FSM

Finite State Machine for Arduino

Code

Initial code : https://playground.arduino.cc/Code/FiniteStateMachine

Finite State Machine Description

A FSM serves as a manager that organizes a set of states, or behaviors. It manages the transition between states, and the state itself. The transitions might be caused by the user, a wall or something other that is external, and they might be caused by some internal logic. Transitions either happen immediately, or they are deferred to the next update. The latter is the most common. It's used because that way you'll know that all code related to the current state, will have executed on the same state.

It is created to help organizing and standardizing the way a FSM could be implemented. This library expects all functionality to be coded in the sketch, and the State class will simply use callbacks to simulate functionality.

All States expects an enter function, an update function and an exit function. These functions are being called according to this scheme:

current.exit(); //exit current state next.enter(); //enter next state current = next; while no transition current.update(); //TODO - extend this section, contact if urgent

Download, install and import Download here: FSM

In the Arduino IDE, create a new sketch (or open one) and

select from the menubar "Sketch->Import Library->FSM".

Once the library is imported, an "#include <FiniteStateMachine.h>" line will appear

at the top of your Sketch.

Creation State Creation

State( enterFunction , updateFunction , exitFunction )

State ethernetDebugState = State( connectToHost , debug , closeConnectionToHost );

Finite State Machine Creation

FiniteStateMachine(State& current) FSM(State& current)

FSM ethernetStateMachine = FSM(ethernetDebugState);

Initializes an FSM object with the current state equal to ethernetDebugState

Functions State Functions

void enter()

This function gets called whenever this state is entered

void update()

This function gets called whenever the state machine updates while in this state

void exit()

This function gets called whenever this state is exited

Finite State Machine Functions

void update()

This function will trigger update on the current State

void transitionTo(State& next)

This function will schedule a state change, the change itself will occur at the beginning of the next update

void immediateTransitionTo(State& next)

This function will instantly change the current state to next state

State& getCurrentState()

Returns the current state

boolean isInState( State &state )

Check if state is equal to the current state of the FSM

Example

Example LED Finite State Machine

We will implement a state machine for an LED.

From a design point of view we want to make the led go on and off, as well as fade in and out. This translates directly to the states for our example:

On Off FadeIn FadeOut The states describe themselves.

We will use external transitions, caused by a user and their button presses. Each button will cause the FSM to advance to the next State in the diagram above.

//http://playground.arduino.cc/uploads/Code/FSM.zip
#include <FiniteStateMachine.h>
//http://playground.arduino.cc/uploads/Code/Button.zip
#include <Button.h>
//http://playground.arduino.cc/uploads/Code/LED.zip
#include <LED.h>
 
const byte NUMBER_OF_STATES = 4; //how many states are we cycling through?
 
//initialize states
State On = State(ledOn);
State Off = State(ledOff);
State FadeIn = State(ledFadeIn);
State FadeOut = State(ledFadeOut);
 
FSM ledStateMachine = FSM(On);     //initialize state machine, start in state: On
 
Button button = Button(12,PULLUP); //initialize the button (wire between pin 12 and ground)
LED led = LED(11);                 //initialize the LED
byte buttonPresses = 0;            //counter variable, hols number of button presses
 
void setup(){ /*nothing to setup*/ }
 
//poor example, but then again; it's just an example
void loop(){
  if (button.uniquePress()){
    //increment buttonPresses and constrain it to [ 0, 1, 2, 3 ]
    buttonPresses = ++buttonPresses % NUMBER_OF_STATES;
    switch (buttonPresses){
      case 0: ledStateMachine.transitionTo(On); break;
      case 1: ledStateMachine.transitionTo(Off); break;
      case 2: ledStateMachine.transitionTo(FadeIn); break;
      case 3: ledStateMachine.transitionTo(FadeOut); break;
    }
  }
  ledStateMachine.update();
}
 
//utility functions
void ledOn(){ led.on(); }
void ledOff(){ led.off(); }
void ledFadeIn(){ led.fadeIn(500); }
void ledFadeOut(){ led.fadeOut(500); }

//end utility functions