I agree with hansknec.
I apologize for my english but..... is the stepper driver that give to the motor the right sequence for microsteps.
Trickle is to reproduce a sine wave using a current sensor on the motor phase and an AtoD converter (high number of bit = high number of microsteps).
Usually these devices are inside dedicated drivers for microsteps.
See ALLEGRO A3972 for 1/16 steps.
regards
andrea