Level II S-function input=output ports are not apearing

Hi everyone,

I am using an level II S-Function to send the position of a robot from Simulink to the MATLAB workspace. In the workspace, a controller computes the appropriate control commands and sends them back to Simulink via another Level-2 S-Function.

In the second S-Function, which is responsible for sending the computed control commands from the workspace to Simulink, I have defined two output ports and zero input ports. However, the Simulink block shows a single input port (due to the argument block) and no output ports.

Can someone explain what I should do to make the output ports visible?

I enclosed the picture of the block in Simulink.

(I am using 2019b release)

Thanks in advance

Here is my code for the second Level-2 S-Function:

function getThrust(block)
    
    setup(block);

end

function setup(block)

    block.NumInputPorts = 0
    block.NumOutputPorts = 2
    
    block.OutputPort(1).Dimensions = 4;
    block.OutputPort(2).Dimensions = 4;
    block.OutputPort(1).Complexity  = 'Real';
    block.OutputPort(2).Complexity  = 'Real';
    block.OutputPort(1).DatatypeID  = 0;
    block.OutputPort(2).DatatypeID  = 0;
    
    block.SampleTimes = [0.1 0];  % stepping time of 0.1 [sec.] 
    block.RegBlockMethod('Outputs',@Outputs);
    
end

function Outputs(block)
    
    try
        RPM_in = evalin('base', 'thrusterPower');
    catch
        RPM_in = zeros(1,4);
    end
    
    try
        alpha_in = evalin('base', 'thrusterAngles')
    catch
        angles = zeros(1,4);
    end
    
    RPM_in = reshape(RPM_in, [1,4]);
    alpha_in = reshape(alpha_in, [1,4]);
    
    block.OutputPort(1).Data = RPM_in;
    block.OutputPort(2).Data = alpha_in;

end

[Aabha]

Hi @mehrzad,

I tried using the code you have provided for the Level-2 MATLAB S-Function, but I don’t seem to face this issue. Here are the steps I followed:

1. Created a MATLAB Script titled “getThrust.m” and copied the code you have provided into it.
2. Created a blank Simulink Model in the same directory as the “getThrust.m” file and added a “Level-2 MATLAB S-Function” block. In the block parameters, I specified the file name “getThrust” in the “S-Function name” dialog.

After updating the model, I can see the S-Function block with 0 input ports and 2 output ports as specified.

There might be some other issue in the model that is causing this.

[mehrzad]

Thanks @Aabha

Sorry for the late reply.

I noticed I was using th wrong block.

I appreaciate your reply thu.

Answer 1

[Aravind]

Hi @mehrzad,

From the image of your model, it seems you are using a “MATLAB Function” block rather than a “Level-2 MATLAB S-Function” block. The “MATLAB Function” block treats the code as a simple function, which means it automatically creates inports for all input variables, including “block.” Additionally, it does not create outports because the first function, “getThrust,” lacks output variables.

In contrast, “Level-2 MATLAB S-Function” blocks follow specific semantics, which allow them to handle initial variables like “block” differently, ignoring it as an input.

“Level-2 MATLAB S-Function” blocks are typically used for modeling dynamic states that cannot be handled by the “MATLAB Function” block. More details on the “MATLAB Function” block can be found here: https://www.mathworks.com/help/simulink/ug/what-is-a-matlab-function-block.html.

For a comparison between MATLAB Function and S-function, you can refer to this MATLAB Answer: https://www.mathworks.com/matlabcentral/answers/447451-difference-between-s-function-and-matlab-function.

To resolve your issue, transfer the code from the “MATLAB Function” block to a “Level-2 MATLAB S-Function” block. This change will give you a block with no inputs and two outputs, as you require.

I hope this helps address your issue.

[mehrzad]

Hi @Aravind

You are correct. I noticed my mistak. Thaks for your reply.