leJOS (pronounced like the Spanish word "lejos" for "far") is a
tiny Java-based operating system that
has been ported to the following platforms:
- Lego Mindstorms NXT
- Lego Mindstorms RCX
- Unix (for emulation of lejos programs only)
leJOS was originally forked out of the TinyVM project.
It contains a VM for Java bytecodes and additional software to load and
run Java programs.
These are some of the features offered:
- Object oriented language (Java)
- Preemptive threads (tasks)
- Arrays, including multi-dimensional ones
- Recursion
- Synchronization
- Exceptions
- Java types including float, long, String, but with some restrictions
- Math class
- Well-documented Robotics API
- You need a Java Development Kit (JDK), preferably 1.5
- Your PATH must contain the JDK's bin directory
- Make sure you have set JAVA_HOME properly to the root directory
of the JDK
- In case you want to build the distribution, your PATH must
contain the ant binary (ant 1.6 or above)
- You need libusb installed. On Windows you should use the libusb-Win32 filter driver
- On Windows you will need the Lego Mindstorms NXT software installed, as its USB drivers are used
Please download the leJOS
documentation from the same location you downloaded this distribution.
- Set your environment variable LEJOS_HOME to the
directory you installed this distribution into
- Add leJOS's bin directory to your PATH
- On Linux, depending on the privilege settings you might need to
adjust the execution permissions in the bin folder
On Linux, you will have to build the distribution first. To do so,
switch to the build folder and run ant.
Note that depending on the privilege settings you might need to adjust
the the execution permissions in the release folder.
- Compile using lejosjc instead of javac
- Link programs using lejoslink
- Download and run programs using lejosdl
- Emulate leJOS programs on the host using emu-lejosrun (currently Linux only)
- Exceptions: Use lejoslink --verbose. Exceptions are shown in the NXT as Method:XXXX, CLASS:YY, where XXXX = method_signature and YY = exception_class_index
Your NXT must be plugged into the USB, switched on, and in firmware update mode to run lejosdl.
To go into firmware update mode press the reset button (at the back of the NXT , upper left corner) for more than 4 seconds.
Your NXT will audibly tick when it is firmware update mode, but is not running a lejos program.
To switch your NXT on, just press the orange button. It will start to audibly tick.
When you use lejosdl your program will download and run. You can stop a program by pressing the ENTER and ESCAPE (orange and grey square) buttons together.
This powers down the NXT immediately. Press the ENTER (orange) button to wake it up again.
You can also power down the NXT with ENTER + ESCAPE, after an Exception occurs.
Due to size constraints, some Java language
features have been omitted. Others just haven't been implemented yet.
Known limitations are:
- Garbage collection is not performed yet.
Hence, the number of objects in your program should be limited
- Switch statements are not supported
- Arithmetic operations on variables of type long are not
supported, although you can cast ints to longs and vice versa
- Maximum array length is 511
- The instanceof operation will always be true for interfaces. In
bytecode, CHECKCAST succeeds on all interface classes (which is a bit
unsafe)
- The instanceof and checkcast operations are rejected by the
linker when they are performed on array classes (e.g. b instanceof
byte[])
- There are no objects of type java.lang.Class, which means that
the ".class" construct won't work. Class.forName() throws
ClassNotFoundException at all times. As a consequence, reflection is
not supported by leJOS
- Most JDK APIs are unavailable
- MONITOREXIT ignores null objects (it assumes
MONITORENTER has handled them). Furthermore, it doesn't check monitor
validity. Until this bug is fixed (actually, at all times) all monitors
should be constants
- Initializers (static or otherwise) are not implicitly
synchronized. This could lead to access of statics before they are
initialized, when multiple threads use a class
Please download the leJOS documentation from
the same location you downloaded this distribution from. The
documentation contains the API docs.
We are continuing to release under the Mozilla Public License
(see the LICENSE file). The runjava utility using David Anderson's libnxt
which is release under a GPL v2 license (see COPYING in the libnxt directory).
Please direct feedback to the lejos-discussion
mailing list mailto:lejos-discussion@lists.sourceforge.net.
To subscribe, see http://lists.sourceforge.net/lists/listinfo/lejos-discussion.
Feel free to take a look at the Lejos
website or its project
page.