How do i acquire the value of current timestep in s fucntion (level 2 M S)?

in the level 2 matab s function, i set the sample time as Inherited sample time:

block.SampleTimes = [-1 0];

then i set the time step in the simulink /configuration parameters /solver, so that each time i want to change the timestep i won't need to modify the s function (the value in the picture just for example, the type could be fixed or auto )

but in the update section in s function, i need the value of current timestep to calculate the state variables,

Xt+1 = f(dt, Xt, u)

so how can i acquire the exact value of current timestep?

really thanks

Answer 1

[Manoj Mirge]

Hi Kefan,

Simulink software creates an instance of Simulink.MSFcnRunTimeBlock class for each Level-2 MATLAB S-Function block in a model. This class allows a Level-2 MATLAB S-function or other MATLAB program to obtain information from Simulink software and provide information to Simulink software about a Level-2 MATLAB S-Function block. The instance of the class is passed to MATLAB S Function as argument ‘block’.

We can access some fields of block object at the time of execution in our S-Function. Although you have set SampleTimes as inherited in setup function of your S-Function, you can get Sample Time of your S-Function configured by your model by just querying SampleTimes field of your block object in your update section. Similarly, you can get Current Simulation time of your model by querying CurrentTime field of your block object.

Below is a code snippet that will give you a clear idea:

% You can get sample time as 1 by 2 row vector by querying SampleTimes field of block object. 
% Similarly, you can get Current Simulation time of your model by querying CurrentTime field of your block object. 
% Your update section 
function update(block) 
Sample_time=block.SampleTimes; 
Curr_simulation_time=block.CurrentTime; 
%Your state update logic 
end 

You can read more about Simulink.MSFcnRunTimeBlock class here.

Hope this helps.