QP state machine framework for Arduino

[Nathan Odle]

We have a small project here and I decided to take the opportunity to teach one of my employees a little more about microcontrollers so we're actually using an Arduino for the task.  I needed a good state machine implementation and discovered that the QP framework has been ported to Arduino (there was already a nice AVR port).  State machines are incredibly useful for anyone wanting to do anything 'serious' (or even no-so-serious) with uCs, and I know the Arduino is the go-to platform for a lot of hobbyists, so if anyone in the group hasn't had the opportunity to play around with them I'd recommend taking a look at QP.  It's open-source, runs on just about any platform under the sun (including DOS of all things), and can has versions for both C and C++.  The online documentation is a bit sparse - and even confusing - but there is a decent companion book ("Practical UML Statecharts in C/C++, Second Edition") that is available on Safari Online so if you have a membership you can read it for free.  As a bonus, the book covers UML state machine concepts in detail.  And no, I'm not affiliated in any way with the QP project :)

The QP website is:  http://www.state-machine.com/index.php

The Arduino port can be found here:  http://arduino.cc/playground/Code/QP

There is another FSM implementation on the Arduino Playground there, but unfortunately it hasn't been updated for v1.0 of the Arduino environment.  It is much simpler than QP, but QP is a much more robust implementation which supports both FSMs (Finite State Machines) and HSMs (Hierarchical State Machines).  Also, I should mention that QP includes a little preemptive kernel for multitasking.

Enjoy!

-N

P.S.  If none of you have heard of Safari Books, it is awesome.  I wonder if they would be open to providing a group membership for CGW?