Class object call as input parameter of a Matlab S-function (Level 2)

hi, my class is defined like this : classdef class_epos properties Device_Name; ProtocolStackName; InterfaceName; PortName; Baudrate; Timeout; EposDll; EposHeader; Position; Speed; Current; end

    methods
    end  
end
In Simulink i used the callback function InitFcn to create an instance of myclass and initialize the propoerties. The idea is to have this instance directly in the workspace,so that i can use it as input parameter of my S-function. I want the following signature of the S-function:
*s_function_name(class_epos obj)*,where obj is an instance of my class class_epos. The idea to pass the class object as input is to use the properties of the object in the S-function.
But when i do that, Simulink does not accept the object as input parameter although an instance of my class is in the workspace.
I do not understand why Simulink does not take into account that an object of my class in the workspace was already created. 
For me, Simulink needs just to consider my object in the workspace and run the simulation, but it does not do that.

I don't know what i'm doing wrong.

may be someone has an idea.

[Kaustubha Govind]

Parameters need to exist in the workspace even before the InitFcn runs. Is there a reason you have to wait so late to create the instance?