Inspect and Modify Data and Messages While Debugging

While your Stateflow® chart is in debugging mode, you can examine the status of the chart by inspecting the values of data, messages, and temporal logic expressions. You can also test the design of the chart by modifying data values and sending local and output messages. This table summarizes the interfaces that you can use to perform these debugging tasks. For more information, see Debugging Stateflow Charts.

Debugging TaskStateflow EditorSymbols PaneBreakpoints and Watch WindowMATLAB® Command Window
Inspect values of data and messagesYesYesYesYes
Inspect temporal logic expressionsYesNoNoNo
Modify values of data and messagesNoYesNoYes
Send messagesNoNoNoYes

View Data in the Stateflow Editor

While the simulation is paused at a breakpoint, you can examine data values by pointing to a state, transition, or function in the chart. A tooltip displays the value of the data and the messages that the selected object uses.

Object TypeTooltip Information
States and transitionsValues of data, messages, and temporal logic expressions that the object uses
Graphical, truth table, and MATLAB functionsValues of local data, messages, inputs, and outputs in the scope of the function

For example, the breakpoint in this chart pauses the simulation when the second state evaluates its during actions. Pointing to the superstate gear displays a tooltip that shows the values of:

  • Temporal logic expressions duration(speed >= up_threshold) and duration(speed <= down_threshold).

  • Data, including speed, up_threshold, and up.

Note

If you select the chart properties Export Chart Level Functions and Treat Exported Functions as Globally Visible, the tooltip does not display temporal logic data.

View and Modify Data in the Symbols Pane

While a chart is in debugging mode, the Symbols pane displays the value of each data and message object in the chart. For example, when this chart pauses at the breakpoint, you can see the values of all chart data listed in the Value column. The highlighted values changed during the last time step.

In the Symbols pane, you can change the value of:

  • Data store memory, local, and output data.

  • Local and output messages.

Click the Value field for a data or message object to enter a new value.

You cannot change the values of constants, parameters, or input data and messages during simulation.

For more information, see Manage Data, Events, and Messages in the Symbols Pane.

View Data in the Breakpoints and Watch Window

In the Stateflow Breakpoints and Watch window, you can view current data and message values while the simulation is paused at a breakpoint. To open the Breakpoints and Watch window, on the Debug tab, click Breakpoints List. Alternatively, open the Breakpoints dialog box and click the Breakpoints List link.

Track Data in the Watch List

You can use the Breakpoints and Watch window to:

  • Add data and message objects to a watch list.

  • Track the values that changed since the last time step.

  • Expand a message to view the message queue and message data values.

For example, you can add speed, up_threshold, and up to the watch list and track their values as you step through the simulation. The highlighting indicates that the values of speed and up_threshold changed during the last time step.

To add a data or message object to the watch list, open the Property Inspector or the Model Explorer. Select the data or message object you want to watch and click the Add to Watch Window link.

Alternatively, in the Stateflow Editor, right-click a state or transition that uses the data or message. Select Add to Watch Window and choose the variable name from the drop-down list.

Format Watch Display

To change the format used to display watch data, select the gear icon at the top of the window. Use the drop-down lists to choose a MATLAB format for each data type.

Remove Data from the Watch List

To remove a data or message object from the watch list, point to the path for the watch data and click the Remove this watch icon that appears to the left of the variable name.

Save and Restore Watch Data

Watch data persists during a MATLAB session. When you close a model, its watch data list remains in the Breakpoints and Watch Window. If you reopen a model during the same MATLAB session, the watch data list for that model is restored.

You can save the breakpoint and watch data lists and reload them in a later MATLAB session. To save a snapshot of the breakpoint and watch data lists, at the top of the Breakpoints and Watch Window, click the Save current breakpoints and watches icon. To restore a snapshot, click the Load breakpoints and watches icon.

View and Modify Data in the MATLAB Command Window

While the simulation is paused at a breakpoint, the MATLAB command prompt changes to debug>>. At this prompt, you can inspect and change the values of Stateflow data, send local and output messages, and interact with the MATLAB workspace.

For example, suppose that the previous chart has reached a breakpoint. To view the data that is visible at the current scope, use the whos command.

whos
  Name                Size            Bytes  Class       Attributes

  TWAIT               1x1                 1  uint8                 
  down                1x1                 1  logical               
  down_th             1x1                 8  double                
  down_threshold      1x1                 8  double                
  gear                1x1                 4  gearType              
  speed               1x1                 8  double                
  throttle            1x1                 8  double                
  up                  1x1                 1  logical               
  up_th               1x1                 8  double                
  up_threshold        1x1                 8  double                

To inspect the values of speed and up_threshold, enter:

speed
speed =

   26.3383
up_threshold
up_threshold =

   41.3601

Modify Data by Using the Debugging Prompt

At the debugging prompt, you can change the value of data store memory, local, and output data. For example, in the previous chart, you can change the value of up_threshold, up, and gear:

up_threshold = 25;
up = true;
gear = gearType.third;
Follow these rules when modifying data at the debugging prompt.

  • To modify vectors and matrices, use MATLAB syntax for indexing, regardless of the action language property of your chart. See Indexing Notation.

    For example, to change the element in the diagonal of a 2-by-2 matrix u, enter:

    u(1,1) = 6.022e23;
    u(2,2) = 6.626e-34

  • You can change the dimensions of variable-size data as long as the new size is within the dimension bounds specified for the data. For example, suppose that v is a variable-size array with a maximum size of [16 16]. To change the value of v to a 5-by-7 array of ones, enter:

    v = ones(5,7);

  • To modify enumerated data, explicitly specify the enumerated type by using prefixed identifiers. See Notation for Enumerated Values.

    For example, suppose that w has an enumerated data type Colors. To change the value of w to the enumerated value Red, enter:

    w = Colors.Red

  • To modify numerical data, cast to an explicit data type by using a MATLAB type conversion function. Explicit casting is not required for data of a type double. See Type Cast Operations.

    For example, suppose that x has type single, y has type int32, and z has type fixpt(1,16,12). To change the value of these data objects, enter:

    x = single(98.6);
    y = int32(100);
    z = fi(0.5413,1,16,12);

  • You cannot change the values of constants, parameters, or input data at the debugging prompt.

Note

To modify data of type int64 or uint64, use the function fi to cast the new value to a fixed-point type. In charts that use C as the action language, int64 is an alias type for fixpt(1,64,0) and uint64 is an alias type for fixpt(0,64,0).

Send Messages by Using the Debugging Prompt

At the debugging prompt, you can send local and output messages. For example, in this chart, the local message M determines which state becomes active after the state DecisionPoint. If the chart receives the message M with a positive value, the state Received becomes active and the chart outputs a value of true. Otherwise, the state Missed becomes active and the chart outputs a value of false.

The initial value of the message is zero. To change the value of the data field to a positive number and send the message to its local queue, enter:

M = 5;
send(M);
When you advance to the next step of the simulation, the message triggers the transition to the state Received. For more information, see Control Chart Execution After a Breakpoint.

Follow these rules when sending messages from the debugging prompt:

  • To read or write to the message data field of a valid message, use the name of the message object. Do not use dot notation syntax.

  • You can send a message from the debugging prompt only when the chart explicitly sends the message by calling the send operator.

  • You cannot send input messages from the debugging prompt.

For more information, see Control Message Activity in Stateflow Charts.

Access the MATLAB Workspace While Debugging

You can enter other MATLAB commands at the debugging prompt, but the results are executed in the Stateflow workspace. For example, you can save all of the chart variables in a MAT-file by using the save function:

save(chartVars)

To enter a command in the MATLAB base workspace, use the evalin command with the first argument 'base'. For example, to list the variables in the MATLAB workspace, use the command:

evalin('base','whos')

See Also

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