MATLAB: Compiling/inlining an M-file S-Function (which calls a MEX file)

matlab s-functionreal time workshopsimulink coder

Hello,

working with Real-Time Workshop (7.6.1) for the first time I am a bit unsure about the possibilities and whether I'm on the right track at all.

I wrote a relatively simple Level-2 MATLAB S-Function which converts its input to a string and utilizes Peter Rydesäter's TCP/UDP/IP toolbox to set up a UDP socket and send data. The TCP toolbox is made up by the source file, pnet.c, and the compiled pnet.mexw32, which I guess I call in my S-function.

The documentation regarding inlining S-functions contains a simple example for writing a TLC file, but as far as I understand that, it is merely replicating the output generation of the S-function in TLC code. Is that what TLC files do? Is there a chance to do the same for my task?

I'm still quite lost, so I'd appreciate any hints.

Thank you

Silvan

Best Answer

Yes, TLC files do indeed define how the outputs are to be calculated in the generated code (this may or may not match simulation - although that is preferred). For example, an S-function that is supposed to represent an LCD Display driver may do nothing in simulation, but generates code that calls into the LCD Display API for the target platform.

In your case, you will need to find the C/C++ equivalent of the TCP toolbox functions that you are currently calling, and call into those C/C++ functions in your TLC code. You can then compile those C files into the generated code. You may contact the author of the toolbox in question to see if they can provide a native binary for your target platform. Since they are already using MEX-functions underneath, it is possible that they are calling into C libraries already.

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MATLAB: What do you mean by “Inlining s-function”

Typically C S-functions are separate MEX-files (DLLs) - if you do not inline them (by providing a TLC-file for it), then the generated code will call into this DLL whenever the block methods need to be executed. The S-function methods require various arguments, one of which is the SimStruct pointer 'S' - this is a fairly large data structure that needs to be passed around. Therefore calling into the S-function DLL from the generate code can produce a large overhead. Instead, providing a TLC-file will result in the methods corresponding to the S-function being inlined (or added) into the model.c file directly. There is no need to make additional calls into external DLLs. Also, there is no need for the SimStruct pointer to be maintained. Therefore, models with all inlined S-functions generate much more efficient code.

MATLAB: M-file function

Your function is calling itself without approaching any convergance or something that will allow it to end. Therefore it will run forever and eventually out of memory (hence the error). Try splitting it up into a script and a function as so:

Script:

 %creating window of plot from -5 to 50 using stepsize 0.25 for t x-axis
 %t should be on the x axis, v should be on the y axis
 k=0; 
for i= -5:.25:50
    k = k+1;
    t(k)=i;
    v(k)=vPieceWise(t(k));
end 
plot(t,v);
 
figure
plot(t,v);
hold on

Function:

%Part A: Mfile function to compute v as a function of t
function v = vPieceWise(t)
 if (t < 0)
        v = 0;
    elseif (0 <= t)&&(8<=16)
        v = -5*t+10*t.^2;
    elseif (8<=16)&&(t<=16)
        v = 624 - 3*t;
    elseif (t<=16)&&(t<=26)
        v = 12*(t-16).^2+36*t;
    elseif (26<t)
        v = 2136*exp(-0.1*(t-26));
 end

Best Answer

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