FSMOS

FSMOS is a tiny and simple finite-state machine based embedded operating system. Currently, it supports Arduino and Linux/macOS platforms.

The codes under examples folder demonstrate how to use FSMOS.

About Finite-State Machine

• https://en.wikipedia.org/wiki/Finite-state_machine

Using FSMOS

Before using FSMOS in Arduino IDE, it need be installed as an Arduino library:

• Clone this project under the Arduino libraries folder (such as ~/Documents/Arduino/libraries on macOS). Or
• Download this project as a ZIP package and usage the menu Sketch/Include Library/Add .ZIP Library... to install it.

Once FSMOS installed, you can use it in your code (by #include <fsmos.h>).

• Declare an instance of FsmOs. This instance manages and schedules all the tasks. The tasks are the subclasses of FsmTask and are based on the finite-state machine model.
• Define and declare the tasks. Add them to the instance of FsmOs declared previously.
• Call the init() method of the FsmOs instance in setup function to initialize the tasks.
• Call the loop() method of the FsmOs instance in loop function to schedule the tasks.

The sample codes show as follows:

#include <fsmos.h>

class Task1 : public FsmTask {
    // ...
};

class Task2 : public FsmTask {
    // ...
};

// ...

class TaskN : public FsmTask {
    // ...
};

FsmOs fsmOs(N); // initialize FsmOs for N tasks

Task1 task1;
Task2 task2;
// ...
TaskN taskN;

void setup() {
    // Add tasks into fsmOs
    fsmOs.addTask(task1);
    fsmOs.addTask(task2);
    // ...
    fsmOs.addTask(taskN);

    // Initialize all tasks in fsmOs
    fsmOs.init();
}

void loop() {
    // let fsmOs schedules the tasks repeatedly
    fsmOs.loop();
}

There are some virtual methods should be implemented when defining the subclass of FsmTask:

• virtual void init() - when executing init() method of the FsmOs instance, this method is called. The initialization codes of the task should be in this method.
• virtual bool on_state_change(int8_t new_state, int8_t old_state) - while task scheduling, if the task should change from one state to another, this method is called.
  • new_state - the state will be changed to
  • old_state - the state will be changed from
  • returns - if the task accepts the change, true should be returned, otherwise false should be returned. Under normal circumstances, true should be returned.
• virtual void in_state(int8_t state) - while scheduling, this method is called repeatedly with the current state as the argument.

In addition, FsmTask also provides some methods for changing state:

• void gotoState(int8_t state) - change to the new state. If the task is waiting for a delay timeout, this method does nothing.
• void gotoStateForce(int8_t state) - change to the new state forcibly. If the task is waiting for a delay timeout, the delay is canceled and the new state is set.
• void delay(unsigned long timeout, int8_t new_state) - change to the new state after the delay of timeout milliseconds.

hello project shows how to use FsmTask and FsmOs：

• LedTask demonstrates how to use init, on_state_change, gotoState and delay.
• ButtonTask demonstrates how to use init, in_state, gotoState, gotoStateForce and delay.
• hello.ino demonstrates how to add, initialize and schedule the tasks.