Fixing DevTimeAns handling

As per discussion with Nicolas Sornin, any device time synchronization
value must be handled as is (monotonically increasing GPS epoch time guaranteed to be monotonic with granularity 1 second).

Once we receive a response to DevTimeReq (i.e., DevTimeAns is received)
we immediately set our local gps time stamp and take a snapshot of our
local monotonic (ticker or equivalent) clock. This is achieved by
calling 'set_gps_time(...)' API in the LoRaWANTimer module.
After that an event is generated to let the application know that a
device time has been synched.

features/lorawan/LoRaWANStack.cpp

@@ -471,8 +471,9 @@ lorawan_status_t LoRaWANStack::set_link_check_request()
     return LORAWAN_STATUS_OK;
 }
 
-void LoRaWANStack::send_device_time_sync_event()
+void LoRaWANStack::handle_device_time_sync_event(lorawan_time_t gps_time)
 {
+    _lora_time.set_gps_time(gps_time);
     send_event_to_application(DEVICE_TIME_SYNCHED);
 }
 
@@ -486,7 +487,7 @@ lorawan_status_t LoRaWANStack::set_device_time_request()
         return LORAWAN_STATUS_NO_NETWORK_JOINED;
     }
 
-    return _loramac.setup_device_time_request(callback(this, &LoRaWANStack::send_device_time_sync_event));
+    return _loramac.setup_device_time_request(callback(this, &LoRaWANStack::handle_device_time_sync_event));
 }
 
 void LoRaWANStack::set_reset_indication()

features/lorawan/LoRaWANStack.h

@@ -576,7 +576,7 @@ private:
     void forced_timer_expiry();
     void process_rejoin_type0();
 
-    void send_device_time_sync_event();
+    void handle_device_time_sync_event(lorawan_time_t gps_time);
 
 private:
     LoRaMac _loramac;

features/lorawan/lorastack/mac/LoRaMac.cpp

@@ -1623,7 +1623,7 @@ void LoRaMac::setup_link_check_request()
     _mac_commands.add_link_check_req();
 }
 
-lorawan_status_t LoRaMac::setup_device_time_request(mbed::Callback<void(void)> notify)
+lorawan_status_t LoRaMac::setup_device_time_request(mbed::Callback<void(lorawan_time_t)> notify)
 {
     return _mac_commands.add_device_time_req(notify);
 }

features/lorawan/lorastack/mac/LoRaMac.h

@@ -333,7 +333,7 @@ public:
      * @brief setup_device_time_request Adds device time request command
      * to be put on next outgoing message (when it fits)
      */
-    lorawan_status_t setup_device_time_request(mbed::Callback<void(void)> notify);
+    lorawan_status_t setup_device_time_request(mbed::Callback<void(lorawan_time_t)> notify);
 
     /**
      * @brief setup_reset_indication Adds reset indication command

features/lorawan/lorastack/mac/LoRaMacCommand.cpp

@@ -332,22 +332,15 @@ lorawan_status_t LoRaMacCommand::process_mac_commands(const uint8_t *payload, ui
                 secs |= (uint32_t) payload[mac_index++] << 8;
                 secs |= (uint32_t) payload[mac_index++] << 16;
                 secs |= (uint32_t) payload[mac_index++] << 24;
-                uint32_t millis = ((uint32_t) payload[mac_index++] * 1000) >> 8;
 
                 // round milliseconds to closest second
-                if (millis > 499) {
+                if (payload[mac_index++] >= 0x80) {
                     secs++;
                 }
 
-                // adjust for Unix to GPS epoch diff
-                secs += UNIX_GPS_EPOCH_DIFF;
-                // adjust for leap seconds since GPS epoch origin
-                secs += (MBED_CONF_LORA_CURRENT_TAI_MINUS_UTC - MBED_CONF_LORA_GPS_EPOCH_TAI_MINUS_UTC);
-                set_time(secs);
-
                 //  notify the stack controller
                 if (_time_sync_cb) {
-                    _time_sync_cb();
+                    _time_sync_cb(secs);
                 }
             }
             break;
@@ -457,7 +450,7 @@ lorawan_status_t LoRaMacCommand::add_device_mode_indication(uint8_t classType)
     return ret;
 }
 
-lorawan_status_t LoRaMacCommand::add_device_time_req(mbed::Callback<void(void)> notify)
+lorawan_status_t LoRaMacCommand::add_device_time_req(mbed::Callback<void(lorawan_time_t)> notify)
 {
     //App developer must know if the server version is 1.0.3 (or greater)
     //1.0.2 does not support this MAC command and our stack does not support pre 1.0.2 versions

features/lorawan/lorastack/mac/LoRaMacCommand.h

@@ -164,7 +164,7 @@ public:
      * @return status  Function status: LORAWAN_STATUS_OK: OK,
      *                                  LORAWAN_STATUS_LENGTH_ERROR: Buffer full
      */
-    lorawan_status_t add_device_time_req(mbed::Callback<void(void)> notify);
+    lorawan_status_t add_device_time_req(mbed::Callback<void(lorawan_time_t)> notify);
 
     /**
      * @brief Set battery level query callback method
@@ -298,7 +298,7 @@ private:
     uint8_t mac_cmd_buffer_to_repeat[LORA_MAC_COMMAND_MAX_LENGTH];
 
     mbed::Callback<uint8_t(void)> _battery_level_cb;
-    mbed::Callback<void(void)> _time_sync_cb;
+    mbed::Callback<void(lorawan_time_t)> _time_sync_cb;
 };
 
 #endif //__LORAMACCOMMAND_H__