A library in C to create simple finite state machines following the logic of "if(condition) then (action), wait(time), reset(if condition, another action)". Initially programmed and tested for ATmega328, but can run with any other architecture as long as there is a function called "millis" that returns the number of milliseconds since the program started.

Finite state machines in general are a practical way to wait for events or creating delays without blocking the whole process, for example this is how async functions in C# are implemented. In the following examples we will see how to wait a button to be pressed without using a inifinte loop, then we wait 1 second without using _delay_ms.

• In your program include the sequence.cpp
• Make sure that there is an implementation of the function "millis" and "millis_init"
• In your code create a "Sequence" object and call the functions If, Do, Wait (optional), Break (optional), Reset with their parameters, order doesn't matter and not necessarily called from the same place

• If : accepts as parameter a function that returns a bool called condition, if the machine is in init state and condition returns true the machine moves to the next step : the state of verified
• Do : has one parameter, a function called action, if the machine is in the state of verified, action is executed then the machine moves to the state of done
• Wait (optional) : adds a delay between Do and Reset, preferably called before Reset or atleast before the reset condition, this function just modifies a variable, the actual waiting (sort of) is done in the function Reset (see below)
• Break (optional) : as a parameter it accepts a function condition to stop the timer. When the timer is reset, calling Wait won't restart it until the machine is reset.
• Reset : has two parameters, codition and action, if the machine is in done state and the timer (optional) is consumed and condition returns true, the function action is executed and the machine returns to init state.

The following example expects a button to be pressed in PB0, an LED in PB1 is turned on, if after 1 second the button is realease, the led is turned off (the function Break is not used)

#include "sequence.cpp"

int main()
{
    Sequence sequence;    
    DDRB = 1 << PB1;
    while (true)
    {
        sequence.
          If([]() -> bool { return PINB & 1; }).
          Do([]() { PORTB |= 1 << PB1; }).
          Wait(1000).
          Reset([]() -> bool {return !(PINB & 1); }, []() { PORTB &= ~(1 << PB1); });
    }

}

In this example we will use another button too interrupt the timer and turn off the LED earlier, this is done with the function Break

          ...
          Wait(1000).
          Break([]() -> bool { return PINB & (1 << PB2);}). // if the button (in PB2) is pressed the led is turned off
          ...

In the following example we will use two machines to command 2 leds with different timers and different on/off buttons, the LED is in PD1, ON button is on PD0 and off button is on PD2 (the two sequences use lambda functions)

DDRB = 1 << PB1;
DDRD = 1 << PD1;
Sequence sequence,sequence2;

while (true)
{
    sequence.
    If([]() -> bool { return PINB & 1; }).
    Do([]() { PORTB |= 1 << PB1; }).
    Wait(1000).
    Break([]() -> bool { return PINB & (1 << PB2);}).
    Reset([]() -> bool {return !(PINB & 1); }, []() { PORTB &= ~(1 << PB1); });

    sequence2.
    If([]() -> bool { return PIND & 1; }).
    Do([]() { PORTD |= 1 << PD1; }).
    Wait(3000).
    Break([]() -> bool { return PIND & (1 << PD2);}).
    Reset([]() -> bool {return !(PIND & 1); }, []() { PORTD &= ~(1 << PD1); });
}