grbl-LPC-CoreXY/stepper_plan.c

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

#include <inttypes.h>
#include <math.h>       
#include <stdlib.h>

#include "stepper_plan.h"
#include "nuts_bolts.h"
#include "stepper.h"
#include "config.h"

struct Block block_buffer[BLOCK_BUFFER_SIZE]; // A ring buffer for motion instructions
volatile int block_buffer_head;           // Index of the next block to be pushed
volatile int block_buffer_tail;           // Index of the block to process now
uint8_t acceleration_management;              // Acceleration management active?

inline uint32_t estimate_acceleration_distance(int32_t current_rate, int32_t target_rate, int32_t acceleration) {
  return((target_rate*target_rate-current_rate*current_rate)/(2*acceleration));
}

inline uint32_t estimate_acceleration_ticks(int32_t start_rate, int32_t acceleration_per_tick, int32_t step_events) {
  return(
    round(
      (sqrt(2*acceleration_per_tick*step_events+(start_rate*start_rate))-start_rate)/
      acceleration_per_tick));
}

// Calculates trapezoid parameters so that the entry- and exit-speed is compensated by the provided factors.
// In practice both factors must be in the range 0 ... 1.0
void calculate_trapezoid_for_block(struct Block *block, double entry_factor, double exit_factor) {
  block->initial_rate = round(block->nominal_rate*entry_factor);
  int32_t final_rate = round(block->nominal_rate*entry_factor);
  int32_t acceleration_per_second = block->rate_delta*ACCELERATION_TICKS_PER_SECOND;
  int32_t acceleration_steps = 
    estimate_acceleration_distance(block->initial_rate, block->nominal_rate, acceleration_per_second);
  int32_t decelleration_steps = 
    estimate_acceleration_distance(block->nominal_rate, final_rate, -acceleration_per_second);
  // Check if the acceleration and decelleration periods overlap. In that case nominal_speed will
  // never be reached but that's okay. Just truncate both periods proportionally so that they
  // fit within the allotted step events.
  int32_t plateau_steps = block->step_event_count-acceleration_steps-decelleration_steps;
  if (plateau_steps < 0) {
    int32_t half_overlap_region = fabs(plateau_steps)/2;
    plateau_steps = 0;
    acceleration_steps = max(acceleration_steps-half_overlap_region,0);
    decelleration_steps = max(decelleration_steps-half_overlap_region,0);
  }
  block->accelerate_ticks = estimate_acceleration_ticks(block->initial_rate, block->rate_delta, acceleration_steps);
  if (plateau_steps) {
    block->plateau_ticks = round(1.0*plateau_steps/(block->nominal_rate*ACCELERATION_TICKS_PER_SECOND));
  } else {
    block->plateau_ticks = 0;
  }
}

inline double estimate_max_speed(double max_acceleration, double target_velocity, double distance) {
  return(sqrt(-2*max_acceleration*distance+target_velocity*target_velocity));
}

inline double estimate_jerk(struct Block *before, struct Block *after) {
  return(max(fabs(before->speed_x-after->speed_x),
    max(fabs(before->speed_y-after->speed_y), 
    fabs(before->speed_z-after->speed_z))));
}

// Builds plan for a single block provided. Returns TRUE if changes were made to this block
// that requires any earlier blocks to be recalculated too.
int8_t build_plan_for_single_block(struct Block *previous, struct Block *current, struct Block *next) {
  if(!current){return(TRUE);}
  double exit_factor;
  double entry_factor = 1.0;
  if (next) {
    exit_factor = next->entry_factor;
  } else {
    exit_factor = 0.0;
  }
  
  if (previous) {
    double jerk = estimate_jerk(previous, current);
    if (jerk > settings.max_jerk) {
      entry_factor = (settings.max_jerk/jerk);
    } 
    if (exit_factor<entry_factor) {
      double max_entry_speed = estimate_max_speed(-settings.acceleration,current->nominal_speed*exit_factor, 
        current->millimeters);
      double max_entry_factor = max_entry_speed/current->nominal_speed;
      if (max_entry_factor < entry_factor) {
        entry_factor = max_entry_factor;
      }
    }    
  } else {
    entry_factor = 0.0;
  }
  // Check if we made a difference for this block. If we didn't, the planner can call it quits
  // here. No need to process any earlier blocks.
  int8_t keep_going = (entry_factor > current->entry_factor ? TRUE : FALSE);  
  // Store result and recalculate trapezoid parameters
  current->entry_factor = entry_factor;
  calculate_trapezoid_for_block(current, entry_factor, exit_factor);
  return(keep_going);
}

void recalculate_plan() {
  int8_t block_index = block_buffer_head;
  struct Block *block[3] = {NULL, NULL, NULL};
  while(block_index != block_buffer_tail) {
    block[2]= block[1];
    block[1]= block[0];
    block[0] = &block_buffer[block_index];
    if (!build_plan_for_single_block(block[0], block[1], block[2])) {return;}
    block_index = (block_index-1) % BLOCK_BUFFER_SIZE;
  }
  if (block[1]) {
    calculate_trapezoid_for_block(block[0], block[0]->entry_factor, block[1]->entry_factor);
  }
}

void plan_enable_acceleration_management() {
  if (!acceleration_management) {
    st_synchronize();
    acceleration_management = TRUE;
  }
}

void plan_disable_acceleration_management() {
  if(acceleration_management) {
    st_synchronize();
    acceleration_management = FALSE;
  }
}

void plan_init() {
  block_buffer_head = 0;
  block_buffer_tail = 0;
  plan_enable_acceleration_management();
}

// Add a new linear movement to the buffer. steps_x, _y and _z is the signed, relative motion in 
// steps. Microseconds specify how many microseconds the move should take to perform. To aid acceleration
// calculation the caller must also provide the physical length of the line in millimeters.
void plan_buffer_line(int32_t steps_x, int32_t steps_y, int32_t steps_z, uint32_t microseconds, double millimeters) {
  // Calculate the buffer head after we push this byte
	int next_buffer_head = (block_buffer_head + 1) % BLOCK_BUFFER_SIZE;	
	// If the buffer is full: good! That means we are well ahead of the robot. 
	// Rest here until there is room in the buffer.
  while(block_buffer_tail == next_buffer_head) { sleep_mode(); }
  // Prepare to set up new block
  struct Block *block = &block_buffer[block_buffer_head];
  // Number of steps for each axis
  block->steps_x = labs(steps_x);
  block->steps_y = labs(steps_y);
  block->steps_z = labs(steps_z);   
  block->step_event_count = max(block->steps_x, max(block->steps_y, block->steps_z));
  // Bail if this is a zero-length block
  if (block->step_event_count == 0) { return; };
  // Calculate speed in mm/minute for each axis
  double multiplier = 60.0*1000000.0/microseconds;
  block->speed_x = block->steps_x*multiplier/settings.steps_per_mm[0];
  block->speed_y = block->steps_y*multiplier/settings.steps_per_mm[1];
  block->speed_z = block->steps_z*multiplier/settings.steps_per_mm[2];
  block->nominal_speed = millimeters*multiplier;
  block->nominal_rate = round(block->step_event_count*multiplier);  
  
  // 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 contant acceleration between blocks the rate_delta must be computed 
  // specifically for each line to compensate for this phenomenon:
  double travel_per_step = (1.0*millimeters)/block->step_event_count;
  block->rate_delta = round(
    (settings.acceleration/(60.0*ACCELERATION_TICKS_PER_SECOND))/ // acceleration mm/min per acceleration_tick
    travel_per_step);                                           // convert to: acceleration steps/min/acceleration_tick    
  if (acceleration_management) {
    calculate_trapezoid_for_block(block,0,0);                     // compute a conservative acceleration trapezoid for now
  } else {
    block->accelerate_ticks = 0;
    block->plateau_ticks = 0;
    block->rate_delta = 0;
  }
  
  // Compute direction bits for this block
  block->direction_bits = 0;
  if (steps_x < 0) { block->direction_bits |= (1<<X_DIRECTION_BIT); }
  if (steps_y < 0) { block->direction_bits |= (1<<Y_DIRECTION_BIT); }
  if (steps_z < 0) { block->direction_bits |= (1<<Z_DIRECTION_BIT); }
  // Move buffer head
  block_buffer_head = next_buffer_head;
}