Code generation with external variables

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!

[Birdman]

Did you try something on the Simulink model? If so, can you share the Simulink model?

[Alexander Babin]

Yes, I believe, I have found the right way to do it, although, probably there could be some issue with code generation

[Alexander Babin]

the variable are set to volatile

[Birdman]

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]

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

Answer 1

[Walter Roberson]

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.

[Alexander Babin]

that is perfect, thanks!