How can I sending a trigger signal from Matlab to SIMULINK

I'm currently using a toolbox in Matlab and I need to send a square wave of a certain frequency towards a SIMULINK model in real-time. I did this using the UDP command however, I noticed that the UDP command introduces random delays and thus it cannot be used in real-time applications. Is there any other way to send a trigger signals from Matlab to SIMULINK with insignificant delays. For my application precise timing is very important. Also, I'm trying to avoid using external hardware as much as possible so this signal has to be internal from Matlab to SIMULINK.

Thanks in advance.

Regards, Norbert