Simulating a LEGO Mindstorms RCX Robot in the Robotran Environment

LEGO Mindstorms robots are very popular with colleges and universities for teaching computer concepts and programming.  These robots elicit excitement in students and provide a nontrivial, real-world platform for exploring algorithmic concepts.  We created a simple algorithmic language, called Robolang, and wrote a translator that turns it into Lejos code, a variant of Java that can be run on the RCX version of the LEGO Mindstorms robots.  Seeing that students were eager to explore programming with the RCX robots at home, we wrote a graphical simulator to visualize actions of our penbot, a configuration of the RCX robot that we used in most assignments.  Using an emulator approach, we intercept the ROM calls to the RCX's hardware made by the TinyVM, the stripped-down Java Virtual Machine that runs compiled Java bytecodes.  Our system then forwards these calls to a software model that represents the actual robot hardware.  The software model creates the graphics to mimic the penbot using Java2D. This approach greatly simplified coding by capitalizing on existing software, namely the Java compiler and the JVM.  Students can program either in Robolang or in actual Lejos and use the simulator to visualize the actions of the robot acting as a sort of visual debugger.