/**
 * Marlin 3D Printer Firmware
 * Copyright (C) 2016 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
 *
 * Based on Sprinter and grbl.
 * Copyright (C) 2011 Camiel Gubbels / Erik van der Zalm
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

/**
 * stepper.cpp - A singleton object to execute motion plans using stepper motors
 * Marlin Firmware
 *
 * Derived from Grbl
 * Copyright (c) 2009-2011 Simen Svale Skogsrud
 *
 * Grbl is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Grbl is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Grbl.  If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * Timer calculations informed by the 'RepRap cartesian firmware' by Zack Smith
 * and Philipp Tiefenbacher.
 */

/**
 *         __________________________
 *        /|                        |\     _________________         ^
 *       / |                        | \   /|               |\        |
 *      /  |                        |  \ / |               | \       s
 *     /   |                        |   |  |               |  \      p
 *    /    |                        |   |  |               |   \     e
 *   +-----+------------------------+---+--+---------------+----+    e
 *   |               BLOCK 1            |      BLOCK 2          |    d
 *
 *                           time ----->
 *
 *  The trapezoid is the shape the speed curve over time. It starts at block->initial_rate, accelerates
 *  first block->accelerate_until step_events_completed, then keeps going at constant speed until
 *  step_events_completed reaches block->decelerate_after after which it decelerates until the trapezoid generator is reset.
 *  The slope of acceleration is calculated using v = u + at where t is the accumulated timer values of the steps so far.
 */

/**
 * Marlin uses the Bresenham algorithm. For a detailed explanation of theory and
 * method see https://www.cs.helsinki.fi/group/goa/mallinnus/lines/bresenh.html
 */

/**
 * Jerk controlled movements planner added Apr 2018 by Eduardo JosÃ© Tagle.
 * Equations based on Synthethos TinyG2 sources, but the fixed-point
 * implementation is new, as we are running the ISR with a variable period.
 * Also implemented the BÃ©zier velocity curve evaluation in ARM assembler,
 * to avoid impacting ISR speed.
 */

#include "Marlin.h"
#include "stepper.h"
#include "endstops.h"
#include "planner.h"
#include "temperature.h"
#include "ultralcd.h"
#include "language.h"
#include "cardreader.h"
#include "speed_lookuptable.h"
#include "delay.h"

#if HAS_DIGIPOTSS
  #include <SPI.h>
#endif

Stepper stepper; // Singleton

// public:

#if ENABLED(X_DUAL_ENDSTOPS) || ENABLED(Y_DUAL_ENDSTOPS) || ENABLED(Z_DUAL_ENDSTOPS)
  bool Stepper::homing_dual_axis = false;
#endif

#if HAS_MOTOR_CURRENT_PWM
  uint32_t Stepper::motor_current_setting[3]; // Initialized by settings.load()
#endif

// private:

block_t* Stepper::current_block = NULL; // A pointer to the block currently being traced

uint8_t Stepper::last_direction_bits = 0,
        Stepper::axis_did_move;

bool Stepper::abort_current_block;

#if DISABLED(MIXING_EXTRUDER)
  uint8_t Stepper::last_moved_extruder = 0xFF;
#endif

#if ENABLED(X_DUAL_ENDSTOPS)
  bool Stepper::locked_X_motor = false, Stepper::locked_X2_motor = false;
#endif
#if ENABLED(Y_DUAL_ENDSTOPS)
  bool Stepper::locked_Y_motor = false, Stepper::locked_Y2_motor = false;
#endif
#if ENABLED(Z_DUAL_ENDSTOPS)
  bool Stepper::locked_Z_motor = false, Stepper::locked_Z2_motor = false;
#endif

uint32_t Stepper::acceleration_time, Stepper::deceleration_time;
uint8_t Stepper::steps_per_isr;

#if DISABLED(ADAPTIVE_STEP_SMOOTHING)
  constexpr
#endif
    uint8_t Stepper::oversampling_factor;

int32_t Stepper::delta_error[XYZE] = { 0 };

uint32_t Stepper::advance_dividend[XYZE] = { 0 },
         Stepper::advance_divisor = 0,
         Stepper::step_events_completed = 0, // The number of step events executed in the current block
         Stepper::accelerate_until,          // The point from where we need to stop acceleration
         Stepper::decelerate_after,          // The point from where we need to start decelerating
         Stepper::step_event_count;          // The total event count for the current block

#if ENABLED(MIXING_EXTRUDER)
  int32_t Stepper::delta_error_m[MIXING_STEPPERS];
  uint32_t Stepper::advance_dividend_m[MIXING_STEPPERS],
           Stepper::advance_divisor_m;
#else
  int8_t Stepper::active_extruder;           // Active extruder
#endif

#if ENABLED(S_CURVE_ACCELERATION)
  int32_t __attribute__((used)) Stepper::bezier_A __asm__("bezier_A");    // A coefficient in BÃ©zier speed curve with alias for assembler
  int32_t __attribute__((used)) Stepper::bezier_B __asm__("bezier_B");    // B coefficient in BÃ©zier speed curve with alias for assembler
  int32_t __attribute__((used)) Stepper::bezier_C __asm__("bezier_C");    // C coefficient in BÃ©zier speed curve with alias for assembler
  uint32_t __attribute__((used)) Stepper::bezier_F __asm__("bezier_F");   // F coefficient in BÃ©zier speed curve with alias for assembler
  uint32_t __attribute__((used)) Stepper::bezier_AV __asm__("bezier_AV"); // AV coefficient in BÃ©zier speed curve with alias for assembler
  bool __attribute__((used)) Stepper::A_negative __asm__("A_negative");   // If A coefficient was negative
  bool Stepper::bezier_2nd_half;    // =false If BÃ©zier curve has been initialized or not
#endif

uint32_t Stepper::nextMainISR = 0;

#if ENABLED(LIN_ADVANCE)

  constexpr uint32_t LA_ADV_NEVER = 0xFFFFFFFF;
  uint32_t Stepper::nextAdvanceISR = LA_ADV_NEVER,
           Stepper::LA_isr_rate = LA_ADV_NEVER;
  uint16_t Stepper::LA_current_adv_steps = 0,
           Stepper::LA_final_adv_steps,
           Stepper::LA_max_adv_steps;

  int8_t   Stepper::LA_steps = 0;

  bool Stepper::LA_use_advance_lead;

#endif // LIN_ADVANCE

int32_t Stepper::ticks_nominal = -1;
#if DISABLED(S_CURVE_ACCELERATION)
  uint32_t Stepper::acc_step_rate; // needed for deceleration start point
#endif

volatile int32_t Stepper::endstops_trigsteps[XYZ];

volatile int32_t Stepper::count_position[NUM_AXIS] = { 0 };
int8_t Stepper::count_direction[NUM_AXIS] = { 0, 0, 0, 0 };

#if ENABLED(X_DUAL_ENDSTOPS) || ENABLED(Y_DUAL_ENDSTOPS) || ENABLED(Z_DUAL_ENDSTOPS)
  #define DUAL_ENDSTOP_APPLY_STEP(A,V)                                                                                        \
    if (homing_dual_axis) {                                                                                                   \
      if (A##_HOME_DIR < 0) {                                                                                                 \
        if (!(TEST(endstops.state(), A##_MIN) && count_direction[_AXIS(A)] < 0) && !locked_##A##_motor) A##_STEP_WRITE(V);    \
        if (!(TEST(endstops.state(), A##2_MIN) && count_direction[_AXIS(A)] < 0) && !locked_##A##2_motor) A##2_STEP_WRITE(V); \
      }                                                                                                                       \
      else {                                                                                                                  \
        if (!(TEST(endstops.state(), A##_MAX) && count_direction[_AXIS(A)] > 0) && !locked_##A##_motor) A##_STEP_WRITE(V);    \
        if (!(TEST(endstops.state(), A##2_MAX) && count_direction[_AXIS(A)] > 0) && !locked_##A##2_motor) A##2_STEP_WRITE(V); \
      }                                                                                                                       \
    }                                                                                                                         \
    else {                                                                                                                    \
      A##_STEP_WRITE(V);                                                                                                      \
      A##2_STEP_WRITE(V);                                                                                                     \
    }
#endif

#if ENABLED(X_DUAL_STEPPER_DRIVERS)
  #define X_APPLY_DIR(v,Q) do{ X_DIR_WRITE(v); X2_DIR_WRITE((v) != INVERT_X2_VS_X_DIR); }while(0)
  #if ENABLED(X_DUAL_ENDSTOPS)
    #define X_APPLY_STEP(v,Q) DUAL_ENDSTOP_APPLY_STEP(X,v)
  #else
    #define X_APPLY_STEP(v,Q) do{ X_STEP_WRITE(v); X2_STEP_WRITE(v); }while(0)
  #endif
#elif ENABLED(DUAL_X_CARRIAGE)
  #define X_APPLY_DIR(v,ALWAYS) \
    if (extruder_duplication_enabled || ALWAYS) { \
      X_DIR_WRITE(v); \
      X2_DIR_WRITE(v); \
    } \
    else { \
      if (movement_extruder()) X2_DIR_WRITE(v); else X_DIR_WRITE(v); \
    }
  #define X_APPLY_STEP(v,ALWAYS) \
    if (extruder_duplication_enabled || ALWAYS) { \
      X_STEP_WRITE(v); \
      X2_STEP_WRITE(v); \
    } \
    else { \
      if (movement_extruder()) X2_STEP_WRITE(v); else X_STEP_WRITE(v); \
    }
#else
  #define X_APPLY_DIR(v,Q) X_DIR_WRITE(v)
  #define X_APPLY_STEP(v,Q) X_STEP_WRITE(v)
#endif

#if ENABLED(Y_DUAL_STEPPER_DRIVERS)
  #define Y_APPLY_DIR(v,Q) do{ Y_DIR_WRITE(v); Y2_DIR_WRITE((v) != INVERT_Y2_VS_Y_DIR); }while(0)
  #if ENABLED(Y_DUAL_ENDSTOPS)
    #define Y_APPLY_STEP(v,Q) DUAL_ENDSTOP_APPLY_STEP(Y,v)
  #else
    #define Y_APPLY_STEP(v,Q) do{ Y_STEP_WRITE(v); Y2_STEP_WRITE(v); }while(0)
  #endif
#else
  #define Y_APPLY_DIR(v,Q) Y_DIR_WRITE(v)
  #define Y_APPLY_STEP(v,Q) Y_STEP_WRITE(v)
#endif

#if ENABLED(Z_DUAL_STEPPER_DRIVERS)
  #define Z_APPLY_DIR(v,Q) do{ Z_DIR_WRITE(v); Z2_DIR_WRITE(v); }while(0)
  #if ENABLED(Z_DUAL_ENDSTOPS)
    #define Z_APPLY_STEP(v,Q) DUAL_ENDSTOP_APPLY_STEP(Z,v)
  #else
    #define Z_APPLY_STEP(v,Q) do{ Z_STEP_WRITE(v); Z2_STEP_WRITE(v); }while(0)
  #endif
#else
  #define Z_APPLY_DIR(v,Q) Z_DIR_WRITE(v)
  #define Z_APPLY_STEP(v,Q) Z_STEP_WRITE(v)
#endif

#if DISABLED(MIXING_EXTRUDER)
  #define E_APPLY_STEP(v,Q) E_STEP_WRITE(active_extruder, v)
#endif

// intRes = longIn1 * longIn2 >> 24
// uses:
// A[tmp] to store 0
// B[tmp] to store bits 16-23 of the 48bit result. The top bit is used to round the two byte result.
// note that the lower two bytes and the upper byte of the 48bit result are not calculated.
// this can cause the result to be out by one as the lower bytes may cause carries into the upper ones.
// B A are bits 24-39 and are the returned value
// C B A is longIn1
// D C B A is longIn2
//
static FORCE_INLINE uint16_t MultiU24X32toH16(uint32_t longIn1, uint32_t longIn2) {
  register uint8_t tmp1;
  register uint8_t tmp2;
  register uint16_t intRes;
  __asm__ __volatile__(
    A("clr %[tmp1]")
    A("mul %A[longIn1], %B[longIn2]")
    A("mov %[tmp2], r1")
    A("mul %B[longIn1], %C[longIn2]")
    A("movw %A[intRes], r0")
    A("mul %C[longIn1], %C[longIn2]")
    A("add %B[intRes], r0")
    A("mul %C[longIn1], %B[longIn2]")
    A("add %A[intRes], r0")
    A("adc %B[intRes], r1")
    A("mul %A[longIn1], %C[longIn2]")
    A("add %[tmp2], r0")
    A("adc %A[intRes], r1")
    A("adc %B[intRes], %[tmp1]")
    A("mul %B[longIn1], %B[longIn2]")
    A("add %[tmp2], r0")
    A("adc %A[intRes], r1")
    A("adc %B[intRes], %[tmp1]")
    A("mul %C[longIn1], %A[longIn2]")
    A("add %[tmp2], r0")
    A("adc %A[intRes], r1")
    A("adc %B[intRes], %[tmp1]")
    A("mul %B[longIn1], %A[longIn2]")
    A("add %[tmp2], r1")
    A("adc %A[intRes], %[tmp1]")
    A("adc %B[intRes], %[tmp1]")
    A("lsr %[tmp2]")
    A("adc %A[intRes], %[tmp1]")
    A("adc %B[intRes], %[tmp1]")
    A("mul %D[longIn2], %A[longIn1]")
    A("add %A[intRes], r0")
    A("adc %B[intRes], r1")
    A("mul %D[longIn2], %B[longIn1]")
    A("add %B[intRes], r0")
    A("clr r1")
      : [intRes] "=&r" (intRes),
        [tmp1] "=&r" (tmp1),
        [tmp2] "=&r" (tmp2)
      : [longIn1] "d" (longIn1),
        [longIn2] "d" (longIn2)
      : "cc"
  );
  return intRes;
}

void Stepper::wake_up() {
  // TCNT1 = 0;
  ENABLE_STEPPER_DRIVER_INTERRUPT();
}

/**
 * Set the stepper direction of each axis
 *
 *   COREXY: X_AXIS=A_AXIS and Y_AXIS=B_AXIS
 *   COREXZ: X_AXIS=A_AXIS and Z_AXIS=C_AXIS
 *   COREYZ: Y_AXIS=B_AXIS and Z_AXIS=C_AXIS
 */
void Stepper::set_directions() {

  #define SET_STEP_DIR(A) \
    if (motor_direction(_AXIS(A))) { \
      A##_APPLY_DIR(INVERT_## A##_DIR, false); \
      count_direction[_AXIS(A)] = -1; \
    } \
    else { \
      A##_APPLY_DIR(!INVERT_## A##_DIR, false); \
      count_direction[_AXIS(A)] = 1; \
    }

  #if HAS_X_DIR
    SET_STEP_DIR(X); // A
  #endif
  #if HAS_Y_DIR
    SET_STEP_DIR(Y); // B
  #endif
  #if HAS_Z_DIR
    SET_STEP_DIR(Z); // C
  #endif

  #if DISABLED(LIN_ADVANCE)
    #if ENABLED(MIXING_EXTRUDER)
      if (motor_direction(E_AXIS)) {
        MIXING_STEPPERS_LOOP(j) REV_E_DIR(j);
        count_direction[E_AXIS] = -1;
      }
      else {
        MIXING_STEPPERS_LOOP(j) NORM_E_DIR(j);
        count_direction[E_AXIS] = 1;
      }
    #else
      if (motor_direction(E_AXIS)) {
        REV_E_DIR(active_extruder);
        count_direction[E_AXIS] = -1;
      }
      else {
        NORM_E_DIR(active_extruder);
        count_direction[E_AXIS] = 1;
      }
    #endif
  #endif // !LIN_ADVANCE

  // A small delay may be needed after changing direction
  #if MINIMUM_STEPPER_DIR_DELAY > 0
    DELAY_NS(MINIMUM_STEPPER_DIR_DELAY);
  #endif
}

#if ENABLED(S_CURVE_ACCELERATION)
  /**
   *  This uses a quintic (fifth-degree) BÃ©zier polynomial for the velocity curve, giving
   *  a "linear pop" velocity curve; with pop being the sixth derivative of position:
   *  velocity - 1st, acceleration - 2nd, jerk - 3rd, snap - 4th, crackle - 5th, pop - 6th
   *
   *  The BÃ©zier curve takes the form:
   *
   *  V(t) = P_0 * B_0(t) + P_1 * B_1(t) + P_2 * B_2(t) + P_3 * B_3(t) + P_4 * B_4(t) + P_5 * B_5(t)
   *
   *  Where 0 <= t <= 1, and V(t) is the velocity. P_0 through P_5 are the control points, and B_0(t)
   *  through B_5(t) are the Bernstein basis as follows:
   *
   *        B_0(t) =   (1-t)^5        =   -t^5 +  5t^4 - 10t^3 + 10t^2 -  5t   +   1
   *        B_1(t) =  5(1-t)^4 * t    =   5t^5 - 20t^4 + 30t^3 - 20t^2 +  5t
   *        B_2(t) = 10(1-t)^3 * t^2  = -10t^5 + 30t^4 - 30t^3 + 10t^2
   *        B_3(t) = 10(1-t)^2 * t^3  =  10t^5 - 20t^4 + 10t^3
   *        B_4(t) =  5(1-t)   * t^4  =  -5t^5 +  5t^4
   *        B_5(t) =             t^5  =    t^5
   *                                      ^       ^       ^       ^       ^       ^
   *                                      |       |       |       |       |       |
   *                                      A       B       C       D       E       F
   *
   *  Unfortunately, we cannot use forward-differencing to calculate each position through
   *  the curve, as Marlin uses variable timer periods. So, we require a formula of the form:
   *
   *        V_f(t) = A*t^5 + B*t^4 + C*t^3 + D*t^2 + E*t + F
   *
   *  Looking at the above B_0(t) through B_5(t) expanded forms, if we take the coefficients of t^5
   *  through t of the BÃ©zier form of V(t), we can determine that:
   *
   *        A =    -P_0 +  5*P_1 - 10*P_2 + 10*P_3 -  5*P_4 +  P_5
   *        B =   5*P_0 - 20*P_1 + 30*P_2 - 20*P_3 +  5*P_4
   *        C = -10*P_0 + 30*P_1 - 30*P_2 + 10*P_3
   *        D =  10*P_0 - 20*P_1 + 10*P_2
   *        E = - 5*P_0 +  5*P_1
   *        F =     P_0
   *
   *  Now, since we will (currently) *always* want the initial acceleration and jerk values to be 0,
   *  We set P_i = P_0 = P_1 = P_2 (initial velocity), and P_t = P_3 = P_4 = P_5 (target velocity),
   *  which, after simplification, resolves to:
   *
   *        A = - 6*P_i +  6*P_t =  6*(P_t - P_i)
   *        B =  15*P_i - 15*P_t = 15*(P_i - P_t)
   *        C = -10*P_i + 10*P_t = 10*(P_t - P_i)
   *        D = 0
   *        E = 0
   *        F = P_i
   *
   *  As the t is evaluated in non uniform steps here, there is no other way rather than evaluating
   *  the BÃ©zier curve at each point:
   *
   *        V_f(t) = A*t^5 + B*t^4 + C*t^3 + F          [0 <= t <= 1]
   *
   * Floating point arithmetic execution time cost is prohibitive, so we will transform the math to
   * use fixed point values to be able to evaluate it in realtime. Assuming a maximum of 250000 steps
   * per second (driver pulses should at least be 2ÂµS hi/2ÂµS lo), and allocating 2 bits to avoid
   * overflows on the evaluation of the BÃ©zier curve, means we can use
   *
   *   t: unsigned Q0.32 (0 <= t < 1) |range 0 to 0xFFFFFFFF unsigned
   *   A:   signed Q24.7 ,            |range = +/- 250000 * 6 * 128 = +/- 192000000 = 0x0B71B000 | 28 bits + sign
   *   B:   signed Q24.7 ,            |range = +/- 250000 *15 * 128 = +/- 480000000 = 0x1C9C3800 | 29 bits + sign
   *   C:   signed Q24.7 ,            |range = +/- 250000 *10 * 128 = +/- 320000000 = 0x1312D000 | 29 bits + sign
   *   F:   signed Q24.7 ,            |range = +/- 250000     * 128 =      32000000 = 0x01E84800 | 25 bits + sign
   *
   * The trapezoid generator state contains the following information, that we will use to create and evaluate
   * the BÃ©zier curve:
   *
   *  blk->step_event_count [TS] = The total count of steps for this movement. (=distance)
   *  blk->initial_rate     [VI] = The initial steps per second (=velocity)
   *  blk->final_rate       [VF] = The ending steps per second  (=velocity)
   *  and the count of events completed (step_events_completed) [CS] (=distance until now)
   *
   *  Note the abbreviations we use in the following formulae are between []s
   *
   *  For Any 32bit CPU:
   *
   *    At the start of each trapezoid, calculate the coefficients A,B,C,F and Advance [AV], as follows:
   *
   *      A =  6*128*(VF - VI) =  768*(VF - VI)
   *      B = 15*128*(VI - VF) = 1920*(VI - VF)
   *      C = 10*128*(VF - VI) = 1280*(VF - VI)
   *      F =    128*VI        =  128*VI
   *     AV = (1<<32)/TS      ~= 0xFFFFFFFF / TS (To use ARM UDIV, that is 32 bits) (this is computed at the planner, to offload expensive calculations from the ISR)
   *
   *    And for each point, evaluate the curve with the following sequence:
   *
   *      void lsrs(uint32_t& d, uint32_t s, int cnt) {
   *        d = s >> cnt;
   *      }
   *      void lsls(uint32_t& d, uint32_t s, int cnt) {
   *        d = s << cnt;
   *      }
   *      void lsrs(int32_t& d, uint32_t s, int cnt) {
   *        d = uint32_t(s) >> cnt;
   *      }
   *      void lsls(int32_t& d, uint32_t s, int cnt) {
   *        d = uint32_t(s) << cnt;
   *      }
   *      void umull(uint32_t& rlo, uint32_t& rhi, uint32_t op1, uint32_t op2) {
   *        uint64_t res = uint64_t(op1) * op2;
   *        rlo = uint32_t(res & 0xFFFFFFFF);
   *        rhi = uint32_t((res >> 32) & 0xFFFFFFFF);
   *      }
   *      void smlal(int32_t& rlo, int32_t& rhi, int32_t op1, int32_t op2) {
   *        int64_t mul = int64_t(op1) * op2;
   *        int64_t s = int64_t(uint32_t(rlo) | ((uint64_t(uint32_t(rhi)) << 32U)));
   *        mul += s;
   *        rlo = int32_t(mul & 0xFFFFFFFF);
   *        rhi = int32_t((mul >> 32) & 0xFFFFFFFF);
   *      }
   *      int32_t _eval_bezier_curve_arm(uint32_t curr_step) {
   *        register uint32_t flo = 0;
   *        register uint32_t fhi = bezier_AV * curr_step;
   *        register uint32_t t = fhi;
   *        register int32_t alo = bezier_F;
   *        register int32_t ahi = 0;
   *        register int32_t A = bezier_A;
   *        register int32_t B = bezier_B;
   *        register int32_t C = bezier_C;
   *
   *        lsrs(ahi, alo, 1);          // a  = F << 31
   *        lsls(alo, alo, 31);         //
   *        umull(flo, fhi, fhi, t);    // f *= t
   *        umull(flo, fhi, fhi, t);    // f>>=32; f*=t
   *        lsrs(flo, fhi, 1);          //
   *        smlal(alo, ahi, flo, C);    // a+=(f>>33)*C
   *        umull(flo, fhi, fhi, t);    // f>>=32; f*=t
   *        lsrs(flo, fhi, 1);          //
   *        smlal(alo, ahi, flo, B);    // a+=(f>>33)*B
   *        umull(flo, fhi, fhi, t);    // f>>=32; f*=t
   *        lsrs(flo, fhi, 1);          // f>>=33;
   *        smlal(alo, ahi, flo, A);    // a+=(f>>33)*A;
   *        lsrs(alo, ahi, 6);          // a>>=38
   *
   *        return alo;
   *      }
   *
   *  This is rewritten in ARM assembly for optimal performance (43 cycles to execute).
   *
   *  For AVR, the precision of coefficients is scaled so the BÃ©zier curve can be evaluated in real-time:
   *  Let's reduce precision as much as possible. After some experimentation we found that:
   *
   *    Assume t and AV with 24 bits is enough
   *       A =  6*(VF - VI)
   *       B = 15*(VI - VF)
   *       C = 10*(VF - VI)
   *       F =     VI
   *      AV = (1<<24)/TS   (this is computed at the planner, to offload expensive calculations from the ISR)
   *
   *    Instead of storing sign for each coefficient, we will store its absolute value,
   *    and flag the sign of the A coefficient, so we can save to store the sign bit.
   *    It always holds that sign(A) = - sign(B) = sign(C)
   *
   *     So, the resulting range of the coefficients are:
   *
   *       t: unsigned (0 <= t < 1) |range 0 to 0xFFFFFF unsigned
   *       A:   signed Q24 , range = 250000 * 6 = 1500000 = 0x16E360 | 21 bits
   *       B:   signed Q24 , range = 250000 *15 = 3750000 = 0x393870 | 22 bits
   *       C:   signed Q24 , range = 250000 *10 = 2500000 = 0x1312D0 | 21 bits
   *       F:   signed Q24 , range = 250000     =  250000 = 0x0ED090 | 20 bits
   *
   *    And for each curve, estimate its coefficients with:
   *
   *      void _calc_bezier_curve_coeffs(int32_t v0, int32_t v1, uint32_t av) {
   *       // Calculate the BÃ©zier coefficients
   *       if (v1 < v0) {
   *         A_negative = true;
   *         bezier_A = 6 * (v0 - v1);
   *         bezier_B = 15 * (v0 - v1);
   *         bezier_C = 10 * (v0 - v1);
   *       }
   *       else {
   *         A_negative = false;
   *         bezier_A = 6 * (v1 - v0);
   *         bezier_B = 15 * (v1 - v0);
   *         bezier_C = 10 * (v1 - v0);
   *       }
   *       bezier_F = v0;
   *      }
   *
   *    And for each point, evaluate the curve with the following sequence:
   *
   *      // unsigned multiplication of 24 bits x 24bits, return upper 16 bits
   *      void umul24x24to16hi(uint16_t& r, uint24_t op1, uint24_t op2) {
   *        r = (uint64_t(op1) * op2) >> 8;
   *      }
   *      // unsigned multiplication of 16 bits x 16bits, return upper 16 bits
   *      void umul16x16to16hi(uint16_t& r, uint16_t op1, uint16_t op2) {
   *        r = (uint32_t(op1) * op2) >> 16;
   *      }
   *      // unsigned multiplication of 16 bits x 24bits, return upper 24 bits
   *      void umul16x24to24hi(uint24_t& r, uint16_t op1, uint24_t op2) {
   *        r = uint24_t((uint64_t(op1) * op2) >> 16);
   *      }
   *
   *      int32_t _eval_bezier_curve(uint32_t curr_step) {
   *        // To save computing, the first step is always the initial speed
   *        if (!curr_step)
   *          return bezier_F;
   *
   *        uint16_t t;
   *        umul24x24to16hi(t, bezier_AV, curr_step);   // t: Range 0 - 1^16 = 16 bits
   *        uint16_t f = t;
   *        umul16x16to16hi(f, f, t);           // Range 16 bits (unsigned)
   *        umul16x16to16hi(f, f, t);           // Range 16 bits : f = t^3  (unsigned)
   *        uint24_t acc = bezier_F;          // Range 20 bits (unsigned)
   *        if (A_negative) {
   *          uint24_t v;
   *          umul16x24to24hi(v, f, bezier_C);    // Range 21bits
   *          acc -= v;
   *          umul16x16to16hi(f, f, t);         // Range 16 bits : f = t^4  (unsigned)
   *          umul16x24to24hi(v, f, bezier_B);    // Range 22bits
   *          acc += v;
   *          umul16x16to16hi(f, f, t);         // Range 16 bits : f = t^5  (unsigned)
   *          umul16x24to24hi(v, f, bezier_A);    // Range 21bits + 15 = 36bits (plus sign)
   *          acc -= v;
   *        }
   *        else {
   *          uint24_t v;
   *          umul16x24to24hi(v, f, bezier_C);    // Range 21bits
   *          acc += v;
   *          umul16x16to16hi(f, f, t);       // Range 16 bits : f = t^4  (unsigned)
   *          umul16x24to24hi(v, f, bezier_B);    // Range 22bits
   *          acc -= v;
   *          umul16x16to16hi(f, f, t);               // Range 16 bits : f = t^5  (unsigned)
   *          umul16x24to24hi(v, f, bezier_A);    // Range 21bits + 15 = 36bits (plus sign)
   *          acc += v;
   *        }
   *        return acc;
   *      }
   *    These functions are translated to assembler for optimal performance.
   *    Coefficient calculation takes 70 cycles. Bezier point evaluation takes 150 cycles.
   */

  // For AVR we use assembly to maximize speed
  void Stepper::_calc_bezier_curve_coeffs(const int32_t v0, const int32_t v1, const uint32_t av) {

    // Store advance
    bezier_AV = av;

    // Calculate the rest of the coefficients
    register uint8_t r2 = v0 & 0xFF;
    register uint8_t r3 = (v0 >> 8) & 0xFF;
    register uint8_t r12 = (v0 >> 16) & 0xFF;
    register uint8_t r5 = v1 & 0xFF;
    register uint8_t r6 = (v1 >> 8) & 0xFF;
    register uint8_t r7 = (v1 >> 16) & 0xFF;
    register uint8_t r4,r8,r9,r10,r11;

    __asm__ __volatile__(
      /* Calculate the BÃ©zier coefficients */
      /*  %10:%1:%0 = v0*/
      /*  %5:%4:%3 = v1*/
      /*  %7:%6:%10 = temporary*/
      /*  %9 = val (must be high register!)*/
      /*  %10 (must be high register!)*/

      /* Store initial velocity*/
      A("sts bezier_F, %0")
      A("sts bezier_F+1, %1")
      A("sts bezier_F+2, %10")    /* bezier_F = %10:%1:%0 = v0 */

      /* Get delta speed */
      A("ldi %2,-1")              /* %2 = 0xFF, means A_negative = true */
      A("clr %8")                 /* %8 = 0 */
      A("sub %0,%3")
      A("sbc %1,%4")
      A("sbc %10,%5")             /*  v0 -= v1, C=1 if result is negative */
      A("brcc 1f")                /* branch if result is positive (C=0), that means v0 >= v1 */

      /*  Result was negative, get the absolute value*/
      A("com %10")
      A("com %1")
      A("neg %0")
      A("sbc %1,%2")
      A("sbc %10,%2")             /* %10:%1:%0 +1  -> %10:%1:%0 = -(v0 - v1) = (v1 - v0) */
      A("clr %2")                 /* %2 = 0, means A_negative = false */

      /*  Store negative flag*/
      L("1")
      A("sts A_negative, %2")     /* Store negative flag */

      /*  Compute coefficients A,B and C   [20 cycles worst case]*/
      A("ldi %9,6")               /* %9 = 6 */
      A("mul %0,%9")              /* r1:r0 = 6*LO(v0-v1) */
      A("sts bezier_A, r0")
      A("mov %6,r1")
      A("clr %7")                 /* %7:%6:r0 = 6*LO(v0-v1) */
      A("mul %1,%9")              /* r1:r0 = 6*MI(v0-v1) */
      A("add %6,r0")
      A("adc %7,r1")              /* %7:%6:?? += 6*MI(v0-v1) << 8 */
      A("mul %10,%9")             /* r1:r0 = 6*HI(v0-v1) */
      A("add %7,r0")              /* %7:%6:?? += 6*HI(v0-v1) << 16 */
      A("sts bezier_A+1, %6")
      A("sts bezier_A+2, %7")     /* bezier_A = %7:%6:?? = 6*(v0-v1) [35 cycles worst] */

      A("ldi %9,15")              /* %9 = 15 */
      A("mul %0,%9")              /* r1:r0 = 5*LO(v0-v1) */
      A("sts bezier_B, r0")
      A("mov %6,r1")
      A("clr %7")                 /* %7:%6:?? = 5*LO(v0-v1) */
      A("mul %1,%9")              /* r1:r0 = 5*MI(v0-v1) */
      A("add %6,r0")
      A("adc %7,r1")              /* %7:%6:?? += 5*MI(v0-v1) << 8 */
      A("mul %10,%9")             /* r1:r0 = 5*HI(v0-v1) */
      A("add %7,r0")              /* %7:%6:?? += 5*HI(v0-v1) << 16 */
      A("sts bezier_B+1, %6")
      A("sts bezier_B+2, %7")     /* bezier_B = %7:%6:?? = 5*(v0-v1) [50 cycles worst] */

      A("ldi %9,10")              /* %9 = 10 */
      A("mul %0,%9")              /* r1:r0 = 10*LO(v0-v1) */
      A("sts bezier_C, r0")
      A("mov %6,r1")
      A("clr %7")                 /* %7:%6:?? = 10*LO(v0-v1) */
      A("mul %1,%9")              /* r1:r0 = 10*MI(v0-v1) */
      A("add %6,r0")
      A("adc %7,r1")              /* %7:%6:?? += 10*MI(v0-v1) << 8 */
      A("mul %10,%9")             /* r1:r0 = 10*HI(v0-v1) */
      A("add %7,r0")              /* %7:%6:?? += 10*HI(v0-v1) << 16 */
      A("sts bezier_C+1, %6")
      " sts bezier_C+2, %7"       /* bezier_C = %7:%6:?? = 10*(v0-v1) [65 cycles worst] */
      : "+r" (r2),
        "+d" (r3),
        "=r" (r4),
        "+r" (r5),
        "+r" (r6),
        "+r" (r7),
        "=r" (r8),
        "=r" (r9),
        "=r" (r10),
        "=d" (r11),
        "+r" (r12)
      :
      : "r0", "r1", "cc", "memory"
    );
  }

  FORCE_INLINE int32_t Stepper::_eval_bezier_curve(const uint32_t curr_step) {

    // If dealing with the first step, save expensive computing and return the initial speed
    if (!curr_step)
      return bezier_F;

    register uint8_t r0 = 0; /* Zero register */
    register uint8_t r2 = (curr_step) & 0xFF;
    register uint8_t r3 = (curr_step >> 8) & 0xFF;
    register uint8_t r4 = (curr_step >> 16) & 0xFF;
    register uint8_t r1,r5,r6,r7,r8,r9,r10,r11; /* Temporary registers */

    __asm__ __volatile(
      /* umul24x24to16hi(t, bezier_AV, curr_step);  t: Range 0 - 1^16 = 16 bits*/
      A("lds %9,bezier_AV")       /* %9 = LO(AV)*/
      A("mul %9,%2")              /* r1:r0 = LO(bezier_AV)*LO(curr_step)*/
      A("mov %7,r1")              /* %7 = LO(bezier_AV)*LO(curr_step) >> 8*/
      A("clr %8")                 /* %8:%7  = LO(bezier_AV)*LO(curr_step) >> 8*/
      A("lds %10,bezier_AV+1")    /* %10 = MI(AV)*/
      A("mul %10,%2")             /* r1:r0  = MI(bezier_AV)*LO(curr_step)*/
      A("add %7,r0")
      A("adc %8,r1")              /* %8:%7 += MI(bezier_AV)*LO(curr_step)*/
      A("lds r1,bezier_AV+2")     /* r11 = HI(AV)*/
      A("mul r1,%2")              /* r1:r0  = HI(bezier_AV)*LO(curr_step)*/
      A("add %8,r0")              /* %8:%7 += HI(bezier_AV)*LO(curr_step) << 8*/
      A("mul %9,%3")              /* r1:r0 =  LO(bezier_AV)*MI(curr_step)*/
      A("add %7,r0")
      A("adc %8,r1")              /* %8:%7 += LO(bezier_AV)*MI(curr_step)*/
      A("mul %10,%3")             /* r1:r0 =  MI(bezier_AV)*MI(curr_step)*/
      A("add %8,r0")              /* %8:%7 += LO(bezier_AV)*MI(curr_step) << 8*/
      A("mul %9,%4")              /* r1:r0 =  LO(bezier_AV)*HI(curr_step)*/
      A("add %8,r0")              /* %8:%7 += LO(bezier_AV)*HI(curr_step) << 8*/
      /* %8:%7 = t*/

      /* uint16_t f = t;*/
      A("mov %5,%7")              /* %6:%5 = f*/
      A("mov %6,%8")
      /* %6:%5 = f*/

      /* umul16x16to16hi(f, f, t); / Range 16 bits (unsigned) [17] */
      A("mul %5,%7")              /* r1:r0 = LO(f) * LO(t)*/
      A("mov %9,r1")              /* store MIL(LO(f) * LO(t)) in %9, we need it for rounding*/
      A("clr %10")                /* %10 = 0*/
      A("clr %11")                /* %11 = 0*/
      A("mul %5,%8")              /* r1:r0 = LO(f) * HI(t)*/
      A("add %9,r0")              /* %9 += LO(LO(f) * HI(t))*/
      A("adc %10,r1")             /* %10 = HI(LO(f) * HI(t))*/
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%7")              /* r1:r0 = HI(f) * LO(t)*/
      A("add %9,r0")              /* %9 += LO(HI(f) * LO(t))*/
      A("adc %10,r1")             /* %10 += HI(HI(f) * LO(t)) */
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%8")              /* r1:r0 = HI(f) * HI(t)*/
      A("add %10,r0")             /* %10 += LO(HI(f) * HI(t))*/
      A("adc %11,r1")             /* %11 += HI(HI(f) * HI(t))*/
      A("mov %5,%10")             /* %6:%5 = */
      A("mov %6,%11")             /* f = %10:%11*/

      /* umul16x16to16hi(f, f, t); / Range 16 bits : f = t^3  (unsigned) [17]*/
      A("mul %5,%7")              /* r1:r0 = LO(f) * LO(t)*/
      A("mov %1,r1")              /* store MIL(LO(f) * LO(t)) in %1, we need it for rounding*/
      A("clr %10")                /* %10 = 0*/
      A("clr %11")                /* %11 = 0*/
      A("mul %5,%8")              /* r1:r0 = LO(f) * HI(t)*/
      A("add %1,r0")              /* %1 += LO(LO(f) * HI(t))*/
      A("adc %10,r1")             /* %10 = HI(LO(f) * HI(t))*/
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%7")              /* r1:r0 = HI(f) * LO(t)*/
      A("add %1,r0")              /* %1 += LO(HI(f) * LO(t))*/
      A("adc %10,r1")             /* %10 += HI(HI(f) * LO(t))*/
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%8")              /* r1:r0 = HI(f) * HI(t)*/
      A("add %10,r0")             /* %10 += LO(HI(f) * HI(t))*/
      A("adc %11,r1")             /* %11 += HI(HI(f) * HI(t))*/
      A("mov %5,%10")             /* %6:%5 =*/
      A("mov %6,%11")             /* f = %10:%11*/
      /* [15 +17*2] = [49]*/

      /* %4:%3:%2 will be acc from now on*/

      /* uint24_t acc = bezier_F; / Range 20 bits (unsigned)*/
      A("clr %9")                 /* "decimal place we get for free"*/
      A("lds %2,bezier_F")
      A("lds %3,bezier_F+1")
      A("lds %4,bezier_F+2")      /* %4:%3:%2 = acc*/

      /* if (A_negative) {*/
      A("lds r0,A_negative")
      A("or r0,%0")               /* Is flag signalling negative? */
      A("brne 3f")                /* If yes, Skip next instruction if A was negative*/
      A("rjmp 1f")                /* Otherwise, jump */

      /* uint24_t v; */
      /* umul16x24to24hi(v, f, bezier_C); / Range 21bits [29] */
      /* acc -= v; */
      L("3")
      A("lds %10, bezier_C")      /* %10 = LO(bezier_C)*/
      A("mul %10,%5")             /* r1:r0 = LO(bezier_C) * LO(f)*/
      A("sub %9,r1")
      A("sbc %2,%0")
      A("sbc %3,%0")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= HI(LO(bezier_C) * LO(f))*/
      A("lds %11, bezier_C+1")    /* %11 = MI(bezier_C)*/
      A("mul %11,%5")             /* r1:r0 = MI(bezier_C) * LO(f)*/
      A("sub %9,r0")
      A("sbc %2,r1")
      A("sbc %3,%0")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= MI(bezier_C) * LO(f)*/
      A("lds %1, bezier_C+2")     /* %1 = HI(bezier_C)*/
      A("mul %1,%5")              /* r1:r0 = MI(bezier_C) * LO(f)*/
      A("sub %2,r0")
      A("sbc %3,r1")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= HI(bezier_C) * LO(f) << 8*/
      A("mul %10,%6")             /* r1:r0 = LO(bezier_C) * MI(f)*/
      A("sub %9,r0")
      A("sbc %2,r1")
      A("sbc %3,%0")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= LO(bezier_C) * MI(f)*/
      A("mul %11,%6")             /* r1:r0 = MI(bezier_C) * MI(f)*/
      A("sub %2,r0")
      A("sbc %3,r1")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= MI(bezier_C) * MI(f) << 8*/
      A("mul %1,%6")              /* r1:r0 = HI(bezier_C) * LO(f)*/
      A("sub %3,r0")
      A("sbc %4,r1")              /* %4:%3:%2:%9 -= HI(bezier_C) * LO(f) << 16*/

      /* umul16x16to16hi(f, f, t); / Range 16 bits : f = t^3  (unsigned) [17]*/
      A("mul %5,%7")              /* r1:r0 = LO(f) * LO(t)*/
      A("mov %1,r1")              /* store MIL(LO(f) * LO(t)) in %1, we need it for rounding*/
      A("clr %10")                /* %10 = 0*/
      A("clr %11")                /* %11 = 0*/
      A("mul %5,%8")              /* r1:r0 = LO(f) * HI(t)*/
      A("add %1,r0")              /* %1 += LO(LO(f) * HI(t))*/
      A("adc %10,r1")             /* %10 = HI(LO(f) * HI(t))*/
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%7")              /* r1:r0 = HI(f) * LO(t)*/
      A("add %1,r0")              /* %1 += LO(HI(f) * LO(t))*/
      A("adc %10,r1")             /* %10 += HI(HI(f) * LO(t))*/
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%8")              /* r1:r0 = HI(f) * HI(t)*/
      A("add %10,r0")             /* %10 += LO(HI(f) * HI(t))*/
      A("adc %11,r1")             /* %11 += HI(HI(f) * HI(t))*/
      A("mov %5,%10")             /* %6:%5 =*/
      A("mov %6,%11")             /* f = %10:%11*/

      /* umul16x24to24hi(v, f, bezier_B); / Range 22bits [29]*/
      /* acc += v; */
      A("lds %10, bezier_B")      /* %10 = LO(bezier_B)*/
      A("mul %10,%5")             /* r1:r0 = LO(bezier_B) * LO(f)*/
      A("add %9,r1")
      A("adc %2,%0")
      A("adc %3,%0")
      A("adc %4,%0")              /* %4:%3:%2:%9 += HI(LO(bezier_B) * LO(f))*/
      A("lds %11, bezier_B+1")    /* %11 = MI(bezier_B)*/
      A("mul %11,%5")             /* r1:r0 = MI(bezier_B) * LO(f)*/
      A("add %9,r0")
      A("adc %2,r1")
      A("adc %3,%0")
      A("adc %4,%0")              /* %4:%3:%2:%9 += MI(bezier_B) * LO(f)*/
      A("lds %1, bezier_B+2")     /* %1 = HI(bezier_B)*/
      A("mul %1,%5")              /* r1:r0 = MI(bezier_B) * LO(f)*/
      A("add %2,r0")
      A("adc %3,r1")
      A("adc %4,%0")              /* %4:%3:%2:%9 += HI(bezier_B) * LO(f) << 8*/
      A("mul %10,%6")             /* r1:r0 = LO(bezier_B) * MI(f)*/
      A("add %9,r0")
      A("adc %2,r1")
      A("adc %3,%0")
      A("adc %4,%0")              /* %4:%3:%2:%9 += LO(bezier_B) * MI(f)*/
      A("mul %11,%6")             /* r1:r0 = MI(bezier_B) * MI(f)*/
      A("add %2,r0")
      A("adc %3,r1")
      A("adc %4,%0")              /* %4:%3:%2:%9 += MI(bezier_B) * MI(f) << 8*/
      A("mul %1,%6")              /* r1:r0 = HI(bezier_B) * LO(f)*/
      A("add %3,r0")
      A("adc %4,r1")              /* %4:%3:%2:%9 += HI(bezier_B) * LO(f) << 16*/

      /* umul16x16to16hi(f, f, t); / Range 16 bits : f = t^5  (unsigned) [17]*/
      A("mul %5,%7")              /* r1:r0 = LO(f) * LO(t)*/
      A("mov %1,r1")              /* store MIL(LO(f) * LO(t)) in %1, we need it for rounding*/
      A("clr %10")                /* %10 = 0*/
      A("clr %11")                /* %11 = 0*/
      A("mul %5,%8")              /* r1:r0 = LO(f) * HI(t)*/
      A("add %1,r0")              /* %1 += LO(LO(f) * HI(t))*/
      A("adc %10,r1")             /* %10 = HI(LO(f) * HI(t))*/
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%7")              /* r1:r0 = HI(f) * LO(t)*/
      A("add %1,r0")              /* %1 += LO(HI(f) * LO(t))*/
      A("adc %10,r1")             /* %10 += HI(HI(f) * LO(t))*/
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%8")              /* r1:r0 = HI(f) * HI(t)*/
      A("add %10,r0")             /* %10 += LO(HI(f) * HI(t))*/
      A("adc %11,r1")             /* %11 += HI(HI(f) * HI(t))*/
      A("mov %5,%10")             /* %6:%5 =*/
      A("mov %6,%11")             /* f = %10:%11*/

      /* umul16x24to24hi(v, f, bezier_A); / Range 21bits [29]*/
      /* acc -= v; */
      A("lds %10, bezier_A")      /* %10 = LO(bezier_A)*/
      A("mul %10,%5")             /* r1:r0 = LO(bezier_A) * LO(f)*/
      A("sub %9,r1")
      A("sbc %2,%0")
      A("sbc %3,%0")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= HI(LO(bezier_A) * LO(f))*/
      A("lds %11, bezier_A+1")    /* %11 = MI(bezier_A)*/
      A("mul %11,%5")             /* r1:r0 = MI(bezier_A) * LO(f)*/
      A("sub %9,r0")
      A("sbc %2,r1")
      A("sbc %3,%0")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= MI(bezier_A) * LO(f)*/
      A("lds %1, bezier_A+2")     /* %1 = HI(bezier_A)*/
      A("mul %1,%5")              /* r1:r0 = MI(bezier_A) * LO(f)*/
      A("sub %2,r0")
      A("sbc %3,r1")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= HI(bezier_A) * LO(f) << 8*/
      A("mul %10,%6")             /* r1:r0 = LO(bezier_A) * MI(f)*/
      A("sub %9,r0")
      A("sbc %2,r1")
      A("sbc %3,%0")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= LO(bezier_A) * MI(f)*/
      A("mul %11,%6")             /* r1:r0 = MI(bezier_A) * MI(f)*/
      A("sub %2,r0")
      A("sbc %3,r1")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= MI(bezier_A) * MI(f) << 8*/
      A("mul %1,%6")              /* r1:r0 = HI(bezier_A) * LO(f)*/
      A("sub %3,r0")
      A("sbc %4,r1")              /* %4:%3:%2:%9 -= HI(bezier_A) * LO(f) << 16*/
      A("jmp 2f")                 /* Done!*/

      L("1")

      /* uint24_t v; */
      /* umul16x24to24hi(v, f, bezier_C); / Range 21bits [29]*/
      /* acc += v; */
      A("lds %10, bezier_C")      /* %10 = LO(bezier_C)*/
      A("mul %10,%5")             /* r1:r0 = LO(bezier_C) * LO(f)*/
      A("add %9,r1")
      A("adc %2,%0")
      A("adc %3,%0")
      A("adc %4,%0")              /* %4:%3:%2:%9 += HI(LO(bezier_C) * LO(f))*/
      A("lds %11, bezier_C+1")    /* %11 = MI(bezier_C)*/
      A("mul %11,%5")             /* r1:r0 = MI(bezier_C) * LO(f)*/
      A("add %9,r0")
      A("adc %2,r1")
      A("adc %3,%0")
      A("adc %4,%0")              /* %4:%3:%2:%9 += MI(bezier_C) * LO(f)*/
      A("lds %1, bezier_C+2")     /* %1 = HI(bezier_C)*/
      A("mul %1,%5")              /* r1:r0 = MI(bezier_C) * LO(f)*/
      A("add %2,r0")
      A("adc %3,r1")
      A("adc %4,%0")              /* %4:%3:%2:%9 += HI(bezier_C) * LO(f) << 8*/
      A("mul %10,%6")             /* r1:r0 = LO(bezier_C) * MI(f)*/
      A("add %9,r0")
      A("adc %2,r1")
      A("adc %3,%0")
      A("adc %4,%0")              /* %4:%3:%2:%9 += LO(bezier_C) * MI(f)*/
      A("mul %11,%6")             /* r1:r0 = MI(bezier_C) * MI(f)*/
      A("add %2,r0")
      A("adc %3,r1")
      A("adc %4,%0")              /* %4:%3:%2:%9 += MI(bezier_C) * MI(f) << 8*/
      A("mul %1,%6")              /* r1:r0 = HI(bezier_C) * LO(f)*/
      A("add %3,r0")
      A("adc %4,r1")              /* %4:%3:%2:%9 += HI(bezier_C) * LO(f) << 16*/

      /* umul16x16to16hi(f, f, t); / Range 16 bits : f = t^3  (unsigned) [17]*/
      A("mul %5,%7")              /* r1:r0 = LO(f) * LO(t)*/
      A("mov %1,r1")              /* store MIL(LO(f) * LO(t)) in %1, we need it for rounding*/
      A("clr %10")                /* %10 = 0*/
      A("clr %11")                /* %11 = 0*/
      A("mul %5,%8")              /* r1:r0 = LO(f) * HI(t)*/
      A("add %1,r0")              /* %1 += LO(LO(f) * HI(t))*/
      A("adc %10,r1")             /* %10 = HI(LO(f) * HI(t))*/
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%7")              /* r1:r0 = HI(f) * LO(t)*/
      A("add %1,r0")              /* %1 += LO(HI(f) * LO(t))*/
      A("adc %10,r1")             /* %10 += HI(HI(f) * LO(t))*/
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%8")              /* r1:r0 = HI(f) * HI(t)*/
      A("add %10,r0")             /* %10 += LO(HI(f) * HI(t))*/
      A("adc %11,r1")             /* %11 += HI(HI(f) * HI(t))*/
      A("mov %5,%10")             /* %6:%5 =*/
      A("mov %6,%11")             /* f = %10:%11*/

      /* umul16x24to24hi(v, f, bezier_B); / Range 22bits [29]*/
      /* acc -= v;*/
      A("lds %10, bezier_B")      /* %10 = LO(bezier_B)*/
      A("mul %10,%5")             /* r1:r0 = LO(bezier_B) * LO(f)*/
      A("sub %9,r1")
      A("sbc %2,%0")
      A("sbc %3,%0")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= HI(LO(bezier_B) * LO(f))*/
      A("lds %11, bezier_B+1")    /* %11 = MI(bezier_B)*/
      A("mul %11,%5")             /* r1:r0 = MI(bezier_B) * LO(f)*/
      A("sub %9,r0")
      A("sbc %2,r1")
      A("sbc %3,%0")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= MI(bezier_B) * LO(f)*/
      A("lds %1, bezier_B+2")     /* %1 = HI(bezier_B)*/
      A("mul %1,%5")              /* r1:r0 = MI(bezier_B) * LO(f)*/
      A("sub %2,r0")
      A("sbc %3,r1")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= HI(bezier_B) * LO(f) << 8*/
      A("mul %10,%6")             /* r1:r0 = LO(bezier_B) * MI(f)*/
      A("sub %9,r0")
      A("sbc %2,r1")
      A("sbc %3,%0")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= LO(bezier_B) * MI(f)*/
      A("mul %11,%6")             /* r1:r0 = MI(bezier_B) * MI(f)*/
      A("sub %2,r0")
      A("sbc %3,r1")
      A("sbc %4,%0")              /* %4:%3:%2:%9 -= MI(bezier_B) * MI(f) << 8*/
      A("mul %1,%6")              /* r1:r0 = HI(bezier_B) * LO(f)*/
      A("sub %3,r0")
      A("sbc %4,r1")              /* %4:%3:%2:%9 -= HI(bezier_B) * LO(f) << 16*/

      /* umul16x16to16hi(f, f, t); / Range 16 bits : f = t^5  (unsigned) [17]*/
      A("mul %5,%7")              /* r1:r0 = LO(f) * LO(t)*/
      A("mov %1,r1")              /* store MIL(LO(f) * LO(t)) in %1, we need it for rounding*/
      A("clr %10")                /* %10 = 0*/
      A("clr %11")                /* %11 = 0*/
      A("mul %5,%8")              /* r1:r0 = LO(f) * HI(t)*/
      A("add %1,r0")              /* %1 += LO(LO(f) * HI(t))*/
      A("adc %10,r1")             /* %10 = HI(LO(f) * HI(t))*/
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%7")              /* r1:r0 = HI(f) * LO(t)*/
      A("add %1,r0")              /* %1 += LO(HI(f) * LO(t))*/
      A("adc %10,r1")             /* %10 += HI(HI(f) * LO(t))*/
      A("adc %11,%0")             /* %11 += carry*/
      A("mul %6,%8")              /* r1:r0 = HI(f) * HI(t)*/
      A("add %10,r0")             /* %10 += LO(HI(f) * HI(t))*/
      A("adc %11,r1")             /* %11 += HI(HI(f) * HI(t))*/
      A("mov %5,%10")             /* %6:%5 =*/
      A("mov %6,%11")             /* f = %10:%11*/

      /* umul16x24to24hi(v, f, bezier_A); / Range 21bits [29]*/
      /* acc += v; */
      A("lds %10, bezier_A")      /* %10 = LO(bezier_A)*/
      A("mul %10,%5")             /* r1:r0 = LO(bezier_A) * LO(f)*/
      A("add %9,r1")
      A("adc %2,%0")
      A("adc %3,%0")
      A("adc %4,%0")              /* %4:%3:%2:%9 += HI(LO(bezier_A) * LO(f))*/
      A("lds %11, bezier_A+1")    /* %11 = MI(bezier_A)*/
      A("mul %11,%5")             /* r1:r0 = MI(bezier_A) * LO(f)*/
      A("add %9,r0")
      A("adc %2,r1")
      A("adc %3,%0")
      A("adc %4,%0")              /* %4:%3:%2:%9 += MI(bezier_A) * LO(f)*/
      A("lds %1, bezier_A+2")     /* %1 = HI(bezier_A)*/
      A("mul %1,%5")              /* r1:r0 = MI(bezier_A) * LO(f)*/
      A("add %2,r0")
      A("adc %3,r1")
      A("adc %4,%0")              /* %4:%3:%2:%9 += HI(bezier_A) * LO(f) << 8*/
      A("mul %10,%6")             /* r1:r0 = LO(bezier_A) * MI(f)*/
      A("add %9,r0")
      A("adc %2,r1")
      A("adc %3,%0")
      A("adc %4,%0")              /* %4:%3:%2:%9 += LO(bezier_A) * MI(f)*/
      A("mul %11,%6")             /* r1:r0 = MI(bezier_A) * MI(f)*/
      A("add %2,r0")
      A("adc %3,r1")
      A("adc %4,%0")              /* %4:%3:%2:%9 += MI(bezier_A) * MI(f) << 8*/
      A("mul %1,%6")              /* r1:r0 = HI(bezier_A) * LO(f)*/
      A("add %3,r0")
      A("adc %4,r1")              /* %4:%3:%2:%9 += HI(bezier_A) * LO(f) << 16*/
      L("2")
      " clr __zero_reg__"         /* C runtime expects r1 = __zero_reg__ = 0 */
      : "+r"(r0),
        "+r"(r1),
        "+r"(r2),
        "+r"(r3),
        "+r"(r4),
        "+r"(r5),
        "+r"(r6),
        "+r"(r7),
        "+r"(r8),
        "+r"(r9),
        "+r"(r10),
        "+r"(r11)
      :
      :"cc","r0","r1"
    );
    return (r2 | (uint16_t(r3) << 8)) | (uint32_t(r4) << 16);
  }

#endif // S_CURVE_ACCELERATION

/**
 * Stepper Driver Interrupt
 *
 * Directly pulses the stepper motors at high frequency.
 */

HAL_STEP_TIMER_ISR {
  HAL_timer_isr_prologue(STEP_TIMER_NUM);

  Stepper::isr();

  HAL_timer_isr_epilogue(STEP_TIMER_NUM);
}

#define STEP_MULTIPLY(A,B) MultiU24X32toH16(A, B)

void Stepper::isr() {
  DISABLE_ISRS();

  // Program timer compare for the maximum period, so it does NOT
  // flag an interrupt while this ISR is running - So changes from small
  // periods to big periods are respected and the timer does not reset to 0
  HAL_timer_set_compare(STEP_TIMER_NUM, HAL_TIMER_TYPE_MAX);

  // Count of ticks for the next ISR
  hal_timer_t next_isr_ticks = 0;

  // Limit the amount of iterations
  uint8_t max_loops = 10;

  // We need this variable here to be able to use it in the following loop
  hal_timer_t min_ticks;
  do {
    // Enable ISRs to reduce USART processing latency
    ENABLE_ISRS();

    // Run main stepping pulse phase ISR if we have to
    if (!nextMainISR) Stepper::stepper_pulse_phase_isr();

    #if ENABLED(LIN_ADVANCE)
      // Run linear advance stepper ISR if we have to
      if (!nextAdvanceISR) nextAdvanceISR = Stepper::advance_isr();
    #endif

    // ^== Time critical. NOTHING besides pulse generation should be above here!!!

    // Run main stepping block processing ISR if we have to
    if (!nextMainISR) nextMainISR = Stepper::stepper_block_phase_isr();

    uint32_t interval =
      #if ENABLED(LIN_ADVANCE)
        MIN(nextAdvanceISR, nextMainISR)  // Nearest time interval
      #else
        nextMainISR                       // Remaining stepper ISR time
      #endif
    ;

    // Limit the value to the maximum possible value of the timer
    NOMORE(interval, HAL_TIMER_TYPE_MAX);

    // Compute the time remaining for the main isr
    nextMainISR -= interval;

    #if ENABLED(LIN_ADVANCE)
      // Compute the time remaining for the advance isr
      if (nextAdvanceISR != LA_ADV_NEVER) nextAdvanceISR -= interval;
    #endif

    /**
     * This needs to avoid a race-condition caused by interleaving
     * of interrupts required by both the LA and Stepper algorithms.
     *
     * Assume the following tick times for stepper pulses:
     *   Stepper ISR (S):  1 1000 2000 3000 4000
     *   Linear Adv. (E): 10 1010 2010 3010 4010
     *
     * The current algorithm tries to interleave them, giving:
     *  1:S 10:E 1000:S 1010:E 2000:S 2010:E 3000:S 3010:E 4000:S 4010:E
     *
     * Ideal timing would yield these delta periods:
     *  1:S  9:E  990:S   10:E  990:S   10:E  990:S   10:E  990:S   10:E
     *
     * But, since each event must fire an ISR with a minimum duration, the
     * minimum delta might be 900, so deltas under 900 get rounded up:
     *  900:S d900:E d990:S d900:E d990:S d900:E d990:S d900:E d990:S d900:E
     *
     * It works, but divides the speed of all motors by half, leading to a sudden
     * reduction to 1/2 speed! Such jumps in speed lead to lost steps (not even
     * accounting for double/quad stepping, which makes it even worse).
     */

    // Compute the tick count for the next ISR
    next_isr_ticks += interval;

    /**
     * The following section must be done with global interrupts disabled.
     * We want nothing to interrupt it, as that could mess the calculations
     * we do for the next value to program in the period register of the
     * stepper timer and lead to skipped ISRs (if the value we happen to program
     * is less than the current count due to something preempting between the
     * read and the write of the new period value).
     */
    DISABLE_ISRS();

    /**
     * Get the current tick value + margin
     * Assuming at least 6Âµs between calls to this ISR...
     * On AVR the ISR epilogue+prologue is estimated at 100 instructions - Give 8Âµs as margin
     * On ARM the ISR epilogue+prologue is estimated at 20 instructions - Give 1Âµs as margin
     */
    min_ticks = HAL_timer_get_count(STEP_TIMER_NUM) + hal_timer_t((STEPPER_TIMER_TICKS_PER_US) * 8);

    /**
     * NB: If for some reason the stepper monopolizes the MPU, eventually the
     * timer will wrap around (and so will 'next_isr_ticks'). So, limit the
     * loop to 10 iterations. Beyond that, there's no way to ensure correct pulse
     * timing, since the MCU isn't fast enough.
     */
    if (!--max_loops) next_isr_ticks = min_ticks;

    // Advance pulses if not enough time to wait for the next ISR
  } while (next_isr_ticks < min_ticks);

  // Now 'next_isr_ticks' contains the period to the next Stepper ISR - And we are
  // sure that the time has not arrived yet - Warrantied by the scheduler

  // Set the next ISR to fire at the proper time
  HAL_timer_set_compare(STEP_TIMER_NUM, hal_timer_t(next_isr_ticks));

  // Don't forget to finally reenable interrupts
  ENABLE_ISRS();
}

/**
 * This phase of the ISR should ONLY create the pulses for the steppers.
 * This prevents jitter caused by the interval between the start of the
 * interrupt and the start of the pulses. DON'T add any logic ahead of the
 * call to this method that might cause variation in the timing. The aim
 * is to keep pulse timing as regular as possible.
 */
void Stepper::stepper_pulse_phase_isr() {

  // If we must abort the current block, do so!
  if (abort_current_block) {
    abort_current_block = false;
    if (current_block) {
      axis_did_move = 0;
      current_block = NULL;
      planner.discard_current_block();
    }
  }

  // If there is no current block, do nothing
  if (!current_block) return;

  // Count of pending loops and events for this iteration
  const uint32_t pending_events = step_event_count - step_events_completed;
  uint8_t events_to_do = MIN(pending_events, steps_per_isr);

  // Just update the value we will get at the end of the loop
  step_events_completed += events_to_do;

  // Get the timer count and estimate the end of the pulse
  hal_timer_t pulse_end = HAL_timer_get_count(PULSE_TIMER_NUM) + hal_timer_t(MIN_PULSE_TICKS);

  const hal_timer_t added_step_ticks = hal_timer_t(ADDED_STEP_TICKS);

  // Take multiple steps per interrupt (For high speed moves)
  do {

    #define _APPLY_STEP(AXIS) AXIS ##_APPLY_STEP
    #define _INVERT_STEP_PIN(AXIS) INVERT_## AXIS ##_STEP_PIN

    // Start an active pulse, if Bresenham says so, and update position
    #define PULSE_START(AXIS) do{ \
      delta_error[_AXIS(AXIS)] += advance_dividend[_AXIS(AXIS)]; \
      if (delta_error[_AXIS(AXIS)] >= 0) { \
        _APPLY_STEP(AXIS)(!_INVERT_STEP_PIN(AXIS), 0); \
        count_position[_AXIS(AXIS)] += count_direction[_AXIS(AXIS)]; \
      } \
    }while(0)

    // Stop an active pulse, if any, and adjust error term
    #define PULSE_STOP(AXIS) do { \
      if (delta_error[_AXIS(AXIS)] >= 0) { \
        delta_error[_AXIS(AXIS)] -= advance_divisor; \
        _APPLY_STEP(AXIS)(_INVERT_STEP_PIN(AXIS), 0); \
      } \
    }while(0)

    // Pulse start
    #if HAS_X_STEP
      PULSE_START(X);
    #endif
    #if HAS_Y_STEP
      PULSE_START(Y);
    #endif
    #if HAS_Z_STEP
      PULSE_START(Z);
    #endif

    // Pulse E/Mixing extruders
    #if ENABLED(LIN_ADVANCE)
      // Tick the E axis, correct error term and update position
      delta_error[E_AXIS] += advance_dividend[E_AXIS];
      if (delta_error[E_AXIS] >= 0) {
        count_position[E_AXIS] += count_direction[E_AXIS];
        delta_error[E_AXIS] -= advance_divisor;

        // Don't step E here - But remember the number of steps to perform
        motor_direction(E_AXIS) ? --LA_steps : ++LA_steps;
      }
    #else // !LIN_ADVANCE - use linear interpolation for E also
      #if ENABLED(MIXING_EXTRUDER)

        // Tick the E axis
        delta_error[E_AXIS] += advance_dividend[E_AXIS];
        if (delta_error[E_AXIS] >= 0) {
          count_position[E_AXIS] += count_direction[E_AXIS];
          delta_error[E_AXIS] -= advance_divisor;
        }

        // Tick the counters used for this mix in proper proportion
        MIXING_STEPPERS_LOOP(j) {
          // Step mixing steppers (proportionally)
          delta_error_m[j] += advance_dividend_m[j];
          // Step when the counter goes over zero
          if (delta_error_m[j] >= 0) E_STEP_WRITE(j, !INVERT_E_STEP_PIN);
        }

      #else // !MIXING_EXTRUDER
        PULSE_START(E);
      #endif
    #endif // !LIN_ADVANCE

    #if MINIMUM_STEPPER_PULSE
      // Just wait for the requested pulse duration
      while (HAL_timer_get_count(PULSE_TIMER_NUM) < pulse_end) { /* nada */ }
    #endif

    // Add the delay needed to ensure the maximum driver rate is enforced
    if (signed(added_step_ticks) > 0) pulse_end += hal_timer_t(added_step_ticks);

    // Pulse stop
    #if HAS_X_STEP
      PULSE_STOP(X);
    #endif
    #if HAS_Y_STEP
      PULSE_STOP(Y);
    #endif
    #if HAS_Z_STEP
      PULSE_STOP(Z);
    #endif

    #if DISABLED(LIN_ADVANCE)
      #if ENABLED(MIXING_EXTRUDER)
        MIXING_STEPPERS_LOOP(j) {
          if (delta_error_m[j] >= 0) {
            delta_error_m[j] -= advance_divisor_m;
            E_STEP_WRITE(j, INVERT_E_STEP_PIN);
          }
        }
      #else // !MIXING_EXTRUDER
        PULSE_STOP(E);
      #endif
    #endif // !LIN_ADVANCE

    // Decrement the count of pending pulses to do
    --events_to_do;

    // For minimum pulse time wait after stopping pulses also
    if (events_to_do) {
      // Just wait for the requested pulse duration
      while (HAL_timer_get_count(PULSE_TIMER_NUM) < pulse_end) { /* nada */ }
      #if MINIMUM_STEPPER_PULSE
        // Add to the value, the time that the pulse must be active (to be used on the next loop)
        pulse_end += hal_timer_t(MIN_PULSE_TICKS);
      #endif
    }

  } while (events_to_do);
}

// This is the last half of the stepper interrupt: This one processes and
// properly schedules blocks from the planner. This is executed after creating
// the step pulses, so it is not time critical, as pulses are already done.

uint32_t Stepper::stepper_block_phase_isr() {

  // If no queued movements, just wait 1ms for the next move
  uint32_t interval = (STEPPER_TIMER_RATE / 1000);

  // If there is a current block
  if (current_block) {

    // If current block is finished, reset pointer
    if (step_events_completed >= step_event_count) {
      axis_did_move = 0;
      current_block = NULL;
      planner.discard_current_block();
    }
    else {
      // Step events not completed yet...

      // Are we in acceleration phase ?
      if (step_events_completed <= accelerate_until) { // Calculate new timer value

        #if ENABLED(S_CURVE_ACCELERATION)
          // Get the next speed to use (Jerk limited!)
          uint32_t acc_step_rate =
            acceleration_time < current_block->acceleration_time
              ? _eval_bezier_curve(acceleration_time)
              : current_block->cruise_rate;
        #else
          acc_step_rate = STEP_MULTIPLY(acceleration_time, current_block->acceleration_rate) + current_block->initial_rate;
          NOMORE(acc_step_rate, current_block->nominal_rate);
        #endif

        // acc_step_rate is in steps/second

        // step_rate to timer interval and steps per stepper isr
        interval = calc_timer_interval(acc_step_rate, oversampling_factor, &steps_per_isr);
        acceleration_time += interval;

        #if ENABLED(LIN_ADVANCE)
          if (LA_use_advance_lead) {
            // Wake up eISR on first acceleration loop and fire ISR if final adv_rate is reached
            if (step_events_completed == steps_per_isr || (LA_steps && LA_isr_rate != current_block->advance_speed)) {
              nextAdvanceISR = 0;
              LA_isr_rate = current_block->advance_speed;
            }
          }
          else {
            LA_isr_rate = LA_ADV_NEVER;
            if (LA_steps) nextAdvanceISR = 0;
          }
        #endif // LIN_ADVANCE
      }
      // Are we in Deceleration phase ?
      else if (step_events_completed > decelerate_after) {
        uint32_t step_rate;

        #if ENABLED(S_CURVE_ACCELERATION)
          // If this is the 1st time we process the 2nd half of the trapezoid...
          if (!bezier_2nd_half) {
            // Initialize the BÃ©zier speed curve
            _calc_bezier_curve_coeffs(current_block->cruise_rate, current_block->final_rate, current_block->deceleration_time_inverse);
            bezier_2nd_half = true;
            // The first point starts at cruise rate. Just save evaluation of the BÃ©zier curve
            step_rate = current_block->cruise_rate;
          }
          else {
            // Calculate the next speed to use
            step_rate = deceleration_time < current_block->deceleration_time
              ? _eval_bezier_curve(deceleration_time)
              : current_block->final_rate;
          }
        #else

          // Using the old trapezoidal control
          step_rate = STEP_MULTIPLY(deceleration_time, current_block->acceleration_rate);
          if (step_rate < acc_step_rate) { // Still decelerating?
            step_rate = acc_step_rate - step_rate;
            NOLESS(step_rate, current_block->final_rate);
          }
          else
            step_rate = current_block->final_rate;
        #endif

        // step_rate is in steps/second

        // step_rate to timer interval and steps per stepper isr
        interval = calc_timer_interval(step_rate, oversampling_factor, &steps_per_isr);
        deceleration_time += interval;

        #if ENABLED(LIN_ADVANCE)
          if (LA_use_advance_lead) {
            if (step_events_completed <= decelerate_after + steps_per_isr ||
               (LA_steps && LA_isr_rate != current_block->advance_speed)
            ) {
              nextAdvanceISR = 0; // Wake up eISR on first deceleration loop
              LA_isr_rate = current_block->advance_speed;
            }
          }
          else {
            LA_isr_rate = LA_ADV_NEVER;
            if (LA_steps) nextAdvanceISR = 0;
          }
        #endif // LIN_ADVANCE
      }
      // We must be in cruise phase otherwise
      else {

        #if ENABLED(LIN_ADVANCE)
          // If there are any esteps, fire the next advance_isr "now"
          if (LA_steps && LA_isr_rate != current_block->advance_speed) nextAdvanceISR = 0;
        #endif

        // Calculate the ticks_nominal for this nominal speed, if not done yet
        if (ticks_nominal < 0) {
          // step_rate to timer interval and loops for the nominal speed
          ticks_nominal = calc_timer_interval(current_block->nominal_rate, oversampling_factor, &steps_per_isr);
        }

        // The timer interval is just the nominal value for the nominal speed
        interval = ticks_nominal;
      }
    }
  }

  // If there is no current block at this point, attempt to pop one from the buffer
  // and prepare its movement
  if (!current_block) {

    // Anything in the buffer?
    if ((current_block = planner.get_current_block())) {

      // Sync block? Sync the stepper counts and return
      while (TEST(current_block->flag, BLOCK_BIT_SYNC_POSITION)) {
        _set_position(
          current_block->position[A_AXIS], current_block->position[B_AXIS],
          current_block->position[C_AXIS], current_block->position[E_AXIS]
        );
        planner.discard_current_block();

        // Try to get a new block
        if (!(current_block = planner.get_current_block()))
          return interval; // No more queued movements!
      }

      // Flag all moving axes for proper endstop handling

      #if IS_CORE
        // Define conditions for checking endstops
        #define S_(N) current_block->steps[CORE_AXIS_##N]
        #define D_(N) TEST(current_block->direction_bits, CORE_AXIS_##N)
      #endif

      #if CORE_IS_XY || CORE_IS_XZ
        /**
         * Head direction in -X axis for CoreXY and CoreXZ bots.
         *
         * If steps differ, both axes are moving.
         * If DeltaA == -DeltaB, the movement is only in the 2nd axis (Y or Z, handled below)
         * If DeltaA ==  DeltaB, the movement is only in the 1st axis (X)
         */
        #if ENABLED(COREXY) || ENABLED(COREXZ)
          #define X_CMP ==
        #else
          #define X_CMP !=
        #endif
        #define X_MOVE_TEST ( S_(1) != S_(2) || (S_(1) > 0 && D_(1) X_CMP D_(2)) )
      #else
        #define X_MOVE_TEST !!current_block->steps[A_AXIS]
      #endif

      #if CORE_IS_XY || CORE_IS_YZ
        /**
         * Head direction in -Y axis for CoreXY / CoreYZ bots.
         *
         * If steps differ, both axes are moving
         * If DeltaA ==  DeltaB, the movement is only in the 1st axis (X or Y)
         * If DeltaA == -DeltaB, the movement is only in the 2nd axis (Y or Z)
         */
        #if ENABLED(COREYX) || ENABLED(COREYZ)
          #define Y_CMP ==
        #else
          #define Y_CMP !=
        #endif
        #define Y_MOVE_TEST ( S_(1) != S_(2) || (S_(1) > 0 && D_(1) Y_CMP D_(2)) )
      #else
        #define Y_MOVE_TEST !!current_block->steps[B_AXIS]
      #endif

      #if CORE_IS_XZ || CORE_IS_YZ
        /**
         * Head direction in -Z axis for CoreXZ or CoreYZ bots.
         *
         * If steps differ, both axes are moving
         * If DeltaA ==  DeltaB, the movement is only in the 1st axis (X or Y, already handled above)
         * If DeltaA == -DeltaB, the movement is only in the 2nd axis (Z)
         */
        #if ENABLED(COREZX) || ENABLED(COREZY)
          #define Z_CMP ==
        #else
          #define Z_CMP !=
        #endif
        #define Z_MOVE_TEST ( S_(1) != S_(2) || (S_(1) > 0 && D_(1) Z_CMP D_(2)) )
      #else
        #define Z_MOVE_TEST !!current_block->steps[C_AXIS]
      #endif

      uint8_t axis_bits = 0;
      if (X_MOVE_TEST) SBI(axis_bits, A_AXIS);
      if (Y_MOVE_TEST) SBI(axis_bits, B_AXIS);
      if (Z_MOVE_TEST) SBI(axis_bits, C_AXIS);
      //if (!!current_block->steps[E_AXIS]) SBI(axis_bits, E_AXIS);
      //if (!!current_block->steps[A_AXIS]) SBI(axis_bits, X_HEAD);
      //if (!!current_block->steps[B_AXIS]) SBI(axis_bits, Y_HEAD);
      //if (!!current_block->steps[C_AXIS]) SBI(axis_bits, Z_HEAD);
      axis_did_move = axis_bits;

      // No acceleration / deceleration time elapsed so far
      acceleration_time = deceleration_time = 0;

      uint8_t oversampling = 0;                         // Assume we won't use it

      #if ENABLED(ADAPTIVE_STEP_SMOOTHING)
        // At this point, we must decide if we can use Stepper movement axis smoothing.
        uint32_t max_rate = current_block->nominal_rate;  // Get the maximum rate (maximum event speed)
        while (max_rate < MIN_STEP_ISR_FREQUENCY) {
          max_rate <<= 1;
          if (max_rate >= MAX_STEP_ISR_FREQUENCY_1X) break;
          ++oversampling;
        }
        oversampling_factor = oversampling;
      #endif

      // Based on the oversampling factor, do the calculations
      step_event_count = current_block->step_event_count << oversampling;

      // Initialize Bresenham delta errors to 1/2
      delta_error[X_AXIS] = delta_error[Y_AXIS] = delta_error[Z_AXIS] = delta_error[E_AXIS] = -int32_t(step_event_count);

      // Calculate Bresenham dividends
      advance_dividend[X_AXIS] = current_block->steps[X_AXIS] << 1;
      advance_dividend[Y_AXIS] = current_block->steps[Y_AXIS] << 1;
      advance_dividend[Z_AXIS] = current_block->steps[Z_AXIS] << 1;
      advance_dividend[E_AXIS] = current_block->steps[E_AXIS] << 1;

      // Calculate Bresenham divisor
      advance_divisor = step_event_count << 1;

      // No step events completed so far
      step_events_completed = 0;

      // Compute the acceleration and deceleration points
      accelerate_until = current_block->accelerate_until << oversampling;
      decelerate_after = current_block->decelerate_after << oversampling;

      #if ENABLED(MIXING_EXTRUDER)
        const uint32_t e_steps = (
          #if ENABLED(LIN_ADVANCE)
            current_block->steps[E_AXIS]
          #else
            step_event_count
          #endif
        );
        MIXING_STEPPERS_LOOP(i) {
          delta_error_m[i] = -int32_t(e_steps);
          advance_dividend_m[i] = current_block->mix_steps[i] << 1;
        }
        advance_divisor_m = e_steps << 1;
      #else
        active_extruder = current_block->active_extruder;
      #endif

      // Initialize the trapezoid generator from the current block.
      #if ENABLED(LIN_ADVANCE)
        #if DISABLED(MIXING_EXTRUDER) && E_STEPPERS > 1
          // If the now active extruder wasn't in use during the last move, its pressure is most likely gone.
          if (active_extruder != last_moved_extruder) LA_current_adv_steps = 0;
        #endif

        if ((LA_use_advance_lead = current_block->use_advance_lead)) {
          LA_final_adv_steps = current_block->final_adv_steps;
          LA_max_adv_steps = current_block->max_adv_steps;
        }
      #endif

      if (current_block->direction_bits != last_direction_bits
        #if DISABLED(MIXING_EXTRUDER)
          || active_extruder != last_moved_extruder
        #endif
      ) {
        last_direction_bits = current_block->direction_bits;
        #if DISABLED(MIXING_EXTRUDER)
          last_moved_extruder = active_extruder;
        #endif
        set_directions();
      }

      // At this point, we must ensure the movement about to execute isn't
      // trying to force the head against a limit switch. If using interrupt-
      // driven change detection, and already against a limit then no call to
      // the endstop_triggered method will be done and the movement will be
      // done against the endstop. So, check the limits here: If the movement
      // is against the limits, the block will be marked as to be killed, and
      // on the next call to this ISR, will be discarded.
      endstops.update();

      #if ENABLED(Z_LATE_ENABLE)
        // If delayed Z enable, enable it now. This option will severely interfere with
        // timing between pulses when chaining motion between blocks, and it could lead
        // to lost steps in both X and Y axis, so avoid using it unless strictly necessary!!
        if (current_block->steps[Z_AXIS]) enable_Z();
      #endif

      // Mark the time_nominal as not calculated yet
      ticks_nominal = -1;

      #if DISABLED(S_CURVE_ACCELERATION)
        // Set as deceleration point the initial rate of the block
        acc_step_rate = current_block->initial_rate;
      #endif

      #if ENABLED(S_CURVE_ACCELERATION)
        // Initialize the BÃ©zier speed curve
        _calc_bezier_curve_coeffs(current_block->initial_rate, current_block->cruise_rate, current_block->acceleration_time_inverse);
        // We haven't started the 2nd half of the trapezoid
        bezier_2nd_half = false;
      #endif

      // Calculate the initial timer interval
      interval = calc_timer_interval(current_block->initial_rate, oversampling_factor, &steps_per_isr);
    }
  }

  // Return the interval to wait
  return interval;
}

#if ENABLED(LIN_ADVANCE)

  // Timer interrupt for E. LA_steps is set in the main routine
  uint32_t Stepper::advance_isr() {
    uint32_t interval;

    if (LA_use_advance_lead) {
      if (step_events_completed > decelerate_after && LA_current_adv_steps > LA_final_adv_steps) {
        LA_steps--;
        LA_current_adv_steps--;
        interval = LA_isr_rate;
      }
      else if (step_events_completed < decelerate_after && LA_current_adv_steps < LA_max_adv_steps) {
             //step_events_completed <= (uint32_t)accelerate_until) {
        LA_steps++;
        LA_current_adv_steps++;
        interval = LA_isr_rate;
      }
      else
        interval = LA_isr_rate = LA_ADV_NEVER;
    }
    else
      interval = LA_ADV_NEVER;

      #if ENABLED(MIXING_EXTRUDER)
        if (LA_steps >= 0)
          MIXING_STEPPERS_LOOP(j) NORM_E_DIR(j);
        else
          MIXING_STEPPERS_LOOP(j) REV_E_DIR(j);
      #else
        if (LA_steps >= 0)
          NORM_E_DIR(active_extruder);
        else
          REV_E_DIR(active_extruder);
      #endif

    // Get the timer count and estimate the end of the pulse
    hal_timer_t pulse_end = HAL_timer_get_count(PULSE_TIMER_NUM) + hal_timer_t(MIN_PULSE_TICKS);

    const hal_timer_t added_step_ticks = hal_timer_t(ADDED_STEP_TICKS);

    // Step E stepper if we have steps
    while (LA_steps) {

      // Set the STEP pulse ON
      #if ENABLED(MIXING_EXTRUDER)
        MIXING_STEPPERS_LOOP(j) {
          // Step mixing steppers (proportionally)
          delta_error_m[j] += advance_dividend_m[j];
          // Step when the counter goes over zero
          if (delta_error_m[j] >= 0) E_STEP_WRITE(j, !INVERT_E_STEP_PIN);
        }
      #else
        E_STEP_WRITE(active_extruder, !INVERT_E_STEP_PIN);
      #endif

      // Enforce a minimum duration for STEP pulse ON
      #if MINIMUM_STEPPER_PULSE
        // Just wait for the requested pulse duration
        while (HAL_timer_get_count(PULSE_TIMER_NUM) < pulse_end) { /* nada */ }
      #endif

      // Add the delay needed to ensure the maximum driver rate is enforced
      if (signed(added_step_ticks) > 0) pulse_end += hal_timer_t(added_step_ticks);

      LA_steps < 0 ? ++LA_steps : --LA_steps;

      // Set the STEP pulse OFF
      #if ENABLED(MIXING_EXTRUDER)
        MIXING_STEPPERS_LOOP(j) {
          if (delta_error_m[j] >= 0) {
            delta_error_m[j] -= advance_divisor_m;
            E_STEP_WRITE(j, INVERT_E_STEP_PIN);
          }
        }
      #else
        E_STEP_WRITE(active_extruder, INVERT_E_STEP_PIN);
      #endif

      // For minimum pulse time wait before looping
      // Just wait for the requested pulse duration
      if (LA_steps) {
        while (HAL_timer_get_count(PULSE_TIMER_NUM) < pulse_end) { /* nada */ }
        #if MINIMUM_STEPPER_PULSE
          // Add to the value, the time that the pulse must be active (to be used on the next loop)
          pulse_end += hal_timer_t(MIN_PULSE_TICKS);
        #endif
      }
    } // LA_steps

    return interval;
  }
#endif // LIN_ADVANCE

// Check if the given block is busy or not - Must not be called from ISR contexts
// The current_block could change in the middle of the read by an Stepper ISR, so
// we must explicitly prevent that!
bool Stepper::is_block_busy(const block_t* const block) {
  #define sw_barrier() asm volatile("": : :"memory");

  // Keep reading until 2 consecutive reads return the same value,
  // meaning there was no update in-between caused by an interrupt.
  // This works because stepper ISRs happen at a slower rate than
  // successive reads of a variable, so 2 consecutive reads with
  // the same value means no interrupt updated it.
  block_t* vold, *vnew = current_block;
  sw_barrier();
  do {
    vold = vnew;
    vnew = current_block;
    sw_barrier();
  } while (vold != vnew);

  // Return if the block is busy or not
  return block == vnew;
}

void Stepper::init() {

  // Init Digipot Motor Current
  #if HAS_DIGIPOTSS || HAS_MOTOR_CURRENT_PWM
    digipot_init();
  #endif

  // Init Microstepping Pins
  #if HAS_MICROSTEPS
    microstep_init();
  #endif

  // Init Dir Pins
  #if HAS_X_DIR
    X_DIR_INIT;
  #endif
  #if HAS_X2_DIR
    X2_DIR_INIT;
  #endif
  #if HAS_Y_DIR
    Y_DIR_INIT;
    #if ENABLED(Y_DUAL_STEPPER_DRIVERS) && HAS_Y2_DIR
      Y2_DIR_INIT;
    #endif
  #endif
  #if HAS_Z_DIR
    Z_DIR_INIT;
    #if ENABLED(Z_DUAL_STEPPER_DRIVERS) && HAS_Z2_DIR
      Z2_DIR_INIT;
    #endif
  #endif
  #if HAS_E0_DIR
    E0_DIR_INIT;
  #endif
  #if HAS_E1_DIR
    E1_DIR_INIT;
  #endif
  #if HAS_E2_DIR
    E2_DIR_INIT;
  #endif
  #if HAS_E3_DIR
    E3_DIR_INIT;
  #endif
  #if HAS_E4_DIR
    E4_DIR_INIT;
  #endif

  // Init Enable Pins - steppers default to disabled.
  #if HAS_X_ENABLE
    X_ENABLE_INIT;
    if (!X_ENABLE_ON) X_ENABLE_WRITE(HIGH);
    #if (ENABLED(DUAL_X_CARRIAGE) || ENABLED(X_DUAL_STEPPER_DRIVERS)) && HAS_X2_ENABLE
      X2_ENABLE_INIT;
      if (!X_ENABLE_ON) X2_ENABLE_WRITE(HIGH);
    #endif
  #endif
  #if HAS_Y_ENABLE
    Y_ENABLE_INIT;
    if (!Y_ENABLE_ON) Y_ENABLE_WRITE(HIGH);
    #if ENABLED(Y_DUAL_STEPPER_DRIVERS) && HAS_Y2_ENABLE
      Y2_ENABLE_INIT;
      if (!Y_ENABLE_ON) Y2_ENABLE_WRITE(HIGH);
    #endif
  #endif
  #if HAS_Z_ENABLE
    Z_ENABLE_INIT;
    if (!Z_ENABLE_ON) Z_ENABLE_WRITE(HIGH);
    #if ENABLED(Z_DUAL_STEPPER_DRIVERS) && HAS_Z2_ENABLE
      Z2_ENABLE_INIT;
      if (!Z_ENABLE_ON) Z2_ENABLE_WRITE(HIGH);
    #endif
  #endif
  #if HAS_E0_ENABLE
    E0_ENABLE_INIT;
    if (!E_ENABLE_ON) E0_ENABLE_WRITE(HIGH);
  #endif
  #if HAS_E1_ENABLE
    E1_ENABLE_INIT;
    if (!E_ENABLE_ON) E1_ENABLE_WRITE(HIGH);
  #endif
  #if HAS_E2_ENABLE
    E2_ENABLE_INIT;
    if (!E_ENABLE_ON) E2_ENABLE_WRITE(HIGH);
  #endif
  #if HAS_E3_ENABLE
    E3_ENABLE_INIT;
    if (!E_ENABLE_ON) E3_ENABLE_WRITE(HIGH);
  #endif
  #if HAS_E4_ENABLE
    E4_ENABLE_INIT;
    if (!E_ENABLE_ON) E4_ENABLE_WRITE(HIGH);
  #endif

  #define _STEP_INIT(AXIS) AXIS ##_STEP_INIT
  #define _WRITE_STEP(AXIS, HIGHLOW) AXIS ##_STEP_WRITE(HIGHLOW)
  #define _DISABLE(AXIS) disable_## AXIS()

  #define AXIS_INIT(AXIS, PIN) \
    _STEP_INIT(AXIS); \
    _WRITE_STEP(AXIS, _INVERT_STEP_PIN(PIN)); \
    _DISABLE(AXIS)

  #define E_AXIS_INIT(NUM) AXIS_INIT(E## NUM, E)

  // Init Step Pins
  #if HAS_X_STEP
    #if ENABLED(X_DUAL_STEPPER_DRIVERS) || ENABLED(DUAL_X_CARRIAGE)
      X2_STEP_INIT;
      X2_STEP_WRITE(INVERT_X_STEP_PIN);
    #endif
    AXIS_INIT(X, X);
  #endif

  #if HAS_Y_STEP
    #if ENABLED(Y_DUAL_STEPPER_DRIVERS)
      Y2_STEP_INIT;
      Y2_STEP_WRITE(INVERT_Y_STEP_PIN);
    #endif
    AXIS_INIT(Y, Y);
  #endif

  #if HAS_Z_STEP
    #if ENABLED(Z_DUAL_STEPPER_DRIVERS)
      Z2_STEP_INIT;
      Z2_STEP_WRITE(INVERT_Z_STEP_PIN);
    #endif
    AXIS_INIT(Z, Z);
  #endif

  #if E_STEPPERS > 0 && HAS_E0_STEP
    E_AXIS_INIT(0);
  #endif
  #if E_STEPPERS > 1 && HAS_E1_STEP
    E_AXIS_INIT(1);
  #endif
  #if E_STEPPERS > 2 && HAS_E2_STEP
    E_AXIS_INIT(2);
  #endif
  #if E_STEPPERS > 3 && HAS_E3_STEP
    E_AXIS_INIT(3);
  #endif
  #if E_STEPPERS > 4 && HAS_E4_STEP
    E_AXIS_INIT(4);
  #endif

  // Init Stepper ISR to 122 Hz for quick starting
  HAL_timer_start(STEP_TIMER_NUM, 122); // OCR1A = 0x4000

  ENABLE_STEPPER_DRIVER_INTERRUPT();

  endstops.enable(true); // Start with endstops active. After homing they can be disabled
  sei();

  set_directions(); // Init directions to last_direction_bits = 0
}

/**
 * Set the stepper positions directly in steps
 *
 * The input is based on the typical per-axis XYZ steps.
 * For CORE machines XYZ needs to be translated to ABC.
 *
 * This allows get_axis_position_mm to correctly
 * derive the current XYZ position later on.
 */
void Stepper::_set_position(const int32_t &a, const int32_t &b, const int32_t &c, const int32_t &e) {
  #if CORE_IS_XY
    // corexy positioning
    // these equations follow the form of the dA and dB equations on http://www.corexy.com/theory.html
    count_position[A_AXIS] = a + b;
    count_position[B_AXIS] = CORESIGN(a - b);
    count_position[Z_AXIS] = c;
  #elif CORE_IS_XZ
    // corexz planning
    count_position[A_AXIS] = a + c;
    count_position[Y_AXIS] = b;
    count_position[C_AXIS] = CORESIGN(a - c);
  #elif CORE_IS_YZ
    // coreyz planning
    count_position[X_AXIS] = a;
    count_position[B_AXIS] = b + c;
    count_position[C_AXIS] = CORESIGN(b - c);
  #else
    // default non-h-bot planning
    count_position[X_AXIS] = a;
    count_position[Y_AXIS] = b;
    count_position[Z_AXIS] = c;
  #endif
  count_position[E_AXIS] = e;
}

/**
 * Get a stepper's position in steps.
 */
int32_t Stepper::position(const AxisEnum axis) {
  const bool was_enabled = STEPPER_ISR_ENABLED();
  if (was_enabled) DISABLE_STEPPER_DRIVER_INTERRUPT();

  const int32_t v = count_position[axis];

  if (was_enabled) ENABLE_STEPPER_DRIVER_INTERRUPT();
  return v;
}

// Signal endstops were triggered - This function can be called from
// an ISR context  (Temperature, Stepper or limits ISR), so we must
// be very careful here. If the interrupt being preempted was the
// Stepper ISR (this CAN happen with the endstop limits ISR) then
// when the stepper ISR resumes, we must be very sure that the movement
// is properly cancelled
void Stepper::endstop_triggered(const AxisEnum axis) {

  const bool was_enabled = STEPPER_ISR_ENABLED();
  if (was_enabled) DISABLE_STEPPER_DRIVER_INTERRUPT();

  #if IS_CORE

    endstops_trigsteps[axis] = 0.5f * (
      axis == CORE_AXIS_2 ? CORESIGN(count_position[CORE_AXIS_1] - count_position[CORE_AXIS_2])
                          : count_position[CORE_AXIS_1] + count_position[CORE_AXIS_2]
    );

  #else // !COREXY && !COREXZ && !COREYZ

    endstops_trigsteps[axis] = count_position[axis];

  #endif // !COREXY && !COREXZ && !COREYZ

  // Discard the rest of the move if there is a current block
  quick_stop();

  if (was_enabled) ENABLE_STEPPER_DRIVER_INTERRUPT();
}

int32_t Stepper::triggered_position(const AxisEnum axis) {
  const bool was_enabled = STEPPER_ISR_ENABLED();
  if (was_enabled) DISABLE_STEPPER_DRIVER_INTERRUPT();

  const int32_t v = endstops_trigsteps[axis];

  if (was_enabled) ENABLE_STEPPER_DRIVER_INTERRUPT();

  return v;
}

void Stepper::report_positions() {

  // Protect the access to the position.
  const bool was_enabled = STEPPER_ISR_ENABLED();
  if (was_enabled) DISABLE_STEPPER_DRIVER_INTERRUPT();

  const int32_t xpos = count_position[X_AXIS],
                ypos = count_position[Y_AXIS],
                zpos = count_position[Z_AXIS];

  if (was_enabled) ENABLE_STEPPER_DRIVER_INTERRUPT();

  #if CORE_IS_XY || CORE_IS_XZ || IS_DELTA || IS_SCARA
    SERIAL_PROTOCOLPGM(MSG_COUNT_A);
  #else
    SERIAL_PROTOCOLPGM(MSG_COUNT_X);
  #endif
  SERIAL_PROTOCOL(xpos);

  #if CORE_IS_XY || CORE_IS_YZ || IS_DELTA || IS_SCARA
    SERIAL_PROTOCOLPGM(" B:");
  #else
    SERIAL_PROTOCOLPGM(" Y:");
  #endif
  SERIAL_PROTOCOL(ypos);

  #if CORE_IS_XZ || CORE_IS_YZ || IS_DELTA
    SERIAL_PROTOCOLPGM(" C:");
  #else
    SERIAL_PROTOCOLPGM(" Z:");
  #endif
  SERIAL_PROTOCOL(zpos);

  SERIAL_EOL();
}

#if ENABLED(BABYSTEPPING)

  #if MINIMUM_STEPPER_PULSE
    #define STEP_PULSE_CYCLES ((MINIMUM_STEPPER_PULSE) * CYCLES_PER_MICROSECOND)
  #else
    #define STEP_PULSE_CYCLES 0
  #endif

  #if ENABLED(DELTA)
    #define CYCLES_EATEN_BABYSTEP (2 * 15)
  #else
    #define CYCLES_EATEN_BABYSTEP 0
  #endif
  #define EXTRA_CYCLES_BABYSTEP (STEP_PULSE_CYCLES - (CYCLES_EATEN_BABYSTEP))

  #define _ENABLE(AXIS) enable_## AXIS()
  #define _READ_DIR(AXIS) AXIS ##_DIR_READ
  #define _INVERT_DIR(AXIS) INVERT_## AXIS ##_DIR
  #define _APPLY_DIR(AXIS, INVERT) AXIS ##_APPLY_DIR(INVERT, true)

  #if EXTRA_CYCLES_BABYSTEP > 20
    #define _SAVE_START const hal_timer_t pulse_start = HAL_timer_get_count(PULSE_TIMER_NUM)
    #define _PULSE_WAIT while (EXTRA_CYCLES_BABYSTEP > (uint32_t)(HAL_timer_get_count(PULSE_TIMER_NUM) - pulse_start) * (PULSE_TIMER_PRESCALE)) { /* nada */ }
  #else
    #define _SAVE_START NOOP
    #if EXTRA_CYCLES_BABYSTEP > 0
      #define _PULSE_WAIT DELAY_NS(EXTRA_CYCLES_BABYSTEP * NANOSECONDS_PER_CYCLE)
    #elif STEP_PULSE_CYCLES > 0
      #define _PULSE_WAIT NOOP
    #elif ENABLED(DELTA)
      #define _PULSE_WAIT DELAY_US(2);
    #else
      #define _PULSE_WAIT DELAY_US(4);
    #endif
  #endif

  #define BABYSTEP_AXIS(AXIS, INVERT, DIR) {            \
      const uint8_t old_dir = _READ_DIR(AXIS);          \
      _ENABLE(AXIS);                                    \
      _APPLY_DIR(AXIS, _INVERT_DIR(AXIS)^DIR^INVERT);   \
      DELAY_NS(MINIMUM_STEPPER_DIR_DELAY);              \
      _SAVE_START;                                      \
      _APPLY_STEP(AXIS)(!_INVERT_STEP_PIN(AXIS), true); \
      _PULSE_WAIT;                                      \
      _APPLY_STEP(AXIS)(_INVERT_STEP_PIN(AXIS), true);  \
      _APPLY_DIR(AXIS, old_dir);                        \
    }

  // MUST ONLY BE CALLED BY AN ISR,
  // No other ISR should ever interrupt this!
  void Stepper::babystep(const AxisEnum axis, const bool direction) {
    cli();

    switch (axis) {

      #if ENABLED(BABYSTEP_XY)

        case X_AXIS:
          #if CORE_IS_XY
            BABYSTEP_AXIS(X, false, direction);
            BABYSTEP_AXIS(Y, false, direction);
          #elif CORE_IS_XZ
            BABYSTEP_AXIS(X, false, direction);
            BABYSTEP_AXIS(Z, false, direction);
          #else
            BABYSTEP_AXIS(X, false, direction);
          #endif
          break;

        case Y_AXIS:
          #if CORE_IS_XY
            BABYSTEP_AXIS(X, false, direction);
            BABYSTEP_AXIS(Y, false, direction^(CORESIGN(1)<0));
          #elif CORE_IS_YZ
            BABYSTEP_AXIS(Y, false, direction);
            BABYSTEP_AXIS(Z, false, direction^(CORESIGN(1)<0));
          #else
            BABYSTEP_AXIS(Y, false, direction);
          #endif
          break;

      #endif

      case Z_AXIS: {

        #if CORE_IS_XZ
          BABYSTEP_AXIS(X, BABYSTEP_INVERT_Z, direction);
          BABYSTEP_AXIS(Z, BABYSTEP_INVERT_Z, direction^(CORESIGN(1)<0));

        #elif CORE_IS_YZ
          BABYSTEP_AXIS(Y, BABYSTEP_INVERT_Z, direction);
          BABYSTEP_AXIS(Z, BABYSTEP_INVERT_Z, direction^(CORESIGN(1)<0));

        #elif DISABLED(DELTA)
          BABYSTEP_AXIS(Z, BABYSTEP_INVERT_Z, direction);

        #else // DELTA

          const bool z_direction = direction ^ BABYSTEP_INVERT_Z;

          enable_X();
          enable_Y();
          enable_Z();

          const uint8_t old_x_dir_pin = X_DIR_READ,
                        old_y_dir_pin = Y_DIR_READ,
                        old_z_dir_pin = Z_DIR_READ;

          X_DIR_WRITE(INVERT_X_DIR ^ z_direction);
          Y_DIR_WRITE(INVERT_Y_DIR ^ z_direction);
          Z_DIR_WRITE(INVERT_Z_DIR ^ z_direction);

          #if MINIMUM_STEPPER_DIR_DELAY > 0
            DELAY_NS(MINIMUM_STEPPER_DIR_DELAY);
          #endif

          _SAVE_START;

          X_STEP_WRITE(!INVERT_X_STEP_PIN);
          Y_STEP_WRITE(!INVERT_Y_STEP_PIN);
          Z_STEP_WRITE(!INVERT_Z_STEP_PIN);

          _PULSE_WAIT;

          X_STEP_WRITE(INVERT_X_STEP_PIN);
          Y_STEP_WRITE(INVERT_Y_STEP_PIN);
          Z_STEP_WRITE(INVERT_Z_STEP_PIN);

          // Restore direction bits
          X_DIR_WRITE(old_x_dir_pin);
          Y_DIR_WRITE(old_y_dir_pin);
          Z_DIR_WRITE(old_z_dir_pin);

        #endif

      } break;

      default: break;
    }
    sei();
  }

#endif // BABYSTEPPING

/**
 * Software-controlled Stepper Motor Current
 */

#if HAS_DIGIPOTSS

  // From Arduino DigitalPotControl example
  void Stepper::digitalPotWrite(const int16_t address, const int16_t value) {
    WRITE(DIGIPOTSS_PIN, LOW);  // Take the SS pin low to select the chip
    SPI.transfer(address);      // Send the address and value via SPI
    SPI.transfer(value);
    WRITE(DIGIPOTSS_PIN, HIGH); // Take the SS pin high to de-select the chip
    //delay(10);
  }

#endif // HAS_DIGIPOTSS

#if HAS_MOTOR_CURRENT_PWM

  void Stepper::refresh_motor_power() {
    for (uint8_t i = 0; i < COUNT(motor_current_setting); ++i) {
      switch (i) {
        #if PIN_EXISTS(MOTOR_CURRENT_PWM_XY)
          case 0:
        #endif
        #if PIN_EXISTS(MOTOR_CURRENT_PWM_Z)
          case 1:
        #endif
        #if PIN_EXISTS(MOTOR_CURRENT_PWM_E)
          case 2:
        #endif
            digipot_current(i, motor_current_setting[i]);
        default: break;
      }
    }
  }

#endif // HAS_MOTOR_CURRENT_PWM

#if HAS_DIGIPOTSS || HAS_MOTOR_CURRENT_PWM

  void Stepper::digipot_current(const uint8_t driver, const int current) {

    #if HAS_DIGIPOTSS

      const uint8_t digipot_ch[] = DIGIPOT_CHANNELS;
      digitalPotWrite(digipot_ch[driver], current);

    #elif HAS_MOTOR_CURRENT_PWM

      if (WITHIN(driver, 0, 2))
        motor_current_setting[driver] = current; // update motor_current_setting

      #define _WRITE_CURRENT_PWM(P) analogWrite(MOTOR_CURRENT_PWM_## P ##_PIN, 255L * current / (MOTOR_CURRENT_PWM_RANGE))
      switch (driver) {
        #if PIN_EXISTS(MOTOR_CURRENT_PWM_XY)
          case 0: _WRITE_CURRENT_PWM(XY); break;
        #endif
        #if PIN_EXISTS(MOTOR_CURRENT_PWM_Z)
          case 1: _WRITE_CURRENT_PWM(Z); break;
        #endif
        #if PIN_EXISTS(MOTOR_CURRENT_PWM_E)
          case 2: _WRITE_CURRENT_PWM(E); break;
        #endif
      }
    #endif
  }

  void Stepper::digipot_init() {

    #if HAS_DIGIPOTSS

      static const uint8_t digipot_motor_current[] = DIGIPOT_MOTOR_CURRENT;

      SPI.begin();
      SET_OUTPUT(DIGIPOTSS_PIN);

      for (uint8_t i = 0; i < COUNT(digipot_motor_current); i++) {
        //digitalPotWrite(digipot_ch[i], digipot_motor_current[i]);
        digipot_current(i, digipot_motor_current[i]);
      }

    #elif HAS_MOTOR_CURRENT_PWM

      #if PIN_EXISTS(MOTOR_CURRENT_PWM_XY)
        SET_OUTPUT(MOTOR_CURRENT_PWM_XY_PIN);
      #endif
      #if PIN_EXISTS(MOTOR_CURRENT_PWM_Z)
        SET_OUTPUT(MOTOR_CURRENT_PWM_Z_PIN);
      #endif
      #if PIN_EXISTS(MOTOR_CURRENT_PWM_E)
        SET_OUTPUT(MOTOR_CURRENT_PWM_E_PIN);
      #endif

      refresh_motor_power();

      // Set Timer5 to 31khz so the PWM of the motor power is as constant as possible. (removes a buzzing noise)
      SET_CS5(PRESCALER_1);

    #endif
  }

#endif

#if HAS_MICROSTEPS

  /**
   * Software-controlled Microstepping
   */

  void Stepper::microstep_init() {
    SET_OUTPUT(X_MS1_PIN);
    SET_OUTPUT(X_MS2_PIN);
    #if HAS_Y_MICROSTEPS
      SET_OUTPUT(Y_MS1_PIN);
      SET_OUTPUT(Y_MS2_PIN);
    #endif
    #if HAS_Z_MICROSTEPS
      SET_OUTPUT(Z_MS1_PIN);
      SET_OUTPUT(Z_MS2_PIN);
    #endif
    #if HAS_E0_MICROSTEPS
      SET_OUTPUT(E0_MS1_PIN);
      SET_OUTPUT(E0_MS2_PIN);
    #endif
    #if HAS_E1_MICROSTEPS
      SET_OUTPUT(E1_MS1_PIN);
      SET_OUTPUT(E1_MS2_PIN);
    #endif
    #if HAS_E2_MICROSTEPS
      SET_OUTPUT(E2_MS1_PIN);
      SET_OUTPUT(E2_MS2_PIN);
    #endif
    #if HAS_E3_MICROSTEPS
      SET_OUTPUT(E3_MS1_PIN);
      SET_OUTPUT(E3_MS2_PIN);
    #endif
    #if HAS_E4_MICROSTEPS
      SET_OUTPUT(E4_MS1_PIN);
      SET_OUTPUT(E4_MS2_PIN);
    #endif
    static const uint8_t microstep_modes[] = MICROSTEP_MODES;
    for (uint16_t i = 0; i < COUNT(microstep_modes); i++)
      microstep_mode(i, microstep_modes[i]);
  }

  void Stepper::microstep_ms(const uint8_t driver, const int8_t ms1, const int8_t ms2) {
    if (ms1 >= 0) switch (driver) {
      case 0: WRITE(X_MS1_PIN, ms1); break;
      #if HAS_Y_MICROSTEPS
        case 1: WRITE(Y_MS1_PIN, ms1); break;
      #endif
      #if HAS_Z_MICROSTEPS
        case 2: WRITE(Z_MS1_PIN, ms1); break;
      #endif
      #if HAS_E0_MICROSTEPS
        case 3: WRITE(E0_MS1_PIN, ms1); break;
      #endif
      #if HAS_E1_MICROSTEPS
        case 4: WRITE(E1_MS1_PIN, ms1); break;
      #endif
      #if HAS_E2_MICROSTEPS
        case 5: WRITE(E2_MS1_PIN, ms1); break;
      #endif
      #if HAS_E3_MICROSTEPS
        case 6: WRITE(E3_MS1_PIN, ms1); break;
      #endif
      #if HAS_E4_MICROSTEPS
        case 7: WRITE(E4_MS1_PIN, ms1); break;
      #endif
    }
    if (ms2 >= 0) switch (driver) {
      case 0: WRITE(X_MS2_PIN, ms2); break;
      #if HAS_Y_MICROSTEPS
        case 1: WRITE(Y_MS2_PIN, ms2); break;
      #endif
      #if HAS_Z_MICROSTEPS
        case 2: WRITE(Z_MS2_PIN, ms2); break;
      #endif
      #if HAS_E0_MICROSTEPS
        case 3: WRITE(E0_MS2_PIN, ms2); break;
      #endif
      #if HAS_E1_MICROSTEPS
        case 4: WRITE(E1_MS2_PIN, ms2); break;
      #endif
      #if HAS_E2_MICROSTEPS
        case 5: WRITE(E2_MS2_PIN, ms2); break;
      #endif
      #if HAS_E3_MICROSTEPS
        case 6: WRITE(E3_MS2_PIN, ms2); break;
      #endif
      #if HAS_E4_MICROSTEPS
        case 7: WRITE(E4_MS2_PIN, ms2); break;
      #endif
    }
  }

  void Stepper::microstep_mode(const uint8_t driver, const uint8_t stepping_mode) {
    switch (stepping_mode) {
      case 1: microstep_ms(driver, MICROSTEP1); break;
      #if ENABLED(HEROIC_STEPPER_DRIVERS)
        case 128: microstep_ms(driver, MICROSTEP128); break;
      #else
        case 2: microstep_ms(driver, MICROSTEP2); break;
        case 4: microstep_ms(driver, MICROSTEP4); break;
      #endif
      case 8: microstep_ms(driver, MICROSTEP8); break;
      case 16: microstep_ms(driver, MICROSTEP16); break;
      default: SERIAL_ERROR_START(); SERIAL_ERRORLNPGM("Microsteps unavailable"); break;
    }
  }

  void Stepper::microstep_readings() {
    SERIAL_PROTOCOLLNPGM("MS1,MS2 Pins");
    SERIAL_PROTOCOLPGM("X: ");
    SERIAL_PROTOCOL(READ(X_MS1_PIN));
    SERIAL_PROTOCOLLN(READ(X_MS2_PIN));
    #if HAS_Y_MICROSTEPS
      SERIAL_PROTOCOLPGM("Y: ");
      SERIAL_PROTOCOL(READ(Y_MS1_PIN));
      SERIAL_PROTOCOLLN(READ(Y_MS2_PIN));
    #endif
    #if HAS_Z_MICROSTEPS
      SERIAL_PROTOCOLPGM("Z: ");
      SERIAL_PROTOCOL(READ(Z_MS1_PIN));
      SERIAL_PROTOCOLLN(READ(Z_MS2_PIN));
    #endif
    #if HAS_E0_MICROSTEPS
      SERIAL_PROTOCOLPGM("E0: ");
      SERIAL_PROTOCOL(READ(E0_MS1_PIN));
      SERIAL_PROTOCOLLN(READ(E0_MS2_PIN));
    #endif
    #if HAS_E1_MICROSTEPS
      SERIAL_PROTOCOLPGM("E1: ");
      SERIAL_PROTOCOL(READ(E1_MS1_PIN));
      SERIAL_PROTOCOLLN(READ(E1_MS2_PIN));
    #endif
    #if HAS_E2_MICROSTEPS
      SERIAL_PROTOCOLPGM("E2: ");
      SERIAL_PROTOCOL(READ(E2_MS1_PIN));
      SERIAL_PROTOCOLLN(READ(E2_MS2_PIN));
    #endif
    #if HAS_E3_MICROSTEPS
      SERIAL_PROTOCOLPGM("E3: ");
      SERIAL_PROTOCOL(READ(E3_MS1_PIN));
      SERIAL_PROTOCOLLN(READ(E3_MS2_PIN));
    #endif
    #if HAS_E4_MICROSTEPS
      SERIAL_PROTOCOLPGM("E4: ");
      SERIAL_PROTOCOL(READ(E4_MS1_PIN));
      SERIAL_PROTOCOLLN(READ(E4_MS2_PIN));
    #endif
  }

#endif // HAS_MICROSTEPS
