muorb: don't start muorb with stop command

Previously using 'muorb stop' would in fact start at least part of the
muorb which is not what it's expected to do.

src/modules/muorb/krait/muorb_main.cpp

@@ -1,6 +1,6 @@
 /****************************************************************************
  *
- *   Copyright (c) 2012-2015 PX4 Development Team. All rights reserved.
+ *   Copyright (c) 2012-2016 PX4 Development Team. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -57,18 +57,26 @@ muorb_main(int argc, char *argv[])
 	 * XXX it would be nice to have a wrapper for this...
 	 */
 	if (!strcmp(argv[1], "start")) {
-		// register the fast rpc channel with UORB.
-		uORB::Manager::get_instance()->set_uorb_communicator(uORB::KraitFastRpcChannel::GetInstance());
+		if (uORB::KraitFastRpcChannel::isInstance()) {
+			PX4_WARN("muorb already running");
+		} else {
+			// register the fast rpc channel with UORB.
+			uORB::Manager::get_instance()->set_uorb_communicator(uORB::KraitFastRpcChannel::GetInstance());
 
-		// start the KaitFastRPC channel thread.
-		uORB::KraitFastRpcChannel::GetInstance()->Start();
+			// start the KaitFastRPC channel thread.
+			uORB::KraitFastRpcChannel::GetInstance()->Start();
+		}
 		return OK;
 
 	}
 
 	if (!strcmp(argv[1], "stop")) {
 
-		uORB::KraitFastRpcChannel::GetInstance()->Stop();
+		if (uORB::KraitFastRpcChannel::isInstance()) {
+			uORB::KraitFastRpcChannel::GetInstance()->Stop();
+		} else {
+			PX4_WARN("muorb not running");
+		}
 		return OK;
 	}
 
@@ -76,6 +84,11 @@ muorb_main(int argc, char *argv[])
 	 * Print driver information.
 	 */
 	if (!strcmp(argv[1], "status")) {
+		if (uORB::KraitFastRpcChannel::isInstance()) {
+			PX4_WARN("muorb running");
+		} else {
+			PX4_WARN("muorb not running");
+		}
 		return OK;
 	}
 

src/modules/muorb/krait/uORBKraitFastRpcChannel.hpp

@@ -62,6 +62,15 @@ public:
 		return _InstancePtr;
 	}
 
+	/**
+	 * Static method to check if there is an instance.
+	 */
+	static bool isInstance()
+	{
+		return (_InstancePtr != nullptr);
+	}
+
+
 	/**
 	 * @brief Interface to notify the remote entity of interest of a
 	 * subscription for a message.