What if Simulink can't achieve specified sample time?

Hello,

I'm trying to create a simulink model to communicate with an external device. I have written a custom Level 2 Matlab S-Function to receive data from the device through TCP/IP, and specified a sample time for this S-Function block of 3 ms. I have added timing measurements and have concluded that the Output function of my custom block tasks a mean of 5.3 ms.

I have two questions about this. First, when happens with the timing if Simulink fails to achieve the specified sample time of a block? Does it just go as fast as it can?

Also, I understand that Matlab S-Functions are executed by running a Matlab Interpreter. However, when I take the exact same code that's in the Output function of my custom block and place it into a regular .m script and use the same timing measurements, then as a standalone script the code takes 2.4 ms to run. What is the reason for this significant slowdown? Below is the code for the Output function. (Note, the device is controlled through a C++ program that writes data to the socket, and this was consistent between the two tests.)

    function Outputs(block)
    global socket  

    socket.readasync();
    if(socket.BytesAvailable > 0)
        A = socket.fgetl();        
        entries = sscanf(A, '%f,'); 
        if(length(entries) ~= 23) %known packet size
            disp('Incorrect data packet format; missing data');
        else  
            %parse data
            block.OutputPort(1).Data = entries(1);       
            block.OutputPort(2).Data = entries(2:8)';   
            block.OutputPort(3).Data = entries(9:15)';   
            block.OutputPort(4).Data = entries(16:22)'; 
            block.OutputPort(5).Data = entries(23);   
        end        
    end
    b = toc;
    block.OutputPort(6).Data = b-a;
    block.OutputPort(7).Data = b;
    %endfunction

Any help would be greatly appreciated! Thank you!