How do I make a device driver block that outputs data from a global array?

I am using Simulink and the Simulink Support Package for Arduino Hardware to generate and run C/C++ code on an Arduino Mega 2560. Everything works great, but I would like to develop a custom device driver. I went through the "Create a Digital Read Block" and I got that working.

For my application I need the source block to output the contents of a global array instead of just a scalar value. Coder.ceval only returns a scaler value.

So my question is how do I modify this function so I can output an array

function y = stepImpl(obj) %#ok<MANU>

y = double(0);

if isempty(coder.target)

% Place simulation output code here

else

% Call C-function implementing device output

y = coder.ceval('source_output');

end

end

Answer 1

[Matt Griffith]

Hey Everyone,

I finally figured out something that works. coder.opaque was not the answer, or if it was I could not get it working. This is probaly somewhat of a hack, but it works. So the really cool part about setting up a device driver block is that it allows you to copy paste cpp code straight from an example arduino sketch and use it, however I couldn't find any way for the device driver block to output a global array that I had defined in my driver cpp file.

The solution was to use a stateflow chart instead. All I had to do was make a structure that had my array in it in my global array in my driver .h file and then include that header file in the configuration paramters -> simulation Target -> header file.

Then I could drop in a stateflow chart that just outputs the array. This example was very helpful.

sf_custom

Answer 2

[Mark McBroom]

You will need create the matrix in your MATLAB function and then pass it to your C Function as an argument, encapsultated in teh coder.wref() function so that MATLAB will pass it by reference to your C code. See this link for details and example: https://www.mathworks.com/help/simulink/slref/coder.wref.html

[Matt Griffith]

Oh I get it now. I read the help on coder.ref() , but I didn't understand I would define my array in Matlab instead of C. Ok one wrinkle.

In my C code I defined my array as volatile, because it is used by a pin change ISR. How do I do that now that I am defining my array in Matlab and then passing the reference to my C function?

[Mark McBroom]

I have never tried it, but you might be able to use coder.opaque() to define your array as volatile.

Declare variable in generated code - MATLAB coder.opaque (mathworks.com)

[Matt Griffith]

Ok I'm having trouble setting up coder.opaque. Inside the matlab command window I can create the system and successfully call .step(). I also have the system in Simulink and I can simulate, no big surprize as it doesn't do anything for simulation, however when I try to build I get the following error message:

Simulink detected an error 'Top-level output parameter y0 has unknown or opaque type.'. The error occurred for MATLAB System block 'EncoderTest/MATLAB System'. To prevent this error, modify the System object to avoid code that does not support code generation.

Maybe coder.opaque isn't the answer. This was supposed to be just a simple test to get things up and running. Ideally what I want to do is return a 6 element array of uint32 type that was declared as volatile. I'm just mentioning that to keep that in mind.

I have attached the .m file for the system and the .slx file, but unfortunately I can't attach .cpp or .h files :( If I had to guess I would say the problem is here:

        function EncoderCounts = stepImpl(obj)   %#ok<MANU>
            EncoderCounts = coder.opaque('int','0');
            if isempty(coder.target)
                % Place simulation output code here
                EncoderCounts = 0;
            else
                % Call C-function implementing device output
                coder.ceval('EncoderDriverStep');
            end
        end