Simulink function with variable-size output - long execution time + unstable behaviour

Currently I am facing an issue with a custom MATLAB function inside a Simulink model. The problem originates from a Simulink model where I use a Pulse generator block to generate a square wave signal. I would like to supply the parameters to this block through Simulink signals instead of through the Block parameters dialog.

I figured that this is not possible, thus I went about to create a MATLAB function that brings the same functionality. I first created the function in MATLAB:

% User inputs
SignalFrequency = 5; % [Hz]
PulseLength = 0.050; % [s]
PhaseShift = 0.060; % [s]
SimDuration = 0.6; % Stop time of simulation [s]
NumberOfDatapoints = 1000; % Corresponds to fixed step size of simulation

% Calculation
SignalPeriod = 1/SignalFrequency;
DutyCycle = (PulseLength/SignalPeriod)*100;
t = linspace(0, SimDuration, NumberOfDatapoints); % Create time vector according to simulation settings
Signal = square(2*pi*SignalFrequency*t - 2*pi*(PhaseShift/SignalPeriod), DutyCycle); % Generate square wave signal, syntax: "x = square(t,duty)"

Signal(Signal<=0) = 0; % Clamp negative values of signal to 0

plot(t, Signal); % Visualise result

I translated this code into a custom MATLAB function inside Simulink, just to test whether this would work:

With the following underlying MATLAB code:

function VectorOutput = fcn(SignalFrequency, PulseLength, PhaseShift, SimDuration, NumberOfDatapoints)

    % Generate signal
    SignalPeriod = 1/SignalFrequency;
    DutyCycle = (PulseLength/SignalPeriod)*100;
    t = linspace(0, SimDuration, NumberOfDatapoints); % Create time vector according to simulation settings
    sig = square(2*pi*SignalFrequency*t-2*pi*(PhaseShift/SignalPeriod), DutyCycle); % Generate square wave signal, syntax: "x = square(t,duty)"
    sig(sig<=0) = 0; % Set zero level
    
    % Write function outputs
    VectorOutput = sig; % Size [1xNumberOfDatapoints]

As the Fixed-step size of the simulation can vary, the size of the function output vector can vary as well. It is in any case a 1xn vector, but the size of "n" can vary. I tried to set the size of VectorOutput in the Ports and Data Manager as follows:

But this really produces instable behaviour. Running the simulation in Simulink takes a couple of minutes and during this time, both Matlab and Simulink remain unresponsive to mouse clicks/commands. Does anyone know what I am doing wrong?