If I am understanding correctly, you are trying to update the output of a MATLAB S-function block conditionally.
The following code depicts a simplified representative case which you can adapt to suit your requirement.
function myMSfunc2(block)
% Level-2 MATLAB file S-Function for continuous time demo
setup(block);
%endfunction
function setup(block)
%%Register number of input and output ports
block.NumInputPorts = 1;
block.NumOutputPorts = 1;
%%Setup functional port properties to dynamically
%%inherited.
block.SetPreCompInpPortInfoToDynamic;
block.SetPreCompOutPortInfoToDynamic;
block.InputPort(1).Dimensions = 2;
block.InputPort(1).DirectFeedthrough = true;
block.OutputPort(1).Dimensions = 2;
%%Set block sample time to continuous
block.SampleTimes = [0 0];
%%Set the block simStateCompliance to default (i.e., same as a built-in block)
block.SimStateCompliance = 'DefaultSimState';
%%Register methods
block.RegBlockMethod('PostPropagationSetup', @DoPostPropSetup);
block.RegBlockMethod('InitializeConditions', @InitConditions);
block.RegBlockMethod('Outputs', @Output);
block.RegBlockMethod('Update', @Update);
%endfunction
function DoPostPropSetup(block)
%%Setup Dwork for data logging/states
block.NumDworks = 1;
block.Dwork(1).Name = 'X';
block.Dwork(1).Dimensions = 2;
block.Dwork(1).DatatypeID = 0;
block.Dwork(1).Complexity = 'Real';
block.Dwork(1).UsedAsDiscState = true;
%endfunction
function InitConditions(block)
%%Initialize Dwork
block.Dwork(1).Data = [0;0];
%endfunction
function Output(block)
block.OutputPort(1).Data = block.Dwork(1).Data;
% changing the output conditionally
if(block.Dwork(1).Data(1)>=0.2)
block.OutputPort(1).Data(1) = 2;
end
%endfunction
function Update(block)
block.Dwork(1).Data = block.InputPort(1).Data;
%endfunction
The Output function has an if statement which updates the output based on a condition; which is what you are looking for. Also, notice the DWork vector used to store state information. It is recommended to use Work vectors instead of global variables to store persistent data. More about DWork vectors can be found here. Also check the article on Writing MATLAB S-functions for more information.
