I've finally constructed my prototype model and now I am experimenting on it. As I mentioned before I was planning to set the current with a digital potentiometer and that also worked fine but there is only a single problem, at idle state motor creates very high pitched weird sounds in every single mode(full, half, 4x, 8x). First I thought maybe digital pot gives an oscillating output and I got rid of it and placed a good old trim-pot with 0.1uF decoupling capacitor at its output. But again these sounds continued, then I tried to measure what is going on with oscilloscope placing the probe on sense connection of the IC (since it is the sense port of chopper circuit where you can see the actual waveform). And the results are interesting, in idle mode there are lots of pikes and while rotating there is something going on in microstepping modes but I would not say that a sinusoidal. I am thinking of PWM timer R, C values might not suit my motor. Any other ideas?. By the way I am using a Lin Engineering 5718M-02S 24V 2.1A motor.