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Data Store Memory

Define data store

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  • Library:

  • Simulink / Signal Routing

  • Data Store Memory block

Description

The Data Store Memory block defines and initializes a named shared data store, which is a memory region usable by Data Store Read and Data Store Write blocks that specify the same data store name.

The location of the Data Store Memory block that defines a data store determines which Data Store Read and Data Store Write blocks can access the data store:

  • If the Data Store Memory block is in the top-level system, Data Store Read and Data Store Write blocks anywhere in the model can access the data store.

  • If the Data Store Memory block is in a subsystem, Data Store Read and Data Store Write blocks in the same subsystem or in any subsystem below it in the model hierarchy can access the data store.

Data Store Read or Data Store Write blocks cannot access a Data Store Memory block that is either in a model that contains a Model block or in a referenced model.

Do not include a Data Store Memory block in a For Each subsystem.

Obtaining correct results from data stores requires ensuring that data store reads and writes occur in the expected order. For details, see:

You can use Simulink.Signal objects in addition to, or instead of, Data Store Memory blocks to define data stores. A data store defined in the base workspace with a signal object is a global data store. Global data stores are accessible to every model, including all referenced models. See Data Stores for more information.

You can select a Data Store Read, Data Store Write, or Data Store Memory block to highlight blocks related to it. To show a related block in an open diagram or new tab, pause on the ellipsis that appears after selection. Then, select Related Blocks Related Blocks button from the action bar. When multiple blocks correspond to the selected block, a list of related blocks opens. You can filter the list of related blocks by entering a search term in the text box. After you select a related block from the list, window focus goes to the open diagram or new tab that shows the related block.

Parameters

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Main

Specify a name for the data store you are defining with this block. Data Store Read and Data Store Write blocks with the same name can read from, and write to, the data store initialized by this block. The name can represent a Data Store Memory block or a sign object defined to be a data store.

Programmatic Use

Block Parameter: DataStoreName
Type: character vector
Values: 'A' | ...
Default: 'A'

Rename this data store everywhere the Data Store Read and Data Store Write blocks use it in a model.

Limitations

You cannot use Rename All to rename a data store if you:

  • Use a Simulink.Signal object in a workspace to control the code generated for the data store

  • Use a Simulink.Signal object instead of a Data Store Memory block to define the data store

You must instead rename the corresponding Simulink.Signal object from Model Explorer. For an example, see Rename Data Store Defined by Signal Object.

List all the Data Store Read and Data Store Write blocks that have the same data store name as the current block, and that are in the current system or in any subsystem below it in the model hierarchy. Clicking a block path displays and highlights that block in your model.

Signal Attributes

Specify the initial value or values of the data store. The Minimum parameter specifies the minimum value for this parameter, and the Maximum parameter specifies the maximum value.

If you specify a nonscalar value and set Dimensions to -1 (the default), the data store has the same dimensions as the array. Data that you write to the data store (by using Data Store Write blocks) must have these dimensions.

If you set the Dimensions parameter to a value other than -1, the initial value dimensions must match the dimensions that you specify, unless the initial value is a scalar or a MATLAB® structure. If you specify a scalar, each element of the data store uses the scalar as the initial value. Use this technique to apply the same initial value (the scalar that you specify) to each element without manually matching the dimensions of the initial value with the dimensions of the data store.

To use this block to initialize a nonvirtual bus signal, specify the initial value as a MATLAB structure and set the model configuration parameter Underspecified initialization detection to Simplified. For more information about initializing nonvirtual bus signals using structures, see Specify Initial Conditions for Bus Elements.

Programmatic Use

Block Parameter: InitialValue
Type: character vector
Values: scalar | vector | matrix | N-D array
Default: '0'

Specify the minimum value that the block should output. The default value is [] (unspecified). This number must be a finite real double scalar value.

Note

If you specify a bus object as the data type for this block, do not set the minimum value for bus data on the block. Simulink ignores this setting. Instead, set the minimum values for bus elements of the bus object specified as the data type. For information on the Minimum property of a bus element, see Simulink.BusElement.

Simulink® uses the minimum value to perform:

Programmatic Use

Block Parameter: OutMin
Type: character vector
Values: scalar
Default: '[ ]'

Specify the maximum value that the block should output. The default value is [] (unspecified). This number must be a finite real double scalar value.

Note

If you specify a bus object as the data type for this block, do not set the maximum value for bus data on the block. Simulink ignores this setting. Instead, set the maximum values for bus elements of the bus object specified as the data type. For information on the Maximum property of a bus element, see Simulink.BusElement.

Simulink uses the maximum value to perform:

Programmatic Use

Block Parameter: OutMax
Type: character vector
Values: scalar
Default: '[ ]'

Specify the output data type. You can set it to:

  • A rule that inherits a data type (for example, Inherit: auto).

  • The name of a built-in data type (for example, single).

  • The name of a data type object (for example, a Simulink.NumericType object).

  • An expression that evaluates to a data type (for example, fixdt(1,16,0)). Do not specify a bus object as the data type in an expression; use Bus: <object name> to specify a bus data type.

Click the Show data type assistant button to display the Data Type Assistant, which helps you set the data type attributes. For more information, see Specify Data Types Using Data Type Assistant.

Programmatic Use

Block Parameter: OutDataTypeStr
Type: character vector
Values: 'Inherit: auto' | 'double' | 'single' | 'half' | 'int8' | 'uint8' | 'int16' | 'uint16' | 'int32' | 'uint32' | 'int64' | 'uint64' | 'boolean' | 'fixdt(1,16,0)' | 'fixdt(1,16,2^0,0)' | 'string' | 'Enum: <class name>'
Default: 'Inherit: auto'

Select this parameter to prevent the fixed-point tools from overriding the Output data type you specify on the block. For more information, see Use Lock Output Data Type Setting (Fixed-Point Designer).

Programmatic Use

Block Parameter: LockScale
Type: character vector
Values: 'off' | 'on'
Default: 'off'

Dimensions of the data store. The default value, -1, enables you to set the dimensions of the data store by using the Initial value parameter. However, in this case, you cannot use scalar expansion with the initial value. You must specify the initial value by using an array that has the dimensions that you want.

If you use a value other than -1, specify the same dimensions as the dimensions of the Initial value parameter, unless you specify the initial value as a scalar (for scalar expansion) or a MATLAB structure. If the data store represents an array of buses, and if you use a MATLAB structure for the initial value, you can specify dimensions to initialize the array of buses with this structure.

Programmatic Use

Block Parameter: Dimensions
Type: character vector
Values: scalar | vector | matrix
Default: '-1'

Specify that the data store interpret vector initial values as one-dimensional.

By default, MATLAB represents vector data as matrices, which have two dimensions. For example, MATLAB represents the vector [1 2 3] as a 1-by-3 matrix.

When you select this parameter, the data store represents vector data by using only one dimension instead of two. For example, if you specify an initial value of [1 2 3], the data store stores a one-dimensional vector with three elements.

For more information, see Determine the Output Dimensions of Source Blocks.

Programmatic Use

Block Parameter: VectorParams1D
Type: character vector
Values: 'off' | 'on'
Default: 'on'

Specify the numeric type, real or complex, of the values in the data store.

Programmatic Use

Block Parameter: SignalType
Type: character vector
Values: 'auto' | 'real' | 'complex'
Default: 'auto'

In a single model reference hierarchy, when you use multiple Model blocks to refer to a model that contains a Data Store Memory block, by default, each instance of the referenced model (each Model block) reads from and writes to a separate copy of the data store. When you select Share across model instances, instead of interacting with a separate copy, all of the instances read from and write to the same data store.

When you set the model configuration parameter Code interface packaging to Reusable function to generate reentrant code from a model (Simulink Coder™), a data store with Share across model instances selected appears in the code as a global symbol that the generated entry-point functions access directly. For example, a global symbol is a global variable or a field of a global structure variable. Therefore, each call that your code makes to the entry-point functions (each instance of the model) shares the data.

For an example, see Share Data Store Between Instances of a Reusable Algorithm. For more information, see Share Data Among Referenced Model Instances.

Programmatic Use

Block Parameter: ShareAcrossModelInstances
Type: character vector
Values: 'off' | 'on'
Default: 'off'

Specify that Simulink software, when compiling the model, searches the model and base workspace for a Simulink.Signal object having the same name, as described in Symbol Resolution. If Simulink does not find such an object, the compilation stops with an error. Otherwise, Simulink compares the attributes of the signal object to the corresponding attributes of the Data Store Memory block. If the block and the object attributes are inconsistent, Simulink halts model compilation and displays an error.

Programmatic Use

Block Parameter: StateMustResolveToSignalObject
Type: character vector
Values: 'off' | 'on'
Default: 'off'

Diagnostics

Select the diagnostic action to take if the model attempts to read data from a data store to which it has not written data in this time step. See also the Detect read before write diagnostic in the Data Store Memory block section of the Model Configuration Parameters > Diagnostics > Data Validity pane.

  • None — Produce no response.

  • Warning — Display a warning and continue the simulation.

  • Error — Terminate the simulation and display an error.

Programmatic Use

Block Parameter: ReadBeforeWriteMsg
Type: character vector
Values: 'none' | 'warning' | 'error'
Default: 'warning'

Select the diagnostic action to take if the model attempts to write data to the data store after previously reading data from it in the current time step. See also the Detect write after read diagnostic in the Data Store Memory block section of the Model Configuration Parameters > Diagnostics > Data Validity pane.

  • None — Produce no response.

  • Warning — Display a warning and continue the simulation.

  • Error — Terminate the simulation and display an error.

Programmatic Use

Block Parameter: WriteAfterReadMsg
Type: character vector
Values: 'none' | 'warning' | 'error'
Default: 'warning'

Select the diagnostic action to take if the model attempts to write data to the data store twice in succession in the current time step. See also the Detect write after write diagnostic in the Data Store Memory block section of the Model Configuration Parameters > Diagnostics > Data Validity pane.

  • None — Produce no response.

  • Warning — Display a warning and continue the simulation.

  • Error — Terminate the simulation and display an error.

Programmatic Use

Block Parameter: WriteAfterWriteMsg
Type: character vector
Values: 'none' | 'warning' | 'error'
Default: 'warning'

Logging

Select this option to save the values of this signal to the MATLAB workspace during simulation. See Signal Logging for details.

Programmatic Use

Block Parameter: DataLogging
Type: character vector
Values: 'off' | 'on'
Default: 'off'

Use this pair of controls, consisting of a list box and an edit field, to specify the name associated with logged signal data.

Simulink uses the signal name as its logging name by default. To specify a custom logging name, select Custom from the list box and enter the custom name in the adjacent edit field.

Programmatic Use

Block Parameter: DataLoggingNameMode
Type: character vector
Values: 'SignalName' | 'Custom'
Default: ''

Note

If you set DataLoggingNameMode to Custom, you must specify the name associated with logged signal data using the DataLoggingName parameter.

Block Parameter: DataLoggingName
Type: character vector
Values: character vector
Default: ''

Discard all but the last N data points, where N is the number that you enter in the adjacent edit field. For more information, see Log Data Stores.

Programmatic Use

Block Parameter: DataLoggingMaxPoints
Type: character vector
Values: nonzero integer
Default: '5000'

Log every Nth data point, where N is the number that you enter in the adjacent edit field. For example, suppose that your model uses a fixed-step solver with a step size of 0.1 s. If you select this option and accept the default decimation value (2), Simulink records data points for this signal at times 0.0, 0.2, 0.4, and so on. For more information, see Log Data Stores.

Programmatic Use

Block Parameter: DataLoggingLimitDataPoints
Type: character vector
Values: non-zero integer
Default: '2'

Model Examples

Share Data Store Between Instances of a Reusable Algorithm

Share Data Store Between Instances of a Reusable Algorithm

To reuse an algorithm, instead of copying and pasting the blocks, you can encapsulate them in a separate model file. Then, you can refer to the model repeatedly with Model blocks. Each Model block is a standalone instance of the algorithm.

Open Model

Block Characteristics

Data Types

Boolean | bus | double | enumerated | fixed point | half | integer | single | string

Direct Feedthrough

yes

Multidimensional Signals

yes

Variable-Size Signals

no

Zero-Crossing Detection

no

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Fixed-Point Conversion
Design and simulate fixed-point systems using Fixed-Point Designer™.

See Also

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Topics

Introduced before R2006a

Simulink Documentation

Support

Model-Based Design for Embedded Control Systems

Model-Based Design for Embedded Control Systems

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