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  - Display a histogram
  - Send information for a different display mode
  - Indicate that the battery is low

  Args:
    command: dictionary representing all data fields from remote.
    configuration: dictionary representing the current state of the messageboard
      configuration.
    display_mode: current display mode; only passed so that we may identify changes.
    low_battery: current battery status; only passed so that we may identify changes.
    to_parent_q: multiprocessing queue, where instructions to send back to messageboard,
      if any, can be placed.
    link: the open serial link.

  Returns:
    A 2-tuple of potentially-updated display_mode, and low_battery.
  """
  # command might update a setting; see if there's a change, and if so, write to disk
  setting_change = False
  log_lines = []
  new_configuration = {}




  setting_keys = ['setting_max_distance', 'setting_max_altitude',
                  'setting_on_time', 'setting_off_time', 'setting_delay']
  for key in setting_keys:
    if command.get(key) != configuration.get(key):
      log_lines.append(' |-->Setting %s updated from %s to %s' % (
          key, str(configuration.get(key)), str(command[key])))
      setting_change = True
    new_configuration[key] = command[key]
  remote_key = 'setting_screen_enabled_bool'
  system_key = 'setting_screen_enabled'
  # remote sees T/F whereas messageboard.py & the web interface expect 'on'/absent key
  if command[remote_key] and system_key not in configuration:
    setting_change = True
    new_configuration[system_key] = 'on'
    log_lines.append(' |-->Setting %s updated from None to on' % system_key)
  elif not command[remote_key] and system_key in configuration:
    setting_change = True

    log_lines.append(' |-->Setting %s updated from on to None' % system_key)

  if setting_change:
    settings_string = messageboard.BuildSettings(new_configuration)
    to_parent_q.put(('update_configuration', (settings_string, )))

  # a command might request info about flight to be (re)displayed, irrespective of
  # whether the screen is on; if so, let's put that message at the front of the message
  # queue, and delete any subsequent messages in queue because presumably the button
  # was pushed either a) when the screen was off (so no messages in queue), or b)
  # because the screen was on, but the last flight details got lost after other screens!
  if command['last_plane']:
    to_parent_q.put(('replay', ()))
    log_lines.append(' |-->Requested last flight (re)display')

  # a command might request a histogram; simply generate and save a histogram file to disk
  if command['histogram_enabled']:
    h_type = GetName(HISTOGRAM_TYPES, command['current_hist_type'])
    h_history = GetName(HISTOGRAM_HISTORY, command['current_hist_history'])
    to_parent_q.put(('histogram', (h_type, h_history)))
    log_lines.append(' |-->Requested %s histogram with %s data' % (h_type, h_history))

  # a command might update us on the display mode; based on the display mode, we might
  # pass different attributes back to the remote




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  - Display a histogram
  - Send information for a different display mode
  - Indicate that the battery is low

  Args:
    command: dictionary representing all data fields from remote.
    configuration: dictionary representing the current state of the messageboard
      configuration.
    display_mode: current display mode; only passed so that we may identify changes.
    low_battery: current battery status; only passed so that we may identify changes.
    to_parent_q: multiprocessing queue, where instructions to send back to messageboard,
      if any, can be placed.
    link: the open serial link.

  Returns:
    A 2-tuple of potentially-updated display_mode, and low_battery.
  """
  # command might update a setting; see if there's a change, and if so, write to disk
  setting_change = False
  log_lines = []
  # makes a copy so as to not modify underlying config; we don't want to modify underlying
  # because otherwise the settings will bounce around (values read from disk ->
  # -> new values set by arduino -> old values from disk -> new values from disk after
  # Arduino update).
  configuration = dict(configuration)
  setting_keys = ['setting_max_distance', 'setting_max_altitude',
                  'setting_on_time', 'setting_off_time', 'setting_delay']
  for key in setting_keys:
    if command.get(key) != configuration.get(key):
      log_lines.append(' |-->Setting %s updated from %s to %s' % (
          key, str(configuration.get(key)), str(command[key])))
      setting_change = True
    configuration[key] = command[key]
  remote_key = 'setting_screen_enabled_bool'
  system_key = 'setting_screen_enabled'
  # remote sees T/F whereas messageboard.py & the web interface expect 'on'/absent key
  if command[remote_key] and system_key not in configuration:
    setting_change = True
    configuration[system_key] = 'on'
    log_lines.append(' |-->Setting %s updated from None to on' % system_key)
  elif not command[remote_key] and system_key in configuration:
    setting_change = True
    configuration.pop(system_key)
    log_lines.append(' |-->Setting %s updated from on to None' % system_key)

  if setting_change:
    settings_string = messageboard.BuildSettings(configuration)
    to_parent_q.put(('update_configuration', (settings_string, )))

  # a command might request info about flight to be (re)displayed, irrespective of
  # whether the screen is on; if so, let's put that message at the front of the message
  # queue, and delete any subsequent messages in queue because presumably the button
  # was pushed either a) when the screen was off (so no messages in queue), or b)
  # because the screen was on, but the last flight details got lost after other screens!
  if command['last_plane']:
    to_parent_q.put(('replay', ()))
    log_lines.append(' |-->Requested last flight (re)display')

  # a command might request a histogram; simply generate and save a histogram file to disk
  if command['histogram_enabled']:
    h_type = GetName(HISTOGRAM_TYPES, command['current_hist_type'])
    h_history = GetName(HISTOGRAM_HISTORY, command['current_hist_history'])
    to_parent_q.put(('histogram', (h_type, h_history)))
    log_lines.append(' |-->Requested %s histogram with %s data' % (h_type, h_history))

  # a command might update us on the display mode; based on the display mode, we might
  # pass different attributes back to the remote




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