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optimisation: calculate steps per unit reciprocal at compile time #336

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optimisation: calculate steps per unit reciprocal at compile time #336

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1 change: 1 addition & 0 deletions src/config/axis.h
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@ struct AxisConfig {
uint8_t iHold; ///< holding current
bool stealth; ///< Default to Stealth mode
long double stepsPerUnit; ///< steps per unit
long double stepsPerUnitReciprocal; ///< reciprocal of step per unit (used to avoid divisions)
int8_t sg_thrs; /// @todo 7bit two's complement for the sg_thrs
};

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3 changes: 3 additions & 0 deletions src/config/config.h
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Expand Up @@ -115,6 +115,7 @@ static constexpr AxisConfig pulley = {
.iHold = 0, /// 17mA in SpreadCycle, freewheel in StealthChop
.stealth = false,
.stepsPerUnit = (200 * 8 / 19.147274),
.stepsPerUnitReciprocal = 1 / ((200 * 8 / 19.147274)),
.sg_thrs = 8,
};

Expand All @@ -140,6 +141,7 @@ static constexpr AxisConfig selector = {
.iHold = 0, /// 17mA in SpreadCycle, freewheel in StealthChop
.stealth = false,
.stepsPerUnit = (200 * 8 / 8.),
.stepsPerUnitReciprocal = 1 / ((200 * 8 / 8.)),
.sg_thrs = 3,
};

Expand Down Expand Up @@ -190,6 +192,7 @@ static constexpr AxisConfig idler = {
.iHold = 5, /// 99mA - parked current
.stealth = false,
.stepsPerUnit = (200 * 16 / 360.),
.stepsPerUnitReciprocal = 1 / ((200 * 16 / 360.)),
.sg_thrs = 7,
};

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9 changes: 5 additions & 4 deletions src/modules/axisunit.h
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Expand Up @@ -94,12 +94,13 @@ constexpr AxisUnit<T, A, U> operator*(const long double f, const AxisUnit<T, A,
struct AxisScale {
unit::UnitBase base;
long double stepsPerUnit;
long double stepsPerUnitReciprocal;
};

static constexpr AxisScale axisScale[config::NUM_AXIS] = {
{ config::pulleyLimits.base, config::pulley.stepsPerUnit },
{ config::selectorLimits.base, config::selector.stepsPerUnit },
{ config::idlerLimits.base, config::idler.stepsPerUnit },
{ config::pulleyLimits.base, config::pulley.stepsPerUnit, config::pulley.stepsPerUnitReciprocal },
{ config::selectorLimits.base, config::selector.stepsPerUnit, config::selector.stepsPerUnitReciprocal },
{ config::idlerLimits.base, config::idler.stepsPerUnit, config::idler.stepsPerUnitReciprocal },
};

/// Convert a unit::Unit to AxisUnit.
Expand All @@ -126,7 +127,7 @@ template <typename U, typename AU, typename T = int32_t>
static constexpr T axisUnitToTruncatedUnit(AU v, long double mul = 1.) {
static_assert(AU::unit == U::unit, "incorrect unit type conversion");
static_assert(U::base == axisScale[AU::axis].base, "incorrect unit base conversion");
return { ((T)v.v / (T)(axisScale[AU::axis].stepsPerUnit / mul)) };
return { ((T)v.v * (T)(axisScale[AU::axis].stepsPerUnitReciprocal * mul)) };
}

/// Truncate an Unit type to an integer (normally int32_t)
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