planner.c

/*
  planner.c - buffers movement commands and manages the acceleration profile plan
  Part of Grbl

   The MIT License (MIT)

  GRBL(tm) - Embedded CNC g-code interpreter and motion-controller
  Copyright (c) 2009-2011 Simen Svale Skogsrud
  Copyright (c) 2011-2013 Sungeun K. Jeon

  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:

  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  THE SOFTWARE.
*/

/* The ring buffer implementation gleaned from the wiring_serial library by David A. Mellis. */

#include <inttypes.h>
#include <stdlib.h>
#include "planner.h"
#include "nuts_bolts.h"
#include "stepper.h"
#include "settings.h"
//#include "config.h"
#include "defaults.h"
#include "protocol.h"
/// 8c1
#ifndef AXIS_T_TYPE
	#error
#endif
#include "gcode.h"	/// to_degrees()

static block_t block_buffer[BLOCK_BUFFER_SIZE];  // A ring buffer for motion instructions
static volatile uint8_t block_buffer_head;       // Index of the next block to be pushed
static volatile uint8_t block_buffer_tail;       // Index of the block to process now
static uint8_t next_buffer_head;                 // Index of the next buffer head

// Define planner variables
typedef struct {
/// 8c1
  int32_t position[N_AXIS];             // The planner position of the tool in absolute steps. Kept separate
                                   // from g-code position for movements requiring multiple line motions,
                                   // i.e. arcs, canned cycles, and backlash compensation.
  float previous_unit_vec[N_AXIS];     // Unit vector of previous path line segment
  float previous_nominal_speed;   // Nominal speed of previous path line segment
} planner_t;
static planner_t pl;

// Returns the index of the next block in the ring buffer
// NOTE: Removed modulo (%) operator, which uses an expensive divide and multiplication.
static uint8_t next_block_index(uint8_t block_index)
{
  block_index++;
  if (block_index == BLOCK_BUFFER_SIZE) { block_index = 0; }
  return(block_index);
}


// Returns the index of the previous block in the ring buffer
static uint8_t prev_block_index(uint8_t block_index)
{
  if (block_index == 0) { block_index = BLOCK_BUFFER_SIZE; }
  block_index--;
  return(block_index);
}


// Calculates the distance (not time) it takes to accelerate from initial_rate to target_rate using the
// given acceleration:
static float estimate_acceleration_distance(float initial_rate, float target_rate, float acceleration)
{
  return( (target_rate*target_rate-initial_rate*initial_rate)/(2*acceleration) );
}


/*                        + <- some maximum rate we don't care about
                         /|\
                        / | \
                       /  |  + <- final_rate
                      /   |  |
     initial_rate -> +----+--+
                          ^  ^
                          |  |
      intersection_distance  distance                                                                           */
// This function gives you the point at which you must start braking (at the rate of -acceleration) if
// you started at speed initial_rate and accelerated until this point and want to end at the final_rate after
// a total travel of distance. This can be used to compute the intersection point between acceleration and
// deceleration in the cases where the trapezoid has no plateau (i.e. never reaches maximum speed)
static float intersection_distance(float initial_rate, float final_rate, float acceleration, float distance)
{
  return( (2*acceleration*distance-initial_rate*initial_rate+final_rate*final_rate)/(4*acceleration) );
}


// Calculates the maximum allowable speed at this point when you must be able to reach target_velocity
// using the acceleration within the allotted distance.
// NOTE: sqrt() reimplimented here from prior version due to improved planner logic. Increases speed
// in time critical computations, i.e. arcs or rapid short lines from curves. Guaranteed to not exceed
// BLOCK_BUFFER_SIZE calls per planner cycle.
static float max_allowable_speed(float acceleration, float target_velocity, float distance)
{
  return( sqrt(target_velocity*target_velocity-2*acceleration*distance) );
}


// The kernel called by planner_recalculate() when scanning the plan from last to first entry.
static void planner_reverse_pass_kernel(block_t *previous, block_t *current, block_t *next)
{
  if (!current) { return; }  // Cannot operate on nothing.

  if (next) {
    // If entry speed is already at the maximum entry speed, no need to recheck. Block is cruising.
    // If not, block in state of acceleration or deceleration. Reset entry speed to maximum and
    // check for maximum allowable speed reductions to ensure maximum possible planned speed.
    if (current->entry_speed != current->max_entry_speed) {

      // If nominal length true, max junction speed is guaranteed to be reached. Only compute
      // for max allowable speed if block is decelerating and nominal length is false.
      if ((!current->nominal_length_flag) && (current->max_entry_speed > next->entry_speed)) {
        current->entry_speed = min( current->max_entry_speed,
          max_allowable_speed(-settings.acceleration,next->entry_speed,current->millimeters));
      } else {
        current->entry_speed = current->max_entry_speed;
      }
      current->recalculate_flag = true;

    }
  } // Skip last block. Already initialized and set for recalculation.
}


// planner_recalculate() needs to go over the current plan twice. Once in reverse and once forward. This
// implements the reverse pass.
static void planner_reverse_pass()
{
  uint8_t block_index = block_buffer_head;
  block_t *block[3] = {NULL, NULL, NULL};
  while(block_index != block_buffer_tail) {
    block_index = prev_block_index( block_index );
    block[2]= block[1];
    block[1]= block[0];
    block[0] = &block_buffer[block_index];
    planner_reverse_pass_kernel(block[0], block[1], block[2] );
  }
  // Skip buffer tail/first block to prevent over-writing the initial entry speed.
}


// The kernel called by planner_recalculate() when scanning the plan from first to last entry.
static void planner_forward_pass_kernel(block_t *previous, block_t *current, block_t *next)
{
  if(!previous) { return; }  // Begin planning after buffer_tail

  // If the previous block is an acceleration block, but it is not long enough to complete the
  // full speed change within the block, we need to adjust the entry speed accordingly. Entry
  // speeds have already been reset, maximized, and reverse planned by reverse planner.
  // If nominal length is true, max junction speed is guaranteed to be reached. No need to recheck.
  if (!previous->nominal_length_flag) {
    if (previous->entry_speed < current->entry_speed) {
      float entry_speed = min( current->entry_speed,
        max_allowable_speed(-settings.acceleration,previous->entry_speed,previous->millimeters) );

      // Check for junction speed change
      if (current->entry_speed != entry_speed) {
        current->entry_speed = entry_speed;
        current->recalculate_flag = true;
      }
    }
  }
}


// planner_recalculate() needs to go over the current plan twice. Once in reverse and once forward. This
// implements the forward pass.
static void planner_forward_pass()
{
  uint8_t block_index = block_buffer_tail;
  block_t *block[3] = {NULL, NULL, NULL};

  while(block_index != block_buffer_head) {
    block[0] = block[1];
    block[1] = block[2];
    block[2] = &block_buffer[block_index];
    planner_forward_pass_kernel(block[0],block[1],block[2]);
    block_index = next_block_index( block_index );
  }
  planner_forward_pass_kernel(block[1], block[2], NULL);
}


/*                             STEPPER RATE DEFINITION
                                     +--------+   <- nominal_rate
                                    /          \
    nominal_rate*entry_factor ->   +            \
                                   |             + <- nominal_rate*exit_factor
                                   +-------------+
                                       time -->
*/
// Calculates trapezoid parameters so that the entry- and exit-speed is compensated by the provided factors.
// The factors represent a factor of braking and must be in the range 0.0-1.0.
// This converts the planner parameters to the data required by the stepper controller.
// NOTE: Final rates must be computed in terms of their respective blocks.
static void calculate_trapezoid_for_block(block_t *block, float entry_factor, float exit_factor)
{
  block->initial_rate = ceil(block->nominal_rate*entry_factor); // (step/min)
  block->final_rate = ceil(block->nominal_rate*exit_factor); // (step/min)
  int32_t acceleration_per_minute = block->rate_delta*ACCELERATION_TICKS_PER_SECOND*60.0; // (step/min^2)
  int32_t accelerate_steps =
    ceil(estimate_acceleration_distance(block->initial_rate, block->nominal_rate, acceleration_per_minute));
  int32_t decelerate_steps =
    floor(estimate_acceleration_distance(block->nominal_rate, block->final_rate, -acceleration_per_minute));

  // Calculate the size of Plateau of Nominal Rate.
  int32_t plateau_steps = block->step_event_count-accelerate_steps-decelerate_steps;

  // Is the Plateau of Nominal Rate smaller than nothing? That means no cruising, and we will
  // have to use intersection_distance() to calculate when to abort acceleration and start braking
  // in order to reach the final_rate exactly at the end of this block.
  if (plateau_steps < 0) {
    accelerate_steps = ceil(
      intersection_distance(block->initial_rate, block->final_rate, acceleration_per_minute, block->step_event_count));
    accelerate_steps = max(accelerate_steps,0); // Check limits due to numerical round-off
    accelerate_steps = min(accelerate_steps,block->step_event_count);
    plateau_steps = 0;
  }

  block->accelerate_until = accelerate_steps;
  block->decelerate_after = accelerate_steps+plateau_steps;
}

/*                            PLANNER SPEED DEFINITION
                                     +--------+   <- current->nominal_speed
                                    /          \
         current->entry_speed ->   +            \
                                   |             + <- next->entry_speed
                                   +-------------+
                                       time -->
*/
// Recalculates the trapezoid speed profiles for flagged blocks in the plan according to the
// entry_speed for each junction and the entry_speed of the next junction. Must be called by
// planner_recalculate() after updating the blocks. Any recalulate flagged junction will
// compute the two adjacent trapezoids to the junction, since the junction speed corresponds
// to exit speed and entry speed of one another.
static void planner_recalculate_trapezoids()
{
  uint8_t block_index = block_buffer_tail;
  block_t *current;
  block_t *next = NULL;

  while(block_index != block_buffer_head) {
    current = next;
    next = &block_buffer[block_index];
    if (current) {
      // Recalculate if current block entry or exit junction speed has changed.
      if (current->recalculate_flag || next->recalculate_flag) {
        // NOTE: Entry and exit factors always > 0 by all previous logic operations.
        calculate_trapezoid_for_block(current, current->entry_speed/current->nominal_speed,
          next->entry_speed/current->nominal_speed);
        current->recalculate_flag = false; // Reset current only to ensure next trapezoid is computed
      }
    }
    block_index = next_block_index( block_index );
  }
  // Last/newest block in buffer. Exit speed is set with MINIMUM_PLANNER_SPEED. Always recalculated.
  calculate_trapezoid_for_block(next, next->entry_speed/next->nominal_speed,
    MINIMUM_PLANNER_SPEED/next->nominal_speed);
  next->recalculate_flag = false;
}

// Recalculates the motion plan according to the following algorithm:
//
//   1. Go over every block in reverse order and calculate a junction speed reduction (i.e. block_t.entry_speed)
//      so that:
//     a. The junction speed is equal to or less than the maximum junction speed limit
//     b. No speed reduction within one block requires faster deceleration than the one, true constant
//        acceleration.
//   2. Go over every block in chronological order and dial down junction speed values if
//     a. The speed increase within one block would require faster acceleration than the one, true
//        constant acceleration.
//
// When these stages are complete all blocks have an entry speed that will allow all speed changes to
// be performed using only the one, true constant acceleration, and where no junction speed is greater
// than the max limit. Finally it will:
//
//   3. Recalculate trapezoids for all blocks using the recently updated junction speeds. Block trapezoids
//      with no updated junction speeds will not be recalculated and assumed ok as is.
//
// All planner computations are performed with doubles (float on Arduinos) to minimize numerical round-
// off errors. Only when planned values are converted to stepper rate parameters, these are integers.

static void planner_recalculate()
{
  planner_reverse_pass();
  planner_forward_pass();
  planner_recalculate_trapezoids();
}

void plan_reset_buffer()
{
  block_buffer_tail = block_buffer_head;
  next_buffer_head = next_block_index(block_buffer_head);
}

void plan_init()
{
  plan_reset_buffer();
  memset(&pl, 0, sizeof(pl)); // Clear planner struct
}

void plan_discard_current_block()
{
  if (block_buffer_head != block_buffer_tail) {
    block_buffer_tail = next_block_index( block_buffer_tail );
  }
}

block_t *plan_get_current_block()
{
  if (block_buffer_head == block_buffer_tail) { return(NULL); }
  return(&block_buffer[block_buffer_tail]);
}

// Returns the availability status of the block ring buffer. True, if full.
uint8_t plan_check_full_buffer()
{
  if (block_buffer_tail == next_buffer_head) { return(true); }
  return(false);
}

// Block until all buffered steps are executed or in a cycle state. Works with feed hold
// during a synchronize call, if it should happen. Also, waits for clean cycle end.
void plan_synchronize()
{
  while (plan_get_current_block() || sys.state == STATE_CYCLE) {
    protocol_execute_runtime();   // Check and execute run-time commands
    if (sys.abort) { return; } // Check for system abort
  }
}

// Add a new linear movement to the buffer. x, y and z is the signed, absolute target position in
// millimeters. Feed rate specifies the speed of the motion. If feed rate is inverted, the feed
// rate is taken to mean "frequency" and would complete the operation in 1/feed_rate minutes.
// All position data passed to the planner must be in terms of machine position to keep the planner
// independent of any coordinate system changes and offsets, which are handled by the g-code parser.
// NOTE: Assumes buffer is available. Buffer checks are handled at a higher level by motion_control.
/// 8c1
void plan_buffer_line(float x, float y, float z, float t, float feed_rate, uint8_t invert_feed_rate, uint8_t t_curve)
{
  // Prepare to set up new block
  block_t *block = &block_buffer[block_buffer_head];

  // Calculate target position in absolute steps
  int32_t target[N_AXIS];
  target[X_AXIS] = lround(x*settings.steps_per_mm[X_AXIS]);
  target[Y_AXIS] = lround(y*settings.steps_per_mm[Y_AXIS]);
  target[Z_AXIS] = lround(z*settings.steps_per_mm[Z_AXIS]);
/// 8c1
  if (t_curve == C_ARC)
    target[T_AXIS] = 0 ;
  else
#if (AXIS_T_TYPE == LINEAR)
    target[T_AXIS] = lround(t*settings.steps_per_mm[T_AXIS]);
#else
	target[T_AXIS] = lround(t*to_degrees(settings.steps_per_mm[T_AXIS]));
#endif

  // Compute direction bits for this block
  block->direction_bits = 0;
  if (target[X_AXIS] < pl.position[X_AXIS]) { block->direction_bits |= (1<<X_DIRECTION_BIT); }
  if (target[Y_AXIS] < pl.position[Y_AXIS]) { block->direction_bits |= (1<<Y_DIRECTION_BIT); }
  if (target[Z_AXIS] < pl.position[Z_AXIS]) { block->direction_bits |= (1<<Z_DIRECTION_BIT); }
/// 8c1
  if (target[T_AXIS] < pl.position[T_AXIS]) { block->direction_bits |= (1<<T_DIRECTION_BIT); }


  // Number of steps for each axis
  block->steps_x = labs(target[X_AXIS]-pl.position[X_AXIS]);
  block->steps_y = labs(target[Y_AXIS]-pl.position[Y_AXIS]);
  block->steps_z = labs(target[Z_AXIS]-pl.position[Z_AXIS]);
/// 8c1
  if (t_curve == C_ARC)
    block->steps_t = 0;
  else
    block->steps_t = labs(target[T_AXIS]-pl.position[T_AXIS]);

  block->step_event_count = max(block->steps_x, max(block->steps_y, max(block->steps_z, block->steps_t)));

  // Bail if this is a zero-length block
  if (block->step_event_count == 0)
	return;

  // Compute path vector in terms of absolute step target and current positions
/// 8c1
  float delta_mm[N_AXIS];
  delta_mm[X_AXIS] = (target[X_AXIS]-pl.position[X_AXIS])/settings.steps_per_mm[X_AXIS];
  delta_mm[Y_AXIS] = (target[Y_AXIS]-pl.position[Y_AXIS])/settings.steps_per_mm[Y_AXIS];
  delta_mm[Z_AXIS] = (target[Z_AXIS]-pl.position[Z_AXIS])/settings.steps_per_mm[Z_AXIS];
/// 8c1
  if (t_curve == C_ARC)
	delta_mm[T_AXIS] = 0;
  else
#if (AXIS_T_TYPE == LINEAR)
	delta_mm[T_AXIS] = (target[T_AXIS]-pl.position[T_AXIS])/settings.steps_per_mm[T_AXIS];
#else
	delta_mm[T_AXIS] = (target[T_AXIS]-pl.position[T_AXIS])/to_degrees(settings.steps_per_mm[T_AXIS]);
#endif
/// <--
  // SKW
  #ifdef FOAM_CUTTER
    block->millimeters = sqrt(max((delta_mm[X_AXIS]*delta_mm[X_AXIS]
                               + delta_mm[Y_AXIS]*delta_mm[Y_AXIS]
                              ),
                             (delta_mm[Z_AXIS]*delta_mm[Z_AXIS]
                               + delta_mm[T_AXIS]*delta_mm[T_AXIS]
                              )));
  #else
    block->millimeters = sqrt(delta_mm[X_AXIS]*delta_mm[X_AXIS]
                              + delta_mm[Y_AXIS]*delta_mm[Y_AXIS]
                              + delta_mm[Z_AXIS]*delta_mm[Z_AXIS]
                              //+ delta_mm[T_AXIS]*delta_mm[T_AXIS]
                              );
    block->millimeters += labs(delta_mm[T_AXIS]);
  #endif

  float inverse_millimeters = 1.0/block->millimeters;  // Inverse millimeters to remove multiple divides

  // Calculate speed in mm/minute for each axis. No divide by zero due to previous checks.
  // NOTE: Minimum stepper speed is limited by MINIMUM_STEPS_PER_MINUTE in stepper.c
  float inverse_minute;
  if (!invert_feed_rate) {
    inverse_minute = feed_rate * inverse_millimeters;
  }
  else {
    inverse_minute = 1.0 / feed_rate;
  }
  block->nominal_speed = block->millimeters * inverse_minute; // (mm/min) Always > 0
  block->nominal_rate = ceil(block->step_event_count * inverse_minute); // (step/min) Always > 0

  // Compute the acceleration rate for the trapezoid generator. Depending on the slope of the line
  // average travel per step event changes. For a line along one axis the travel per step event
  // is equal to the travel/step in the particular axis. For a 45 degree line the steppers of both
  // axes might step for every step event. Travel per step event is then sqrt(travel_x^2+travel_y^2).
  // To generate trapezoids with constant acceleration between blocks the rate_delta must be computed
  // specifically for each line to compensate for this phenomenon:
  // Convert universal acceleration for direction-dependent stepper rate change parameter
  block->rate_delta = ceil( block->step_event_count*inverse_millimeters *
        settings.acceleration / (60 * ACCELERATION_TICKS_PER_SECOND )); // (step/min/acceleration_tick)

  // Compute path unit vector
/// 8c0
  float unit_vec[N_AXIS];
  unit_vec[X_AXIS] = delta_mm[X_AXIS]*inverse_millimeters;
  unit_vec[Y_AXIS] = delta_mm[Y_AXIS]*inverse_millimeters;
  unit_vec[Z_AXIS] = delta_mm[Z_AXIS]*inverse_millimeters;
/// 8c1  for t_arc  -> 0
  unit_vec[T_AXIS] = delta_mm[T_AXIS]*inverse_millimeters;

  // SKW TODO: handle T_AXIS and decouple XY / UV planes

  // Compute maximum allowable entry speed at junction by centripetal acceleration approximation.
  // Let a circle be tangent to both previous and current path line segments, where the junction
  // deviation is defined as the distance from the junction to the closest edge of the circle,
  // colinear with the circle center. The circular segment joining the two paths represents the
  // path of centripetal acceleration. Solve for max velocity based on max acceleration about the
  // radius of the circle, defined indirectly by junction deviation. This may be also viewed as
  // path width or max_jerk in the previous grbl version. This approach does not actually deviate
  // from path, but used as a robust way to compute cornering speeds, as it takes into account the
  // nonlinearities of both the junction angle and junction velocity.
  // NOTE: This is basically an exact path mode (G61), but it doesn't come to a complete stop unless
  // the junction deviation value is high. In the future, if continuous mode (G64) is desired, the
  // math here is exactly the same. Instead of motioning all the way to junction point, the machine
  // will just need to follow the arc circle defined above and check if the arc radii are no longer
  // than half of either line segment to ensure no overlapping. Right now, the Arduino likely doesn't
  // have the horsepower to do these calculations at high feed rates.
  float vmax_junction = MINIMUM_PLANNER_SPEED; // Set default max junction speed

  // Skip first block or when previous_nominal_speed is used as a flag for homing and offset cycles.
  if ((block_buffer_head != block_buffer_tail) && (pl.previous_nominal_speed > 0.0)) {
    // Compute cosine of angle between previous and current path. (prev_unit_vec is negative)
    // NOTE: Max junction velocity is computed without sin() or acos() by trig half angle identity.

    #ifdef FOAM_CUTTER
      float cos_theta1 = - pl.previous_unit_vec[X_AXIS] * unit_vec[X_AXIS]
                         - pl.previous_unit_vec[Y_AXIS] * unit_vec[Y_AXIS];

      float cos_theta2 = - pl.previous_unit_vec[Z_AXIS] * unit_vec[Z_AXIS]
                         - pl.previous_unit_vec[T_AXIS] * unit_vec[T_AXIS];

      // Skip and use default max junction speed for 0 degree acute junction.
      if (cos_theta1 < 0.95) {
        vmax_junction = min(pl.previous_nominal_speed, block->nominal_speed);
        // Skip and avoid divide by zero for straight junctions at 180 degrees. Limit to min() of nominal speeds.
        if (cos_theta1 > -0.95) {
          // Compute maximum junction velocity based on maximum acceleration and junction deviation
          float sin_theta_d21 = sqrt(0.5*(1.0-cos_theta1)); // Trig half angle identity. Always positive.
          vmax_junction = min(vmax_junction,
            sqrt(settings.acceleration * settings.junction_deviation * sin_theta_d21/(1.0-sin_theta_d21)) );
        }
      }

      if (cos_theta2 < 0.95) {
        vmax_junction = min(pl.previous_nominal_speed, block->nominal_speed);
        // Skip and avoid divide by zero for straight junctions at 180 degrees. Limit to min() of nominal speeds.
        if (cos_theta2 > -0.95) {
          // Compute maximum junction velocity based on maximum acceleration and junction deviation
          float sin_theta_d22 = sqrt(0.5*(1.0-cos_theta2)); // Trig half angle identity. Always positive.
          vmax_junction = min(vmax_junction,
            sqrt(settings.acceleration * settings.junction_deviation * sin_theta_d22/(1.0-sin_theta_d22)) );
        }
      }      
    #else // original code
      float cos_theta = - pl.previous_unit_vec[X_AXIS] * unit_vec[X_AXIS]
                         - pl.previous_unit_vec[Y_AXIS] * unit_vec[Y_AXIS]
                         - pl.previous_unit_vec[Z_AXIS] * unit_vec[Z_AXIS]
                        /// 8c1  no T_AXIS
                          ;

      // Skip and use default max junction speed for 0 degree acute junction.
      if (cos_theta < 0.95) {
        vmax_junction = min(pl.previous_nominal_speed,block->nominal_speed);
        // Skip and avoid divide by zero for straight junctions at 180 degrees. Limit to min() of nominal speeds.
        if (cos_theta > -0.95) {
          // Compute maximum junction velocity based on maximum acceleration and junction deviation
          float sin_theta_d2 = sqrt(0.5*(1.0-cos_theta)); // Trig half angle identity. Always positive.
          vmax_junction = min(vmax_junction,
            sqrt(settings.acceleration * settings.junction_deviation * sin_theta_d2/(1.0-sin_theta_d2)) );
        }
      }
    #endif
  }
  block->max_entry_speed = vmax_junction;

  // Initialize block entry speed. Compute based on deceleration to user-defined MINIMUM_PLANNER_SPEED.
  float v_allowable = max_allowable_speed(-settings.acceleration,MINIMUM_PLANNER_SPEED,block->millimeters);
  block->entry_speed = min(vmax_junction, v_allowable);

  // Initialize planner efficiency flags
  // Set flag if block will always reach maximum junction speed regardless of entry/exit speeds.
  // If a block can de/ac-celerate from nominal speed to zero within the length of the block, then
  // the current block and next block junction speeds are guaranteed to always be at their maximum
  // junction speeds in deceleration and acceleration, respectively. This is due to how the current
  // block nominal speed limits both the current and next maximum junction speeds. Hence, in both
  // the reverse and forward planners, the corresponding block junction speed will always be at the
  // the maximum junction speed and may always be ignored for any speed reduction checks.
  if (block->nominal_speed <= v_allowable) { block->nominal_length_flag = true; }
  else { block->nominal_length_flag = false; }
  block->recalculate_flag = true; // Always calculate trapezoid for new block

  // Update previous path unit_vector and nominal speed
  memcpy(pl.previous_unit_vec, unit_vec, sizeof(unit_vec)); // pl.previous_unit_vec[] = unit_vec[]
  pl.previous_nominal_speed = block->nominal_speed;

  // Update buffer head and next buffer head indices
  block_buffer_head = next_buffer_head;
  next_buffer_head = next_block_index(block_buffer_head);

  // Update planner position
  memcpy(pl.position, target, sizeof(target)); // pl.position[] = target[]

  planner_recalculate();
}

// Reset the planner position vector (in steps). Called by the system abort routine.
/// 8c1
void plan_set_current_position(int32_t x, int32_t y, int32_t z, int32_t t)
{
  pl.position[X_AXIS] = x;
  pl.position[Y_AXIS] = y;
  pl.position[Z_AXIS] = z;
  pl.position[T_AXIS] = t;
}

// Re-initialize buffer plan with a partially completed block, assumed to exist at the buffer tail.
// Called after a steppers have come to a complete stop for a feed hold and the cycle is stopped.
void plan_cycle_reinitialize(int32_t step_events_remaining)
{
  block_t *block = &block_buffer[block_buffer_tail]; // Point to partially completed block

  // Only remaining millimeters and step_event_count need to be updated for planner recalculate.
  // Other variables (step_x, step_y, step_z, rate_delta, etc.) all need to remain the same to
  // ensure the original planned motion is resumed exactly.
  block->millimeters = (block->millimeters*step_events_remaining)/block->step_event_count;
  block->step_event_count = step_events_remaining;

  // Re-plan from a complete stop. Reset planner entry speeds and flags.
  block->entry_speed = 0.0;
  block->max_entry_speed = 0.0;
  block->nominal_length_flag = false;
  block->recalculate_flag = true;
  planner_recalculate();
}