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Monitor Chart Activity by Using Active State Data

This example uses:

Open Model
Step 6 of 7 in Model Finite State Machines

If your Stateflow® chart includes data that is correlated to the chart hierarchy, you can simplify your design by using active state data. By enabling active state data, you can:

  • Avoid manual data updates reflecting chart activity.

  • Log and monitor chart activity in the Simulation Data Inspector.

  • Use chart activity data to control other subsystems.

  • Export chart activity data to other Simulink blocks.

For example, in this model of a traffic signal, the state that is active determines the value of the output signal color. You can simplify the design of the chart by enabling active state data. In this case, the Stateflow chart can provide the color of the traffic signal by tracking state activity, so you do not have to explicitly update the value of color.

To enable active state data, select a state to monitor. Then, in the Property Inspector:

1. Select Create output for monitoring.

2. Select one of these activity types:

  • Self activity — Boolean value that indicates whether the state is active

  • Child activity — Enumerated value that indicates which child state is active

  • Leaf state activity — Enumerated value that indicates which leaf state is active

3. Enter the Data name for the active state data symbol.

4. Optionally, for Child activity or Leaf state activity, enter the Enum name for the active state data type.

By default, Stateflow charts report state activity as output data to the Simulink model. To change the scope of an active state data symbol to local data, use the Symbols pane.

Model a Traffic Signal Controller

This example uses active state data to model the controller system for a pair of traffic lights.

Inside the Traffic Controller chart, two parallel subcharts manage the logic that controls the traffic lights. The subcharts have an identical hierarchy that consists of three child states: Red, Yellow, and Green. The output data Light1 and Light2 correspond to the active child states in the subcharts. These signals:

  • Determine the phase of the animated traffic lights.

  • Contribute to the number of cars waiting at each light.

  • Drive a Safety Assertion subsystem that verifies that the two traffic lights are never green simultaneously.

To see the subcharts inside the Traffic Controller chart, click the arrow at the bottom-left corner of the chart.

Each traffic controller cycles through its child states, from Red to Green to Yellow and back to Red. Each state corresponds to a phase in the traffic light cycle. The output signals Light1 and Light2 indicate which state is active at any given time.

Red Light

The traffic light cycle begins when the Red state becomes active. After a short delay, the controller checks for cars waiting at the intersection. If it detects at least one car, or if a fixed length of time elapses, then the controller requests a green light by setting greenLightRequest to true. After making the request, the controller remains in the Red state for a short length of time until it detects that the other traffic signal is red. The controller then makes the transition to Green.

Green Light

When the Green state becomes active, the controller cancels its green light request by setting greenLightRequest to false. The controller sets greenLightLocked to true to prevent the other traffic signal from turning green. After a short delay, the controller checks for a green light request from the other controller. If it receives a request, or if a fixed length of time elapses, then the controller transitions to the Yellow state.

Yellow Light

When the Yellow state becomes inactive, the controller sets greenLightLocked to false, indicating that the other traffic light can safely turn green. The controller remains in the Yellow state for a fixed amount of time before transitioning to the Red state. The traffic light cycle then begins again.

Timing of Traffic Lights

Several parameters define the timing of the traffic light cycle. To change the timing of the traffic lights, double-click the Traffic Controller chart and, in the dialog box, enter new values for these parameters:

  • REDDELAY — Length of time before the controller checks for cars at the intersection. This value is also the minimum length of time before the traffic light can turn green after the controller requests a green light. The default value is 6 seconds.

  • MAXREDDELAY — Maximum length of time that the controller checks for cars before requesting a green light. The default value is 360 seconds.

  • GREENDELAY — Maximum length of time that the traffic light remains green. The default value is 180 seconds.

  • MINGREENDELAY — Minimum length of time that the traffic light remains green. The default value is 120 seconds.

  • YELLOWDELAY — Length of time that the traffic light remains yellow. The default value is 15 seconds.

Explore the Example

  1. Open the chart by clicking the arrow in the bottom-left corner.

  2. In the Symbols pane, select greenLightRequested. Then, in the Property Inspector, under Logging, select Log signal data.

  3. Repeat the previous step for greenLightLocked, Light1, and Light2.

  4. In the Simulation tab, click Run.

  5. In the Simulation tab, under Review Results, click Data Inspector.

  6. In the Simulation Data Inspector, display the logged signals in separate axes. The Boolean signals greenLightRequested and greenLightLocked appear as numeric values of zero or one. The state activity signals Light1 and Light2 are enumerated data with values of Green, Yellow, Red, and None.

To trace the chart activity during the simulation, you can use the zoom and cursor buttons in the Simulation Data Inspector. For example, these are the key moments during the first 300 seconds of the simulation:

  • $t = 0$ — At the start of the simulation, both traffic lights are red. Light1 and Light2 are Red, greenLightRequested is false, and greenLightLocked is false.

  • $t = 6$ — After 6 seconds, the default value of REDDELAY, there are cars waiting in both streets, so both traffic lights request a green light. Light1 and Light2 are still Red, greenLightRequested is true, and greenLightLocked is false.

  • $t = 12$ — After another 6 seconds, the default value of REDDELAY, Light 1 becomes green, cancels the green light request, and sets greenLightLocked to true. Then, Light 2 requests a green light. Light1 is Green, Light2 is Red, greenLightRequested becomes false and then true, and greenLightLocked is true.

  • $t = 132$ — After 120 seconds, the default value of MINGREENDELAY, Light 1 turns yellow. Light1 is Yellow, Light2 is Red, greenLightRequested is true, and greenLightLocked is true.

  • $t = 147$ — After 15 seconds, the default value of YELLOWDELAY, Light 1 turns red and sets greenLightLocked to false. Then, Light 2 turns green, cancels the green light request, and sets greenLightLocked to true. Light1 is Red, Light2 is Green, greenLightRequested is false, and greenLightLocked becomes false and then true.

  • $t = 153$ — After 6 seconds, the default value of REDDELAY, Light 1 requests a green light. Light1 is Red, Light2 is Green, greenLightRequested is true, and greenLightLocked is true.

  • $t = 267$ — After Light 2 is green for 120 seconds, the default value of MINGREENDELAY, Light 2 turns yellow. Light1 is Red, Light2 is Yellow, greenLightRequested is true, and greenLightLocked is true.

  • $t = 282$ — After 15 seconds, the default value of YELLOWDELAY, Light 2 turns red and sets greenLightLocked to false. Then, Light 1 turns green, cancels the green light request, and sets greenLightLocked to true. Light1 is Green, Light2 is Red, greenLightRequested is false, and greenLightLocked becomes false and then true.

  • $t = 288$ — After 6 seconds, the default value of REDDELAY, Light 2 requests a green light. Light1 is Green, Light2 is Red, greenLightRequested is true, and greenLightLocked is true.

The cycle repeats until the simulation ends at $t = 1000$ seconds.

Related Topics

Model Finite State Machines
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