TinyVM: NetRexx for Lego RCX

This page describes how to run NetRexx programs in the Lego Mindstorms^TM RCX, which is part of Lego's Robotics Invention System. This is achieved with the help of the TinyVM system.

Requirements

This has been tested on CygWin with JDK 1.2.2 and TinyVM 0.2.1. Other setups should also work.
Same requirements as TinyVM. See User's Guide

Setup

Download TinyVM 0.2.1+ and install it as usual.
Download NetRexx. You only need to unzip the file.

You may want to create a compilation script, e.g. tvmnrxc, which may look like this:



## Modify configuration variables below

TINYVM_HOME=//d/projects/tinyvm
NETREXX_HOME=//d/projects/NetRexx
JAVA_HOME=//d/jdk1.2.2

if [ -f "${JAVA_HOME}/lib/tools.jar" ];
then
  TOOLS_FILE="${JAVA_HOME}/lib/tools.jar"
else
  TOOLS_FILE="${JAVA_HOME}/lib/classes.zip"
fi

if [ "${OSTYPE}" = "cygwin32" ];
then
  TOOLS_FILE="`cygpath -w "${TOOLS_FILE}"`"
  TINYVM_CLASSES="`cygpath -w "${TINYVM_HOME}/lib/classes.jar"`"
  TINYVM_HOME="`cygpath -w "${TINYVM_HOME}"`"
  NETREXX_HOME="`cygpath -w "${NETREXX_HOME}"`"
  CLASSPATH="${TINYVM_CLASSES};${CLASSPATH}"
  CLASSPATH="${CLASSPATH};${NETREXX_HOME}\\lib\\NetRexxC.jar"
  CLASSPATH="${CLASSPATH};${TOOLS_FILE}"
else
  CLASSPATH=${TINYVM_HOME}/lib/classes.jar:${CLASSPATH}
  CLASSPATH=${CLASSPATH}:${NETREXX_HOME}/lib/NetRexxC.jar:${TOOLS_FILE}
fi

export CLASSPATH

java -ms4M COM.ibm.netrexx.process.NetRexxC $*

Example

Follow these instructions to run a simple program that continuously displays the raw value of sensor 2.

Download the firmware, if you haven't done so yet, with tvmfirmdl.

Copy the following NetRexx program into a file named sensors.nrx.


/* Use of SensorListener */

import tinyvm.rcx.

class sensors implements SensorListener

 /** One of the methods in SensorListener */
 method stateChanged(source=Sensor, value=boolean)
 
 /** Another of the methods in SensorListener */
 method stateChanged(source=Sensor, value=int) 
   /* This method is called whenever the raw value changes */
   LCD.showNumber(value)
   Time.sleep(2)
   
 /** Main method */
 method main(s=String[]) static           
   /* Create a sensor listener instance */
   listener = sensors()
   /* Active sensor 2 */
   Sensor.S2.activate()
   /* Add the listener to sensor 2 */
   Sensor.S2.addSensorListener(listener)
   /* Programs runs forever when sensor listener is active */

Set CLASSPATH to . (dot).
Compile sensors.nrx with your NetRexx compilation script.
Download program with tvmld sensors -d.
You can press Run as soon as the standing man figure appears.

Limitations

In addition to TinyVM's limitations, you won't be able to use all of the NetRexx constructs, e.g. the say command. In most cases, the linker will complain if you try to use these constructs.

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