Configure Data Stores for C Code Generation

Data stores enable subsystems and referenced models to share data without using I/O ports to pass the data from level to level (see Data Store Basics and Data Stores in Generated Code). Types of data stores include the types listed in this table.

Type of Data Store	Description
Local data store	Data store that is accessible from anywhere in a model hierarchy that is at or below the level at which you define the data store. You can define a local data store graphically in a model by including a Data Store Memory block.
Shared local data store	Data Store Memory block with the block parameter Share across model instances set. These data stores are accessible only in the model where they are defined. The data store value is shared across instances of the model.
Global data store	Data store that is defined by a signal object in the base workspace or in a data dictionary. Multiple models in an application can use these data stores.

When you open a model in the Simulink Coder app, local and shared local data stores appear in the Code Mappings editor, where you can configure the data stores for code generation. If a model uses global data stores, you can view them in the Code Mappings editor by clicking the Refresh link that appears to the right of the data store name. That link initiates an update diagram and adds global data stores that the model uses in the editor view.

Configure data stores to:

Make data accessible for interaction while the generated code executes.
Control where the code generator places data in memory.
Improve readability and traceability of generated code.

For code generation, examples show how to configure a data store for model rtwdemo_configrpinterface. You can configure code mappings by using the Code Mappings Editor or code mappings API (coder.mapping.api.CodeMapping).

Choose Customization Options for Data Stores

By default, local data stores in a model appear in generated code as fields of a global data structure named model_DW. Shared local data stores appear as a field of global data structure model_SharedDSM. Based on your code interface requirements, decide whether to customize code generation of data stores. If you do not configure customizations, the code generator determines whether to eliminate or change the representation of data stores in generated code for optimization purposes. If you configure customizations, decide:

Whether to set up a default configuration
If a model includes a significant number (for example, more than 10) of data stores for a given category that must be accessible during program execution, it is more efficient to configure the data stores with a default setting, and then override that setting for special cases. If the model includes a few data stores for a given category that have unique source, naming, or placement requirements, consider configuring the data stores individually.
How to declare and handle model data stores in the generated code
- As separate global variables
- To read from data stores as global variables defined in external code
- As calls to access functions. Requires Embedded Coder^®
For more information about these options, see Control Data and Function Interface in Generated Code.

Other considerations for model parameters include whether to:

Name data stores in the generated code by using data store names in the model or by using unique code identifiers.
Include the static type qualifier in global variable definitions and declarations, for example, to prevent name clashes. Requires Embedded Coder. See Prevent Name Clashes by Configuring Data Item as static (Embedded Coder).
Include the volatile type qualifier in global variable definitions and declarations. Requires Embedded Coder. See Protect Global Data with const and volatile Type Qualifiers (Embedded Coder).
Generate a global data structure with a name that you specify. Requires Embedded Coder. See Organize Data into Structures in Generated Code (Embedded Coder).
Place data stores in a specific area of memory. Requires Embedded Coder. See Control Data and Function Placement in Memory by Inserting Pragmas (Embedded Coder).

For a list of interface requirements that are relevant to data stores with corresponding storage classes and storage class properties, see Choose Storage Class and Storage Class Properties for Data Stores.

For example model rtwdemo_configrpinterface, data store requirements are:

Represent local and shared local data stores as separate global variables.
Apply prefix ds_ to names of variables that represent data stores.

For this example, you set the default representation for local and shared local data stores in the generated code as global variables . Then, you configure the local data store in the model to use the default storage class and a unique code identifier that includes the required prefix ds_. The code identifier capability enables you to specify code generation identifiers without having to modify the model design.

Configure Default Code Generation Settings for Data Stores

Default code generation settings for data stores can reduce the effort of preparing a model for code generation, especially if a model has a significant number of data stores that you want to gain access to while the generated code executes. Choose configuration settings once, and the code generator applies those settings to data stores across the model. Simulink^® stores the default configuration as part of the model.

Consider configuring default code generation settings for model data stores if your model uses multiple data stores for a given category that do not have unique requirements.

This example shows how to use the Code Mappings Editor to configure default settings for data stores. Use the Code Mappings editor to set the default storage class for local and shared local data stores in model rtwdemo_configrpinterface to ExportedGlobal. With those storage class settings, the code generator represents the data stores in the generated code as global variables.

Open model rtwdemo_configrpinterface. Save a copy of the model to a writable location.
Open the Simulink Coder app.
In the C Code tab, select Code Interface > Default Code Mappings.
Configure default code mappings for local data stores. In the Code Mappings editor, on the Data Defaults tab, expand the Signals node. Select category Signals, states, and internal data. Set the storage class to ExportedGlobal.
Configure default code mappings for shared local data stores. Select category Shared local data stores. Set the storage class to ExportedGlobal.
Save the model.

Configure Code Generation for Individual Data Stores

You can configure individual data stores for code generation. For example, if a model has two data stores of the same category that have unique code generation requirements, configure the data stores individually. Or, if you configure default settings for a category of data stores, you can override those settings for specific data stores.

If your model meets at least one of these criteria, consider configuring code generation settings for data stores individually:

Uses multiple data stores of the same category that have unique source, naming, or placement requirements.
Uses a few data stores of the same category.
Has a default configuration for a category of data stores and you need to override the configuration for some specific states.

This example shows how to use the Code Mappings editor to apply your default storage class setting to the Data Store Memory block mode in model rtwdemo_configinterface. The example also shows how configure a code identifier for that data store.

If you have not already done so, complete the steps in Configure Default Code Generation Settings for Data Stores.
In the Code Mappings editor, click the Data Stores tab. Expand Local Data Stores. The storage class for data store mode is set to Auto, which means that the code generator might eliminate or change the representation of relevant code for optimization purposes. If optimizations are not possible, the code generator applies the model default configuration. For this example, the model default configuration specifies the storage class ExportedGlobal.
- To avoid optimizations and force the code generator to use the default configuration, set the storage class to Model default.
- To override the default configuration, specify the storage class that meets the code generation requirements for that data store.
In the Code Mappings editor, select local data store mode. Set the storage class to Model default: ExportedGlobal.
Configure the code identifier for the data store with a name that includes the prefix ds_. In the Code Mappings editor, select shared local data store mode. In the Property Inspector, expand the Code node. Set the storage class property Identifier to ds_mode.
Save the model.

Generate and view the code. For example, in rtwdemo_configrpinterface.c, find the data definitions for the data store.

boolean_T ds_mode;

Find where the state data is used in the step entry-point function.

.
.
.
  ds_mode = ((input1 > rtwdemo_configrpinterface_UPPER) || (input1 <
              rtwdemo_configrpinterface_LOWER));
.
.
.
  if (ds_mode) {
    output = (real_T)mp_K1 * dout_Table1;
  } else {
    output = dstate_X;
  }
.
.
.

Configure Code Generation Settings for Data Stores Programmatically

To automate configuration of data stores for code generation, use the programming interface for code mappings. For example, when creating custom block libraries or part of an application test environment, use the programming interface to automate data configuration.

This example shows how to use the programming interface to configure data stores for model rtwdemo_configrpinterface. Set the default representation of local and shared local data stores in the generated code as global variables. Configure the Data Store Memory block mode to use the default storage class and a unique code identifier that includes the required prefix ds_.

Open the example model.

open_system('rtwdemo_configrpinterface')

Create object cm by calling function coder.mapping.api.get. The object stores the data code generation configuration for model rtwdemo_configrpinterface.
```
cm = coder.mapping.api.get('rtwdemo_configrpinterface');
```
Configure default settings for local data stores by calling function setDataDefault. For the arguments, specify these values:
- The object returned by coder.mapping.api.get
- InternalData for the default category
- Property name StorageClass with property value ExportedGlobal
```
setDataDefault(cm,'InternalData','StorageClass','ExportedGlobal');
```
Configure default settings for shared local data stores by calling function setDataDefault. Specify these values for arguments:
- The object returned by coder.mapping.api.get.
- SharedLocalDataStore for the default category.
- Property name StorageClass with property value ExportedGlobal.
```
setDataDefault(cm,'SharedLocalDataStore','StorageClass','ExportedGlobal');
```
Verify your default configuration settings for local and shared local data stores. Issue a call to getDataDefault that specifies the object returned by coder.mapping.api.get, category InternalData, and the property StorageClass. In a second call to getDataDefault, replace the category with SharedLocalDataStore.
```
getDataDefault(cm,'InternalData','StorageClass')

ans =

    'ExportedGlobal'

getDataDefault(cm,'SharedLocalDataStore','StorageClass')

ans =

    'ExportedGlobal'
```
Apply the default configuration for local data store mode.
By default, Simulink sets the storage class for data stores to Auto. When the storage class is Auto, the code generator:
- Determines whether to eliminate the data from the generated code for optimization purposes.
- If retaining the data, determines how to efficiently represent the data in the generated code, taking into account default configuration settings.
To control the configuration for an individual data store, call function setDataStore. Issue a call to setDataStore that specifies:
- Object returned by coder.mapping.api.get
- Data store name mode
- Default storage class previously set for the data store by using property StorageClass and property value Model default.
- Property Identifier and property value ds_mode
```
setDataStore(cm,'mode','StorageClass','Model default','Identifier','ds_mode');
```
Verify your configuration changes by calling function getDataStore. Specify the object returned by coder.mapping.api.get, the name of the data store, and property StorageClass or Identifier.
```
getDataStore(cm,'mode','StorageClass')

ans =

    'Model default'

getDataStore(cm,'mode','Identifier')

ans =

    'ds_mode'
```
Save the model.

Generate and view the code. For example, in rtwdemo_configrpinterface.c, find the data definition for the data store.

boolean_T ds_mode;

Find where the data store is used in the step entry-point function.

.
.
.
  ds_mode = ((input1 > rtwdemo_configrpinterface_UPPER) || (input1 <
              rtwdemo_configrpinterface_LOWER));
.
.
.
  if (ds_mode) {
    output = (real_T)mp_K1 * dout_Table1;
  } else {
    output = dstate_X;
  }
.
.
.

Choose Storage Class and Storage Class Properties for Data Stores

Depending on your code generation requirements, choose from these storage classes to configure code generation for data stores.

Requirements	Storage Class
Enable optimizations, potentially generating more efficient code.	Auto (Individual mappings only)
For data elements that cannot be optimized, represent data as a field of a standard data structure.	Default (Default mapping only)
Prevent optimizations from eliminating storage for a data element and use the default storage class for the data element category.	Model Default (Individual mappings only) , `Dictionary Default` (Individual mappings only)
Generate a global variable definition and declaration.	ExportedGlobal
Generate code that reads from and writes to a global variable or global variable pointer defined by your external code.	ImportedExtern, ImportedExternPointer

The list of available storage classes might include other project-specific storage classes defined in an Embedded Coder Dictionary. If you have special requirements that are not met by the listed storage classes and you have Embedded Coder software, you can define a storage class. See Define Storage Classes, Memory Sections, and Function Templates for Software Architecture (Embedded Coder).

For an individual data store, use the Identifier storage class property to configure a name for the variable representing the data store in the generated code.

Documentation