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If Action Subsystem

Subsystem whose execution is enabled by If block

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  • If Action Subsystem block

Libraries:
Simulink / Ports & Subsystems

Description

The If Action Subsystem block is a Subsystem block preconfigured as a starting point for creating a subsystem whose execution is controlled by an If block. The If block evaluates a logical expression and then, depending on the result of the evaluation, outputs an action signal. Execution of the subsystem is controlled by an Action Port block placed inside the subsystem.

Simulink® ignores a priority set on an If Action Subsystem block. Instead, set the priority on the If block that initiates execution of the subsystem.

Merge Signals from If Action Subsystem Blocks

This example shows how to merge signals controlled by an If block. For more information, see Select Subsystem Execution.

Model ex_if_block

The If block selects the execution of an If Action Subsystem block from a set of subsystems. Regardless of which subsystem the If block selects, you can create one output signal with a Merge block.

All blocks in an If Action Subsystem block must execute at the same rate as the driving If block. To satisfy this requirement, set the sample time parameter for each block to either inherited (-1) or the same value as the If block sample time.

Support for Fixed-Point Data Type

The If block does not directly support fixed-point data types. However, you can use the Compare To Constant block to work around this limitation. For more information, Fixed-Point Data Type Support for If Block.

Examples

Simulink Subsystem Semantics

Simulink Subsystem Semantics

This set of examples shows different types of Simulink® Subsystems and what semantics are used when simulating these subsystems. Each example provides a description of the model and the subtleties governing how the model is executed.

If-Then-Else Blocks

If-Then-Else Blocks

The effect of feeding a sine wave into If Action Subsystem blocks. It is designed to illustrate the similarity between the If Action Subsystem block and the Enabled Subsystem block.

Modeling Clutch Lock-Up Using If Blocks

Modeling Clutch Lock-Up Using If Blocks

Use If/Else subsystems to build a clutch model. An 'If' subsystem models the clutch dynamics in the locked position while an 'Else' subsystem models the unlocked position. One or the other is enabled using the 'If' block. The dot-dashed lines from the 'If' block denote control signals, which are used to enable If/Else (or other conditional) subsystems. Checking any of the boxes on the GUI produces a plot of any of the selected variables (versus time).

Ports

Input

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Placing an Inport block in a subsystem block adds an external input port to the block. The port label matches the name of the Inport block.

Use Inport blocks to get signals from the local environment.

Data Types: half | single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point | enumerated | bus

The Action Port block in a subsystem block adds an external input port to the block and changes the block to an If Action Subsystem block.

Note

The Action Port block is not available in the Simulink Library Browser. When using the If Action Subsystem block, you can access the Action Port block only from within the If Action Subsystem block.

Dot-dash lines from an If block to an If Action Subsystem block represent action signals. An action signal is a control signal connected to the Action port of an If Action Subsystem block. A message on the action signal initiates execution of the subsystem.

Data Types: action

Output

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Placing an Outport block in a subsystem block adds an output port from the block. The port label on the subsystem block is the name of the Outport block.

Use Outport blocks to send signals to the local environment.

Data Types: half | single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | Boolean | fixed point | enumerated | bus

Parameters

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To edit block parameters interactively, use the Property Inspector. From the Simulink Toolstrip, on the Simulation tab, in the Prepare gallery, select Property Inspector.

Main

Select how to display port labels on the Subsystem block icon.

  • none — Do not display port labels.

  • FromPortIcon — If the corresponding port icon displays a signal name, display the signal name on the Subsystem block. Otherwise, display the port block name or the port number if the block name is a default name.

  • FromPortBlockName — Display the name of the corresponding port block on the Subsystem block.

  • SignalName — If the signal connected to the port is named, display the name of the signal on the Subsystem block. Otherwise, display the name of the corresponding port block.

For port label editing on Subsystem blocks, see Edit Port Labels on Subsystem Blocks.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: ShowPortLabels
Values: 'FromPortIcon' (default) | 'FromPortBlockName' | 'SignalName' | 'none'

Control user access to the contents of the subsystem.

  • ReadWrite — Enable opening and modification of subsystem contents.

  • ReadOnly — Enable opening but not modification of the subsystem. If the subsystem resides in a block library, you can create and open links to the subsystem and can make and modify local copies of the subsystem but cannot change the permissions or modify the contents of the original library instance.

  • NoReadOrWrite — Disable opening or modification of subsystem. If the subsystem resides in a library, you can create links to the subsystem in a model but cannot open, modify, change permissions, or create local copies of the subsystem.

You do not receive a response if you attempt to view the contents of a subsystem whose Read/Write permissions parameter is set to NoReadOrWrite. For example, when double-clicking such a subsystem, the software does not open the subsystem and does not display any messages.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: Permissions
Values: 'ReadWrite' (default) | 'ReadOnly' | 'NoReadOrWrite'

Enter the name of a function to be called if an error occurs while the software executes the subsystem.

The software passes two arguments to the function: the handle of the subsystem and a character vector that specifies the error type. If no function is specified, the software displays a generic error message if executing the subsystem causes an error.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: ErrorFcn
Values: '' (default) | function name in quotes
Data Types: char | string

Select whether to resolve names of workspace variables referenced by this subsystem.

For more information, see Symbol Resolution and Symbol Resolution Process.

  • All — Resolve all names of workspace variables used by this subsystem, including those used to specify block parameter values and Simulink data objects (for example, Simulink.Signal objects).

  • ExplicitOnly — Resolve only names of workspace variables used to specify block parameter values, data store memory (where no block exists), signals, and states marked as “must resolve”.

  • None — Do not resolve any workspace variable names.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: PermitHierarchicalResolution
Values: 'All' (default) | 'ExplicitOnly' | 'None'

Select this parameter to display the reinitialize event ports. Clear this parameter to remove the ports.

Dependencies

To enable this parameter, select Treat as atomic unit.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: ShowSubsystemReinitializePorts
Values: 'off' (default) | 'on'

Code Generation

Parameters on the Code Generation tab require a Simulink Coder™ or Embedded Coder® license.

Select the code format to be generated for an atomic (nonvirtual) subsystem.

  • Auto — The software chooses the optimal format for you based on the type and number of instances of the subsystem that exist in the model.

  • Inline — The software inlines the subsystem unconditionally.

  • Nonreusable function — If Filename options is set to Auto, the software packages separate functions in the model file. If File name options is set to Use subsystem name, Use function name, or User specified using different filenames, the software packages separate functions in separate files.

    Subsystems with this setting generate functions that might have arguments depending on the Function interface parameter setting. You can name the generated function and file using parameters Function name and File name (no extension), respectively. These functions are not reentrant.

  • Reusable function — The software generates a function with arguments that allows reuse of subsystem code when a model includes multiple instances of the subsystem.

    This option also generates a function with arguments that allows subsystem code to be reused in the generated code of a model reference hierarchy that includes multiple instances of a subsystem across referenced models. In this case, the subsystem must be in a library.

For more information, see:

The default value depends on the block configuration. For example, the default value for the Subsystem block is Auto. The default value for the CodeReuseSubsystem block is Reusable function.

Tips

  • When you want multiple instances of a subsystem to be represented as one reusable function, you can designate each one of them as Auto or as Reusable function. Using one or the other is best, as using both creates two reusable functions, one for each designation. The outcomes of these choices differ only when reuse is not possible. Selecting Auto does not allow control of the function or filename for the subsystem code.

  • The Reusable function and Auto options both try to determine if multiple instances of a subsystem exist and if the code can be reused. The difference between the behavior of each option is that when reuse is not possible:

    • Auto yields inlined code, or if circumstances prohibit inlining, separate functions for each subsystem instance.

    • Reusable function yields a separate function with arguments for each subsystem instance in the model.

  • If you select Reusable function while your generated code is under source control, set File name options to Use subsystem name, Use function name, or User specified. Otherwise, the names of your code files change whenever you modify your model, which prevents source control on your files.

  • If you select an option other than Auto or Inline and the model configuration parameter States, the code generator produces separate output and update methods. The code generator does not take into account the Combine output and update methods for code generation and simulation specification.

Dependencies

  • This parameter requires a Simulink Coder license for code generation.

  • To enable this parameter, select Treat as atomic unit.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: RTWSystemCode
Values: 'Auto' | 'Inline' | 'Nonreusable function' | 'Reusable function'

Select how the software names the function it generates for the subsystem.

If you have an Embedded Coder license, you can control function names with options on the Configuration Parameter Code Generation > Identifiers pane.

  • Auto — Assign a unique function name using the default naming convention, model_subsystem(), where model is the name of the model and subsystem is the name of the subsystem, or that of an identical one when code is being reused.

    If you select Reusable function for the Function packaging parameter and a model reference hierarchy contains multiple instances of the reusable subsystem, in order to generate reusable code for the subsystem, Function name options must be set to Auto.

  • Use subsystem name — Use the subsystem name as the function name. By default, the function name uses the naming convention model_subsystem.

    When a subsystem is in a library block and the subsystem parameter Function packaging is set to Reusable function, if you set the Use subsystem name option, the code generator uses the name of the library block for the subsystem function name and filename.

  • User specified — Enable the Function name field. Enter any legal C or C++ function name, which must be unique.

For more information, see Generate Subsystem Code as Separate Function and Files (Simulink Coder).

The default value depends on the block configuration. For example, the default value for the Subsystem block is Auto. The default value for the CodeReuseSubsystem block is Use subsystem name.

Dependencies

  • This parameter requires a Simulink Coder license.

  • To enable this parameter, set Function packaging to Nonreusable function or Reusable function.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: RTWFcnNameOpts
Values: 'Auto' | 'Use subsystem name' | 'User specified'

Specify a unique, valid C or C++ function name for subsystem code.

Use this parameter if you want to give the function a specific name instead of allowing the Simulink Coder code generator to assign its own autogenerated name or use the subsystem name. For more information, see Generate Subsystem Code as Separate Function and Files (Simulink Coder).

Dependencies

  • This parameter requires a Simulink Coder license.

  • To enable this parameter, set Function name options to User specified.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: RTWFcnName
Values: '' (default) | function name in quotes
Data Types: char | string

Select how the software names the separate file for the function it generates for the subsystem.

  • Auto — Depending on the configuration of the subsystem and how many instances are in the model, Auto yields different results.

    • If the code generator does not generate a separate file for the subsystem, the subsystem code is generated within the code module generated from the subsystem parent system. If the subsystem parent is the model itself, the subsystem code is generated within model.c or model.cpp.

    • If you select Reusable function for the Function packaging parameter and your generated code is under source control, consider specifying a File name options value other than Auto. This prevents the generated filename from changing due to unrelated model modifications, which is problematic for using source control to manage configurations.

    • If you select Reusable function for the Function packaging parameter and a model reference hierarchy contains multiple instances of the reusable subsystem, in order to generate reusable code for the subsystem, File name options must be set to Auto.

  • Use subsystem name — The code generator generates a separate file, using the subsystem (or library block) name as the filename.

    When File name options is set to Use subsystem name, the subsystem filename is mangled if the model contains Model blocks, or if a model reference target is being generated for the model. In these situations, the filename for the subsystem consists of the subsystem name prefixed by the model name.

  • Use function name — The code generator uses the function name specified by Function name options as the filename.

  • User specified — This option enables the File name (no extension) text entry field. The code generator uses the name you enter as the filename. Enter any filename, but do not include the .c or .cpp (or any other) extension. This filename need not be unique.

    While a subsystem source filename need not be unique, you must avoid giving nonunique names that result in cyclic dependencies. For example, sys_a.h includes sys_b.h, sys_b.h includes sys_c.h, and sys_c.h includes sys_a.h.

The default value depends on the block configuration. For example, the default value for the Subsystem block is Auto. The default value for the CodeReuseSubsystem block is Use function name.

Dependencies

  • This parameter requires a Simulink Coder license.

  • To enable this parameter, set Function packaging to Nonreusable function or Reusable function.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: RTWFileNameOpts
Values: 'Auto' | 'Use subsystem name' | 'Use function name' | 'User specified'

The filename that you specify does not have to be unique. However, avoid giving non-unique names that result in cyclic dependencies. For example, sys_a.h includes sys_b.h, sys_b.h includes sys_c.h, and sys_c.h includes sys_a.h.

For more information, see Generate Subsystem Code as Separate Function and Files (Simulink Coder).

Dependencies

  • This parameter requires a Simulink Coder license.

  • To enable this parameter, set File name options to User specified.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: RTWFileName
Values: '' (default) | filename in quotes
Data Types: char | string

Select how to use arguments with the generated function.

  • void_void — Generate a function without arguments and pass data as global variables. For example: 

    void subsystem_function(void)

  • Allow arguments (Optimized) — Generate a function that uses arguments instead of passing data as global variables. This specification reduces global RAM. This option might reduce code size and improve execution speed and enable the code generator to apply additional optimizations. For example:

    void subsystem_function(real_T rtu_In1, real_T rtu_In2, 
                        real_T *rty_Out1)

    In some cases, when generating optimized code, the code generator might not generate a function that has arguments.

  • Allow arguments (Match graphical interface) — Generate a function interface that uses arguments that match the Subsystem graphical block interface. The generated function interface is predictable and does not change. A predictable interface can be useful for debugging and testing your code and integrating with external applications. For example, if a model has two Inport blocks and two Outport blocks, then the generated function interface is:

    void subsystem_function(real_T rtu_In1, real_T rtu_In2, 
                        real_T *rty_Out1, real_T *rty_Out2)

For more information, see:

Dependencies

  • This parameter requires an Embedded Coder license and an ERT-based system target file.

  • To enable this parameter, set Function packaging to Nonreusable function.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: FunctionInterfaceSpec
Values: 'void_void' (default) | 'Allow arguments (Optimized)' | 'Allow arguments (Match graphical interface)'

Generate subsystem function code in which the internal data for an atomic subsystem is separated from its parent model and is owned by the subsystem.

  • off — Do not generate subsystem function code in which the internal data for an atomic subsystem is separated from its parent model and is owned by the subsystem.

  • on — Generate subsystem function code in which the internal data for an atomic subsystem is separated from its parent model and is owned by the subsystem. The subsystem data structure is declared independently from the parent model data structures. A subsystem with separate data has its own block I/O and DWork data structure. As a result, the generated code for the subsystem is easier to trace and test. The data separation also tends to reduce the maximum size of global data structures throughout the model, because they are split into multiple data structures.

For details on how to generate modular function code for an atomic subsystem, see Generate Modular Function Code for Nonvirtual Subsystems (Embedded Coder).

For details on how to apply memory sections to atomic subsystems, see Override Default Memory Placement for Subsystem Functions and Data (Embedded Coder).

Dependencies

  • This parameter requires an Embedded Coder license and an ERT-based system target file.

  • To enable this parameter, set Function packaging to Nonreusable function.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: FunctionWithSeparateData
Values: 'off' (default) | 'on'

Select how the software applies memory sections to the subsystem initialization and termination functions.

  • Inherit from model — Apply the root model memory sections to the subsystem function code.

  • Default — Do not apply memory sections to the subsystem system code, overriding any model-level specification.

  • Apply one of the model memory sections to the subsystem.

Tips

Dependencies

  • This parameter requires an Embedded Coder license and an ERT-based system target file.

  • To enable this parameter, set Function packaging to Nonreusable function or Reusable function.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: RTWMemSecFuncInitTerm
Values: 'Inherit from model' (default) | 'Default' | model memory section in quotes

Select how Embedded Coder applies memory sections to the subsystem execution functions.

  • Inherit from model — Apply the root model memory sections to the subsystem function code.

  • Default — Do not apply memory sections to the subsystem system code, overriding any model-level specification.

  • Apply one of the model memory sections to the subsystem.

Tips

Dependencies

  • This parameter requires an Embedded Coder license and an ERT-based system target file.

  • To enable this parameter, set Function packaging to Nonreusable function or Reusable function.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: RTWMemSecFuncExecute
Values: 'Inherit from model' (default) | 'Default' | model memory section in quotes

Select how the software applies memory sections to the subsystem constants.

  • Inherit from model — Apply the root model memory sections to the subsystem data.

  • Default — Do not apply memory sections to the subsystem data, overriding any model-level specification.

  • Apply one of the model memory sections to the subsystem.

Tips

  • The memory section that you specify applies to the corresponding global data structures in the generated code. For basic information about the global data structures generated for atomic subsystems, see Standard Data Structures (Simulink Coder).

  • The possible values vary depending on what, if any, package of memory sections you have set for the model configuration. See Control Data and Function Placement in Memory by Inserting Pragmas (Embedded Coder).

  • If you have not configured the model with a package, Inherit from model is the only available value. Otherwise, the list includes Default and all memory sections the model package contains.

  • These options can be useful for overriding the model memory section settings for the given subsystem. For details on how to apply memory sections to atomic subsystems, see Override Default Memory Placement for Subsystem Functions and Data (Embedded Coder).

Dependencies

  • This parameter requires an Embedded Coder license and an ERT-based system target file.

  • To enable this parameter, set Function packaging to Nonreusable function and select the Function with separate data parameter.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: RTWMemSecDataConstants
Values: 'Inherit from model' (default) | 'Default' | model memory section in quotes

Select how the software applies memory sections to the subsystem internal data.

  • Inherit from model — Apply the root model memory sections to the subsystem data.

  • Default — Do not apply memory sections to the subsystem data, overriding any model-level specification.

  • Apply one of the model memory sections to the subsystem.

Tips

  • The memory section that you specify applies to the corresponding global data structures in the generated code. For basic information about the global data structures generated for atomic subsystems, see Standard Data Structures (Simulink Coder).

  • The possible values vary depending on what, if any, package of memory sections you have set for the model configuration. See Control Data and Function Placement in Memory by Inserting Pragmas (Embedded Coder).

  • If you have not configured the model with a package, Inherit from model is the only available value. Otherwise, the list includes Default and all memory sections the model package contains.

  • These options can be useful for overriding the model memory section settings for the given subsystem. For details on how to apply memory sections to atomic subsystems, see Override Default Memory Placement for Subsystem Functions and Data (Embedded Coder).

Dependencies

  • This parameter requires an Embedded Coder license and an ERT-based system target file.

  • To enable this parameter, set Function packaging to Nonreusable function and select the Function with separate data parameter.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: RTWMemSecDataInternal
Values: 'Inherit from model' (default) | 'Default' | model memory section in quotes

Select how the software applies memory sections to the subsystem parameters.

  • Inherit from model — Apply the root model memory sections to the subsystem function code.

  • Default — Do not apply memory sections to the subsystem system code, overriding any model-level specification.

  • Apply one of the model memory sections to the subsystem.

Tips

  • The memory section that you specify applies to the corresponding global data structure in the generated code. For basic information about the global data structures generated for atomic subsystems, see Standard Data Structures (Simulink Coder).

  • The possible values vary depending on what, if any, package of memory sections you have set for the model configuration. See Control Data and Function Placement in Memory by Inserting Pragmas (Embedded Coder).

  • If you have not configured the model with a package, Inherit from model is the only available value. Otherwise, the list includes Default and all memory sections the model package contains.

  • These options can be useful for overriding the model memory section settings for the given subsystem. For details on how to apply memory sections to atomic subsystems, see Override Default Memory Placement for Subsystem Functions and Data (Embedded Coder).

Dependencies

  • This parameter requires an Embedded Coder license and an ERT-based system target file.

  • To enable this parameter, set Function packaging to Nonreusable function and select the Function with separate data parameter.

Programmatic Use

To set the block parameter value programmatically, use the set_param function.

Parameter: RTWMemSecDataParameters
Values: 'Inherit from model' (default) | 'Default' | model memory section in quotes

Block Characteristics

Data Types

Booleana | busa | doublea | enumerateda | fixed pointa | halfa | imagea | integera | singlea | stringa

Direct Feedthrough

no

Multidimensional Signals

yesa

Variable-Size Signals

yesa

Zero-Crossing Detection

no

a Actual data type or capability support depends on block implementation.

Extended Capabilities

Version History

Introduced before R2006a

See Also

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