S-Function Examples

These examples show you how to work with a variety of S-functions or programs that use S-functions, including C/C++ S-functions, Fortran S-functions, S-function Builder, Level 2 MATLAB^® S-functions, and Blockset Designer. Each section explains how to open the files and what is in them. These are good places to continue to develop an understanding of S-functions after learning the basics. These do not represent all the examples available for S-functions, but a relevant subsection.

Access S-Function Examples

Most of the S-function examples are run through sfundemos. This example library contains S-function models and is grouped by coding type, such as C S-functions or C++ S-functions.

To run an example from sfundemos:

In the MATLAB Command Window, enter sfundemos.
The S-function example library opens.
Each block represents a category of S-function examples.
Double-click a category to display the examples that it includes. For example, click C-files.
Double-click a block to open and run the example that it represents.

It might be helpful to examine some sample S-functions as you read the next chapters. Code for the examples is stored in the following folder under the MATLAB root folder.

MATLAB code	`toolbox/simulink/sfuntemplates`
C, C++, and Fortran code	`toolbox/simulink/sfuntemplates/src`

Level-2 MATLAB S-Function Examples

The matlabroot/toolbox/simulink/sfuntemplates folder (open) contains many Level-2 MATLAB S-functions. Consider starting off by looking at these files. For more on Level-2 MATLAB S-functions, see Write Level-2 MATLAB S-Functions.

Filename	Model Name	Description
`msfcn_dsc.m`	`msfcndemo_sfundsc1`	Implement an S-function with an inherited sample time.
`msfcn_limintm.m`	`msfcndemo_limintm`	Implement a continuous limited integrator where the output is bounded by lower and upper bounds and includes initial conditions.
`msfcn_multirate.m`	`msfcndemo_multirate`	Implement a multirate system.
`msfcn_times_two.m`	`msfcndemo_timestwo`	Implement an S-function that doubles its input.
`msfcn_unit_delay.m`	`msfcndemo_sfundsc2`	Implement a unit delay.
`msfcn_varpulse.m`	`msfcndemo_varpulse`	Implement a variable pulse width generator by calling the `set_param` function within a Level-2 MATLAB S-function. Also demonstrates how to use custom set and get methods for the block operating point.
`msfcn_vs.m`	`msfcndemo_vsfunc`	Implement a variable sample time block in which the first input is delayed by an amount of time determined by the second input.

C S-Function Examples

The matlabroot/toolbox/simulink/sfuntemplates/src folder (open) contains examples of C MEX S-functions, many of which have a MATLAB S-function counterpart. The C MEX S-functions are listed in the following table. For more on C S-functions, see C/C++ S-Function Basics and Build S-Functions Automatically Using S-Function Builder.

Filename	Model Name	Description
`csfunc.c`	`sfcndemo_csfunc`	Implement a continuous system.
`dlimintc.c`	No model available	Implement a discrete-time limited integrator.
`dsfunc.c`	`sfcndemo_dsfunc`	Implement a discrete system.
`limintc.c`	No model available	Implement a limited integrator.
`mixedm.c`	`sfcndemo_mixedm`	Implement a hybrid dynamic system consisting of a continuous integrator (1/s) in series with a unit delay (1/z).
`mixedmex.c`	`sfcndemo_mixedmex`	Implement a hybrid dynamic system with a single output and two inputs.
`slexQuantizeSFcn.c`	`sfcndemo_sfun_quantize`	Implement a vectorized quantizer. Quantizes the input into steps as specified by the quantization interval parameter, `q`.
`sdotproduct.c`	`sfcndemo_sdotproduct`	Compute dot product (multiply-accumulate) of two real or complex vectors.
`sfbuilder_bususage.c`	`sfbuilder_bususage`	Access S-Function Builder with a bus input and output.
`sfbuilder_movingAverage.c`	`sfbuilder_movingAverage`	Implement simple time window moving average using Start and Terminate.
`sftable2.c`	`sfcndemo_sftable2`	Implement a two-dimensional table lookup.
`sfun_atol.c`	`sfcndemo_sfun_atol`	Set different absolute tolerances for each continuous state.
`sfun_cplx.c`	`sfcndemo_cplx`	Add complex data for an S-function with one input port and one parameter.
`sfun_directlook.c`	No model available	Implement a direct 1-D lookup.
`sfun_dtype_io.c`	`sfcndemo_dtype_io`	Implement an S-function that uses Simulink^® data types for inputs and outputs.
`sfun_dtype_param.c`	`sfcndemo_dtype_param`	Implement an S-function that uses Simulink data types for parameters.
`sfun_dynsize.c`	`sfcndemo_sfun_dynsize`	Implements dynamically-sized outputs.
`sfun_errhdl.c`	`sfcndemo_sfun_errhdl`	Check parameters using the `mdlCheckParameters` S-function routine.
`sfun_fcncall.c`	`sfcndemo_sfun_fcncall`	Execute function-call subsystems on the first and second output elements.
`sfun_frmad.c`	`sfcndemo_frame`	Implement a frame-based A/D converter.
`sfun_frmda.c`	`sfcndemo_frame`	Implement a frame-based D/A converter.
`sfun_frmdft.c`	`sfcndemo_frame`	Implement a multichannel frame-based Discrete-Fourier transformation (and its inverse).
`sfun_frmunbuff.c`	`sfcndemo_frame`	Implement a frame-based unbuffer block.
`sfun_multiport.c`	`sfcndemo_sfun_multiport`	Configure multiple input and output ports.
`sfun_manswitch_mode.c`	No model available	Implement a manual switch.
`sfun_matadd.c`	`sfcndemo_matadd`	Add matrices in an S-function with one input port, one output port, and one parameter.
`sfun_multirate.c`	`sfcndemo_sfun_multirate`	Demonstrate how to specify port-based sample times.
`sfun_port_constant.c`	`sfcndemo_port_constant`	Demonstrate how to specify constant port-based sample times.
`sfun_port_triggered.c`	`sfcndemo_port_triggered`	Demonstrate how to use port-based sample times in a triggered subsystem.
`sfun_runtime1.c`	`sfcndemo_runtime`	Implement run-time parameters for all tunable parameters.
`sfun_runtime2.c`	`sfcndemo_runtime`	Register individual run-time parameters.
`sfun_runtime3.c`	`sfcndemo_runtime`	Register dialog parameters as run-time parameters.
`sfun_runtime4.c`	`sfcndemo_runtime`	Implement run-time parameters as a function of multiple dialog parameters.
`sfun_zc.c`	`sfcndemo_sfun_zc`	Demonstrate use of nonsampled zero crossings to implement `abs(u)`. This S-function is designed to be used with a variable-step solver.
`sfun_zc_sat.c`	`sfcndemo_sfun_zc_sat`	Demonstrate zero crossings with saturation.
`sfun_zc_cstate_sat.c`	`sfcndemo_sfun_zc_cstate_sat`	Implement a continuous integrator with saturation limits and zero-crossing detection.
`sfun_integrator_localsolver.c`	`sfcndemo_sfun_localsolver`	Demonstrate a continuous integrator where the continuous states are solved using a separate local solver instead of that used by the model.
`sfun_angle_events.c`	`sfcndemo_angle_events`	Implement a method for robust and efficient detection of a rotating body crossing specified angles.
`sfun_angle_events.c`	No model available	Demonstrate angle detection and incorporate Stateflow^® to schedule function calls.
`sfunmem.c`	`sfcndemo_sfunmem`	Implement a one-integration-step delay and hold memory function.
`simomex.c`	`sfcndemo_simomex`	Implement a single-input, two-output state-space dynamic system described by the state-space equations: dx/dt = Ax + Bu y = Cx + Du where `x` is the state vector, `u` is vector of inputs, and `y` is the vector of outputs.
`stspace.c`	`sfcndemo_stspace`	Implement a set of state-space equations. You can turn this into a new block by using the S-Function block and mask facility. This example MEX file performs the same function as the built-in State-Space block. This is an example of a MEX file where the number of inputs, outputs, and states is dependent on the parameters passed in from the workspace.
`stvctf.c`	`sfcndemo_stvctf`	Implement a continuous-time transfer function whose transfer function polynomials are passed in via the input vector. This is useful for continuous time adaptive control applications.
`stvdtf.c`	`sfcndemo_stvdtf`	Implement a discrete-time transfer function whose transfer function polynomials are passed in via the input vector. This is useful for discrete-time adaptive control applications.
`stvmgain.c`	`sfcndemo_stvmgain`	Implement a time-varying matrix gain.
`table3.c`	No model available	Implement a 3-D lookup table.
`timestwo.c`	`sfcndemo_timestwo`	Implement a C MEX S-function that doubles its input.
`vdlmintc.c`	No model available	Implement a discrete-time vectorized limited integrator.
`vdpmex.c`	`sfcndemo_vdpmex`	Implement the Van der Pol equation.
`vlimintc.c`	No model available	Implement a vectorized limited integrator.
`vsfunc.c`	`sfcndemo_vsfunc`	Illustrate how to create a variable sample time block. This block implements a variable-step delay in which the first input is delayed by an amount of time determined by the second input.
`sfun_pwm.c`	`sfcndemo_pwm`	Illustrate how to create a controllable sample time block.
`sfun_d2c`	`sfcndemo_d2c`	Illustrate how to convert a discrete input signal into a smooth continuous output signal
`sfun_pulse_delay.c`	`sfcndemo_vco`	Illustrate how to implement an algorithm to efficiently delay a discrete valued input signal by a variable amount using variable sample time.

Fortran S-Function Examples

The following table lists sample Fortran^® S-functions available in the matlabroot/toolbox/simulink/sfuntemplates/src folder (open). For more on Fortran S-functions, see Create Level-2 Fortran S-Functions.

Filename	Model Name	Description
`sfun_atmos.c` `sfun_atmos_sub.F`	`sfcndemo_atmos`	Calculate the 1976 standard atmosphere to 86 km using a Fortran subroutine.

C++ S-Function Examples

The following table lists sample C++ S-functions available in the matlabroot/toolbox/simulink/sfuntemplates/src folder (open). For more on C++ S-functions, see C/C++ S-Function Basics and Build S-Functions Automatically Using S-Function Builder.

Filename	Model Name	Description
`sfun_counter_cpp.cpp`	`sfcndemo_counter_cpp`	Store a C++ object in the pointers vector `PWork`.
`sfbuilder_permute.cpp`	`sfbuilder_permutation`	Implement permutation by calling external C++ classes using Start and Terminate.
`sfbuilder_linfilt.cpp`	`sfbuilder_upsampling`	Implement linear filtering with C++ STL algorithms for the upsampling of a sign wave.

Organizing S-Function in a Project

The following example shows how to arrange S-function artifacts into a project. This is accomplished using the Blockset Designer feature. For more on Blockset Designer, see Create a Blockset Project.

Filename	Description
`slexBlocksetDesignerExample`	Organize S-function artifacts into a single project using Blockset Designer.