MATLAB Examples

Bind a Function-Call Subsystem to a State

This model triggers a function-call subsystem with a trigger event E that binds to a state of a chart. In the Solver pane of the Model Configuration Parameters dialog box, the model specifies a fixed-step solver with a fixed-step size of 1.

The chart contains two states. Event E binds to state A with the action

  bind:E

Event E is defined for the chart with a scope of Output to Simulink and a trigger type of function-call.

The function-call subsystem contains a trigger port block, an input port, an output port, and a simple block diagram. The block diagram increments a counter by 1 at each time step, using a Unit Delay block.

The Block Parameters dialog box for the trigger port contains these settings:

  • Trigger type: function-call.
  • States when enabling: reset. This setting resets the state values for the function-call subsystem to zero when it is enabled.
  • Sample time type: triggered. This setting sets the function-call subsystem to execute only when it is triggered by a calling event while it is enabled.

Setting Sample time type to periodic enables the Sample time field below it, which defaults to 1. These settings force the function-call subsystem to execute for each time step specified in the Sample time field while it is enabled. To accomplish this, the state that binds the calling event for the function-call subsystem must send an event for the time step coinciding with the specified sampling rate in the Sample time field. States can send events with entry or during actions at the simulation sample rate.

  • For fixed-step sampling, the Sample time value must be an integer multiple of the fixed-step size.
  • For variable-step sampling, the Sample time value has no limitations.

To see how a state controls a bound function-call subsystem, begin simulating the model.

  • At time t = 0, the default transition to state A occurs. State A executes its bind and entry actions. The binding action binds event E to state A, enabling the function-call subsystem and reseting its state variables to 0. The entry action triggers the function-call subsystem and executes its block diagram. The block diagram increments a counter by 1 using a Unit Delay block. The Unit Delay block outputs a value of 0 and holds the new value of 1 until the next call to the subsystem.
  • At time t = 1, the next update event from the model tests state A for an outgoing transition. The transition to state B does not occur because the temporal operator after(10,tick) allows the transition to be taken only after ten update events are received. State A remains active and its during action triggers the function-call subsystem. The Unit Delay block outputs its held value of 1. The subsystem also increments its counter to produce the value of 2, which the Unit Delay block holds until the next triggered execution.
  • The next eight update events increment the subsystem output by one at each time step.
  • At time t = 10, the transition from state A to state B occurs. Because the binding to state A is no longer active, the function-call subsystem is disabled, and its output drops back to 0.
  • At time t = 11, the transition from state B to state A occurs. Again, the binding action enables the function-call subsystem. Subsequent update events increment the subsystem output by one at each time step until the next transition to state B occurs at time t = 21.