Call C code function from Stateflow with an array as an input

I have a C-code function that takes in an array and a size value. I am trying to call the function in Stateflow and I am not having any success no matter what I try. I did add the appropriate includes to the C-code in the model config under simulation target/custom code. The only way I can get Stateflow to update/compile is when I change the C-code to not take in an array, but just a single element.

This is the function call I am trying to use:

The function ElbowFindFxn() works as a Simulink custom code block, if finds and uses the external C-code just fine.

The variable vecV is defined as a 100 element float array (max size, use less than that in practice). I've tried passing in the array in multiple different ways:

&vecV[0]

(float*)vecV

vecV[] - this gave a syntax error right away, but was worth a shot

and a few others I don't remember.

I even tried putting the function into a Stateflow graphical function.

For the most part I don't get just a single error, but the compiler seems to blow up and spill its guts.

I know it's not the C-code, because that code has worked just fine in other applications, and in Simulink custom code block.

Answer 1

[Rajanya]

Hi @Ken Seiders,

I understand that you are trying to call a C function which takes an array as an argument, from a Stateflow chart.

Custom code functions with non-scalar or pointer arguments are not directly supported for function call in MATLAB based blocks. Stateflow suggests us to use ‘coder.ceval’ to call such functions instead.

To demonstrate the working, I have created a sample C function ‘myExternalFunction’ which takes in an array and returns the second element in the array. The array is sent as input to a Stateflow state, and it is called from that state to display the output. The function and the Stateflow chart are shown below.

‘coder.rref’ passes the input array as a reference. If the function takes in other arguments, they are added in the ‘coder.ceval’ call with comma separations after the reference is passed.

After the proper configurations are added in Simulation target/Custom code and the model is updated, the simulation runs properly. For demonstration purposes, the array is passed as input from a constant block. The array passed is [1 2 3 4].

For more information on ‘coder.ceval’, refer - https://www.mathworks.com/help/simulink/slref/coder.ceval.html

Since the documentation for MATLAB R2018b is not available online, you can use the command to view the same by running it in command window.

web(fullfile(docroot, 'simulink/slref/coder.ceval.html'))

Hope this helps!

[Ken Seiders]

This does not seem to work for me, perhaps because for my model the Stateflow action language is C.

I tried it in a .m file and that seemed to accept it.

I get the error:

Unresolved function 'coder.ceval'