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Event-driven state machine framework for Arduino

e14 Contributor
Background
Traditionally, Arduino programs are written in a sequential manner, which means that whenever an Arduino program needs to synchronize with some external event, such as a button press, arrival of a character  through the serial port, or a time delay, it explicitly waits in-line for the occurrence of the event. Waiting in-line means that the Arduino processor spends all of its cycles constantly checking for some condition in a tight loop (called the polling loop).
Although this approach is functional in many situations, it doesn't work very well when there are multiple possible sources of events whose arrival times and order you cannot predict and where it is important to handle the events in a timely manner. The fundamental problem is that while a sequential program is waiting for one kind of event (e.g., a button press), it is not doing any other work and is not responsive to other events (e.g., characters from the serial port).
For these and other reasons (such as power dissipation) experienced programmers turn to the long-know design strategy called event-driven programming, which requires a distinctly different way of thinking than conventional sequential programs. All event-driven programs are naturally divided into the application, which actually handles the events, and the supervisory event-driven infrastructure (framework), which waits for events and dispatches them to the application. The control resides in the event-driven framework, so from the application standpoint, the control is inverted compared to a traditional sequential program.
QP Framework for Arduino
QP is a lightweight, open source, state machine framework for microcontrollers such as Arduino. QP enables you to build well-structured and power-efficient event-driven programs as systems of concurrently executing state machines (UML statecharts). You can think of QP as a modern real-time operating system (RTOS) specifically designed for executing state machines. The QP framework does everything you can expect from a traditional RTOS, only more efficiently, plus many things an RTOS can't do at all.
QP is also an excellent target for automatic code generation. To this end, QP is now supported by the the free graphical QM modeling tool, which can automatically generate complete Arduino sketches from state diagrams. Thus QP is your entry into graphical programming for Arduino.
QP improves productivity, because you no longer need to struggle with convoluted if-else "spaghetti" code and you don't need to worry about semaphores and other such low-level RTOS mechanisms. Instead, you can work at a higher level of abstraction of events and state machines.
Downloads and Documentation
QP for Arduino code download: qp_arduino.zip http://www.state-machine.com/arduino/qp_arduino.zip
Application Note "Event-Driven Arduino Programming with QP" (http://www.state-machine.com/arduino/AN_Event-Driven_Arduino.pdf)
QP page at Arduino Playground: http://arduino.cc/playground/Code/QP
Arduino page at state-machine.com: http://www.state-machine.com/arduino
Free QM graphical modeling tool: http://www.state-machine.com/qm

Background

Traditionally, Arduino programs are written in a sequential manner, which means that whenever an Arduino program needs to synchronize with some external event, such as a button press, arrival of a character  through the serial port, or a time delay, it explicitly waits in-line for the occurrence of the event. Waiting in-line means that the Arduino processor spends all of its cycles constantly checking for some condition in a tight loop (called the polling loop).

 

Although this approach is functional in many situations, it doesn't work very well when there are multiple possible sources of events whose arrival times and order you cannot predict and where it is important to handle the events in a timely manner. The fundamental problem is that while a sequential program is waiting for one kind of event (e.g., a button press), it is not doing any other work and is not responsive to other events (e.g., characters from the serial port).

 

For these and other reasons (such as power dissipation) experienced programmers turn to the long-know design strategy called event-driven programming, which requires a distinctly different way of thinking than conventional sequential programs. All event-driven programs are naturally divided into the application, which actually handles the events, and the supervisory event-driven infrastructure (framework), which waits for events and dispatches them to the application. The control resides in the event-driven framework, so from the application standpoint, the control is inverted compared to a traditional sequential program.

 

QP Framework for Arduino

QP is a lightweight, open source, state machine framework for microcontrollers such as Arduino. QP enables you to build well-structured and power-efficient event-driven programs as systems of concurrently executing state machines (UML statecharts). You can think of QP as a modern real-time operating system (RTOS) specifically designed for executing state machines. The QP framework does everything you can expect from a traditional RTOS, only more efficiently, plus many things an RTOS can't do at all.

 

Graphical State Machine Programming for Arduino

QP is also an excellent target for automatic code generation. To this end, QP is now supported by the the free graphical QM modeling tool, which can automatically generate complete Arduino sketches from state diagrams. Thus QP is your entry into graphical programming for Arduino.

QP improves productivity, because you no longer need to struggle with convoluted if-else "spaghetti" code and you don't need to worry about semaphores and other such low-level RTOS mechanisms. Instead, you can work at a higher level of abstraction of events and state machines.

 

Downloads and Documentation

 

 

Miro Samek