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Optimize advance_spread further

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This commit is contained in:
Yuri D'Elia 2019-05-26 14:58:57 +02:00
parent daa8007de5
commit a28fb65bb2
1 changed files with 17 additions and 10 deletions

27
Firmware/stepper.cpp
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@ -709,6 +709,14 @@ FORCE_INLINE void stepper_tick_highres()
#ifdef LIN_ADVANCE #ifdef LIN_ADVANCE
// @wavexx: fast uint16_t division for small dividends<5
// q/3 based on "Hacker's delight" formula
FORCE_INLINE uint16_t fastdiv(uint16_t q, uint8_t d)
{
if(d != 3) return q >> (d / 2);
else return ((uint32_t)0xAAAB * q) >> 17;
}
FORCE_INLINE void advance_spread(uint16_t timer) FORCE_INLINE void advance_spread(uint16_t timer)
{ {
if(eISR_Err > timer) if(eISR_Err > timer)
@ -734,14 +742,14 @@ FORCE_INLINE void advance_spread(uint16_t timer)
else else
eISR_Err -= timer - block; eISR_Err -= timer - block;
if (ticks == 1) if (ticks <= 4)
eISR_Rate = timer; eISR_Rate = fastdiv(timer, ticks);
else if (ticks == 2)
eISR_Rate = timer / 2;
else if (ticks == 4)
eISR_Rate = timer / 4;
else else
{
// >4 ticks are still possible on slow moves
eISR_Rate = timer / ticks; eISR_Rate = timer / ticks;
}
nextAdvanceISR = eISR_Rate / 2; nextAdvanceISR = eISR_Rate / 2;
} }
#endif #endif
@ -811,10 +819,9 @@ FORCE_INLINE void isr() {
LA_phase = (eISR_Rate > main_Rate); LA_phase = (eISR_Rate > main_Rate);
else else
{ {
// avoid overflow through division (TODO: this can be // avoid overflow through division. warning: we need to _guarantee_ step_loops
// improved as both step_loops and e_step_loops are // and e_step_loops are <= 4 due to fastdiv's limit
// currently guaranteed to be powers of two) LA_phase = (fastdiv(eISR_Rate, step_loops) > fastdiv(main_Rate, e_step_loops));
LA_phase = (eISR_Rate / step_loops > main_Rate / e_step_loops);
} }
} }
} }