How to create variable length buffer in Simulink for holding the value with unknown dimensions ?

i want to store a value of one signal in Simulink until the my trigger becomes high. Every time when trigger becomes high, the number of values of signal between two triggers are different.

i tried to use the following approach in MATLAB function block but it didn't worked

function = func(trigger , SignalA)
  persistent store;
  if isempty(store)
      store=[];
  end
if(trigger ==0)
    store= [store SignalA];
end
end

it gives me following error

Assigning empty arrays to persistent variables is not supported.

Any other method to do this thing?

[Dyuman Joshi]

The variable store is empty at the moment you are checking for the same.

Why reassign it?

It's redundant. Remove the if condition block.

Answer 1

[Walter Roberson]

You are going to have trouble with that approach unless you use dynamic memory allocation.

Better is to set a maximum length between triggers, and use something more like

function buffer = func(trigger, SignalA )
    Buffer_Length = 20480;
    persistent store counter
    if isempty(store)
      counter = 0;
      store = zeros(1, Buffer_Length);
    end
    if trigger == 0
        if counter <= Buffer_Length
            counter = counter + 1;
            store(1, counter) = SignalA;
        else
            %do nothing, drop the sample
        end
        buffer = [];
    else
        buffer = store(1:counter);
        counter = 0;
        store = zeros(1, Buffer_Length);
    end
end

As long as trigger is 0, this records the signal; if the recording would be too long then it drops the samples.

As soon as the trigger becomes non-zero, it releases all of the stored samples in one go, and resets the buffer.