MATLAB: How to reduce the number of global variables in the generated code

coderglobalreducesimulinksimulink coder

Hi,

I'm currently generating C code using Simulink Coder and one thing that makes it complicate to integrate with my application is the amount of random Global structures that it creates. Even for inputs or outputs it is creating copies in globals.

Can anybody recommend techniques to reduce this?

thanks

Best Answer

You can make the inputs and outpus define as struct which are stored in .h files. For this purpose, go to Configuration Parameters-Code Generation-Interface and there is a subsection called Code interface packaging. Select Reusable function and for Pass root level I/O as Structure Reference. Hope this helps.

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You are correct in stating that persistent variables are not declared as static in generated code. But they are in fact declared as extern global variables by being outside any function calls, and the "extern" keyword added to their definition. This is a more general behavior than "static" as it is accessible by all modules, and displays the same memory persistence throughout the lifecycle of the program.

Now, every C file that wants to use a global variable must have "#include header.h" of the extern variable. Since persistent variables in MATLAB functions are to be used as "states" of the function itself, the notion of other files (and potentially other functions) accessing this data is not part of the persistent keyword.

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To avoid this issue you can call the two functions in a separate function. This will lead to the code to be generated in a way that there are no name conflicts.

To illustrate this, attached you find a small test project consisting of the following folders:

myfun
myfun2
parent

In myfun and myfun2 we call max() with different arguments, which leads to different implentations of max() in the generated C code (as described earlier).

Now examine the parent function. Here we again call myfun and myfun2 with different arguments:

>> emlc parent.m -eg {rand(10,1),rand(5,1), rand(7,1), rand(7,1)} -O disable:inline

With this the compiler sees that max() is used with different arguments and return values, and it generates two different implementations which are used:

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Best Answer

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MATLAB: I use persistent variables in a MATLAB Function Block, but do not see them declared as static in generated code? Why is this

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