The Gumstix Game Plan

    The last few weeks have been rather busy, but with at least two light weeks in front of me, it’s time to get started with something serious. My first project with the Gumstix will be to use them to drive the Hemisson robots. I had thought about creating some sort of a simple “Robot Control Language” and then have the Gumstix translate that into serial commands to drive the Hemisson. However inventing a computer language, no matter how simple isn’t an easy task and I would like to have my first project be something simpler.

The point of using a Gumstix to talk to the Hemisson is so that a user can write higher-level algorithms without worrying about details such as making the wheel turn. I also want to use a programming language that has a relatively small amount of syntactical baggage and where it is easy to use function libraries without endless recompiling and linking. Luckily I know just such a language — Python. Python’s modules make it easy to create, use and distribute useful code. Being interpreted, there is no compilation needed which means that a user can easily write and debug programs on a host and then run them on the Gumstix without any change. Also important is the existence of the pySerial module which allows simple access to a machines serial ports: something which will invaluable to me.

Eventually performance might become an issue: the Gumstix is after all, somewhat limited in terms of its hardware and users might want to implement complex algorithms to determine the behavior of the robots.  It may become necessary to re-implement the control library in C for the added performance edge. However since Python can easily operate with C functions, the Python programs won’t have to be rewritten (though some alterations will also be needed). You could say that in some ways the Python module will be a prototype for a more powerful and efficient C implementation sometime in the future, but I can’t guarantee that at the moment.

My first step is to brush up on Python and get used to the pySerial module and see what functionality it offers. I’m not going to be using the Gumstix for a while, but rather communicating directly from laptop to the Hemisson until I have at least a rough working implementation. But before I start working on a final implementation, I will be testing the serial connection between the Gumstix and the Hemisson and making sure that Pyserial can work with it as well. With all the preliminary steps completed I can start work on a robust, full-featured module. I’m not quite certain how much work the module should handle i.e. should it just translate movement instructions from the Python code to serial or should it have algorithms to implement things like turning through angles or rotating? These are not decisions to be taken lightly because they will have a direct effect on how users will be writing their programs, and its something that I’ll be discussing with my professor. The best idea might be to implement some higher level functions but leave the underlying simpler functions open as well.

I’m not going to venture a timeline for the project, because I have other priorities which take precedence (classes for example). But I would like to have a working version by the end of the semester (beginning of May), progressing to something which is full-featured and reasonably bug-free by the end of summer (late August). With Spring Break starting in a week, I should be able to familiarize myself with both Pyserial and the Hemisson serial interface in two weeks time. After that its just a matter of proper planning and getting things working.

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Shrutarshi Basu

Programmer, writer and engineer, currently working out of Cornell University in Ithaca, New York.

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