Verilog-A, one time execution function

Hi, 

I am developing a verilog-A model for a device. I want to write a function that is executed only one time in the simulation during the device first transition from high resistive state to a low resistive state. I looked at analog events but did not find a function that provides this functionality I want. I tried to do it using an if..else statement but it gave me convergence error. 

Can someone help me with that?

Thanks