MATLAB: How to work with static or global variables in CMEX S-functions? What are work vectors

%sfunctionglobalsfunctionsimulinkvectorswork

For example, I would like to track the previous value of each input signal element entering one of the ports of my S-function block. I would like to obtain this type of persistent storage of variables, and I wonder if I should use static or global variables. Doing this could lead to a reentrancy problem that I would like to avoid.

Best Answer

This enhancement has been incorporated in Release 2008a (R2008a). For previous product releases, read below for any possible workarounds:

Simulink has Work Vectors that you can allocate for storing static double, integer, and pointer variables. Work vectors allow you to create a reentrant S-function, and should be used instead of static or global variables. Work Vectors are discussed in detail with examples starting on page 7-24 of the Simulink 4.0 on-line version of the Writing S-functions Guide, available here:

http://www.mathworks.com/help/releases/R13sp2/toolbox/simulink/sfg/sfun_features16.html

To allocate storage, use the API macro ssSetNumXWork, where X could be: R for real, I for integer, or P for pointer. This is done in mdlInitializesizes.

Once allocated, you can then obtain these values using other macros, such as ssGetRWork, which returns a pointer to the allocated work vector.

This mechanism allows variables to be used in any function of the S-function, and assures the integrity of the variable, since calls between various functions using GLOBAL is not good practice.

Related Solutions

MATLAB: Is there an example that explains how to use a PWork vector in an S-function in Simulink 7.3 (R2009a)

The ability to use a PWork vector in an S-function is available in Simulink 7.3 (R2009a). Download the attached files for a complete example that illustrates the setup and very simple use of a PWork vector in an S-Function. It uses a PWork vector to store a counter.

Refer to the steps below, which is a snippet of the attached code, in order to use a PWork vector in an S-function.

1) Set the number of pointers in the PWork vector.

ssSetNumPWork

2) Allocate the memory.

p_work_vector_target_data_handle = (double *) malloc( sizeof(double) );

3) Initialize the counter to 0.

(*p_work_vector_target_data_handle) = 0.0;

4) Retrieve the PWork vector value.

p_work_vector_element = ssGetPWorkValue(S, 0);

5) Increment and set the PWork vector value.

(*p_work_vector_element) = (*p_work_vector_element) + 1  
(*output_port_data_pointer) = (*p_work_vector_element);

6) Set the PWork vector to NULL.

void ** p_work_vector = NULL;

7) Clear the memory.

free(p_work_vector_element);

MATLAB: How to create a persistent work vector in S-function

You may consider using the Pointer Work Vector to have the struct persists for each instance of the S-function.

To read more about it and see an example, refer to this page:

https://www.mathworks.com/help/releases/R2016b/simulink/sfg/elementary-work-vectors.html

The example is under the Elementary Work Vector Examples > Pointer Work Vector section.

To work with Pointer Work Vector in S-function, you will need to write your own S-function instead of using the Legacy Code Tool.

Best Answer

Related Solutions

MATLAB: Is there an example that explains how to use a PWork vector in an S-function in Simulink 7.3 (R2009a)

MATLAB: How to create a persistent work vector in S-function

Related Question