Lora: Fix battery_level callback

Application can give battery_level callback method what Lora stack
uses to query battery level for DevStatusReq MAC command response.
The problem was that this callback was never called.

This commit fixes this problem and if application does not set
battery_level callback at all, value 255 (= The end-device was not able to
measure the battery level.) will be returned to lora gateway.

Author: Kimmo Vaisanen

features/lorawan/LoRaWANStack.cpp

@@ -134,6 +134,7 @@ lorawan_status_t LoRaWANStack::set_lora_callbacks(const lorawan_app_callbacks_t
 
     if (callbacks->battery_level) {
         _callbacks.battery_level = callbacks->battery_level;
+        _loramac.set_batterylevel_callback(callbacks->battery_level);
     }
 
     return LORAWAN_STATUS_OK;

features/lorawan/lorastack/mac/LoRaMac.cpp

@@ -661,6 +661,11 @@ void LoRaMac::handle_data_frame(const uint8_t* const payload,
                                  _params.ack_timeout_retry_counter, _params.max_ack_timeout_retries );
 }
 
+void LoRaMac::set_batterylevel_callback(mbed::Callback<uint8_t(void)> battery_level)
+{
+    _mac_commands.set_batterylevel_callback(battery_level);
+}
+
 void LoRaMac::on_radio_rx_done(const uint8_t* const payload, uint16_t size,
                                int16_t rssi, int8_t snr)
 {

features/lorawan/lorastack/mac/LoRaMac.h

@@ -437,6 +437,11 @@ class LoRaMac {
     void post_process_mlme_request(void);
     void post_process_mlme_ind(void);
 
+    /**
+     * Set battery level query callback
+     */
+    void set_batterylevel_callback(mbed::Callback<uint8_t(void)> battery_level);
+
     /**
      * These locks trample through to the upper layers and make
      * the stack thread safe.

features/lorawan/lorastack/mac/LoRaMacCommand.cpp

@@ -233,10 +233,11 @@ lorawan_status_t LoRaMacCommand::process_mac_commands(const uint8_t *payload, ui
             }
                 break;
             case SRV_MAC_DEV_STATUS_REQ: {
-                uint8_t batteryLevel = BAT_LEVEL_NO_MEASURE;
-                // we don't have a mechanism at the moment to measure
-                // battery levels
-                ret_value = add_dev_status_ans(batteryLevel, snr & 0x3F);
+                uint8_t battery_level = BAT_LEVEL_NO_MEASURE;
+                if (_battery_level_cb) {
+                    battery_level = _battery_level_cb();
+                }
+                ret_value = add_dev_status_ans(battery_level, snr & 0x3F);
                 break;
             }
             case SRV_MAC_NEW_CHANNEL_REQ: {
@@ -329,6 +330,11 @@ int32_t LoRaMacCommand::cmd_buffer_remaining() const
     return sizeof(mac_cmd_buffer) - mac_cmd_buf_idx_to_repeat - mac_cmd_buf_idx;
 }
 
+void LoRaMacCommand::set_batterylevel_callback(mbed::Callback<uint8_t(void)> battery_level)
+{
+    _battery_level_cb = battery_level;
+}
+
 lorawan_status_t LoRaMacCommand::add_link_check_req()
 {
     lorawan_status_t ret = LORAWAN_STATUS_LENGTH_ERROR;

features/lorawan/lorastack/mac/LoRaMacCommand.h

@@ -147,6 +147,12 @@ class LoRaMacCommand {
      */
     lorawan_status_t add_link_check_req();
 
+    /**
+     * @brief Set battery level query callback method
+     *        If callback is not set, BAT_LEVEL_NO_MEASURE is returned.
+     */
+    void set_batterylevel_callback(mbed::Callback<uint8_t(void)> battery_level);
+
 private:
     /**
      * @brief Get the remaining size of the MAC command buffer
@@ -261,6 +267,8 @@ class LoRaMacCommand {
      * Buffer containing the MAC layer commands which must be repeated
      */
     uint8_t mac_cmd_buffer_to_repeat[LORA_MAC_COMMAND_MAX_LENGTH];
+
+    mbed::Callback<uint8_t(void)> _battery_level_cb;
 };
 
 #endif //__LORAMACCOMMAND_H__

features/lorawan/lorawan_types.h

@@ -274,8 +274,17 @@ typedef struct  {
       * Optional
       */
      mbed::Callback<void(uint8_t, uint8_t)> link_check_resp;
+
+     /**
+      * Battery level return value must follow the specification
+      * for DevStatusAns MAC command:
+      *
+      *     0       The end-device is connected to an external power source
+      *     1 - 254 The battery level, 1 being at minimum and 254 being at maximum
+      *     255     The end-device was not able to measure the battery level.
+      */
      mbed::Callback<uint8_t(void)> battery_level;
- } lorawan_app_callbacks_t;
+} lorawan_app_callbacks_t;
 
 /**
  * DO NOT MODIFY, WILL BREAK THE API!