MarlinFirmware/Marlin/src/module/stepper.h

/**
 * Marlin 3D Printer Firmware
 * Copyright (c) 2020 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 <https://www.gnu.org/licenses/>.
 *
 */
#pragma once

/**
 * stepper.h - stepper motor driver: executes motion plans of planner.c using the stepper motors
 * 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 <https://www.gnu.org/licenses/>.
 */

#include "../inc/MarlinConfig.h"

#include "planner.h"
#include "stepper/indirection.h"
#ifdef __AVR__
  #include "speed_lookuptable.h"
#endif

// Disable multiple steps per ISR
//#define DISABLE_MULTI_STEPPING

//
// Estimate the amount of time the Stepper ISR will take to execute
//

/**
 * The method of calculating these cycle-constants is unclear.
 * Most of them are no longer used directly for pulse timing, and exist
 * only to estimate a maximum step rate based on the user's configuration.
 * As 32-bit processors continue to diverge, maintaining cycle counts
 * will become increasingly difficult and error-prone.
 */

#ifdef CPU_32_BIT
  /**
   * Duration of START_TIMED_PULSE
   *
   * ...as measured on an LPC1768 with a scope and converted to cycles.
   * Not applicable to other 32-bit processors, but as long as others
   * take longer, pulses will be longer. For example the SKR Pro
   * (stm32f407zgt6) requires ~60 cyles.
   */
  #define TIMER_READ_ADD_AND_STORE_CYCLES 34UL

  // The base ISR takes 792 cycles
  #define ISR_BASE_CYCLES  792UL

  // Linear advance base time is 64 cycles
  #if ENABLED(LIN_ADVANCE)
    #define ISR_LA_BASE_CYCLES 64UL
  #else
    #define ISR_LA_BASE_CYCLES 0UL
  #endif

  // S curve interpolation adds 40 cycles
  #if ENABLED(S_CURVE_ACCELERATION)
    #define ISR_S_CURVE_CYCLES 40UL
  #else
    #define ISR_S_CURVE_CYCLES 0UL
  #endif

  // Stepper Loop base cycles
  #define ISR_LOOP_BASE_CYCLES 4UL

  // To start the step pulse, in the worst case takes
  #define ISR_START_STEPPER_CYCLES 13UL

  // And each stepper (start + stop pulse) takes in worst case
  #define ISR_STEPPER_CYCLES 16UL

#else
  // Cycles to perform actions in START_TIMED_PULSE
  #define TIMER_READ_ADD_AND_STORE_CYCLES 13UL

  // The base ISR takes 752 cycles
  #define ISR_BASE_CYCLES  752UL

  // Linear advance base time is 32 cycles
  #if ENABLED(LIN_ADVANCE)
    #define ISR_LA_BASE_CYCLES 32UL
  #else
    #define ISR_LA_BASE_CYCLES 0UL
  #endif

  // S curve interpolation adds 160 cycles
  #if ENABLED(S_CURVE_ACCELERATION)
    #define ISR_S_CURVE_CYCLES 160UL
  #else
    #define ISR_S_CURVE_CYCLES 0UL
  #endif

  // Stepper Loop base cycles
  #define ISR_LOOP_BASE_CYCLES 32UL

  // To start the step pulse, in the worst case takes
  #define ISR_START_STEPPER_CYCLES 57UL

  // And each stepper (start + stop pulse) takes in worst case
  #define ISR_STEPPER_CYCLES 88UL

#endif

// Add time for each stepper
#if HAS_X_STEP
  #define ISR_X_STEPPER_CYCLES       ISR_STEPPER_CYCLES
#else
  #define ISR_X_STEPPER_CYCLES       0UL
#endif
#if HAS_Y_STEP
  #define ISR_Y_STEPPER_CYCLES       ISR_STEPPER_CYCLES
#else
  #define ISR_START_Y_STEPPER_CYCLES 0UL
  #define ISR_Y_STEPPER_CYCLES       0UL
#endif
#if HAS_Z_STEP
  #define ISR_Z_STEPPER_CYCLES       ISR_STEPPER_CYCLES
#else
  #define ISR_Z_STEPPER_CYCLES       0UL
#endif

// E is always interpolated, even for mixing extruders
#define ISR_E_STEPPER_CYCLES         ISR_STEPPER_CYCLES

// If linear advance is disabled, the loop also handles them
#if DISABLED(LIN_ADVANCE) && ENABLED(MIXING_EXTRUDER)
  #define ISR_MIXING_STEPPER_CYCLES ((MIXING_STEPPERS) * (ISR_STEPPER_CYCLES))
#else
  #define ISR_MIXING_STEPPER_CYCLES  0UL
#endif

// And the total minimum loop time, not including the base
#define MIN_ISR_LOOP_CYCLES (ISR_X_STEPPER_CYCLES + ISR_Y_STEPPER_CYCLES + ISR_Z_STEPPER_CYCLES + ISR_E_STEPPER_CYCLES + ISR_MIXING_STEPPER_CYCLES)

// Calculate the minimum MPU cycles needed per pulse to enforce, limited to the max stepper rate
#define _MIN_STEPPER_PULSE_CYCLES(N) _MAX(uint32_t((F_CPU) / (MAXIMUM_STEPPER_RATE)), ((F_CPU) / 500000UL) * (N))
#if MINIMUM_STEPPER_PULSE
  #define MIN_STEPPER_PULSE_CYCLES _MIN_STEPPER_PULSE_CYCLES(uint32_t(MINIMUM_STEPPER_PULSE))
#elif HAS_DRIVER(LV8729)
  #define MIN_STEPPER_PULSE_CYCLES uint32_t((((F_CPU) - 1) / 2000000) + 1) // 0.5µs, aka 500ns
#else
  #define MIN_STEPPER_PULSE_CYCLES _MIN_STEPPER_PULSE_CYCLES(1UL)
#endif

// Calculate the minimum pulse times (high and low)
#if MINIMUM_STEPPER_PULSE && MAXIMUM_STEPPER_RATE
  constexpr uint32_t _MIN_STEP_PERIOD_NS = 1000000000UL / MAXIMUM_STEPPER_RATE;
  constexpr uint32_t _MIN_PULSE_HIGH_NS = 1000UL * MINIMUM_STEPPER_PULSE;
  constexpr uint32_t _MIN_PULSE_LOW_NS = _MAX((_MIN_STEP_PERIOD_NS - _MIN(_MIN_STEP_PERIOD_NS, _MIN_PULSE_HIGH_NS)), _MIN_PULSE_HIGH_NS);
#elif MINIMUM_STEPPER_PULSE
  // Assume 50% duty cycle
  constexpr uint32_t _MIN_PULSE_HIGH_NS = 1000UL * MINIMUM_STEPPER_PULSE;
  constexpr uint32_t _MIN_PULSE_LOW_NS = _MIN_PULSE_HIGH_NS;
#elif MAXIMUM_STEPPER_RATE
  // Assume 50% duty cycle
  constexpr uint32_t _MIN_PULSE_HIGH_NS = 500000000UL / MAXIMUM_STEPPER_RATE;
  constexpr uint32_t _MIN_PULSE_LOW_NS = _MIN_PULSE_HIGH_NS;
#else
  #error "Expected at least one of MINIMUM_STEPPER_PULSE or MAXIMUM_STEPPER_RATE to be defined"
#endif

// But the user could be enforcing a minimum time, so the loop time is
#define ISR_LOOP_CYCLES (ISR_LOOP_BASE_CYCLES + _MAX(MIN_STEPPER_PULSE_CYCLES, MIN_ISR_LOOP_CYCLES))

// If linear advance is enabled, then it is handled separately
#if ENABLED(LIN_ADVANCE)

  // Estimate the minimum LA loop time
  #if ENABLED(MIXING_EXTRUDER) // ToDo: ???
    // HELP ME: What is what?
    // Directions are set up for MIXING_STEPPERS - like before.
    // Finding the right stepper may last up to MIXING_STEPPERS loops in get_next_stepper().
    //   These loops are a bit faster than advancing a bresenham counter.
    // Always only one e-stepper is stepped.
    #define MIN_ISR_LA_LOOP_CYCLES ((MIXING_STEPPERS) * (ISR_STEPPER_CYCLES))
  #else
    #define MIN_ISR_LA_LOOP_CYCLES ISR_STEPPER_CYCLES
  #endif

  // And the real loop time
  #define ISR_LA_LOOP_CYCLES _MAX(MIN_STEPPER_PULSE_CYCLES, MIN_ISR_LA_LOOP_CYCLES)

#else
  #define ISR_LA_LOOP_CYCLES 0UL
#endif

// Now estimate the total ISR execution time in cycles given a step per ISR multiplier
#define ISR_EXECUTION_CYCLES(R) (((ISR_BASE_CYCLES + ISR_S_CURVE_CYCLES + (ISR_LOOP_CYCLES) * (R) + ISR_LA_BASE_CYCLES + ISR_LA_LOOP_CYCLES)) / (R))

// The maximum allowable stepping frequency when doing x128-x1 stepping (in Hz)
#define MAX_STEP_ISR_FREQUENCY_128X ((F_CPU) / ISR_EXECUTION_CYCLES(128))
#define MAX_STEP_ISR_FREQUENCY_64X  ((F_CPU) / ISR_EXECUTION_CYCLES(64))
#define MAX_STEP_ISR_FREQUENCY_32X  ((F_CPU) / ISR_EXECUTION_CYCLES(32))
#define MAX_STEP_ISR_FREQUENCY_16X  ((F_CPU) / ISR_EXECUTION_CYCLES(16))
#define MAX_STEP_ISR_FREQUENCY_8X   ((F_CPU) / ISR_EXECUTION_CYCLES(8))
#define MAX_STEP_ISR_FREQUENCY_4X   ((F_CPU) / ISR_EXECUTION_CYCLES(4))
#define MAX_STEP_ISR_FREQUENCY_2X   ((F_CPU) / ISR_EXECUTION_CYCLES(2))
#define MAX_STEP_ISR_FREQUENCY_1X   ((F_CPU) / ISR_EXECUTION_CYCLES(1))

// The minimum step ISR rate used by ADAPTIVE_STEP_SMOOTHING to target 50% CPU usage
// This does not account for the possibility of multi-stepping.
// Perhaps DISABLE_MULTI_STEPPING should be required with ADAPTIVE_STEP_SMOOTHING.
#define MIN_STEP_ISR_FREQUENCY (MAX_STEP_ISR_FREQUENCY_1X / 2)

//
// Stepper class definition
//
class Stepper {

  public:

    #if EITHER(HAS_EXTRA_ENDSTOPS, Z_STEPPER_AUTO_ALIGN)
      static bool separate_multi_axis;
    #endif

    #if HAS_MOTOR_CURRENT_PWM
      #ifndef PWM_MOTOR_CURRENT
        #define PWM_MOTOR_CURRENT DEFAULT_PWM_MOTOR_CURRENT
      #endif
      static uint32_t motor_current_setting[3];
      static bool initialized;
    #endif

  private:

    static block_t* current_block;          // A pointer to the block currently being traced

    static uint8_t last_direction_bits,     // The next stepping-bits to be output
                   axis_did_move;           // Last Movement in the given direction is not null, as computed when the last movement was fetched from planner

    static bool abort_current_block;        // Signals to the stepper that current block should be aborted

    // Last-moved extruder, as set when the last movement was fetched from planner
    #if EXTRUDERS < 2
      static constexpr uint8_t last_moved_extruder = 0;
    #elif DISABLED(MIXING_EXTRUDER)
      static uint8_t last_moved_extruder;
    #endif

    #if ENABLED(X_DUAL_ENDSTOPS)
      static bool locked_X_motor, locked_X2_motor;
    #endif
    #if ENABLED(Y_DUAL_ENDSTOPS)
      static bool locked_Y_motor, locked_Y2_motor;
    #endif
    #if EITHER(Z_MULTI_ENDSTOPS, Z_STEPPER_AUTO_ALIGN)
      static bool locked_Z_motor, locked_Z2_motor
                  #if NUM_Z_STEPPER_DRIVERS >= 3
                    , locked_Z3_motor
                    #if NUM_Z_STEPPER_DRIVERS >= 4
                      , locked_Z4_motor
                    #endif
                  #endif
                  ;
    #endif

    static uint32_t acceleration_time, deceleration_time; // time measured in Stepper Timer ticks
    static uint8_t steps_per_isr;         // Count of steps to perform per Stepper ISR call

    #if ENABLED(ADAPTIVE_STEP_SMOOTHING)
      static uint8_t oversampling_factor; // Oversampling factor (log2(multiplier)) to increase temporal resolution of axis
    #else
      static constexpr uint8_t oversampling_factor = 0;
    #endif

    // Delta error variables for the Bresenham line tracer
    static xyze_long_t delta_error;
    static xyze_ulong_t advance_dividend;
    static uint32_t advance_divisor,
                    step_events_completed,  // The number of step events executed in the current block
                    accelerate_until,       // The point from where we need to stop acceleration
                    decelerate_after,       // The point from where we need to start decelerating
                    step_event_count;       // The total event count for the current block

    #if EXTRUDERS > 1 || ENABLED(MIXING_EXTRUDER)
      static uint8_t stepper_extruder;
    #else
      static constexpr uint8_t stepper_extruder = 0;
    #endif

    #if ENABLED(S_CURVE_ACCELERATION)
      static int32_t bezier_A,     // A coefficient in Bézier speed curve
                     bezier_B,     // B coefficient in Bézier speed curve
                     bezier_C;     // C coefficient in Bézier speed curve
      static uint32_t bezier_F,    // F coefficient in Bézier speed curve
                      bezier_AV;   // AV coefficient in Bézier speed curve
      #ifdef __AVR__
        static bool A_negative;    // If A coefficient was negative
      #endif
      static bool bezier_2nd_half; // If Bézier curve has been initialized or not
    #endif

    #if ENABLED(LIN_ADVANCE)
      static constexpr uint32_t LA_ADV_NEVER = 0xFFFFFFFF;
      static uint32_t nextAdvanceISR, LA_isr_rate;
      static uint16_t LA_current_adv_steps, LA_final_adv_steps, LA_max_adv_steps; // Copy from current executed block. Needed because current_block is set to NULL "too early".
      static int8_t LA_steps;
      static bool LA_use_advance_lead;
    #endif

    #if ENABLED(INTEGRATED_BABYSTEPPING)
      static constexpr uint32_t BABYSTEP_NEVER = 0xFFFFFFFF;
      static uint32_t nextBabystepISR;
    #endif

    #if ENABLED(DIRECT_STEPPING)
      static page_step_state_t page_step_state;
    #endif

    static int32_t ticks_nominal;
    #if DISABLED(S_CURVE_ACCELERATION)
      static uint32_t acc_step_rate; // needed for deceleration start point
    #endif

    // Exact steps at which an endstop was triggered
    static xyz_long_t endstops_trigsteps;

    // Positions of stepper motors, in step units
    static xyze_long_t count_position;

    // Current stepper motor directions (+1 or -1)
    static xyze_int8_t count_direction;

    #if ENABLED(LASER_POWER_INLINE_TRAPEZOID)

      typedef struct {
        bool enabled;       // Trapezoid needed flag (i.e., laser on, planner in control)
        uint8_t cur_power;  // Current laser power
        bool cruise_set;    // Power set up for cruising?

        #if DISABLED(LASER_POWER_INLINE_TRAPEZOID_CONT)
          uint32_t last_step_count, // Step count from the last update
                   acc_step_count;  // Bresenham counter for laser accel/decel
        #else
          uint16_t till_update;     // Countdown to the next update
        #endif
      } stepper_laser_t;

      static stepper_laser_t laser_trap;

    #endif

  public:
    // Initialize stepper hardware
    static void init();

    // Interrupt Service Routine and phases

    // The stepper subsystem goes to sleep when it runs out of things to execute.
    // Call this to notify the subsystem that it is time to go to work.
    static inline void wake_up() { ENABLE_STEPPER_DRIVER_INTERRUPT(); }

    static inline bool is_awake() { return STEPPER_ISR_ENABLED(); }

    static inline bool suspend() {
      const bool awake = is_awake();
      if (awake) DISABLE_STEPPER_DRIVER_INTERRUPT();
      return awake;
    }

    // The ISR scheduler
    static void isr();

    // The stepper pulse ISR phase
    static void pulse_phase_isr();

    // The stepper block processing ISR phase
    static uint32_t block_phase_isr();

    #if ENABLED(LIN_ADVANCE)
      // The Linear advance ISR phase
      static uint32_t advance_isr();
      FORCE_INLINE static void initiateLA() { nextAdvanceISR = 0; }
    #endif

    #if ENABLED(INTEGRATED_BABYSTEPPING)
      // The Babystepping ISR phase
      static uint32_t babystepping_isr();
      FORCE_INLINE static void initiateBabystepping() {
        if (nextBabystepISR == BABYSTEP_NEVER) {
          nextBabystepISR = 0;
          wake_up();
        }
      }
    #endif

    // Check if the given block is busy or not - Must not be called from ISR contexts
    static bool is_block_busy(const block_t* const block);

    // Get the position of a stepper, in steps
    static int32_t position(const AxisEnum axis);

    // Set the current position in steps
    static void set_position(const int32_t &a, const int32_t &b, const int32_t &c, const int32_t &e);
    static inline void set_position(const xyze_long_t &abce) { set_position(abce.a, abce.b, abce.c, abce.e); }
    static void set_axis_position(const AxisEnum a, const int32_t &v);

    // Report the positions of the steppers, in steps
    static void report_a_position(const xyz_long_t &pos);
    static void report_positions();

    // Discard current block and free any resources
    FORCE_INLINE static void discard_current_block() {
      #if ENABLED(DIRECT_STEPPING)
        if (IS_PAGE(current_block))
          page_manager.free_page(current_block->page_idx);
      #endif
      current_block = nullptr;
      axis_did_move = 0;
      planner.release_current_block();
    }

    // Quickly stop all steppers
    FORCE_INLINE static void quick_stop() { abort_current_block = true; }

    // The direction of a single motor
    FORCE_INLINE static bool motor_direction(const AxisEnum axis) { return TEST(last_direction_bits, axis); }

    // The last movement direction was not null on the specified axis. Note that motor direction is not necessarily the same.
    FORCE_INLINE static bool axis_is_moving(const AxisEnum axis) { return TEST(axis_did_move, axis); }

    // The extruder associated to the last movement
    FORCE_INLINE static uint8_t movement_extruder() {
      return (EXTRUDERS > 1 && DISABLED(MIXING_EXTRUDER)) ? last_moved_extruder : 0;
    }

    // Handle a triggered endstop
    static void endstop_triggered(const AxisEnum axis);

    // Triggered position of an axis in steps
    static int32_t triggered_position(const AxisEnum axis);

    #if HAS_DIGIPOTSS || HAS_MOTOR_CURRENT_PWM
      static void digitalPotWrite(const int16_t address, const int16_t value);
      static void digipot_current(const uint8_t driver, const int16_t current);
    #endif

    #if HAS_MICROSTEPS
      static void microstep_ms(const uint8_t driver, const int8_t ms1, const int8_t ms2, const int8_t ms3);
      static void microstep_mode(const uint8_t driver, const uint8_t stepping);
      static void microstep_readings();
    #endif

    #if EITHER(HAS_EXTRA_ENDSTOPS, Z_STEPPER_AUTO_ALIGN)
      FORCE_INLINE static void set_separate_multi_axis(const bool state) { separate_multi_axis = state; }
    #endif
    #if ENABLED(X_DUAL_ENDSTOPS)
      FORCE_INLINE static void set_x_lock(const bool state) { locked_X_motor = state; }
      FORCE_INLINE static void set_x2_lock(const bool state) { locked_X2_motor = state; }
    #endif
    #if ENABLED(Y_DUAL_ENDSTOPS)
      FORCE_INLINE static void set_y_lock(const bool state) { locked_Y_motor = state; }
      FORCE_INLINE static void set_y2_lock(const bool state) { locked_Y2_motor = state; }
    #endif
    #if EITHER(Z_MULTI_ENDSTOPS, Z_STEPPER_AUTO_ALIGN)
      FORCE_INLINE static void set_z1_lock(const bool state) { locked_Z_motor = state; }
      FORCE_INLINE static void set_z2_lock(const bool state) { locked_Z2_motor = state; }
      #if NUM_Z_STEPPER_DRIVERS >= 3
        FORCE_INLINE static void set_z3_lock(const bool state) { locked_Z3_motor = state; }
        #if NUM_Z_STEPPER_DRIVERS >= 4
          FORCE_INLINE static void set_z4_lock(const bool state) { locked_Z4_motor = state; }
        #endif
      #endif
      static inline void set_all_z_lock(const bool lock, const int8_t except=-1) {
        set_z1_lock(lock ^ (except == 0));
        set_z2_lock(lock ^ (except == 1));
        #if NUM_Z_STEPPER_DRIVERS >= 3
          set_z3_lock(lock ^ (except == 2));
          #if NUM_Z_STEPPER_DRIVERS >= 4
            set_z4_lock(lock ^ (except == 3));
          #endif
        #endif
      }
    #endif

    #if ENABLED(BABYSTEPPING)
      static void do_babystep(const AxisEnum axis, const bool direction); // perform a short step with a single stepper motor, outside of any convention
    #endif

    #if HAS_MOTOR_CURRENT_PWM
      static void refresh_motor_power();
    #endif

    // Set direction bits for all steppers
    static void set_directions();

  private:

    // Set the current position in steps
    static void _set_position(const int32_t &a, const int32_t &b, const int32_t &c, const int32_t &e);
    FORCE_INLINE static void _set_position(const abce_long_t &spos) { _set_position(spos.a, spos.b, spos.c, spos.e); }

    FORCE_INLINE static uint32_t calc_timer_interval(uint32_t step_rate, uint8_t* loops) {
      uint32_t timer;

      // Scale the frequency, as requested by the caller
      step_rate <<= oversampling_factor;

      uint8_t multistep = 1;
      #if DISABLED(DISABLE_MULTI_STEPPING)

        // The stepping frequency limits for each multistepping rate
        static const uint32_t limit[] PROGMEM = {
          (  MAX_STEP_ISR_FREQUENCY_1X     ),
          (  MAX_STEP_ISR_FREQUENCY_2X >> 1),
          (  MAX_STEP_ISR_FREQUENCY_4X >> 2),
          (  MAX_STEP_ISR_FREQUENCY_8X >> 3),
          ( MAX_STEP_ISR_FREQUENCY_16X >> 4),
          ( MAX_STEP_ISR_FREQUENCY_32X >> 5),
          ( MAX_STEP_ISR_FREQUENCY_64X >> 6),
          (MAX_STEP_ISR_FREQUENCY_128X >> 7)
        };

        // Select the proper multistepping
        uint8_t idx = 0;
        while (idx < 7 && step_rate > (uint32_t)pgm_read_dword(&limit[idx])) {
          step_rate >>= 1;
          multistep <<= 1;
          ++idx;
        };
      #else
        NOMORE(step_rate, uint32_t(MAX_STEP_ISR_FREQUENCY_1X));
      #endif
      *loops = multistep;

      #ifdef CPU_32_BIT
        // In case of high-performance processor, it is able to calculate in real-time
        timer = uint32_t(STEPPER_TIMER_RATE) / step_rate;
      #else
        constexpr uint32_t min_step_rate = (F_CPU) / 500000U;
        NOLESS(step_rate, min_step_rate);
        step_rate -= min_step_rate; // Correct for minimal speed
        if (step_rate >= (8 * 256)) { // higher step rate
          const uint8_t tmp_step_rate = (step_rate & 0x00FF);
          const uint16_t table_address = (uint16_t)&speed_lookuptable_fast[(uint8_t)(step_rate >> 8)][0],
                         gain = (uint16_t)pgm_read_word(table_address + 2);
          timer = MultiU16X8toH16(tmp_step_rate, gain);
          timer = (uint16_t)pgm_read_word(table_address) - timer;
        }
        else { // lower step rates
          uint16_t table_address = (uint16_t)&speed_lookuptable_slow[0][0];
          table_address += ((step_rate) >> 1) & 0xFFFC;
          timer = (uint16_t)pgm_read_word(table_address)
                - (((uint16_t)pgm_read_word(table_address + 2) * (uint8_t)(step_rate & 0x0007)) >> 3);
        }
        // (there is no need to limit the timer value here. All limits have been
        // applied above, and AVR is able to keep up at 30khz Stepping ISR rate)
      #endif

      return timer;
    }

    #if ENABLED(S_CURVE_ACCELERATION)
      static void _calc_bezier_curve_coeffs(const int32_t v0, const int32_t v1, const uint32_t av);
      static int32_t _eval_bezier_curve(const uint32_t curr_step);
    #endif

    #if HAS_DIGIPOTSS || HAS_MOTOR_CURRENT_PWM
      static void digipot_init();
    #endif

    #if HAS_MICROSTEPS
      static void microstep_init();
    #endif

};

extern Stepper stepper;