Stateflow

Creating a Graphical Function

To create a graphical function, do the following:

1. Create a state in your model where you want the function to appear.

• A function can reside anywhere in a diagram, either at the top level or within any state or subchart. The location of a function determines its scope, that is, the set of states and transitions that can invoke the function. In particular, the scope of a function is the scope of its parent state or chart, with the following exceptions.
  • The chart containing the function exports its graphical functions.

  • In this case, the scope of the function is the entire Stateflow machine, which encompasses all the charts in the model. See Exporting Graphical Functions for more information.

  • A child of the function's parent defines a function of the same name.

  • In this case, the function defined in the parent is not visible anywhere in the child or its children. In other words, a function defined in a state or subchart overrides any functions of the same name defined in the ancestors of that state or subchart.

2. Select Function from the Type submenu of the newly created state's shortcut menu.

1. Stateflow converts the state to a graphical function.

   

   The new function appears as an unnamed object in the Stateflow Explorer.

   

3. Enter a function prototype in the function label.

• The function prototype specifies a name for the function and formal names for its arguments and return value. A prototype has the syntax

  • y = f(a1,a2,...an)
    

  where f is the function's name, a1, a2, an are formal names for its arguments, and y is the formal name for its return value. The following example shows a prototype for a graphical function named f1 that takes two arguments and returns a value.

  

1. The return values and arguments that you declare in the prototype appear in the Explorer as data items parented by the function object.

   

   The Scope field in the Explorer indicates the role of the corresponding argument or return value. Arguments have scope Input. Return values have scope Output. The number that appears in parentheses for the scope of each argument is the order in which the argument appears in the function's prototype. When a Stateflow action invokes a function, it passes arguments to the function in the same order.

• In the context of graphical function prototypes, the term scope refers to the role (argument or return value) of the data items specified by the function's prototype. The term scope can also refer to a data item's visibility. In this sense, arguments and return values have local scope. They are visible only in the flow diagram that implements the function.

Note    You can use the Stateflow editor to change the prototype of a graphical function at any time. When you are done editing the prototype, Stateflow updates the data dictionary and the Explorer to reflect the changes.

4. Specify the data properties (data type, initial value, and so on) of the function's arguments and return values (if it has any).

1. See Setting Data Properties for information on setting data properties. The following restrictions apply to argument and return value properties.
   • A function cannot return more than one value.
   • Arguments and return values cannot be arrays.
   • Arguments cannot have initial values.
   • Arguments must have scope Input.
   • Return values must have scope Output.

5. Create any additional data items that the function might need to process when it is invoked.

1. See Adding Data to the Data Dictionary for information on how to create data items. A function can access only items that it owns. Thus, any items that you create for use by the function must be created as children of the function. The items that you create can have any of the following scopes:
   • Local

   • A local data item persists from invocation to invocation. For example, if the item is equal to 1 when the function returns from one invocation, the item will equal 1 the next time the function is invoked.

   • Temporary

   • Stateflow creates and initializes a copy of a temporary item for each invocation of the function.

   • Constant

   • Constant data retains its initial value through all invocations of the function.

Note    You can also assign Input and Output scope to data items that you create (that is, to items that do not correspond to the function's formal arguments and return value). However, input and output items that do not correspond to your function's formal arguments and return values cause parse errors. In other words, you cannot create arguments or return values by creating data items.

• All data items (other than arguments and return values) parented by a graphical function can be initialized from the workspace. However, only local items can be saved to the workspace.

6. Create a flow diagram within the function that performs the action to be performed when the function is invoked.

1. At a minimum, the flow diagram must include a default transition terminated by a junction. The following example shows a minimal flow diagram for a graphical function that computes the product of its arguments.

   

7. If you prefer, hide the function's contents by selecting Subcharted from the Make Contents menu of the function's shortcut menu.

   

Using Graphical Functions in Stateflow Charts

Calling Graphical Functions