AC_Avoid: add singleton

libraries/AC_Avoidance/AC_Avoid.cpp

@@ -57,6 +57,8 @@ AC_Avoid::AC_Avoid(const AP_AHRS& ahrs, const AC_Fence& fence, const AP_Proximit
       _proximity(proximity),
       _beacon(beacon)
 {
+    _singleton = this;
+
     AP_Param::setup_object_defaults(this, var_info);
 }
 
@@ -571,3 +573,15 @@ void AC_Avoid::get_proximity_roll_pitch_pct(float &roll_positive, float &roll_ne
         }
     }
 }
+
+// singleton instance
+AC_Avoid *AC_Avoid::_singleton;
+
+namespace AP {
+
+AC_Avoid *ac_avoid()
+{
+    return AC_Avoid::get_singleton();
+}
+
+}

libraries/AC_Avoidance/AC_Avoid.h

@@ -34,6 +34,11 @@ public:
     AC_Avoid(const AC_Avoid &other) = delete;
     AC_Avoid &operator=(const AC_Avoid&) = delete;
 
+    // get singleton instance
+    static AC_Avoid *get_singleton() {
+        return _singleton;
+    }
+
     /*
      * Adjusts the desired velocity so that the vehicle can stop
      * before the fence/object.
@@ -140,4 +145,10 @@ private:
     AP_Int8 _behavior;          // avoidance behaviour (slide or stop)
 
     bool _proximity_enabled = true; // true if proximity sensor based avoidance is enabled (used to allow pilot to enable/disable)
+
+    static AC_Avoid *_singleton;
+};
+
+namespace AP {
+    AC_Avoid *ac_avoid();
 };