APM_RC - Interupt safe get_last_update();

libraries/APM_RC/APM_RC.h

@@ -49,14 +49,20 @@ public:
     virtual void            Force_Out2_Out3(void) = 0;
     virtual void            Force_Out6_Out7(void) = 0;
 
-    // get the time of the last radio update
-    virtual uint32_t        get_last_update() { return _last_update; };
+    // get the time of the last radio update (_last_update modified by interrupt, so reading of variable must be interrupt safe)
+    virtual uint32_t        get_last_update() {
+        
+        uint32_t _tmp = _last_update;
+        while( _tmp != _last_update ) _tmp = _last_update;
+
+        return _tmp;
+    };
 
 protected:
     uint16_t                _map_speed(uint16_t speed_hz) {
         return 2000000UL / speed_hz;
     }
-    static uint32_t         _last_update;
+    static volatile uint32_t         _last_update; // Modified by interrupt
 
 };