S-Function Block of time delay on Matlab-language.

Hello! I try create S-Function block of time delay element (analog of element 'On Delay' in Simulink). I write m-script on level-1 function, but it is not work. I please you help me: 1.How to define variable. which will change on each simulation step? It is variable 'tt' in my code. 2. I want to set type boolean for my input. 3. Also can I input type for double and boolean?. Thanks for answers!

Code:

function [sys,x0,str,ts,simStateCompliance] = sfunPicDelay(t,x,u,flag)
%SFUNDSC2 Example unit delay MATLAB File S-function
%   The MATLAB file S-function is an example of how to implement a unit
%   delay.
%   
%   See sfuntmpl.m for a general S-function template.
%
%   See also SFUNTMPL.

%   Copyright 1990-2009 The MathWorks, Inc.

tset=0.02;
tt=0;

switch flag,

    %%%%%%%%%%%%%%%%%%
    % Initialization %
    %%%%%%%%%%%%%%%%%%
    case 0,                                                
      [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes(tset,tt);    

    %%%%%%%%%% 
    % Update %
    %%%%%%%%%%
    case 2,                                               
      sys = mdlUpdate(t,x,u,tset,tt);

    %%%%%%%%%%
    % Output %
    %%%%%%%%%%
    case 3,                                               
      sys = mdlOutputs(t,x,u);   

    %%%%%%%%%%%%%
    % Terminate %
    %%%%%%%%%%%%%
    case 9,                                               
      sys = [];

    otherwise
      DAStudio.error('Simulink:blocks:unhandledFlag', num2str(flag))
  end

%end sfundsc2

%
%=============================================================================
% mdlInitializeSizes
% Return the sizes, initial conditions, and sample times for the S-function.
%=============================================================================
%
function [sys,x0,str,ts,simStateCompliance]=mdlInitializeSizes(tset,tt)

sizes = simsizes;

sizes.NumContStates  = 0;
sizes.NumDiscStates  = -1;
sizes.NumOutputs     = -1;
sizes.NumInputs      = -1;
sizes.DirFeedthrough = 1;
sizes.NumSampleTimes = 1;

sys = simsizes(sizes);

x0  = [0];
str = [];
ts  = [0.001 0]; % Sample period of 0.1 seconds (10Hz)

% speicfy that the simState for this s-function is same as the default
simStateCompliance = 'UnknownSimState';

% end mdlInitializeSizes

%
%=======================================================================
% mdlUpdate
% Handle discrete state updates, sample time hits, and major time step
% requirements.
%=======================================================================
%
function [sys,tt] = mdlUpdate(t,x,u,tset,tt)

if u==1.0
    tt = tt + 0.001;
else 
    tt = 0;
end

if tt>=tset
    sys = u;
else
    sys = 0;
end

%end mdlUpdate

%
%=======================================================================
% mdlOutputs
% Return the output vector for the S-function
%=======================================================================
%
function sys = mdlOutputs(t,x,u)
sys = x;

%end mdlOutputs