Tag Archives: LeJOS

Installing LeJOS NXJ on Mac OS X 10.6 (Snow Leopard)

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The intensity of the term has lulled, marginally, so last night I completed my migration from PC to Mac.  I installed LeJOS NXJ, a Java programming environment for the LEGO Mindstorms NXT. It lets us program LEGO robots in Java.

LeJOS is an open source project hosted in the sourceforge repository. It was forked from the TinyVM project which implemented a Java VM for the LEGO Mindstorms RCX system.

By installing I mean adding these to my Macbook Pro and successfully installing the first item on the list on my LEGO Mindstorms NXT brick:

  1. Replacement firmware for the NXT that includes a Java Virtual Machine
  2. A library of Java classes that implement the leJOS NXJ API
  3. A linker for linking user Java classes with classes.jar to form a binary file that can be uploaded and run on the NXT
  4. PC tools for flashing the firmware, uploading programs, debugging, etc
  5. A PC API for writing PC programs that communicate with leJOS NXJ programs using Java streams over Bluetooth, USB, or the LEGO Communications Protocol (LCP)

I’ve blogged about my introduction to LeJOS and Mindstorms and have successfully used LeJOS on Windows Vista and Windows 7 as well as Ubuntu.   Configuring the environment on my Mac was, as usual, easiest of the three.

Recall that I am using a mid-2010 MacBook Pro running Mac OS X 10.6. LeJOS NXJ requires some of the drivers from the original LEGO brand software that ships with the robot.  I tried using the CD that came with my Mindstorms (purchased in May 2008) to install the original LEGO system, but it didn’t install.  There were no error messages but the app never appeared in my apps folder.  This is how I solved the problem:

1. A little probing on the LEGO website and I found a Snow Leopard fix which I used to complete the installation.  I also found and installed the latest LEGO firmware update (version 1.29).

2. Because of the difficulty I’ve had with drivers on both Windows and Ubuntu, I also installed the Fantom Driver on top of the MindStorms app.

All of these are at: http://mindstorms.lego.com/en-us/support/files/Driver.aspx#Driver

3. Download and unzip LeJOS NXJ: http://sourceforge.net/projects/lejos/files/lejos-NXJ/

4. Set the permissions in the downloaded folder:
chmod -R 755 /pathto/lejos_nxj/

5. Edit etc/launchd.conf to include (I already had this from a former install):
setenv JAVA_HOME /Library/Java/Home

6. Edit ~/.bash_profile to include
LEJOS_HOME=/pathto/lejos_nxj
NXJ_HOME="$LEJOS_HOME"
DYLD_LIBRARY_PATH=/pathto/lejos_nxj/bin
export LEJOS_HOME NXJ_HOME DYLD_LIBRARY_PATH
PATH="$LEJOS_HOME/bin:$PATH"
export PATH

This is where I got stuck.  No matter how I adjusted these environment variables, every time I connected the NXT brick by USB and tried to flash the LeJOS firmware onto it, I received some permutation of

Bad news: An error has occurred lejos.pc.comm.NXTCommException: Cannot load a comm driver!

It’s always something with LeJOS and it’s always something I’ve overlooked.  In this case, my Java defaults to 64 bit and LeJOS needs to use 32 bit.  I recently upgraded my RAM to 8GB and in order for the Win 7 virtual drive in my Virtual Box to use 4 GB of memory I have to boot Snow Leopard in 64 bit kernel mode (by holding the 6 and the 4 down during startup).  It is necessary to:

7. Manually add the -d32 flag to the LEJOS scripts. Setting the Java version in system preferences won’t do the trick.  Open all the non-binary files (the ones that don’t end with .bin) in the /pathto/lejos_nxj/bin/ folder and edit all calls to “java” to include -d32 to make them run in 32-bit mode.

Worked like a charm.

I was motivated by more than the opportune free evening.  I am considering enrolling in September in a directed studies course at UBC in which students make a proposal to a faculty member to investigate a topic that goes beyond that which is covered in existing courses.  I’ve enjoyed working (and playing!) with Mindstorms (what red-blooded Canadian wouldn’t!) and last term I enjoyed learning Haskell and Prolog.  This term’s course in internet computing is beginning to stand out as a favourite.  I’m also itching to learn Erlang.  Somewhere in this there is some interesting work…

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LeJOS NXJ

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LeJOS is replacement firmware for the Lego Mindstorms RCX and NXT bricks. It’s based on the Java programming language and includes a JVM, or Java Virtual Machine, which allows Lego Mindstorms robots to be programmed in Java.

LeJOS is an open source project which means you can participate in its development, or download the source code and turn it into a creation of your own.

The current version is 0.85 released September 2009.

Lego Mindstorms Robotics Kits:
http://mindstorms.lego.com/
LeJOS Java for Lego Mindstorms
http://lejos.sourceforge.net/
Official LeJOS Developer Forum:
http://lejos.sourceforge.net/forum/
Lego Digital Designer:
http://ldd.lego.com/
Installing Lejos on Ubuntu 8.04 (old but still applicable):
http://lejos.sourceforge.net/forum/viewtopic.php?p=3785
http://ubuntuforums.org/showthread.php?t=854846

In 2008 at BCIT I worked with a team of 4 others in a software development project using LeJOS. BCIT owns a large room full (and I mean FULL) of Lego Mindstorms Lego. We applied what we had learned about iterative development and project management during our first year to a 5-week software development lifecycle, from requirements gathering to specification to implementation and delivery. We applied two terms of Java to a series of architecture and programming milestones and a final tournament based on the competitions organized by the First Lego League.

Our team (Hadaga) finished in 2nd place out of 23 (winner score: 495 / average score: 320 / our score: 395 ). I’ve included some of our code and design documents as an example of great teamwork and good clean fun.

Our Team Hadaga Tournament Code (Uncompiled Java):
Nano table [3 KB] Power table [12 KB]
Team Hadaga Robot Building Instructions (Lego Digital Designer format):
Hadaga_Building_Instructions.lxf [28 KB]
Team Hadaga Design Docs (pdf):
Team Agreement [73 KB] Concept Document [224 KB] Design Document [3.4 MB]
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AT91SAM7S256 aka the NXT Brain

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The Lego MindStorms NXT Brick is controlled by a pair of Atmel microcontrollers:

The AT91SAM7S256 is part of an Atmel series of low pin-count Flash microcontrollers based on the 32-bit ARM7DMI ARM Thumb RISC processor. It features:

  • a maximum clock speed of 55 MHz (48 MHz in the NXT)
  • 64 KB of high-speed on-chip SRAM
  • 256 KB of integrated high-speed Flash memory
  • 11 peripheral DMA channels
  • 1 USB 2.0 (12 MB/s) device port
  • three 16-bit timers
  • four PWM controllers
  • 32 I/O pins
  • and requires a 3.0- to 3.6-volt power supply

The key facts here are:

  • The RISC–reduced instruction set architecture–is based on ARMv4T Von Neumann architecture. The ARM7DMI processor provides 0.9 MIPS (millions of instructions per second).
  • ARM–32-bit instruction set
  • Thumb–critical subset of the ARM 32-bit instruction set that has been encoded into a 16-bit instruction set
  • Flash memory–can be programmed in-system via the JTAG-ICE interface or through a parallel interface on a production programmer prior to mounting

The ARM7DML can execute both the high-performance 320bit ARM and high-density 16-bit Thumb instruction sets. The instruction sets are toggled by the processor as an ARM state or a Thumb state. In the ARM state, the 32-bit instructions are executed conditionally, while the 16-bit Thumb state instructions are a re-encoded subset of the ARM instruction set. The stegosaurus had a brain in its arse, and basically so does the NXT Brick. The AVR 8-bit ATmega48 microcontroller acts as a co-processor. Inside it there are:

  • 4 KB reprogrammable Flash program memory
  • 512 Byte SRAM
  • 256 Byte EEPROM
  • 8-channel, 10-bit AéD converter (TQGPéMLF)
  • 23 I/O pins
  • 4 MHz clock speed

Here’s the interesting thing. The ATmega48 is much smaller than the main AT91SAM7S256 processor, but this 8-bit microprocessor achieves almost 1 MIPS per MHz by executing its RISC instruction set in a single clock cycle.

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