January 2010 – Observations from Uppsala

Neat Register Design to Avoid Races

racecondition In his most recent Embedded Bridge Newsletter, Gary Stringham describes a solution to a common read-modify-write race-condition hazard on device registers accessed by multiple software units in parallel. Some of the solutions are really neat!

I have seen the “write 1 clears” solution before in real hardware, but I was not aware of the other two variants. The idea of having a “write mask” in one half of a 32-bit word is really clever.

However, this got me thinking about what the fundamental issue here really is.

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Compiler Code Size Comparisons (for Possible Embarrassment)

whyc An embedded researcher friend of mine has posted some data on code sizes from various compilers at http://embed.cs.utah.edu/embarrassing/. The “embarrassing” bit is the idea that compiler writes should be ashamed when other compilers do better than theirs. It is worth looking over the data, even though the methodology and benchmarks are not yet perfect by any means.

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Contributing to the Reversible GDB

Last week, I finally got the last “OK” from the maintainers of GDB, the Gnu Debugger, indicating that my contribution to the GDB project was accepted. This is my first contribution to an open-source project, and the piece of code that has my name on it is positively puny. It is actually not really code at all, it is just a piece of documentation, for the extensions to the GDB-MI command set needed to support reversible debugging. The actual code doing the work was contributed by a colleague of mine, Tomas Holmberg, credit where credit is due.

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Eclipse: Changing the Java Heap Size

eclipseicon I just won a battle against Eclipse, managing to finally rid myself of a string of strange out-of-heap warnings. It is a long story, involving lots of web searching and fiddling with the eclipse.ini file options for the JVM. It just never seemed to work as I wanted it to, despite changing the -Xmx VM argument to 256, then 512, and finally 1024m.

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Concurrency in Lego Mindstorms NXT

lego mindstorms nxt2

For my parental leave, I have just bought myself a Lego Mindstorm NXT 2.0 kit. It is not much fun for our youngest, who mostly gets a bit scared by a piece of Lego driving around making noises, but I hope to be able to use it to teach my older child (almost five) to program. Let’s see how that turns out. It looks hard to make the NXT environment provide the kind of Roborally-style programming blocks that I had hoped to create, as I cannot for some reason get a sufficiently custom icon onto custom blocks.

It also presented me with an opportunity to try some domain-specific high-level graphical programming. The programming environment provided for the NXT series of Mindstorms kits is based on LabView from National Instruments, and it really does seem to work. It even features parallel tasks, which I tried to use…

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Parental Leave

jakob on parental leave_1

For the next few months, I will be on parental leave, so there is likely to be less blogging about technical subjects (and less blogging overall). There is simply less inspiration about virtual platforms, and a bit more about toys.

Off-Topic: Old and New Lego

During the Christmas holidays, I got the chance to compare my oldest child’s brand new Lego set with some from the mid-1980s. It is quite striking how much larger the things in the sets have become, and how much more affordable (in relative terms) Lego has become since then.

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