Square Pulse for Stepper Motor in Real time

Hi,

I would like to control the speed of stepper motor using Simulink signal. I have interfaced Raspberry Pi 3 in Simulink, which will be used to send the pulse signal to the stepper driver. The required speed/frequency range is 500Hz to 5.5KHz. The motor and driver works perfectly when connected to Arduino and uploaded the code from Arduino IDE. However in Simulink, I have tried some models from File Exchange to generate pulse between this range, But I couldn't get stable pulses as it was very fluctuating. Is there any other solution to generate stable square pulses with variable frequency for the stepper motor from Simulink? Thank you.