Les Smithson's C++ for LegOS

Introduction

I couldn't find any C++ support for Markus L. Noga's excellent LegOS Version 0.2.3, so I did it myself. I make it available here for others to use. The work consisted of building a C++ egcs/gcc compiler and writing some runtime support code for it. Once this was done, I started to write some class wrappers around the LegOS library.

Some Caveats

I've only tried this on Linux, but there's no reason it shouldn't work on Windows.

The C++ run-time support is incomplete & not properly tested. C++ exceptions are not supported, and I haven't explored the more esoteric features of inheritance & polymorphism. I'd appreciate some help with this.

Downloads

Building the C++ Compiler

I pretty much followed Luis Villa's LegOS HOWTO instructions to the letter, with the following exceptions:

You might like to try the original instructions first, then try these. It worked for me.

Runtime Support Code

LegOS 0.2.3 comes with some C++ support code in lib/c++. This consists of a Makefile, and the files hack.c and sensors.cpp. The Makefile builds lib/libc++, which you should link with your C++ code. Hack.c contains some elementary run-time functions required to link C++ applications. Sensor.cpp looks like wrapper code for Lego rotation sensors. I ignored it.

To get me compiling real, usable C++ LegOS programs, I hacked hack.c some more, and added tinfo.cc to support typeinfo stuff for virtuals. Here is a tar file with the files required to build the new libc++.a.

Before building anything, you should modify the TOOLPREFIX line in Makefile.common to point to the path you installed your new compiler in.

Caveat

I don't really know what I'm doing with this stuff. I just hacked 'till things worked. In particular, I'm somewhat mystified by tinfo.cc, which I found in the gcc source directory. Having said that, it seems to work with simple class definitions, single inheritance, and the virtual keyword does what it should.

Compiling C++ programs for LegOS

To compile a C++ program for LegOS, you should first build the C++ cross-compiler as described here, then build the modified run-time support code. This assumes you've modified TOOLPREFIX as described above.

You should now be ready to compile a C++ program & download it to the RCX. Here is a tar file with a simple 'hello world' C++ program & makefile for you to test. The makefile assumes its running in a directory below the main LegOS one, parallel to the demo directory.

LegOS Wrapper Classes

I started on some rudimentary C++ wrappers around the LegOS calls. You can download this from here. The aim was to develop classes that are building blocks representing real Lego objects, such as motors, sensors, things that move etc. These can then be assembled to control real robots.

This is only the first cut. The classes are very incomplete, but useful at demonstrating the idea. I've used them to build rovers & line-followers.

Bloat

You will notice that the .lx files get quite large. A simple rover written in C is about 500 bytes (including libc.a). Written in C++, this grows to about 6k! 2.5k of this is in wrappers++.o, and another 2.5k is in libc++.a.

Some work will have to go into making this smaller, maybe with judicious use of inlining.

TODO List

All help appreciated!

A Debugger

See here for information about my attempt to get gdb woring with legOS, C & C++.

Disclaimer

You are free to use this code in any way you see fit, subject to the LegOS disclaimers & copyrights. I make no representations about the suitability of this software for any purpose. It is provided "AS-IS" without warranty of any kind, either express or implied. So there.

Contact Me

Question, Comments, Suggestions & Bugs to lsmithso@hare.demon.co.uk. Or see my Home Page.

(c) Copyright L. Smithson 2000. Last updated January 28 2000
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