Microstepping

Microstepping lets steppers work much faster and more reliably, not to mention smoother ride :P

The TCA3727 (looks like it will be obsolete shortly) has the following nice diagram explaining microstepping currents.

Stepping table is as follows:

#define I10 _BV(STEPPER_I10_PIN)
#define I11 _BV(STEPPER_I11_PIN)
#define PH1 _BV(STEPPER_PH1_PIN)
#define I20 _BV(STEPPER_I20_PIN)
#define I21 _BV(STEPPER_I21_PIN)
#define PH2 _BV(STEPPER_PH2_PIN)

static const u08
stepper_steps[] PROGMEM =  {
 I10 | I11 |   0 | PH2 |   0 |   0,  // 0
   0 | I11 | PH1 | PH2 |   0 |   0,  // 1
 I10 |   0 | PH1 | PH2 |   0 |   0,  // 2
   0 |   0 | PH1 | PH2 |   0 |   0,  // 3
   0 |   0 | PH1 | PH2 | I20 |   0,  // 4
   0 |   0 | PH1 | PH2 |   0 | I21,  // 5
   0 |   0 | PH1 | PH2 | I20 | I21,  // 6
   0 |   0 | PH1 |   0 |   0 | I21,  // 7
   0 |   0 | PH1 |   0 | I20 |   0,  // 8
   0 |   0 | PH1 |   0 |   0 |   0,  // 9
 I10 |   0 | PH1 |   0 |   0 |   0,  // 10
   0 | I11 | PH1 |   0 |   0 |   0,  // 11
 I10 | I11 | PH1 |   0 |   0 |   0,  // 12
   0 | I11 |   0 |   0 |   0 |   0,  // 13
 I10 |   0 |   0 |   0 |   0 |   0,  // 14
   0 |   0 |   0 |   0 |   0 |   0,  // 15
   0 |   0 |   0 |   0 | I20 |   0,  // 16
   0 |   0 |   0 |   0 |   0 | I21,  // 17
   0 |   0 |   0 |   0 | I20 | I21,  // 18
   0 |   0 |   0 | PH2 |   0 | I21,  // 19
   0 |   0 |   0 | PH2 | I20 |   0,  // 20
   0 |   0 |   0 | PH2 |   0 |   0,  // 21
 I10 |   0 |   0 | PH2 |   0 |   0,  // 22
   0 | I11 |   0 | PH2 |   0 |   0  // 23
};

#undef I10
#undef I11
#undef PH1
#undef I20
#undef I21
#undef PH2

When doing it step-by-step, some steps seem to be less "powerful" than others. It doesn't run _very_ smoothly on higher speeds. Perhaps some tweaking with step timings is neede in order to achieve really smooth operation.