The values parameter by default contains an array of IntTokens with values 1 and 0. The default offsets array is {0.0, 1.0}. Thus, the default output will be alternating 1 and 0 with 50% duty cycle. The default period is 2.0.
The type of the output can be any token type. This type is inferred from the element type of the values parameter.
If the period is changed at any time, either by providing an input or by changing the parameter, then the new period will take effect as soon as possible. That is, if there is already a period in progress, it may be cut short if the new period is shorter so that its time matches the new period. But it will only be cut short if current time has not passed the cycle start time plus the new period. Otherwise, the period in progress will run to completion.
This actor can generate finite sequences by specifying a finite numberOfCycles. The numberOfCycles has a default value UNBOUNDED, indicating infinite length of executions. If numberOfCycles is a positive number, once the specified number of cycles has been completed, then this actor returns false from the postfire() method, which indicates to the director that the actor should not be fired again. (A cycle is "completed" each time the last event in the values array is produced).
The actor can also generate a finite sequence by giving a finite value to the stopTime parameter. This gives a time rather than a number of cycles, and thus can be used to stop the clock in the middle of a cycle, unlike numberOfCycles. Just like numberOfCycles, when the stop time is reached, the actor's postfire() method returns false.
If the trigger input is connected, then an output will only be produced if a input has been received since the last output. The trigger input has no effect on the first output. After the first output event, no further output event will be produced until a time greater than or equal to the time at which a trigger input is received. At that time, the output produced will have whatever value would have been produced if the trigger input was not connected. Note that this trigger is typically useful in a feedback situation, where the output of the clock eventually results in a trigger input. If the time-stamp of that trigger input is less than the time between clock events, then the clock will behave as if there were no trigger input. Otherwise, it will "skip beats."
This actor can be a bit tricky to use inside a ModalModel. In particular, if the actor is in a state refinement, then it may "skip a beat" because of the state not being the current state at the time of the beat. If this occurs, the clock will simply stop firing, and will produce no further outputs. To prevent this, the clock may be reinitialized (by setting the reset flag of a modal model transition). Alternatively, you can assign a value to the the period of the Clock in the setActions of the transition. This will also have the effect of waking up the clock, but with a subtle difference. If you use a reset transition, the clock starts over upon entering the destination state. If you set the period parameter instead, then the clock behaves as if it had been running all along (except that its period may get changed). Thus, in the first case, the output events are aligned with the time of the transition, while in the second case, they are aligned with the start time of the model execution.
This actor is a timed source; the untimed version is Pulse. @author Edward A. Lee, Haiyang Zheng @version $Id: Clock.java,v 1.112 2007/12/06 21:56:29 cxh Exp $ @since Ptolemy II 0.3 @Pt.ProposedRating Yellow (eal) @Pt.AcceptedRating Yellow (yuhong)
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