uORB: add Subscription method to change instance

src/modules/uORB/Subscription.cpp

@@ -88,4 +88,29 @@ void Subscription::unsubscribe()
 	_last_generation = 0;
 }
 
+bool Subscription::ChangeInstance(uint8_t instance)
+{
+	if (instance != _instance) {
+		DeviceMaster *device_master = uORB::Manager::get_instance()->get_device_master();
+
+		if (device_master != nullptr) {
+			if (!device_master->deviceNodeExists(_orb_id, _instance)) {
+				return false;
+			}
+
+			// if desired new instance exists, unsubscribe from current
+			unsubscribe();
+			_instance = instance;
+			subscribe();
+			return true;
+		}
+
+	} else {
+		// already on desired index
+		return true;
+	}
+
+	return false;
+}
+
 } // namespace uORB

src/modules/uORB/Subscription.hpp

@@ -127,6 +127,12 @@ public:
 	 */
 	bool copy(void *dst) { return advertised() && _node->copy(dst, _last_generation); }
 
+	/**
+	 * Change subscription instance
+	 * @param instance The new multi-Subscription instance
+	 */
+	bool ChangeInstance(uint8_t instance);
+
 	uint8_t  get_instance() const { return _instance; }
 	unsigned get_last_generation() const { return _last_generation; }
 	orb_id_t get_topic() const { return get_orb_meta(_orb_id); }

src/modules/uORB/SubscriptionCallback.hpp

@@ -98,6 +98,37 @@ public:
 		_registered = false;
 	}
 
+	/**
+	 * Change subscription instance
+	 * @param instance The new multi-Subscription instance
+	 */
+	bool ChangeInstance(uint8_t instance)
+	{
+		bool ret = false;
+
+		if (instance != get_instance()) {
+			const bool registered = _registered;
+
+			if (registered) {
+				unregisterCallback();
+			}
+
+			if (_subscription.ChangeInstance(instance)) {
+				ret = true;
+			}
+
+			if (registered) {
+				registerCallback();
+			}
+
+		} else {
+			// already on desired index
+			return true;
+		}
+
+		return ret;
+	}
+
 	virtual void call() = 0;
 
 protected: