static int voice_probe_fn(struct ubmodem_s *modem, const int timer_id,
                          void * const arg)
{
  int ret;

  modem->voice.probe_timerid = -1;

  if (!modem->voice.pm_activity_enabled)
    {
      return OK;
    }

  /* Start CMEE probe task. */

  if (!modem->voice.probe_task_queued)
    {
      ret = __ubmodem_add_task(modem, voice_probe_check_cmee, modem);
      MODEM_DEBUGASSERT(modem, ret != ERROR);
      modem->voice.probe_task_queued = true;
    }

  /* Reregister timer. */

  modem->voice.probe_timerid = __ubmodem_set_timer(modem,
                                 VOICE_MODEM_PROBE_SECS * 1000,
                                 voice_probe_fn, modem);
  MODEM_DEBUGASSERT(modem, modem->voice.probe_timerid >= 0);

  return OK;
}
static int network_register_timeout_handler(struct ubmodem_s *modem,
                                            const int timer_id,
                                            void * const arg)
{
  struct modem_sub_setup_network_s *sub = &modem->sub.setup_network;
  struct timespec curr_ts;
  const char *reason;
  int ret;

  MODEM_DEBUGASSERT(modem, modem->creg_timer_id == timer_id);

  if (timer_id != -1)
    {
      /* One-shot timer, not registered anymore. */

      modem->creg_timer_id = -1;

      ubmodem_pm_set_activity(modem, UBMODEM_PM_ACTIVITY_HIGH, false);
    }

  (void)clock_gettime(CLOCK_MONOTONIC, &curr_ts);

  if (curr_ts.tv_sec - sub->net_reg_start_ts.tv_sec <=
      MODEM_CMD_NETWORK_REGISTRATION_TIMEOUT / 10)
    {
      /* Too soon, reregister timer. */

      ret = __ubmodem_set_timer(modem, NETWORK_REGISTRATION_CHECK_SECS * 1000,
                                &network_register_timeout_handler, sub);
      MODEM_DEBUGASSERT(modem, ret != ERROR);

      modem->creg_timer_id = ret;

      ubmodem_pm_set_activity(modem, UBMODEM_PM_ACTIVITY_HIGH, true);

      return OK;
    }

  /* Could not register in time. Disable RF. */

  if (timer_id == -1)
    reason = "NETWORK: Denied.";
  else
    reason = "NETWORK: Timeout.";

  /* Mark for retry, 'level transition failed' can modify the actual target
   * level. */

  __ubmodem_network_cleanup(modem);
  __ubmodem_retry_current_level(modem, UBMODEM_LEVEL_SIM_ENABLED);

  /* Failed to connect network. */

  __ubmodem_level_transition_failed(modem, "%s", reason);

  return OK;
}
static void set_ATpCOPS_handler(struct ubmodem_s *modem,
                                const struct at_cmd_def_s *cmd,
                                const struct at_resp_info_s *info,
                                const uint8_t *resp_stream,
                                size_t stream_len, void *priv)
{
  struct modem_sub_setup_network_s *sub = priv;
  int ret;
  int status = info->status;

  /*
   * Response handler for AT+COPS=0
   */

  MODEM_DEBUGASSERT(modem, cmd == &cmd_ATpCOPS);

  if (status == RESP_STATUS_CME_ERROR)
    {
      if (handle_cops_cme_error(modem, info))
        return;
    }
  else if (resp_status_is_error_or_timeout(status))
    {
      __ubmodem_common_failed_command(modem, cmd, info, "=0");
      return;
    }
  else if (status != RESP_STATUS_OK)
    {
      MODEM_DEBUGASSERT(modem, false); /* Should not get here. */
      return;
    }

  /*
   * Now waiting for +CREG URC.
   *
   * Register timer for timeout.
   */

  sub->network_state = NETWORK_SETUP_WAITING_NETWORK_REGISTRATION;

  ret = __ubmodem_set_timer(modem, MODEM_CMD_NETWORK_TIMEOUT * 100,
                            &network_register_timer_handler, sub);
  if (ret == ERROR)
    {
      /* Error here? Add assert? Or just try bailout? */

      MODEM_DEBUGASSERT(modem, false);

      (void)network_register_timer_handler(modem, -1, sub);
      return;
    }

  modem->creg_timer_id = ret;
}
static void retry_ATpCOPS_handler(struct ubmodem_s *modem,
                                  const struct at_cmd_def_s *cmd,
                                  const struct at_resp_info_s *info,
                                  const uint8_t *resp_stream,
                                  size_t stream_len, void *priv)
{
  struct modem_sub_setup_network_s *sub = &modem->sub.setup_network;
  int status = info->status;
  int ret;

  /*
   * Response handler for retried AT+COPS=0
   */

  MODEM_DEBUGASSERT(modem, cmd == &cmd_ATpCOPS);

  if (status == RESP_STATUS_CME_ERROR)
    {
      if (handle_cops_cme_error(modem, info))
        return;
    }
  else if (resp_status_is_error_or_timeout(status))
    {
      __ubmodem_common_failed_command(modem, cmd, info, "=0");
      return;
    }
  else if (info->status != RESP_STATUS_OK)
    {
      MODEM_DEBUGASSERT(modem, false); /* Should not get here. */
      return;
    }

  DEBUGASSERT(
      sub->network_state == NETWORK_SETUP_RETRYING_NETWORK_REGISTRATION);
  sub->network_state = NETWORK_SETUP_WAITING_NETWORK_REGISTRATION;

  /*
   * Now waiting for +CREG URC.
   *
   * Register timer for timeout.
   */

  ret = __ubmodem_set_timer(modem, NETWORK_REGISTRATION_CHECK_SECS * 1000,
                            &network_register_timeout_handler, sub);
  MODEM_DEBUGASSERT(modem, ret != ERROR);

  modem->creg_timer_id = ret;

  ubmodem_pm_set_activity(modem, UBMODEM_PM_ACTIVITY_HIGH, true);
}
static void modem_voice_pm_activity(struct ubmodem_s *modem,
                                    bool ringing_or_active)
{
  if (ringing_or_active == modem->voice.pm_activity_enabled)
    {
      /* Already in this state. */

      return;
    }

  modem->voice.pm_activity_enabled = ringing_or_active;

  modem->voice.probe_fails = 0;
  if (modem->voice.probe_timerid >= 0)
    {
      __ubmodem_remove_timer(modem, modem->voice.probe_timerid);
      modem->voice.probe_timerid = -1;
    }

  if (ringing_or_active)
    {
      /* Voice call incoming, ringing. After ringing call is eventually
       * disconnected. Report low activity so that we get disconnect URC from
       * modem after hangup (no ring-indication anymore to wake-up MCU). */

      ubmodem_pm_set_activity(modem, UBMODEM_PM_ACTIVITY_LOW, true);

      /* Start probing to detect modem hang-ups (low voltage situation etc). */

      modem->voice.probe_timerid = __ubmodem_set_timer(modem,
                                     VOICE_MODEM_PROBE_SECS * 1000,
                                     voice_probe_fn, modem);
      MODEM_DEBUGASSERT(modem, modem->voice.probe_timerid >= 0);
    }
  else
    {
      /* Voice call disconnected, report change of activity to
       * power-management. */

      ubmodem_pm_set_activity(modem, UBMODEM_PM_ACTIVITY_LOW, false);
    }
}
static void set_ATpCOPS_off_handler(struct ubmodem_s *modem,
                                    const struct at_cmd_def_s *cmd,
                                    const struct at_resp_info_s *info,
                                    const uint8_t *resp_stream,
                                    size_t stream_len, void *priv)
{
  struct modem_sub_setup_network_s *sub = &modem->sub.setup_network;
  int ret;

  /*
   * Response handler for AT+COPS=2
   */

  MODEM_DEBUGASSERT(modem, cmd == &cmd_ATpCOPS);

  if (resp_status_is_error_or_timeout(info->status))
    {
      __ubmodem_common_failed_command(modem, cmd, info, "=2");
      return;
    }
  else if (info->status != RESP_STATUS_OK)
    {
      MODEM_DEBUGASSERT(modem, false); /* Should not get here. */
      return;
    }

  /* Wait for sometime so modem can complete unregistering from network. */

  ubmodem_pm_set_activity(modem, UBMODEM_PM_ACTIVITY_HIGH, true);
  ret = __ubmodem_set_timer(modem, 1500, &network_unregister_timer_handler,
                            sub);
  if (ret == ERROR)
    {
      /* Error here? Add assert? Or just try bailout? */

      MODEM_DEBUGASSERT(modem, false);

      (void)network_unregister_timer_handler(modem, -1, sub);
      return;
    }
}
static void registration_urc_pCREG_handler(struct ubmodem_s *modem,
                                           const struct at_cmd_def_s *cmd,
                                           const struct at_resp_info_s *info,
                                           const uint8_t *resp_stream,
                                           size_t stream_len, void *priv)
{
  struct modem_sub_setup_network_s *sub = &modem->sub.setup_network;
  int8_t val;
  int ret;

  DEBUGASSERT(modem->state == MODEM_STATE_IN_SUBSTATE);

  /*
   * Response handler for +CREG URC.
   */

  MODEM_DEBUGASSERT(modem, cmd == &urc_ATpCREG);

  if (info->status != RESP_STATUS_URC)
    {
      /* Should not happen. */

      MODEM_DEBUGASSERT(modem, false);
      return;
    }

  if (!__ubmodem_stream_get_int8(&resp_stream, &stream_len, &val))
    {
      /* Should not happen. */

      MODEM_DEBUGASSERT(modem, false);
      return;
    }

  dbg("Network registration URC, +CREG=%d.\n", val);

  if (val >= 0 && val < ARRAY_SIZE(creg_strings))
    {
      dbg("%s\n", creg_strings[val]);
    }
  else
    {
      dbg("Unknown +CREG status: %d\n", val);
    }

  if (sub->network_state < NETWORK_SETUP_WAITING_NETWORK_REGISTRATION)
    {
      /* Not ready yet, spurious +CREG URC? */

      ubdbg("Ignored spurious +CREG URC.\n");

      return;
    }

  switch (val)
  {
    case 1:
    case 5:
      /*
       * If 'val' is 1, registered: home network.
       * If 'val' is 5, registered: roamed.
       */

      if (sub->network_state == NETWORK_SETUP_RETRYING_NETWORK_REGISTRATION)
        {
          /* Cannot do state transition to UBMODEM_LEVEL_NETWORK right now
           * as still retrying AT+COPS=0. Defer handling to
           * retry_ATpCOPS_handler. */

          sub->received_creg_while_retrying = val;
        }
      else
        {
          network_registration_successed(modem, sub);
        }

      return;

    case 0:
      /*
       * MT not searching for connection.
       */

      if (sub->network_state == NETWORK_SETUP_WAITING_NETWORK_REGISTRATION)
        {
          /* Stop timer before issuing command. */

          if (modem->creg_timer_id >= 0)
            {
              __ubmodem_remove_timer(modem, modem->creg_timer_id);

              modem->creg_timer_id = -1;

              ubmodem_pm_set_activity(modem, UBMODEM_PM_ACTIVITY_HIGH, false);
            }

          /* Keep retrying automatic network registration until timeout. */

          sub->network_state = NETWORK_SETUP_RETRYING_NETWORK_REGISTRATION;
          sub->received_creg_while_retrying = -1;

          ret = __ubmodem_set_timer(modem, 1000,
                                    &network_retry_registration_timer_handler,
                                    sub);
          MODEM_DEBUGASSERT(modem, ret != ERROR);

          modem->creg_timer_id = ret;

          ubmodem_pm_set_activity(modem, UBMODEM_PM_ACTIVITY_HIGH, true);
        }

      return;

    case 4:
      /*
       * If 'val' is 4, unknown registration error.
       *
       * Network registration flow-chart in "AT Commands Examples"
       * (UBX-13001820, R09, p.24) tells that proper action for this
       * event is to 'Wait'.
       */

      return;

    case 3:
      /*
       * If 'val' is 3, registration was denied.
       *
       * Network registration flow-chart in "AT Commands Examples"
       * (UBX-13001820, R09, p.24) tells that proper action for this
       * event is 'DTE intervention may be required'. Further information
       * on event type '3':
       *
       * "3: the registration fails after a Location Update Reject;
       *     possible causes are:
       *     - Illegal MS
       *     - Illegal ME
       *     - IMSI unknown at HLR
       *     - PLMN not allowed
       *     - Location area not allowed
       *     - Roaming not allowed in this location area
       *     - Network failure
       *     - Network congestion
       *
       *   If the registration type is manual, then no further attempt is
       *   made to search for a new PLMN or register with it. If the
       *   registration type is automatic, the MS may look for an allowed
       *   PLMN if the rejection cause was roaming restriction. In case of
       *   illegal MS / ME, there could be possible problems with either
       *   the SIM card or with the MT's identity (IMEI): user intervention
       *   may be required."
       *
       * Modem can still be continuing connection effort after this event
       * especially in roaming conditions. Thus, we do not react on this
       * message but keep waiting for timeout or other indication of
       * network error.
       */

      return;

    case 2:
      /*
       * If 'val' is 2, modem is trying to register.
       */

      return;

    default:
      /*
       * Unknown.
       */

      return;
  }
}
static void monitor_urc_pCREG_handler(struct ubmodem_s *modem,
                                      const struct at_cmd_def_s *cmd,
                                      const struct at_resp_info_s *info,
                                      const uint8_t *resp_stream,
                                      size_t stream_len, void *priv)
{
  int8_t val;
  int ret;

  (void)ret;

  /*
   * Response handler for +CREG URC.
   */

  MODEM_DEBUGASSERT(modem, cmd == &urc_ATpCREG);

  if (info->status != RESP_STATUS_URC)
    {
      /* Should not happen. */

      MODEM_DEBUGASSERT(modem, false);
      return;
    }

  if (!__ubmodem_stream_get_int8(&resp_stream, &stream_len, &val))
    {
      /* Should not happen. */

      MODEM_DEBUGASSERT(modem, false);
      return;
    }

  dbg("Network registration URC, +CREG=%d.\n", val);

  if (val >= 0 && val < ARRAY_SIZE(creg_strings))
    {
      dbg("%s\n", creg_strings[val]);
    }
  else
    {
      dbg("Unknown +CREG status: %d\n", val);
    }

  if (modem->creg_timer_id >= 0)
    {
      __ubmodem_remove_timer(modem, modem->creg_timer_id);

      modem->creg_timer_id = -1;

      ubmodem_pm_set_activity(modem, UBMODEM_PM_ACTIVITY_HIGH, false);
    }

  switch (val)
    {
      default: /* Unknown? */
      case 1: /* Switched to home network? */
      case 5: /* Switched to roaming? */
        return;

      case 2: /* Looking for connection. */
#ifdef CONFIG_UBMODEM_CREG_WAIT_NETWORK_TO_RESTORE
        /* Start connection search timeout timer. */

        ret = __ubmodem_set_timer(modem, MODEM_CMD_NETWORK_TIMEOUT * 100,
                                  &network_reregister_timer_handler, modem);
        MODEM_DEBUGASSERT(modem, ret != ERROR);

        modem->creg_timer_id = ret;

        ubmodem_pm_set_activity(modem, UBMODEM_PM_ACTIVITY_HIGH, true);

        return;
#else
        /* Reset network through SIM reinitialization. Appears to work
         * better in roaming conditions. TODO: Study why, do we understand
         * function of modem in low-signal environments properly? */
#endif

      case 3: /* Registration failed? */
      case 4: /* Unknown registration error? */
      case 0: /* MT not searching for connection. */

        /* Unregister +CREG URC */

        __ubparser_unregister_response_handler(&modem->parser,
                                               urc_ATpCREG.name);
        modem->creg_urc_registered = false;

        /* Issue new task. We cannot issue new state machine work from
         * URC 'context' as other work might be active in main state
         * machine. Task will be run with main state machine in proper
         * state. */

        __ubmodem_add_task(modem, retry_network_through_sim, NULL);

        return;
    }
}
static void urc_pCREG_handler(struct ubmodem_s *modem,
                              const struct at_cmd_def_s *cmd,
                              const struct at_resp_info_s *info,
                              const uint8_t *resp_stream,
                              size_t stream_len, void *priv)
{
  int8_t val;
  int err;
  int ret;

  /*
   * Response handler for +CREG URC.
   */

  MODEM_DEBUGASSERT(modem, cmd == &urc_ATpCREG);

  if (info->status != RESP_STATUS_URC)
    {
      /* Should not happen. */

      MODEM_DEBUGASSERT(modem, false);
      return;
    }

  if (!__ubmodem_stream_get_int8(&resp_stream, &stream_len, &val))
    {
      /* Should not happen. */

      MODEM_DEBUGASSERT(modem, false);
      return;
    }

  dbg("Network registration URC, +CREG=%d.\n", val);

  if (val >= 0 && val < ARRAY_SIZE(creg_strings))
    {
      dbg("%s\n", creg_strings[val]);
    }
  else
    {
      dbg("Unknown +CREG status: %d\n", val);
    }

  if (modem->level < UBMODEM_LEVEL_NETWORK)
    {
      struct modem_sub_setup_network_s *sub = &modem->sub.setup_network;

      DEBUGASSERT(modem->state == MODEM_STATE_IN_SUBSTATE);

      if (sub->network_state < NETWORK_SETUP_WAITING_NETWORK_REGISTRATION)
        {
          /* Not ready yet, spurious +CREG URC? */

          ubdbg("Ignored spurious +CREG URC.\n");

          return;
        }

      switch (val)
      {
        case 1:
        case 5:
          /*
           * If 'val' is 1, registered: home network.
           * If 'val' is 5, registered: roamed.
           */

          if (sub->network_state == NETWORK_SETUP_RETRYING_NETWORK_REGISTRATION)
            {
              /* Cannot do state transition to UBMODEM_LEVEL_NETWORK right now
               * as still retrying AT+COPS=0. Defer handling to
               * retry_ATpCOPS_handler. */

              sub->received_creg_while_retrying = val;
            }
          else
            {
              /* Report successful cellular network connection. */

              sub->keep_creg_urc = true;
              __ubmodem_reached_level(modem, UBMODEM_LEVEL_NETWORK);
            }

          return;

        case 0:
          /*
           * MT not searching for connection.
           */

          if (sub->network_state == NETWORK_SETUP_WAITING_NETWORK_REGISTRATION)
            {
              /* Keep retrying automatic network registration until timeout. */

              sub->network_state = NETWORK_SETUP_RETRYING_NETWORK_REGISTRATION;
              sub->received_creg_while_retrying = -1;

              err = __ubmodem_send_cmd(modem, &cmd_ATpCOPS,
                                       retry_ATpCOPS_handler, sub, "%s", "=0");
              MODEM_DEBUGASSERT(modem, err == OK);
            }

          return;

        case 4:
          /*
           * If 'val' is 4, unknown registration error.
           */

          /* no break */

        case 3:
          /*
           * If 'val' is 3, registration was denied.
           */

          /* Perform fail-over code from timeout handler. */

          network_register_timer_handler(modem, -1, sub);

          return;

        case 2:
          /*
           * If 'val' is 2, modem is trying to register.
           */

          return;

        default:
          /*
           * Unknown.
           */

          return;
      }
    }
  else
    {
      /* Current level is UBMODEM_LEVEL_NETWORK or higher. */

      switch (val)
        {
          default: /* Unknown? */
          case 1: /* Switched to home network? */
          case 5: /* Switched to roaming? */

            if (modem->creg_timer_id >= 0)
              {
                __ubmodem_remove_timer(modem, modem->creg_timer_id);
                modem->creg_timer_id = -1;
              }

            return;

          case 2: /* Looking for connection. */

            /* Start connection search timeout timer. */

            ret = __ubmodem_set_timer(modem, MODEM_CMD_NETWORK_TIMEOUT * 100,
                                      &network_reregister_timer_handler, modem);
            if (ret == ERROR)
              {
                /* Error here? Add assert? Or just try bailout? */

                MODEM_DEBUGASSERT(modem, false);

                (void)network_reregister_timer_handler(modem, -1, modem);
                return;
              }

            modem->creg_timer_id = ret;

            return;

          case 3: /* Registration failed? */
          case 4: /* Unknown registration error? */
          case 0: /* MT not searching for connection. */

            /* Unregister +CREG URC */

            __ubparser_unregister_response_handler(&modem->parser,
                                                   urc_ATpCREG.name);
            modem->creg_urc_registered = false;

            /* Issue new task. We cannot issue new state machine work from
             * URC 'context' as other work might be active in main state
             * machine. Task will be run with main state machine in proper
             * state. */

            __ubmodem_add_task(modem, retry_network_through_sim, NULL);

            return;
        }
    }
}