reports RING notifications.
 100             call_setup_time_max: the maximum time between when the transmitter
 101                 dials the number and the receiver reports RING notifications.
 102                 Waiting this time after dialing ensures that the receiver has
 103                 received _at_least_ one ring. The default chosen here have been
 104                 tested to work fine with old analog modems, provided that there
 105                 is some more distance between two calls, and with Android
 106                 receivers.
 107             ring_time_min: the minimum time between two consecutive RINGs
 108                 in the same call.
 109             ring_time_max: the maximum time between two consecutive RINGs
 110                 in the same call, the standard interval is about 5 seconds, but
 111                 line and/or software delays can make it vary.  This is needed
 112                 in order to ignore multiple ring in the same call when multiple
 113                 RING in the same call are notified, and then be able to
 114                 discriminate between two different calls.
 115             add_inter_call_distance: specify if it is needed to wait an extra
 116                 fixed time between calls.
 117             """
 118
 119         self.modem = modem
 120         self.translator = MorseTranslator()
 121
 122         self.destination_number = ""
 123
 124         self.call_setup_time_min = call_setup_time_min
 125         self.call_setup_time_max = call_setup_time_max
 126
 127         self.ring_time_min = ring_time_min
 128         self.ring_time_max = ring_time_max
 129
 130         if add_inter_call_distance:
 131             # Analog modems don't like to dial a new call immediately after
 132             # they hung up the previous one; an extra delay of about one
 133             # ring time makes them happy.
 134             inter_symbol_distance = ring_time_max
 135         else:
 136             inter_symbol_distance = 0
 137
 138         self.dot_time = SymbolTime(call_setup_time_min,
 139                                    call_setup_time_max, 0,
 140                                    inter_symbol_distance)
 141         self.dash_time = SymbolTime(call_setup_time_min,
 142                                     call_setup_time_max, 1,
 143                                     inter_symbol_distance)
 144         self.signalspace_time = SymbolTime(call_setup_time_min,
 145                                            call_setup_time_max, 2,
 146                                            inter_symbol_distance)
 147         self.wordspace_time = SymbolTime(call_setup_time_min,
 148                                          call_setup_time_max, 3,
 149                                          inter_symbol_distance)
 150         self.eom_time = SymbolTime(call_setup_time_min,
 151                                    call_setup_time_max, 4,
 152                                    inter_symbol_distance)
 153
 154         logging.debug("call setup time between %.2f and %.2f "
 155                       "--------- dot transmit time: %.2f + %.2f "
 156                       "receive time: between %.2f and %.2f",
 157                       self.call_setup_time_min,
 158                       self.call_setup_time_max,
 159                       self.call_setup_time_max,
 160                       self.dot_time.dist,
 161                       self.dot_time.min,
 162                       self.dot_time.max)
 163         logging.debug("call setup time between %.2f and %.2f "
 164                       "-------- dash transmit time: %.2f + %.2f "
 165                       "receive time: between %.2f and %.2f",
 166                       self.call_setup_time_min,
 167                       self.call_setup_time_max,
 168                       self.call_setup_time_max,
 169                       self.dash_time.dist,
 170                       self.dash_time.min,
 171                       self.dash_time.max)
 172         logging.debug("call setup time between %.2f and %.2f "
 173                       "- signalspace transmit time: %.2f + %.2f "
 174                       "receive time: between %.2f and %.2f",
 175                       self.call_setup_time_min,
 176                       self.call_setup_time_max,
 177                       self.call_setup_time_max,
 178                       self.signalspace_time.dist,
 179                       self.signalspace_time.min,
 180                       self.signalspace_time.max)
 181         logging.debug("call setup time between %.2f and %.2f "
 182                       "--- wordspace transmit time: %.2f + %.2f "
 183                       "receive time: between %.2f and %.2f",
 184                       self.call_setup_time_min,
 185                       self.call_setup_time_max,
 186                       self.call_setup_time_max,
 187                       self.wordspace_time.dist,
 188                       self.wordspace_time.min,
 189                       self.wordspace_time.max)
 190         logging.debug("call setup time between %.2f and %.2f "
 191                       "--------- EOM transmit time: %.2f + %.2f "
 192                       "receive time: between %.2f and inf",
 193                       self.call_setup_time_min,
 194                       self.call_setup_time_max,
 195                       self.call_setup_time_max,
 196                       self.eom_time.dist,
 197                       self.eom_time.min)
 198
 199         self.previous_ring_time = -1
 200         self.previous_call_time = -1
 201
 202         self.morse_message = ""
 203         self.text_message = ""
 204
 205         self.end_of_message = False
 206
 207     def log_symbol(self, distance, symbol, extra_info=""):
 208         logging.info("distance: %.2f Received \"%s\" %s", distance, symbol,
 209                      extra_info)
 210
 211     def receive_character(self):
 212         current_ring_time = time.time()
 213
 214         if self.previous_ring_time == -1:
 215             self.previous_ring_time = current_ring_time
 216             self.previous_call_time = current_ring_time
 217             self.log_symbol(0, "", "(The very first ring)")
 218             return
 219
 220         ring_distance = current_ring_time - self.previous_ring_time
 221         logging.debug("RINGs distance: %.2f", ring_distance)
 222         self.previous_ring_time = current_ring_time
 223
 224         # Ignore multiple rings in the same call
 225         if ring_distance > self.ring_time_min and \
 226            ring_distance <= self.ring_time_max:
 227             logging.debug("multiple rings in the same call, distance: %.2f",
 228                           ring_distance)
 229             return
 230
 231         call_distance = current_ring_time - self.previous_call_time
 232         self.previous_call_time = current_ring_time
 233
 234         if call_distance > self.dot_time.min and \
 235            call_distance <= self.dot_time.max:
 236             self.log_symbol(call_distance, '.')
 237             self.morse_message += "."
 238             return
 239
 240         if call_distance > self.dash_time.min and \
 241            call_distance <= self.dash_time.max:
 242             self.log_symbol(call_distance, '-')
 243             self.morse_message += "-"
 244             return
 245
 246         if call_distance > self.signalspace_time.min and \
 247            call_distance <= self.signalspace_time.max:
 248             signal = self.morse_message.strip().split(' ')[-1]
 249             character = self.translator.signal_to_character(signal)
 250             self.log_symbol(call_distance, ' ', "got \"%s\"" % character)
 251             self.morse_message += " "
 252             return
 253
 254         if call_distance > self.wordspace_time.min and \
 255            call_distance <= self.wordspace_time.max:
 256             signal = self.morse_message.strip().split(' ')[-1]
 257             character = self.translator.signal_to_character(signal)
 258             self.log_symbol(call_distance, '/', "got \"%s\"" % character)
 259             self.morse_message += " / "
 260             return
 261
 262         if call_distance > self.eom_time.min:
 263             signal = self.morse_message.strip().split(' ')[-1]
 264             character = self.translator.signal_to_character(signal)
 265             self.log_symbol(call_distance, 'EOM', "got \"%s\"" % character)
 266             self.end_of_message = True
 267             self.previous_ring_time = -1
 268             self.previous_call_time = -1
 269             return
 270
 271         # if the code made it up to here, something fishy is going on
 272         logging.error("Unexpected distance: %.2f", call_distance)
 273         logging.error("Check the transmitter and receiver parameters")
 274
 275     def receive_loop(self):
 276         while not self.end_of_message:
 277             self.modem.get_response("RING")
 278             self.receive_character()
 279             logging.debug("Current message: %s", self.morse_message)
 280
 281         self.end_of_message = False
 282         self.text_message = self.translator.morse_to_text(self.morse_message)
 283         self.morse_message = ""
 284
 285     def get_text(self):
 286         return self.text_message
 287
 288     def transmit_symbol(self, symbol):
 289         if symbol == ".":
 290             sleep_time = self.dot_time.dist
 291         elif symbol == "-":
 292             sleep_time = self.dash_time.dist
 293         elif symbol == " ":
 294             sleep_time = self.signalspace_time.dist
 295         elif symbol == "/":
 296             sleep_time = self.wordspace_time.dist
 297         elif symbol == "EOM":
 298             sleep_time = self.eom_time.dist
 299         elif symbol is None:
 300             # To terminate the transmission just call and hangup, with no extra
 301             # distance
 302             sleep_time = 0
 303
 304         logging.info("Dial and wait %.2f = %.2f + %.2f seconds "
 305                      "(transmitting '%s')",
 306                      self.call_setup_time_max + sleep_time,
 307                      self.call_setup_time_max,
 308                      sleep_time,
 309                      symbol)
 310
 311         # Dial, then wait self.call_setup_time_max to make sure the receiver
 312         # gets at least one RING, and then hangup and sleep the time needed to
 313         # transmit a symbol.
 314         self.modem.send_command("ATDT" + self.destination_number + ";")
 315         time.sleep(self.call_setup_time_max)
 316         self.modem.send_command("ATH")
 317         self.modem.get_response()
 318         time.sleep(sleep_time)
 319
 320     def transmit_signal(self, signal):
 321         logging.debug("Transmitting signal: %s", signal)
 322         for symbol in signal:
 323             self.transmit_symbol(symbol)
 324
 325     def transmit(self, message, destination_number):
 326         self.destination_number = destination_number
 327
 328         morse_message = self.translator.text_to_morse(message)
 329         signals = morse_message.split()
 330
 331         logging.debug("Starting the transmission")
 332         for i, signal in enumerate(signals):
 333             logging.debug("Transmitting '%s' as '%s'", message[i], signal)
 334             self.transmit_signal(signal)
 335
 336             # Transmit a signal separator only when strictly necessary:
 337             #  - after the last symbol, we are going to transmit an EOM
 338             #    anyway, and that will mark the end of the last symbol.
 339             #  - between words the word separator act as a symbol separator
 340             #    too.
 341             if i != len(signals) - 1 and signals[i + 1] != "/" and signal != "/":
 342                 self.transmit_symbol(" ")
 343
 344         self.transmit_symbol("EOM")
 345
 346         # Since the Morse signals are encoded in the distance between calls, an
 347         # extra call is needed in order for receiver actually get the EOM and
 348         # see that the transmission has terminated.
 349         self.transmit_symbol(None)
 350
 351     def estimate_transmit_duration(self, message):
 352         morsemessage = self.translator.text_to_morse(message)
 353         signals = morsemessage.split()
 354
 355         logging.debug(signals)
 356
 357         transmitting_time = 0
 358         for i, signal in enumerate(signals):
 359             logging.debug("signal: %s", signal)
 360
 361             for symbol in signal:
 362                 transmitting_time += self.call_setup_time_max
 363                 if symbol == ".":
 364                     transmitting_time += self.dot_time.dist
 365                 elif symbol == "-":
 366                     transmitting_time += self.dash_time.dist
 367                 elif symbol == "/":
 368                     transmitting_time += self.wordspace_time.dist
 369
 370                 if i != len(signals) - 1 and signals[i + 1] != "/" and symbol != "/":
 371                     transmitting_time += self.call_setup_time_max
 372                     transmitting_time += self.signalspace_time.dist
 373
 374         transmitting_time += self.call_setup_time_max
 375         transmitting_time += self.eom_time.dist
 376
 377         # The final call needed for the receiver to get the EOM
 378         transmitting_time += self.call_setup_time_max
 379
 380         logging.debug("Estimated transmitting time: %.2f seconds",
 381                       transmitting_time)
 382
 383
 384 def test_send_receive():
 385     logging.basicConfig(level=logging.DEBUG)
 386     call_setup_time_min = 0
 387     call_setup_time_max = 0.01
 388     ring_time_min = 0
 389     ring_time_max = 0
 390
 391     import random
 392
 393     class DummyModem(object):
 394         """Always receive a '.', a '/' and then EOM, which results in 'E '."""
 395
 396         def __init__(self):
 397             self.ring_count = 0
 398
 399             # Take trasmission times from a transceiver
 400             self.transceiver = None
 401
 402             random.seed(None)
 403
 404         def send_command(self, command):
 405             pass
 406
 407         def get_response(self, response):
 408             # pylint: disable=unused-argument
 409
 410             setup_time = random.uniform(self.transceiver.call_setup_time_min,
 411                                         self.transceiver.call_setup_time_max)
 412
 413             if self.ring_count == 0:
 414                 # dummy ring
 415                 pass
 416             elif self.ring_count == 1:
 417                 # received a '.'
 418                 time.sleep(setup_time + self.transceiver.dot_time.dist)
 419             elif self.ring_count == 2:
 420                 # received a '/'
 421                 time.sleep(setup_time + self.transceiver.wordspace_time.dist)
 422             else:
 423                 # received an 'EOM'
 424                 time.sleep(setup_time + self.transceiver.eom_time.dist)
 425
 426             self.ring_count += 1
 427             self.ring_count %= 4
 428
 429     modem = DummyModem()
 430
 431     xcv = CallDistanceTransceiver(modem,
 432                                   call_setup_time_min, call_setup_time_max,
 433                                   ring_time_min, ring_time_max, True)
 434
 435     modem.transceiver = xcv
 436
 437     while True:
 438         xcv.receive_loop()
 439         modem.ring_count = 0
 440         print()
 441         print("Message received!")
 442         print("\"%s\"" % xcv.get_text(), flush=True)
 443
 444
 445 if __name__ == "__main__":
 446     test_send_receive()