Share Data Globally

When Do You Need to Use Global Data?

You might need to use global data with a MATLAB Function block if:

You have multiple MATLAB^® functions that use global variables and you want to call these functions from MATLAB Function blocks.
You have an existing model that uses a large amount of global data and you are adding a MATLAB Function block to this model, and you want to avoid cluttering your model with additional inputs and outputs.
You want to scope the visibility of data to parts of the model.

Using Global Data with the MATLAB Function Block

In Simulink^®, you store global data using data store memory. You implement data store memory using either Data Store Memory blocks or Simulink.Signal objects. How you store global data depends on the number and scope of your global variables. For more information, see Local and Global Data Stores and Choosing How to Store Global Data.

How MATLAB Globals Relate to Data Store Memory

In MATLAB functions in Simulink, global declarations are not mapped to the MATLAB global workspace. Instead, you register global data with the MATLAB Function block to map the data to data store memory. This difference allows global data in MATLAB functions to inter-operate with the Simulink solver and to provide diagnostics if they are misused.

A global variable resolves hierarchically to the closest data store memory with the same name in the model. The same global variable occurring in two different MATLAB Function blocks might resolve to different data store memory depending on the hierarchy of your model. You can use this ability to scope the visibility of data to a subsystem.

How to Use Globals with the MATLAB Function Block

To use global data in your MATLAB Function block, or in any code that this block calls, you must:

Declare a global variable in your MATLAB Function block, or in any code that is called by the MATLAB Function block.
Register a Data Store Memory block or Simulink.Signal object that has the same name as the global variable with the MATLAB Function block.

For more information, see Storing Data Using Data Store Memory Blocks and Storing Data Using Simulink.Signal Objects.

Choosing How to Store Global Data

The following table summarizes whether to use Data Store Memory blocks or Simulink.Signal objects.

If you want to:	Use:	For more information:
Use a small number of global variables in a single model that does not use model reference.	Data Store Memory blocks. Note Using Data Store Memory blocks scopes the data to the model.	Storing Data Using Data Store Memory Blocks
Use a large number of global variables in a single model that does not use model reference.	`Simulink.Signal` objects defined in the model workspace. `Simulink.Signal` objects offer these advantages: You do not have to add numerous Data Store Memory blocks to your model. You can load the `Simulink.Signal` objects in from a MAT-file.	Storing Data Using Simulink.Signal Objects
Share data between multiple models (including referenced models).	`Simulink.Signal` objects defined in the base workspace Note If you use Data Store Memory blocks as well as `Simulink.Signal`, note that using Data Store Memory blocks scopes the data to the model.	Storing Data Using Simulink.Signal Objects

Storing Data Using Data Store Memory Blocks

This model demonstrates how a MATLAB Function block uses the global data stored in a Data Store Memory block A.

Open the dsm_demo.mdl model.
Double-click the MATLAB Function block to open the MATLAB Function Block Editor.
The MATLAB Function block code declares a global variable A. The block modifies the value of A during each execution.
```
function y = fcn
%#codegen
global A;
A = A+1;
y = A;
```
Make sure the global variable is registered to the MATLAB Function block. See Adding Data to a MATLAB Function Block.
1. In the MATLAB Function Block Editor, select Edit Data to open the Ports and Data Manager dialog box.
2. In the Ports and Data Manager, select the data A in the left pane. This data uses the same name as the global variable.
3. The Scope of the data is set to Data Store Memory.
See also Ports and Data Manager.
Double-click the Data Store Memory block A. In the Block Parameters dialog box, you see that the Data store name A matches the global variable name. The block has an initial value of 25.
When you add a Data Store Memory to your model:
1. Set the Data store name to match the name of the global variable in your MATLAB Function block code.
2. Set Data type to an explicit data type. The data type cannot be auto.
3. Set the Signal type and specify an Initial value.
Simulate the model.
The MATLAB Function block reads the initial value of global data stored in A and updates the value of A each time it executes.

Storing Data Using `Simulink.Signal` Objects

This model demonstrates how a MATLAB Function block uses the global data stored in a Simulink.Signal object A.

Open the simulink_signal_local model.
The model uses a Simulink.Signal object in the model workspace.

Note
To use the global data with multiple models, create a Simulink.Signal object in the base workspace .
Make sure that the Simulink.Signal object is added to the Model Explorer.
1. In the Modeling tab, click Model Explorer.
2. In the left pane of the Model Explorer, select the model workspace for the simulink_signal_local model.
  The Contents pane displays the data in the model workspace.
3. Click the Simulink.Signal object A.
  In the right pane, make sure that the Model Explorer displays these attributes for A.
  
  Attribute Value
  Data type double
  Complexity real
  Dimensions 1
  Initial value 5
See also Model Explorer.
Double-click the MATLAB Function block to open its editor.
The MATLAB Function block modifies the value of global data A each time it executes.
```
function y = fcn
%#codegen
global A;
A = A+1;
y = A;
```
Make sure the Simulink.Signal object is registered to the MATLAB Function block.
1. In the MATLAB Function Block Editor, select Edit Data to open the Ports and Data Manager dialog box.
2. In the Ports and Data Manager, select the data A in the left pane. This data uses the same name as the global variable.
3. Set the Scope of the data to Data Store Memory.
See also Ports and Data Manager.
Simulate the model.
The MATLAB Function block reads the initial value of global data stored in A and updates the value of A each time it executes.

Attribute	Value
Data type	`double`
Complexity	`real`
Dimensions	`1`
Initial value	`5`

Using Data Store Diagnostics to Detect Memory Access Issues

You can configure your model to provide run-time and compile-time diagnostics for avoiding problems with data stores. Diagnostics are available in the Configuration Parameters dialog box and the parameters dialog box for the Data Store Memory block. These diagnostics are available for Data Store Memory blocks only, not for Simulink.Signal objects. For more information on using data store diagnostics, see Data Store Diagnostics.

Note

If you pass data store memory arrays to functions, optimizations such as A=foo(A) might result in the code generation software marking the entire contents of the array as read or written even though only some elements were accessed.

Documentation