IP Protection via Static-Library-Based S-Function

This example shows how to generate code for a Simulink® model that contains an S-Function that relies on a static library. Static libraries can encapsulate proprietary algorithms and provide an interface to be used in generated code and Simulink. Using a static library is one technique to protect your model intellectual property (IP). Alternatively, you may use S-Function objects. Shared libraries, or a Simulink® Protected model for IP protection, etc.

Example Static Library
Use Static Library in Simulink® Model via S-Function
Create RTDB and Generate Code

Example Static Library

Example Requirements

Given that the model code must run on the SimWB real-time host, which uses a Linux platform, this example focuses on the Linux workflow. You must work through this example on an instance of MATLAB® running on a MATLAB and SimWB-supported Linux platform.

Library Source Code

Suppose that your proprietary library calculates the hypotenuse of a right-angled triangle, given the two sides. The following are the contents of <MLTOOLKITROOT>/examples/use_lib/pythagoras.c.

                #include <stdio.h>
                #include <math.h>
                double hypotenuse(double a, double b){
                    return sqrt(pow(a,2)+pow(b,2));
                }

pythagoras.h is a companion header file for pythagoras.c , provided as an interface to the library. Its contents are as follows:

                #ifndef HYPOTENUSE_H_
                #define HYPOTENUSE_H_
                double hypotenuse(double a, double b);
                #endif

Build Static Library

Using the GCC compiler and the ar tool, you can create the static library for pythagoras.c by executing the following at the MATLAB command prompt:

                % using the bang operator (!) as a shell escape
                !gcc -c -o pythagoras.o pythagoras.c -fPIC
                !ar rsv libpythagoras.a pythagoras.o

For more information regarding these commands, type man gcc or man ar at a shell terminal.

Use Static Library in Simulink Model via S-Function

Create S-Function

Write an S-Function that uses the hypotenuse method of the library. For an example, see <MLTOOLKITROOT>/examples/use_lib/use_lib.c. Create a MEX-file for simulation using the following command at the MATLAB command prompt:

                mex use_lib.c libpythagoras.a

The model <MLTOOLKITROOT>/examples/use_lib/ccur_calc_hyp.mdl (developed in MATLAB version 7.11 (R2010b)) contains an S-Function block that uses the use_lib S-Function. Constant blocks (SW_a, SW_b) supply the required inputs and the output can be viewed via the Display block (SW_out). You can run this model in Simulink® for different values of SW_a and SW_b to verify the algorithm behavior.

Distribution Files

To distribute this S-Function to a third party, you must provide your user with the following files. Notice that the list excludes the pythagoras.c file, which contains the IP to be protected.

use_lib.c — S-Function source file
pythagoras.h — Library interface header file
libpythagoras.a — Proprietary library
use_lib.mexa64 — S-Function MEX file to facilitate simulation in Simulink
ccur_calc_hyp.mdl (Optional) — S-Function example

Create RTDB and Generate Code

The process to create the RTDB and generate SimWB-compliant code for this model is described in this example.

Note: To ensure that the static library is ported to the real-time host along with the model source files, you must modify the Simulink model's Configuration Parameters > Code Generation > Custom Code > Include list of additional > Libraries list to include libpythagoras.a.