Make Simulink remember the time, when a variable first exceeds a specific value

I want to implement some kind of storage that remembers something when something else happened. in my case i want to remember the simulation time when the velocity gets lower than 22.5 m/s. i tried to do it with a matlab-function-block that has to input ports (the velocity and a clock) and with the following code:

function y=f(v,t)
  y=0
  if v==22.5
    y=t;
  end

i thought this would do nothing after the velocity fell below 22.5, but in fact it sets y to 0. It feels like i chose a pretty odd way to achieve my goal, can you tell me how to do it better or how to get it to work?

[Max E.]

does nooone have an answer to this question, or does noone get, what i mean? It's really important to me!