Timer

An example, Ex_Timer, shows how to define a concrete atomic class from Atomic. In this example, we define a class SimplestTimer which generates an output, op, every 3.3 seconds as illustrated in Figure 3.1.

Figure 3.1: SimplestTimer (a) State Transition Diagram (b) Event Segment (c) $t_e$ Trajectory

SimplestTimer has one output port, op. In the constructor, op is assigned by calling AddOP. The function init() does nothing because the class has no internal variable. The function tau() returns 3.3 all the time.

class SimplestTimer: public Atomic {
public:
    OutputPort* op;

    SimplestTimer(const string& name=""): Atomic(name), n(0)
    { op = AddOP("op"); }

    /*virtual*/ void init(){}
    /*virtual*/ Time tau() const {
        return 3.3;
    }

Since there is no input transition defined, delta_x has the null body. However, delta_y returns the output op.

    /*virtual*/ bool delta_x(const PortValue& x) {return false;}
    /*virtual*/ void delta_y(PortValue& y)
    {
        y.Set(op);
    }

The display function Get_s() returns the current status, which is constantly Working.

    /*virtual*/ string Get_s() const {
        return string("Working");
    }
};

If you try step, you can see the animation is increasing the elapsed time. The following display shows the state at time 2.188 where the schedule time t_s=3.3 and the elapsed time t_e=2.188.

    (STimer:Working, t_s=3.300, t_e=2.188) at 2.188

The simulation run will stop at 3.3 because its run mode is step-by-step when using step. At that time, it will display the discrete state transition as follows.

    (STimer:Working, t_s=3.300, t_e=3.300)
     --({!STimer.op},t_c=3.3)-->
    (STimer:Working, t_s=3.300, t_e=0.000)

The first state is the source of state transition. An arc shows a triggering event which is the output op of STimer at the current time=3.3. The second state is the destination of the state transition in which the lifespan is also 3.3 but the elapsed time has been reset to zero.

Exercise 4.1   Consider the example Ex_Timer.

a.

Let's change the display mode from te to tr by applying the command dtmode. Then preset the simulation ending time to ``5'' by pause_at 5. Now run until the simulation stops. When it stops at t_c=5, print the total state using pinrt with option q. What are the values of t_s and t_r, respectively? Guess the value of t_e at this moment.

b.

Add one more state variable int n in SimplestTimer class. n should be set = zero in init(), and it should increase by one in delta_y(). Get_s() shows n in the C print format of "Working, n=%d" .