leJOS RCX

A tiny Java Virtual Machine for the Lego MindStorms RCX, containing a VM for Java bytecodes and additional software to load and run Java programs.

Notes

The source code as available in the leJOS RCX repository on SourceForge does not successfully and reliably finish a complete build. The following initial updates have been implemented by Matthew Sheets in an effort to be able to reliably build the project:

• The librcx float code has been updated based on the latest patches in brickOS
• During builds, CodePacker random size-packing testing would randomly fail to generate a valid file that could be used by the linker, especially for small firmware sizes
• There is an unfortunate mixing and matching of ant and make; as such some configuration settings must be made in multiple places
• Configuration settings
  • Build configurations are set to support Debian/Ubuntu to provide support for the greatest number of use cases
    • Linux, both 32-bit and 64-bit
    • Windows, via both Windows Subsystem for Linux and as a Hyper-V "Quick Create" option
  • In build.properties
    • Change the "lejos.ostype" property according to your particular platform type
    • Firmware building, which requires the h8/300 cross-toolchain is currently configured to be built by default; comment out the property "build.lejos.firmware" to skip this

Known Issues

1. Floating Point Disabled: Internal error thrown by the version of the h8/300 cross-toolchain available on Debian/Ubuntu

void do_fcmp (JFLOAT f1, JFLOAT f2, STACKWORD def)
{
  if (f1 > f2)
    push_word (1);
  else if (f1 == f2)
    push_word (0);
  else if (f1 < f2)
    push_word (-1);
  else 
    push_word (def);
}

src/javavm/Makefile.include:3: recipe for target 'interpreter.o' failed
src/javavm/interpreter.c: In function `engine':
src/javavm/interpreter.c:78: internal compiler error: in byte_reg, at config/h8300/h8300.c:342
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.
make: *** [interpreter.o] Error 1

BUILD FAILED

2. The "vision.jar" target is currently disabled due to dependencies on deprecated package com.sun.image.codec.jpeg

IDE Configurations

• Eclipse: Plugins available at the leJOS-RCX-Eclipse project site
• Netbeans: Archived Makezine article

Alternate API

• leJOS-RCX-Alt-API: An alternative to part of the standard leJOS API designed to fit an objects-early approach to teaching programming
  • Perhaps could be incorporated into the mainstream leJOS-RCX release at some point?

Utilities

• leJOS-RCX-MindStormsTools
  • A small toolkit to aid in the uploading of Java programs to LEGO MindStorms RCX bricks, providing functionality of the leJOS library in the development environment for this purpose
• leJOS-RCX-Tools
  • A visual interface for leJOS. RCXDownload automatically sets the JDK-, leJOS- and ClassPaths, compiles the chosen Java-Source, shows the compiler messages and is able to link and load both the compiled classes and the leJOS-firmware.
• leJOS-RCX-TextLCDApplet
  • Java Applet GUI for testing josx.platform.rcx.TextLCD

Java Support

As time passes, it has become more of a challenge to use leJOS with newer Java versions. Some work has been done to try to mitigate these challenges.

• oversticht/lego-rcx-lejos (external)
  • Based on leJOS v2.1 instead of v3.0-RC2 that is in the repository in this BrickBot organization
• HaikuVM (external)
  • A spinoff Java VM approach referenced by @oversticht