When building a Simulink model, my s-function output is generated as a constant and the build process stops with an error

I've created an S-Function block with 6 inputs and 1 output, but when I build the project, the output is being generated as a constant and the build exits with an error.

In the TLC file I use the InitializeConditions function to initialize the output, but it crashes because the output is being generated as a constant:

"f_test_ecu.c", line 9529: error (etoa:4137): expression must be a modifiable lvalue

f_test_ecu_ConstB.SFunction = 4;

^

What are the constrainst that may cause an output of a S-Function to be generated as a constant?

Is it something that must be specified in the S-Function? I've compared with other working S-Functions and I don't see diferences.

Answer 1

[Amit Dhakite]

Hi Nelson,

As per my understanding, your S-Function block is generating a constant as the output, which results in an error in the build process.

Upon further investigation, I have identified certain constraints within the S-Function which causes the output port to generate constant values. To address this, I recommend reviewing the information provided in the following link, which contains valuable insights on the topic:

https://www.mathworks.com/help/simulink/sfg/sample-times-cpp.html#:~:text=In%20the%20S%2Dfunction%20code,also%20has%20a%20constant%20value.

[Nelson Bernardino]

Thank you. The S-Function sample time was set to -1 (inherit) and all the inputs where of the constant type with sample time inf.

After setting the sample times to different values, I had success.