Arduino Mega servo controlling delay

Hi

I am using Simulink to program my Arduino mega board. Using analogue read and servo write (part of the support package for Arduino). When I download my model on the board I am getting around 0.5 second delay between my input and output (while in normal programming by Arduino software everything is instance). I also scale the input to 180 steps and I get around 8 steps in output. Please let me know if anybody knows what the problem is?

Thank you