How to create function that control speed of stepper motor?

Hello every one..

I want to control stepper motor using arduino and matlab and stepper motor driver l298d, but without using adafruit motor shield v2 library. so i write this code

delete(instrfindall)
close all;
clear;
clc;
prompt = 'How many steps to move? ';   % enter number of steps to move
steps_to_move = input(prompt);
step_number = 0;
number_of_steps = 200;
 last_step_time = 0;                   % the time of last step
 whatSpeed = 60;
 %% initialization arduino pins
a = arduino();
configurePin(a,"D7","DigitalOutput");
configurePin(a,"D6","DigitalOutput");
configurePin(a,"D5","DigitalOutput");
configurePin(a,"D4","DigitalOutput");
%% determine delay time and dirction 
steps_left = abs(steps_to_move);
step_delay = uint64(double(60*10^6)/number_of_steps / whatSpeed)       % time between steps
if (steps_to_move)
    direc = 1;
else
    direc = 0;
end
%%
      timeVal = tic;                                     % start counting time
  while (steps_left > 0)
         now = uint64(toc(timeVal)*10^6);                % time of right moment
          if(now - last_step_time >= step_delay)         % if now - last step time  bigger than delay time 
                                                         % then move the motor
                                                         
           last_step_time = now;                         % store the time
           if (direc == 1)
              step_number = step_number + 1;
                 if (step_number == number_of_steps)
                     step_number = 0;
                 end
           else
               if (step_number == 0)
                   step_number = number_of_steps;
               end
                step_number = step_number - 1;
           end
            steps_left = steps_left - 1;
          end
          stepMotor(a,mod(step_number,4));               % function to move motor
  end

function stepMotor(ardObj,thisStep)

        switch (thisStep) 

            case 0  % step 1
                writeDigitalPin(ardObj,"D7",1);
                writeDigitalPin(ardObj,"D6",0);
                writeDigitalPin(ardObj,"D5",1);
                writeDigitalPin(ardObj,"D4",0);

           case 1  % step 2
                writeDigitalPin(ardObj,"D7",0);
                writeDigitalPin(ardObj,"D6",1);
                writeDigitalPin(ardObj,"D5",1);
                writeDigitalPin(ardObj,"D4",0);
           
           case 2  % step 3
                writeDigitalPin(ardObj,"D7",0);
                writeDigitalPin(ardObj,"D6",1);
                writeDigitalPin(ardObj,"D5",0);
                writeDigitalPin(ardObj,"D4",1);

           case 3  % step 4
                writeDigitalPin(ardObj,"D7",1);
                writeDigitalPin(ardObj,"D6",0);
                writeDigitalPin(ardObj,"D5",0);
                writeDigitalPin(ardObj,"D4",1);
        end
end

the motor does not move correctly, there is no control speed.

i write the code with help of stepper motor library for arduino.

so any one could help me to correct the code or using other equation or ideas??