Code generation with external variables

Question

Alexander Babin 2021-1-25

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/726203-code-generation-with-external-variables

评论： Alexander Babin 2021-1-25

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

Dear friends!

I am not sure if the word 'external' in the question is correct, but here is what i am talking about:

The program takes a 0 or a 1 at each ime step and outputs a 0 or 1 depending on some simple logic. What I want is to define some variable before this logic starts, and then update the variables withing the logic. The code in C/C++ would look like this:

void main(void)
{
    int c1 = 0; // a '1' counter
    int c0 = 0; // a '0' counter
    
    int in = 0; // current bit
    
    while(1)
    {
        in = ReadBit(); // function reads a bit (in simulink i just have a .mat file with all bits read already)
        
        if (in == 1)
            c1++;
        else
            c0++;
        
        if (c1 == 2*c0)
        {
            doSomething();
            
            // reset the counters
            c1 = 0;
            c0 = 0;
        }
    }
    
}

So, i want to have a subsystem in a Simulink model, that reads initial values of some parameters, then it will update some counters and flags and then, as it gets another bit, it could use the 'previous' values of the counters and flags.

I belive it can be somehow done with a Data Store Memory block, but I've never used it, so I am not sure.

Thanks a lot in advance!

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Birdman 2021-1-25

As far as I understand from your problem, if you want to be able to write to a specific variable at one time step and keep it the same until the next writing, either MATLAB Function approach our usage of Enabled Subsystem approach should work. If you will go on with MATLAB Function, then I suggest you to use persistent variable. Take a look:

Persistent Variables

They are compliant with code generation.

Alexander Babin 2021-1-25

@Birdman thanks, man, im afraid i cant mark your answer as accepted, since its a comment, but i send you a + to karma

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Answer 1

Walter Roberson 2021-1-25

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/726203-code-generation-with-external-variables#answer_605813

在 MATLAB Online 中打开

You can translate that pretty directly into a MATLAB function block that uses some persistent variables.

function triggered = fcn(in)
   persistent in, c0, c1;
   if isempty(in)
       in = 0; c0 = 0; c1 = 0;
   end
   triggered = 0;
   if in == 1
       c1 = c1 + 1;
   else
       c0 = c0 + 1;
   end
   if c1 == 2*c0
       triggered = 1;
       c0 = 0;
       c1 = 0;
   end
end

The output of this would be a signal that would be 1 if you need to doSomething, so you would push the output through an if block or use a triggered subsystem.