grbl/limits.c

/*
  limits.c - code pertaining to limit-switches and performing the homing cycle
  Part of Grbl

  Copyright (c) 2009-2011 Simen Svale Skogsrud
  Copyright (c) 2012-2013 Sungeun K. Jeon

  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 <util/delay.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include "stepper.h"
#include "settings.h"
#include "nuts_bolts.h"
#include "config.h"
#include "spindle_control.h"
#include "motion_control.h"
#include "planner.h"
#include "protocol.h"
#include "limits.h"
#include "report.h"

#define MICROSECONDS_PER_ACCELERATION_TICK  (1000000/ACCELERATION_TICKS_PER_SECOND)

void limits_init() 
{
  LIMIT_DDR &= ~(LIMIT_MASK); // Set as input pins
  LIMIT_PORT |= (LIMIT_MASK); // Enable internal pull-up resistors. Normal high operation.
  if (bit_istrue(settings.flags,BITFLAG_HARD_LIMIT_ENABLE)) {
    LIMIT_PCMSK |= LIMIT_MASK; // Enable specific pins of the Pin Change Interrupt
    PCICR |= (1 << LIMIT_INT); // Enable Pin Change Interrupt
  } else {
    LIMIT_PCMSK &= ~LIMIT_MASK; // Disable
    PCICR &= ~(1 << LIMIT_INT); 
  }
}

// This is the Limit Pin Change Interrupt, which handles the hard limit feature. A bouncing 
// limit switch can cause a lot of problems, like false readings and multiple interrupt calls.
// If a switch is triggered at all, something bad has happened and treat it as such, regardless
// if a limit switch is being disengaged. It's impossible to reliably tell the state of a 
// bouncing pin without a debouncing method.
// NOTE: Do not attach an e-stop to the limit pins, because this interrupt is disabled during
// homing cycles and will not respond correctly. Upon user request or need, there may be a
// special pinout for an e-stop, but it is generally recommended to just directly connect
// your e-stop switch to the Arduino reset pin, since it is the most correct way to do this.
ISR(LIMIT_INT_vect) 
{
  // Ignore limit switches if already in an alarm state or in-process of executing an alarm.
  // When in the alarm state, Grbl should have been reset or will force a reset, so any pending 
  // moves in the planner and serial buffers are all cleared and newly sent blocks will be 
  // locked out until a homing cycle or a kill lock command. Allows the user to disable the hard
  // limit setting if their limits are constantly triggering after a reset and move their axes.
  if (sys.state != STATE_ALARM) { 
    if (bit_isfalse(sys.execute,EXEC_ALARM)) {
      mc_reset(); // Initiate system kill.
      sys.execute |= EXEC_CRIT_EVENT; // Indicate hard limit critical event
    }
  }
}


// Moves all specified axes in same specified direction (positive=true, negative=false)
// and at the homing rate. Homing is a special motion case, where there is only an 
// acceleration followed by abrupt asynchronous stops by each axes reaching their limit 
// switch independently. Instead of shoehorning homing cycles into the main stepper 
// algorithm and overcomplicate things, a stripped-down, lite version of the stepper 
// algorithm is written here. This also lets users hack and tune this code freely for
// their own particular needs without affecting the rest of Grbl.
// NOTE: Only the abort runtime command can interrupt this process.
static void homing_cycle(uint8_t cycle_mask, int8_t pos_dir, bool invert_pin, float homing_rate) 
{

  /* TODO: Change homing routine to call planner instead moving at the maximum seek rates
     and (max_travel+10mm?) for each axes during the search phase. The routine should monitor
     the state of the limit pins and when a pin is triggered, it can disable that axes by 
     setting the respective step_x, step_y, or step_z value in the executing planner block.
     This keeps the stepper algorithm counters from triggering the step on that particular
     axis. When all axes have been triggered, we can then disable the steppers and reset
     the stepper and planner buffers. This same method can be used for the locate cycles. 
     This will also fix the slow max feedrate of the homing 'lite' stepper algorithm.
     
     Need to check if setting the planner steps will require them to be volatile or not. */
  
  
  // Determine governing axes with finest step resolution per distance for the Bresenham
  // algorithm. This solves the issue when homing multiple axes that have different 
  // resolutions without exceeding system acceleration setting. It doesn't have to be
  // perfect since homing locates machine zero, but should create for a more consistent 
  // and speedy homing routine.
  // NOTE: For each axes enabled, the following calculations assume they physically move 
  // an equal distance over each time step until they hit a limit switch, aka dogleg.
  uint32_t step_event_count = 0;
  uint8_t i, dist = 0;
  uint32_t steps[N_AXIS];
  clear_vector(steps);
  for (i=0; i<N_AXIS; i++) {
    if (cycle_mask & (1<<i)) { 
      dist++;
      steps[i] = lround(settings.steps_per_mm[i]); 
      step_event_count = max(step_event_count,steps[i]);
    }
  }
  
  // To ensure global acceleration is not exceeded, reduce the governing axes nominal rate
  // by adjusting the actual axes distance traveled per step. This is the same procedure
  // used in the main planner to account for distance traveled when moving multiple axes.
  // NOTE: When axis acceleration independence is installed, this will be updated to move
  // all axes at their maximum acceleration and rate.
  float ds = step_event_count/sqrt(dist);

  // Compute the adjusted step rate change with each acceleration tick. (in step/min/acceleration_tick)
  uint32_t delta_rate = ceil( ds*settings.acceleration[X_AXIS]/(60*ACCELERATION_TICKS_PER_SECOND));
  
  #ifdef HOMING_RATE_ADJUST
    // Adjust homing rate so a multiple axes moves all at the homing rate independently.
    homing_rate *= sqrt(dist); // Eq. only works if axes values are 1 or 0.
  #endif
  
  // Nominal and initial time increment per step. Nominal should always be greater then 3
  // usec, since they are based on the same parameters as the main stepper routine. Initial
  // is based on the MINIMUM_STEPS_PER_MINUTE config. Since homing feed can be very slow,
  // disable acceleration when rates are below MINIMUM_STEPS_PER_MINUTE.
  uint32_t dt_min = lround(1000000*60/(ds*homing_rate)); // Cruising (usec/step)
  uint32_t dt = 1000000*60/MINIMUM_STEPS_PER_MINUTE; // Initial (usec/step)
  if (dt > dt_min) { dt = dt_min; } // Disable acceleration for very slow rates.
      
  // Set default out_bits. 
  uint8_t out_bits0 = settings.invert_mask;
  out_bits0 ^= (settings.homing_dir_mask & DIRECTION_MASK); // Apply homing direction settings
  if (!pos_dir) { out_bits0 ^= DIRECTION_MASK; }   // Invert bits, if negative dir.
  
  // Initialize stepping variables
  int32_t counter_x = -(step_event_count >> 1); // Bresenham counters
  int32_t counter_y = counter_x;
  int32_t counter_z = counter_x;
  uint32_t step_delay = dt-settings.pulse_microseconds;  // Step delay after pulse
  uint32_t step_rate = 0;  // Tracks step rate. Initialized from 0 rate. (in step/min)
  uint32_t trap_counter = MICROSECONDS_PER_ACCELERATION_TICK/2; // Acceleration trapezoid counter
  uint8_t out_bits;
  uint8_t limit_state;
  for(;;) {
  
    // Reset out bits. Both direction and step pins appropriately inverted and set.
    out_bits = out_bits0;
    
    // Get limit pin state.
    limit_state = LIMIT_PIN;
    if (invert_pin) { limit_state ^= LIMIT_MASK; } // If leaving switch, invert to move.
    
    // Set step pins by Bresenham line algorithm. If limit switch reached, disable and
    // flag for completion.
    if (cycle_mask & (1<<X_AXIS)) {
      counter_x += steps[X_AXIS];
      if (counter_x > 0) {
        if (limit_state & (1<<X_LIMIT_BIT)) { out_bits ^= (1<<X_STEP_BIT); }
        else { cycle_mask &= ~(1<<X_AXIS); }
        counter_x -= step_event_count;
      }
    }
    if (cycle_mask & (1<<Y_AXIS)) {
      counter_y += steps[Y_AXIS];
      if (counter_y > 0) {
        if (limit_state & (1<<Y_LIMIT_BIT)) { out_bits ^= (1<<Y_STEP_BIT); }
        else { cycle_mask &= ~(1<<Y_AXIS); }
        counter_y -= step_event_count;
      }
    }
    if (cycle_mask & (1<<Z_AXIS)) {
      counter_z += steps[Z_AXIS];
      if (counter_z > 0) {
        if (limit_state & (1<<Z_LIMIT_BIT)) { out_bits ^= (1<<Z_STEP_BIT); }
        else { cycle_mask &= ~(1<<Z_AXIS); }
        counter_z -= step_event_count;
      }
    }        
    
    // Check if we are done or for system abort
    if (!(cycle_mask) || (sys.execute & EXEC_RESET)) { return; }
        
    // Perform step.
    STEPPING_PORT = (STEPPING_PORT & ~STEP_MASK) | (out_bits & STEP_MASK);
    delay_us(settings.pulse_microseconds);
    STEPPING_PORT = out_bits0;
    delay_us(step_delay);
    
    // Track and set the next step delay, if required. This routine uses another Bresenham
    // line algorithm to follow the constant acceleration line in the velocity and time 
    // domain. This is a lite version of the same routine used in the main stepper program.
    if (dt > dt_min) { // Unless cruising, check for time update.
      trap_counter += dt; // Track time passed since last update.
      if (trap_counter > MICROSECONDS_PER_ACCELERATION_TICK) {
        trap_counter -= MICROSECONDS_PER_ACCELERATION_TICK;
        step_rate += delta_rate; // Increment velocity
        dt = (1000000*60)/step_rate; // Compute new time increment
        if (dt < dt_min) {dt = dt_min;}  // If target rate reached, cruise.
        step_delay = dt-settings.pulse_microseconds;
      }
    }
  }
}


void limits_go_home() 
{  
  // Enable only the steppers, not the cycle. Cycle should be inactive/complete.
  st_wake_up();
  
  // Search to engage all axes limit switches at faster homing seek rate.
  homing_cycle(HOMING_SEARCH_CYCLE_0, true, false, settings.homing_seek_rate);  // Search cycle 0
  #ifdef HOMING_SEARCH_CYCLE_1
    homing_cycle(HOMING_SEARCH_CYCLE_1, true, false, settings.homing_seek_rate);  // Search cycle 1
  #endif
  #ifdef HOMING_SEARCH_CYCLE_2
    homing_cycle(HOMING_SEARCH_CYCLE_2, true, false, settings.homing_seek_rate);  // Search cycle 2
  #endif
  delay_ms(settings.homing_debounce_delay); // Delay to debounce signal
    
  // Now in proximity of all limits. Carefully leave and approach switches in multiple cycles
  // to precisely hone in on the machine zero location. Moves at slower homing feed rate.
  int8_t n_cycle = N_HOMING_LOCATE_CYCLE;
  while (n_cycle--) {
    // Leave all switches to release them. After cycles complete, this is machine zero.
    homing_cycle(HOMING_LOCATE_CYCLE, false, true, settings.homing_feed_rate);
    delay_ms(settings.homing_debounce_delay);
    
    if (n_cycle > 0) {
      // Re-approach all switches to re-engage them.
      homing_cycle(HOMING_LOCATE_CYCLE, true, false, settings.homing_feed_rate);
      delay_ms(settings.homing_debounce_delay);
    }
  }

  st_go_idle(); // Call main stepper shutdown routine.  
}


// Performs a soft limit check. Called from mc_line() only. Assumes the machine has been homed,
// and the workspace volume is in all negative space.
void limits_soft_check(float *target)
{
  uint8_t idx;
  for (idx=0; idx<N_AXIS; idx++) { 
    if (target[idx] > 0 || target[idx] < settings.max_travel[idx]) {  // NOTE: max_travel is stored as negative
    
      // Force feed hold if cycle is active. All buffered blocks are guaranteed to be within 
      // workspace volume so just come to a controlled stop so position is not lost. When complete
      // enter alarm mode.
      if (sys.state == STATE_CYCLE) {
        st_feed_hold();
        while (sys.state == STATE_HOLD) {
          protocol_execute_runtime();
          if (sys.abort) { return; }
        }
      }
      
      mc_reset(); // Issue system reset and ensure spindle and coolant are shutdown.
      sys.execute |= EXEC_CRIT_EVENT; // Indicate soft limit critical event
      protocol_execute_runtime(); // Execute to enter critical event loop and system abort
      return;
    
    }
  }
}