Control sending frequency for serial communication

I am trying to read/write data from an arduino over serial using Simulink. I am sending two floats down (as sin waves for now) and echoing them back to valdiate my communication is working. However I seem to be having a problem with overriding the serial buffer by writting to fast.

My question is can you control the writing rate in simulink so that is only sends a messsage over xx ms or maybe only write when simulink gets a reply message?

Here is my simulink model

THis is the responce I am getting back:

One of the sine waves is very noise. I think that his has to do with the control rate. I am sending values to fast and the arduino cannot keep up.

How can I slow down the rate at which message are being send over the Serial bus? This is just a simple example, i plan on incooperating this into my controller down the line.