Jon Simpson’s Weblog

A paper describing the implementation of a ‘native’ Transterpreter virtual machine port, to create a first-class occam-pi runtime environment on a commonly available small robotics platform, the LEGO Mindstorms RCX. This paper was presented on July 11th, 2007 at Communicating Process Architectures 2007, University of Surrey, England.

Abstract

The LEGO Mindstorms RCX is a widely deployed educational robotics platform. This paper presents a concurrent operating environment for the Mindstorms RCX, implemented natively using occam-pi running on the Transterpreter virtual machine. A concurrent hardware abstraction layer aids both the developer of the operating system and facilitates the provision of process-oriented interfaces to the underlying hardware for students and hobbyists interested in small robotics platforms

BibTeX information

@InProceedings{SimpsonJacobsenJadud07,
  title = "{A} {N}ative {T}ransterpreter for the {LEGO} {M}indstorms {R}CX"
	author = "Jonathan Simpson and Christian L. Jacobsen and Matthew C. Jadud",
  editor= "Alistair A. McEwan and Steve Schneider and Wilson Ifill and Peter H. Welch",
  pages = "339-348",
  booktitle= "{C}ommunicating {P}rocess {A}rchitectures 2007",
  publisher = "IOS Press",
  isbn= "978-1-58603-767-3",
  year= "2007",
  month= "jul",
  abstract= "The LEGO Mindstorms RCX is a widely deployed educational robotics platform. This paper presents a concurrent operating environment for the Mindstorms RCX, implemented natively using occam-pi running on the Transterpreter virtual machine. A concurrent hardware abstraction layer aids both the developer of the operating system and facilitates the provision of process-oriented interfaces to the underlying hardware for students and hobbyists interested in small robotics platforms.",
}

PDF Download

• Paper, PDF Format (305K)
• Presentation, PDF Format (979K)

After upgrading the computer that holds the majority of the files on my network to Windows Vista Ultimate, I had a few problems accessing it from the Mac running Tiger. Turns out some of the network security options and authentication defaults have changed between XP and Vista.

As Mac OS X 10.4.9 does not appear to have a version of Samba that supports the more secure default authentication of Vista, it’s neccessary to tell the Vista PC to use the older methods of authentication and only the newer if requested. To achieve this, a modification to Group Policy is required. Read the rest of this entry »

As part of the Transterpreter California roadshow, Matt, Christian and myself gave a Google TechTalk on Thursday 29th March. We started out with background and an introduction to the occam-pi language, a coverage of parallel models and then progressed to cover the application work from my CPA 2006 paper, Robot Control using the Subsumption Architecture.

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Along with Matt and Christian, I was able to attend and take part in the ‘Robots and Robot Venues‘ track at the AAAI Spring Symposium at Stanford in Palo Alto, California. It proved to be an extremely interesting three days, spending time around others working with educational robotics platforms and gaining an insight into some of the challenges that go with large-scale robotics projects. Read the rest of this entry »

I’ve taken up managing my deployed web applications with subversion, similar to how I manage my wordpress installs.

However, a new issue arises. The source code to my apps is not neccessarily a public domain, open source deal (like Wordpress), and there is nothing to stop someone going to http://example.com/.svn/ or http://example.com/some_directory/.svn/ and poking around at the code. This problem gets even worse if the configuration is being version controlled (think database usernames/passwords).

A fix, the aggregate of several posts on subversion-users. Add the following lines to your Apache configuration file (tested on Apache 2).

  <DirectoryMatch /\.svn(/|$)>
    Order allow,deny
    deny from all
  </DirectoryMatch>

Well recommended for anyone using svn in publicly visible directories on web servers.

Since mplayer got decent support for SSA/ASS subtitles, complete with embedded fonts I’d been meaning to check the feature out. Recent subversion builds of mplayer had required an upgrade to freetype 2.2.1 from whatever ancient version Apple ship with OS X 10.4, and after enabling passing ‘-ass -embeddedfonts’ to the media file, I was slightly disappointed with the result.

A little googling later, and it turns out that upgrading fontconfig from 1.0.1 (4 years old, as shipped with OS X) is probably a good idea when depending on it to work happily with the new freetype and embedded fonts in the MKV file. However, things were not well as the new fontconfig refused to link properly with my new, self-compiled freetype 2.2.1 library. Modifications to freetype files, enabling the correct linker flags to propagate to fontconfig were in order..

For future use, a few relevant pointers, for when I (almost certainly) need to fix this problem again:

• The solution for compiling fontconfig 2.4.2 against freetype 2.2.1 on OS X
• mplayer-dev-eng Bug report on the MKV multiple font problem (with fontconfig as shipped by Apple)

Great to see that Lego have committed to a timescale on releasing the firmware for their new NXT robotics kits. A port of the Transterpreter to the Lego Mindstorms NXT for christmas? who knows…

Things have been quiet around here, I hope to write more over the coming weeks when things slow down for christmas.

An exploration of Brooks’ Subsumption Architecture in combination with the occam-pi language for creating robotic control systems. This paper was presented on September 18, 2006 at Communicating Process Architectures 2006, Napier University, Scotland.

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In trying to program for real-time control, good platform-assisted concurrency is vastly useful. It seems sensible to keep the limitations of a sequential execution process out of the actual software and instead, in the underlying runtime. (see TVM). Highly concurrent runtimes for small devices aren’t prevalent, and a lot of work with small robotics devices in an educational scenario is an almost LOGO style approach of entirely sequential actions.
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In continuation of the theme ‘using my blog as a personal notepad’, here’s a small snippet for use in an Apache .htaccess file to ensure that visitors/incoming links not using the www. form of your site’s domain are redirected correctly.

RewriteEngine On
RewriteCond %{HTTP_HOST} ^example\.co\.uk
RewriteRule (.*) http://www.example.co.uk/$1 [R=301,L]

Make sure to escape periods in the RewriteCond line with backslashes. Reasons you might wish to do this mostly relate to search-engine friendliness and unity of web stats.