MATLAB: Can the S-Function have variable number of inputs and outputs

dynamicinportinputoutportoutputportssimulink

I have a masked subsystem which contains a S-Function. I want the user to enter the desired number of input ports for the S-Function through the mask.

Best Answer

It is possible to have variable number of inputs and outputs for a S-Function. Please see the attached model "testsfcn.mdl". This model contains a S-Function named "testtimestwo". You need to take the number of input ports as a parameter from the S-Function and then set the number of inputs to this number. Please see the attached C-File "testtimestwo.c" which demonstrates the S-Function with variable number of inputs.

For example, you can execute the attached example by performing the following steps:

1. Download the attached MDL-file and C-file.

2. Compile the "testtimestwo.c" file using the following command

mex testtimestwo.c

3. Double-click the S-Function block in the model and enter the desired number of inputs.

You will notice that the number of inputs for the S-Function block changes to the desired number that was entered in step 3 above.

Related Solutions

MATLAB: How to get the port name of a C-MEX S-function in Simulink

Following is an example of how to obtain the port name of a C-MEX S-function in Simulink.

If you open up the callbacks of the S-function block in the attached model, you will notice the following lines in the 'InitFcn':

q=get_param('bsp/my_block','PortHandles');
portname=get_param(q.Inport,'Name');

Here the first line gets the port handles of the S-function block and the second line assigns the input port name of the S-function to the variable “portname”. The string variable “portname” is passed as a parameter into the S-function.

If you open up the attached S-function source file, you will notice the following lines in mdlOutputs:

buflen = mxGetN((ssGetSFcnParam(S, 0)))*sizeof(mxChar)+1; 
Port_name = mxMalloc(buflen); 
status = mxGetString((ssGetSFcnParam(S, 0)),Port_name,buflen); 
mexPrintf("The Input Port Name is - %s\n ", Port_name);

Here the first two lines allocate memory for the string parameter that is being passed into the S-function. Then you would use "mxGetString" to store this string in a Character array. In this example the parameter is being stored in a "char *" called "Port_name" . The parameter "buflen" will be the length of this string.

MATLAB: How to write a Level-2 MATLAB S-Function where the input and output might have unknown dimensions, or even be variable-size signals

In the setup function of your MATLAB S-Function, you need to configure port properties to be inherited or dynamic:

>> block.SetPreCompInpPortInfoToDynamic;

>> block.SetPreCompOutPortInfoToDynamic;

You can then override the only properties that you known, as for example:

>> block.InputPort(1).DatatypeID = 0;

>> block.InputPort(1).Complexity = 'Real';

>> block.InputPort(1).DirectFeedthrough = true;

>> block.OutputPort(1).DatatypeID = 0;

>> block.OutputPort(1).Complexity = 'Real';

>> block.OutputPort(2).Dimensions = 1;

>> block.OutputPort(2).DatatypeID = 0;

>> block.OutputPort(2).Complexity = 'Real';

Note how the field 'Dimensions' has not been set for InputPort(1) and OutputPort(1).

Similar to A), but the required input and output ports need to be configured so that they can handle variable-size signals:

>> block.InputPort(1).DimensionsMode = 'Variable';

>> block.OutputPort(1).DimensionsMode = 'Variable';

In addition, in the Outputs function, you need to set the current dimensions of the output port:

>> block.OutputPort(1).CurrentDimensions = block.InputPort(1).CurrentDimensions;

For further details, please refer to the attached files:

A) matlabSfunUnknownSize.m and simpleTestMsfUnknownSize.slx

B) matlabSfunVarSize.m and simpleTestMsfVarSize.slx

and simulate the models step-by-step.

For more information on:

- how to write your own Level-2 MATLAB S-Function: https://uk.mathworks.com/help/simulink/sfg/writing-level-2-matlab-s-functions.html

- variable-size signals: https://uk.mathworks.com/help/simulink/ug/variable-size-signal-basics.html

- MATLAB and C S-Functions with variable-size signals: https://uk.mathworks.com/help/simulink/ug/s-functions-using-variable-size-signals.html

Best Answer

Related Solutions

MATLAB: How to get the port name of a C-MEX S-function in Simulink

MATLAB: How to write a Level-2 MATLAB S-Function where the input and output might have unknown dimensions, or even be variable-size signals

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