init: init nachos hw01, should pass jenkins os_group_20_hw job but fail on os_group_20_ta job

code/machine/callback.h

@@ -0,0 +1,44 @@
+// callback.h 
+//	Data structure to allow an object to register a "callback".
+//	On an asynchronous operation, the call to start the operation
+//	returns immediately.  When the operation completes, the called 
+//	object must somehow notify the caller of the completion.
+//	In the general case, the called object doesn't know the type
+//	of the caller.
+//
+//	We implement this using virtual functions in C++.  An object
+//	that needs to register a callback is set up as a derived class of
+//	the abstract base class "CallbackObj".  When we pass a
+//	pointer to the object to a lower level module, that module
+//	calls back via "obj->CallBack()", without knowing the
+//	type of the object being called back.
+//
+// 	Note that this isn't a general-purpose mechanism, 
+//	because a class can only register a single callback.
+//
+//  DO NOT CHANGE -- part of the machine emulation
+//
+// Copyright (c) 1992-1996 The Regents of the University of California.
+// All rights reserved.  See copyright.h for copyright notice and limitation 
+// of liability and disclaimer of warranty provisions.
+//
+
+#ifndef CALLBACK_H
+#define CALLBACK_H 
+
+#include "copyright.h"
+
+// Abstract base class for objects that register callbacks
+
+class CallBackObj {
+   public:
+     virtual void CallBack() = 0;
+   protected:
+     CallBackObj() {};	// to prevent anyone from creating
+				// an instance of this class.  Only
+				// allow creation of instances of
+				// classes derived from this class.
+     virtual ~CallBackObj() {};
+};
+
+#endif