AP_Baro: make AP_Baro a singleton

for AP_Airspeed

libraries/AP_Baro/AP_Baro.cpp

@@ -141,11 +141,16 @@ const AP_Param::GroupInfo AP_Baro::var_info[] = {
     AP_GROUPEND
 };
 
+// singleton instance
+AP_Baro *AP_Baro::_instance;
+
 /*
   AP_Baro constructor
  */
 AP_Baro::AP_Baro()
 {
+    _instance = this;
+    
     AP_Param::setup_object_defaults(this, var_info);
 }
 

libraries/AP_Baro/AP_Baro.h

@@ -30,6 +30,11 @@ public:
     AP_Baro(const AP_Baro &other) = delete;
     AP_Baro &operator=(const AP_Baro&) = delete;
 
+    // get singleton
+    static AP_Baro *get_instance(void) {
+        return _instance;
+    }
+
     // barometer types
     typedef enum {
         BARO_TYPE_AIR,
@@ -164,6 +169,9 @@ public:
     void set_pressure_correction(uint8_t instance, float p_correction);
 
 private:
+    // singleton
+    static AP_Baro *_instance;
+    
     // how many drivers do we have?
     uint8_t _num_drivers;
     AP_Baro_Backend *drivers[BARO_MAX_DRIVERS];