nullsub · August 2, 2012 17:37 · offon · Feb 12, 2013 · offon · Feb 12, 2013
diff --git a/config.h b/config.h
 /*
  config.h - compile time configuration
  Part of Grbl

  Copyright (c) 2009-2011 Simen Svale Skogsrud
  Copyright (c) 2011 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/>.
 */

 #ifndef config_h
 #define config_h

 // IMPORTANT: Any changes here requires a full re-compiling of the source code to propagate them.

 #define BAUD_RATE 9600

 // Updated default pin-assignments from 0.6 onwards 
 // (see bottom of file for a copy of the old config)

 #define STEPPERS_DISABLE_DDR     DDRB
 #define STEPPERS_DISABLE_PORT    PORTB
 #define STEPPERS_DISABLE_BIT         0

 //#define STEPPING_DDR       DDRD
 //#define STEPPING_PORT      PORTD
 #define X_STEP_BIT           2
 #define Y_STEP_BIT           3
 #define Z_STEP_BIT           4
 #define X_DIRECTION_BIT      5
 #define Y_DIRECTION_BIT      6
 #define Z_DIRECTION_BIT      7

 #define LIMIT_DDR      DDRB
 #define LIMIT_PIN     PINB
 #define X_LIMIT_BIT          1
 #define Y_LIMIT_BIT          2
 #define Z_LIMIT_BIT          3

 #define SPINDLE_ENABLE_DDR DDRB
 #define SPINDLE_ENABLE_PORT PORTB
 #define SPINDLE_ENABLE_BIT 4

 #define SPINDLE_DIRECTION_DDR DDRB
 #define SPINDLE_DIRECTION_PORT PORTB
 #define SPINDLE_DIRECTION_BIT 5

 // This parameter sets the delay time before disabling the steppers after the final block of movement.
 // A short delay ensures the steppers come to a complete stop and the residual inertial force in the 
 // CNC axes don't cause the axes to drift off position. This is particularly important when manually 
 // entering g-code into grbl, i.e. locating part zero or simple manual machining. If the axes drift,
 // grbl has no way to know this has happened, since stepper motors are open-loop control. Depending
 // on the machine, this parameter may need to be larger or smaller than the default time.
 // NOTE: If defined 0, the delay will not be compiled.
 #define STEPPER_IDLE_LOCK_TIME 25 // (milliseconds) - Integer >= 0

 // The temporal resolution of the acceleration management subsystem. Higher number give smoother
 // acceleration but may impact performance.
 // NOTE: Increasing this parameter will help any resolution related issues, especially with machines 
 // requiring very high accelerations and/or very fast feedrates. In general, this will reduce the 
 // error between how the planner plans the motions and how the stepper program actually performs them.
 // However, at some point, the resolution can be high enough, where the errors related to numerical 
 // round-off can be great enough to cause problems and/or it's too fast for the Arduino. The correct
 // value for this parameter is machine dependent, so it's advised to set this only as high as needed.
 // Approximate successful values can range from 30L to 100L or more.
 #define ACCELERATION_TICKS_PER_SECOND 50L

 // Minimum planner junction speed. Sets the default minimum speed the planner plans for at the end
 // of the buffer and all stops. This should not be much greater than zero and should only be changed
 // if unwanted behavior is observed on a user's machine when running at very slow speeds.
 #define MINIMUM_PLANNER_SPEED 0.0 // (mm/min)

 // Minimum stepper rate. Sets the absolute minimum stepper rate in the stepper program and never runs
 // slower than this value, except when sleeping. This parameter overrides the minimum planner speed.
 // This is primarily used to guarantee that the end of a movement is always reached and not stop to
 // never reach its target. This parameter should always be greater than zero.
 #define MINIMUM_STEPS_PER_MINUTE 800 // (steps/min) - Integer value only

 // Number of arc generation iterations by small angle approximation before exact arc trajectory 
 // correction. This parameter maybe decreased if there are issues with the accuracy of the arc
 // generations. In general, the default value is more than enough for the intended CNC applications
 // of grbl, and should be on the order or greater than the size of the buffer to help with the 
 // computational efficiency of generating arcs.
 #define N_ARC_CORRECTION 25 // Integer (1-255)

 #endif

 // Pin-assignments from Grbl 0.5

 // #define STEPPERS_DISABLE_DDR     DDRD
 // #define STEPPERS_DISABLE_PORT    PORTD
 // #define STEPPERS_DISABLE_BIT         2
 // 
 // #define STEPPING_DDR       DDRC
 // #define STEPPING_PORT      PORTC 
 // #define X_STEP_BIT           0
 // #define Y_STEP_BIT           1
 // #define Z_STEP_BIT           2
 // #define X_DIRECTION_BIT            3
 // #define Y_DIRECTION_BIT            4
 // #define Z_DIRECTION_BIT            5
 // 
 // #define LIMIT_DDR      DDRD
 // #define LIMIT_PORT     PORTD
 // #define X_LIMIT_BIT          3
 // #define Y_LIMIT_BIT          4
 // #define Z_LIMIT_BIT          5
 // 
 // #define SPINDLE_ENABLE_DDR DDRD
 // #define SPINDLE_ENABLE_PORT PORTD
 // #define SPINDLE_ENABLE_BIT 6
 // 
 // #define SPINDLE_DIRECTION_DDR DDRD
 // #define SPINDLE_DIRECTION_PORT PORTD
 // #define SPINDLE_DIRECTION_BIT 7
diff --git a/limits.c b/limits.c
 /*
  limits.h - code pertaining to limit-switches and performing the homing cycle
  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 <util/delay.h>
 #include <avr/io.h>
 #include "stepper.h"
 #include "settings.h"
 #include "nuts_bolts.h"
 #include "config.h"

 void limits_init() {
  //LIMIT_DDR &= ~(LIMIT_MASK);
 }

 static void homing_cycle(bool x_axis, bool y_axis, bool z_axis, bool reverse_direction, uint32_t microseconds_per_pulse) { 
  // First home the Z axis
 /* NOT SUPPORTED
 * uint32_t step_delay = microseconds_per_pulse - settings.pulse_microseconds;
  uint8_t out_bits = DIRECTION_MASK;
  uint8_t limit_bits;
  
  if (x_axis) { out_bits |= (1<<X_STEP_BIT); }
  if (y_axis) { out_bits |= (1<<Y_STEP_BIT); }
  if (z_axis) { out_bits |= (1<<Z_STEP_BIT); }
  
  // Invert direction bits if this is a reverse homing_cycle
  if (reverse_direction) {
    out_bits ^= DIRECTION_MASK;
  }
  
  // Apply the global invert mask
  out_bits ^= settings.invert_mask;
  
  // Set direction pins
  STEPPING_PORT = (STEPPING_PORT & ~DIRECTION_MASK) | (out_bits & DIRECTION_MASK);
  
  for(;;) {
    limit_bits = LIMIT_PIN;
    if (reverse_direction) {         
      // Invert limit_bits if this is a reverse homing_cycle
      limit_bits ^= LIMIT_MASK;
    }
    if (x_axis && !(LIMIT_PIN & (1<<X_LIMIT_BIT))) {
      x_axis = false;
      out_bits ^= (1<<X_STEP_BIT);      
    }    
    if (y_axis && !(LIMIT_PIN & (1<<Y_LIMIT_BIT))) {
      y_axis = false;
      out_bits ^= (1<<Y_STEP_BIT);
    }    
    if (z_axis && !(LIMIT_PIN & (1<<Z_LIMIT_BIT))) {
      z_axis = false;
      out_bits ^= (1<<Z_STEP_BIT);
    }
    // Check if we are done
    if(!(x_axis || y_axis || z_axis)) { return; }
    STEPPING_PORT |= out_bits & STEP_MASK;
    delay_us(settings.pulse_microseconds);
    STEPPING_PORT ^= out_bits & STEP_MASK;
    delay_us(step_delay);
  }*/
  return;
 }

 static void approach_limit_switch(bool x, bool y, bool z) {
  homing_cycle(x, y, z, false, 100000);
 }

 static void leave_limit_switch(bool x, bool y, bool z) {
  homing_cycle(x, y, z, true, 500000);
 }

 void limits_go_home() {
  st_synchronize();
  // Store the current limit switch state
  uint8_t original_limit_state = LIMIT_PIN;
  approach_limit_switch(false, false, true); // First home the z axis
  approach_limit_switch(true, true, false);  // Then home the x and y axis
  // Xor previous and current limit switch state to determine which were high then but have become 
  // low now. These are the actual installed limit switches.
  uint8_t limit_switches_present = (original_limit_state ^ LIMIT_PIN) & LIMIT_MASK;
  // Now carefully leave the limit switches
  leave_limit_switch(
    limit_switches_present & (1<<X_LIMIT_BIT), 
    limit_switches_present & (1<<Y_LIMIT_BIT),
    limit_switches_present & (1<<Z_LIMIT_BIT));
 }
diff --git a/stepper.c b/stepper.c
 /*
  stepper.c - stepper motor driver: executes motion plans using stepper motors
  Part of Grbl

  Copyright (c) 2009-2011 Simen Svale Skogsrud
  Copyright (c) 2011 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/>.
 */

 /* The timer calculations of this module informed by the 'RepRap cartesian firmware' by Zack Smith
   and Philipp Tiefenbacher. */

 #include "stepper.h"
 #include "config.h"
 #include "settings.h"
 #include <math.h>
 #include <stdlib.h>
 #include <util/delay.h>
 #include "nuts_bolts.h"
 #include <avr/interrupt.h>
 #include "planner.h"
 #include "limits.h"

 // Some useful constants
 #define STEP_MASK ((1<<X_STEP_BIT)|(1<<Y_STEP_BIT)|(1<<Z_STEP_BIT)) // All step bits
 #define DIRECTION_MASK ((1<<X_DIRECTION_BIT)|(1<<Y_DIRECTION_BIT)|(1<<Z_DIRECTION_BIT)) // All direction bits
 #define STEPPING_MASK (STEP_MASK | DIRECTION_MASK) // All stepping-related bits (step/direction)

 #define TICKS_PER_MICROSECOND (F_CPU/1000000)
 #define CYCLES_PER_ACCELERATION_TICK ((TICKS_PER_MICROSECOND*1000000)/ACCELERATION_TICKS_PER_SECOND)

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

 // Variables used by The Stepper Driver Interrupt
 static uint8_t out_bits;        // The next stepping-bits to be output
 static int32_t counter_x,       // Counter variables for the bresenham line tracer
               counter_y, 
               counter_z;       
 static uint32_t step_events_completed; // The number of step events executed in the current block
 static volatile uint8_t busy; // true when SIG_OUTPUT_COMPARE1A is being serviced. Used to avoid retriggering that handler.

 // Variables used by the trapezoid generation
 static uint32_t cycles_per_step_event;        // The number of machine cycles between each step event
 static uint32_t trapezoid_tick_cycle_counter; // The cycles since last trapezoid_tick. Used to generate ticks at a steady
                                              // pace without allocating a separate timer
 static uint32_t trapezoid_adjusted_rate;      // The current rate of step_events according to the trapezoid generator
 static uint32_t min_safe_rate;  // Minimum safe rate for full deceleration rate reduction step. Otherwise halves step_rate.
 static uint8_t cycle_start;     // Cycle start flag to indicate program start and block processing.

 //         __________________________
 //        /|                        |\     _________________         ^
 //       / |                        | \   /|               |\        |
 //      /  |                        |  \ / |               | \       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 by block->rate_delta
 //  during the 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 always +/- block->rate_delta and is applied at a constant rate following the midpoint rule
 //  by the trapezoid generator, which is called ACCELERATION_TICKS_PER_SECOND times per second.

 static void set_step_events_per_minute(uint32_t steps_per_minute);

 // Stepper state initialization
 static void st_wake_up() 
 {
  // Enable stepper driver interrupt
  TIMSK1 |= (1<<OCIE1A);
 }

 // Stepper shutdown
 static void st_go_idle() 
 {
  // Cycle finished. Set flag to false.
  cycle_start = false; 
  // Disable stepper driver interrupt
  TIMSK1 &= ~(1<<OCIE1A); 
  // Force stepper dwell to lock axes for a defined amount of time to ensure the axes come to a complete
  // stop and not drift from residual inertial forces at the end of the last movement.
 }

 // Initializes the trapezoid generator from the current block. Called whenever a new 
 // block begins.
 static void trapezoid_generator_reset() 
 {
  trapezoid_adjusted_rate = current_block->initial_rate;
  min_safe_rate = current_block->rate_delta + (current_block->rate_delta >> 1); // 1.5 x rate_delta
  trapezoid_tick_cycle_counter = CYCLES_PER_ACCELERATION_TICK/2; // Start halfway for midpoint rule.
  set_step_events_per_minute(trapezoid_adjusted_rate); // Initialize cycles_per_step_event
 }

 // This function determines an acceleration velocity change every CYCLES_PER_ACCELERATION_TICK by
 // keeping track of the number of elapsed cycles during a de/ac-celeration. The code assumes that 
 // step_events occur significantly more often than the acceleration velocity iterations.
 static uint8_t iterate_trapezoid_cycle_counter() 
 {
  trapezoid_tick_cycle_counter += cycles_per_step_event;  
  if(trapezoid_tick_cycle_counter > CYCLES_PER_ACCELERATION_TICK) {
    trapezoid_tick_cycle_counter -= CYCLES_PER_ACCELERATION_TICK;
    return(true);
  } else {
    return(false);
  }
 }          

 #define DIR_FORWARD 	(0)
 #define DIR_BACKWARD	(1)

 #define STEPPER_X_A1 	(0x01<<PINB0)	
 #define STEPPER_X_A2 	(0x01<<PINB1)	
 #define STEPPER_X_B1 	(0x01<<PINB2)	
 #define STEPPER_X_B2 	(0x01<<PINB3)	

 #define STEPPER_Y_A1 	(0x01<<PIND4)	
 #define STEPPER_Y_A2 	(0x01<<PIND5)	
 #define STEPPER_Y_B1 	(0x01<<PIND6)	
 #define STEPPER_Y_B2 	(0x01<<PIND7)

 #define STEPPER_Z_A1 	(0x01<<PINC0)	
 #define STEPPER_Z_A2 	(0x01<<PINC1)	
 #define STEPPER_Z_B1 	(0x01<<PINC2)	
 #define STEPPER_Z_B2 	(0x01<<PINC3)

 #define STEPPING_PORT_Z		PORTC
 #define STEPPING_PORT_Y		PORTD
 #define STEPPING_PORT_X		PORTB

 #define STEPPING_DDR_Z		DDRC
 #define STEPPING_DDR_Y		DDRD
 #define STEPPING_DDR_X		DDRB

 //#define STEPPER_X_ENABLE (0x01<<25)
 //#define STEPPER_Y_ENABLE (0x01<<26)

 #define ALL_STEPPER_PINS_X (STEPPER_X_A1|STEPPER_X_A2|STEPPER_X_B1|STEPPER_X_B2)
 #define ALL_STEPPER_PINS_Y (STEPPER_Y_A1|STEPPER_Y_A2|STEPPER_Y_B1|STEPPER_Y_B2)
 #define ALL_STEPPER_PINS_Z (STEPPER_Z_A1 |STEPPER_Z_A2|STEPPER_Z_B1|STEPPER_Z_B2)

 const int stepper_pins[3][4] = {
 		{STEPPER_X_A1, STEPPER_X_A2, STEPPER_X_B1, STEPPER_X_B2},
 		{STEPPER_Y_A1, STEPPER_Y_A2, STEPPER_Y_B1, STEPPER_Y_B2},
 		{STEPPER_Z_A1, STEPPER_Z_A2, STEPPER_Z_B1, STEPPER_Z_B2},
 		};

 void do_full_step(int direction, int axis) 
 {
 	static unsigned int crrnt_step[3] = {0,0,0};
 	
 	if(direction == DIR_FORWARD) {
 		crrnt_step[axis] ++;
 		if (crrnt_step[axis] >= 4)
 			crrnt_step[axis] = 0;
 	}
 	else{
 		if(crrnt_step[axis] == 0)
 			crrnt_step[axis] = 4;
 		crrnt_step[axis] --;			
 	}
 	
 	if(axis == X_AXIS) { // Z_AXIS is on a different I/O port
 		switch(crrnt_step[axis]) {
 			case 0:
 				STEPPING_PORT_X &= ~(stepper_pins[axis][0]|stepper_pins[axis][2]);
 				STEPPING_PORT_X |= stepper_pins[axis][3] | stepper_pins[axis][1];
 				break;
 			case 1:			
 				STEPPING_PORT_X &= ~(stepper_pins[axis][1] | stepper_pins[axis][2]);
 				STEPPING_PORT_X |= stepper_pins[axis][0] | stepper_pins[axis][3];
 				break;
 			case 2:				
 				STEPPING_PORT_X &= ~(stepper_pins[axis][1] | stepper_pins[axis][3]);
 				STEPPING_PORT_X |= stepper_pins[axis][2] | stepper_pins[axis][0];
 				break;
 			case 3:	
 				STEPPING_PORT_X &= ~(stepper_pins[axis][0] | stepper_pins[axis][3]);
 				STEPPING_PORT_X |= (stepper_pins[axis][1] | stepper_pins[axis][2]);
 				break;
 			return;
 		}
 	}
 	if(axis == Y_AXIS) { 
 		switch(crrnt_step[axis]) {
 			case 0:
 				STEPPING_PORT_Y &= ~(stepper_pins[axis][0]|stepper_pins[axis][2]);
 				STEPPING_PORT_Y |= stepper_pins[axis][3] | stepper_pins[axis][1];
 				break;
 			case 1:			
 				STEPPING_PORT_Y &= ~(stepper_pins[axis][1] | stepper_pins[axis][2]);
 				STEPPING_PORT_Y |= stepper_pins[axis][0] | stepper_pins[axis][3];
 				break;
 			case 2:				
 				STEPPING_PORT_Y &= ~(stepper_pins[axis][1] | stepper_pins[axis][3]);
 				STEPPING_PORT_Y |= stepper_pins[axis][2] | stepper_pins[axis][0];
 				break;
 			case 3:	
 				STEPPING_PORT_Y &= ~(stepper_pins[axis][0] | stepper_pins[axis][3]);
 				STEPPING_PORT_Y |= (stepper_pins[axis][1] | stepper_pins[axis][2]);
 				break;
 			return;
 		}
 	}
 	if(axis == Z_AXIS) { // Z_AXIS is on a different I/O port
 		switch(crrnt_step[axis]) {
 			case 0:
 				STEPPING_PORT_Z &= ~(stepper_pins[axis][0]|stepper_pins[axis][2]);
 				STEPPING_PORT_Z |= stepper_pins[axis][3] | stepper_pins[axis][1];
 				break;
 			case 1:			
 				STEPPING_PORT_Z &= ~(stepper_pins[axis][1] | stepper_pins[axis][2]);
 				STEPPING_PORT_Z |= stepper_pins[axis][0] | stepper_pins[axis][3];
 				break;
 			case 2:				
 				STEPPING_PORT_Z &= ~(stepper_pins[axis][1] | stepper_pins[axis][3]);
 				STEPPING_PORT_Z |= stepper_pins[axis][2] | stepper_pins[axis][0];
 				break;
 			case 3:	
 				STEPPING_PORT_Z &= ~(stepper_pins[axis][0] | stepper_pins[axis][3]);
 				STEPPING_PORT_Z |= (stepper_pins[axis][1] | stepper_pins[axis][2]);
 				break;
 			return;
 		}
 	}

 }

 // "The Stepper Driver Interrupt" - This timer interrupt is the workhorse of Grbl. It is executed at the rate set with
 // config_step_timer. It pops blocks from the block_buffer and executes them by pulsing the stepper pins appropriately. 
 // It is supported by The Stepper Port Reset Interrupt which it uses to reset the stepper port after each pulse. 
 // The bresenham line tracer algorithm controls all three stepper outputs simultaneously with these two interrupts.
 ISR(TIMER1_COMPA_vect)
 {        
  if (busy) { return; } // The busy-flag is used to avoid reentering this interrupt
  
 /* 
 // Set the direction pins a couple of nanoseconds before we step the steppers
  STEPPING_PORT = (STEPPING_PORT & ~DIRECTION_MASK) | (out_bits & DIRECTION_MASK);
  // Then pulse the stepping pins
  STEPPING_PORT = (STEPPING_PORT & ~STEP_MASK) | out_bits;
  // Enable step pulse reset timer so that The Stepper Port Reset Interrupt can reset the signal after
  // exactly settings.pulse_microseconds microseconds, independent of the main Timer1 prescaler.
  TCNT2 = -(((settings.pulse_microseconds-2)*TICKS_PER_MICROSECOND) >> 3); // Reload timer counter
  TCCR2B = (1<<CS21); // Begin timer2. Full speed, 1/8 prescaler
 */

 	if(out_bits & (1<<X_STEP_BIT)) {
 		if(out_bits & (1<<X_DIRECTION_BIT)) {
 			//do_half_step(DIR_FORWARD, X_AXIS);
 			do_full_step(DIR_FORWARD, X_AXIS);
 		} else {
 //			do_half_step(DIR_BACKWARD, X_AXIS);
 			do_full_step(DIR_BACKWARD, X_AXIS);
 		}
 	}	
 	if(out_bits & (1<<Y_STEP_BIT)) {
 		if(out_bits & (1<<Y_DIRECTION_BIT)) {
 //			do_half_step(DIR_FORWARD, Y_AXIS);
 			do_full_step(DIR_FORWARD, Y_AXIS);
 		} else {
 	//		do_half_step(DIR_BACKWARD, Y_AXIS);
 			do_full_step(DIR_BACKWARD, Y_AXIS);
 		}	
 	}
 	if(out_bits & (1<<Z_STEP_BIT)) {
 		if(out_bits & (1<<Z_DIRECTION_BIT)) {
 //			do_half_step(DIR_FORWARD, Z_AXIS);
 			do_full_step(DIR_FORWARD, Z_AXIS);
 		} else {
 //			do_half_step(DIR_BACKWARD, Z_AXIS);
 			do_full_step(DIR_BACKWARD, Z_AXIS);
 		}	
 	}


  busy = true;
  // Re-enable interrupts to allow ISR_TIMER2_OVERFLOW to trigger on-time and allow serial communications
  // regardless of time in this handler. The following code prepares the stepper driver for the next
  // step interrupt compare and will always finish before returning to the main program.
  sei();
  
  // If there is no current block, attempt to pop one from the buffer
  if (current_block == NULL) {
    // Anything in the buffer? If so, initialize next motion.
    current_block = plan_get_current_block();
    if (current_block != NULL) {
      trapezoid_generator_reset();
      counter_x = -(current_block->step_event_count >> 1);
      counter_y = counter_x;
      counter_z = counter_x;
      step_events_completed = 0;     
    } else {
      st_go_idle();
    }    
  } 

  if (current_block != NULL) {
    // Execute step displacement profile by bresenham line algorithm
    out_bits = current_block->direction_bits;
    counter_x += current_block->steps_x;
    if (counter_x > 0) {
      out_bits |= (1<<X_STEP_BIT);
      counter_x -= current_block->step_event_count;
    }
    counter_y += current_block->steps_y;
    if (counter_y > 0) {
      out_bits |= (1<<Y_STEP_BIT);
      counter_y -= current_block->step_event_count;
    }
    counter_z += current_block->steps_z;
    if (counter_z > 0) {
      out_bits |= (1<<Z_STEP_BIT);
      counter_z -= current_block->step_event_count;
    }
    
    step_events_completed++; // Iterate step events

    // While in block steps, check for de/ac-celeration events and execute them accordingly.
    if (step_events_completed < current_block->step_event_count) {
      // The trapezoid generator always checks step event location to ensure de/ac-celerations are 
      // executed and terminated at exactly the right time. This helps prevent over/under-shooting
      // the target position and speed. 
      // NOTE: By increasing the ACCELERATION_TICKS_PER_SECOND in config.h, the resolution of the 
      // discrete velocity changes increase and accuracy can increase as well to a point. Numerical 
      // round-off errors can effect this, if set too high. This is important to note if a user has 
      // very high acceleration and/or feedrate requirements for their machine.
      if (step_events_completed < current_block->accelerate_until) {
        // Iterate cycle counter and check if speeds need to be increased.
        if ( iterate_trapezoid_cycle_counter() ) {
          trapezoid_adjusted_rate += current_block->rate_delta;
          if (trapezoid_adjusted_rate >= current_block->nominal_rate) {
            // Reached nominal rate a little early. Cruise at nominal rate until decelerate_after.
            trapezoid_adjusted_rate = current_block->nominal_rate;
          }
          set_step_events_per_minute(trapezoid_adjusted_rate);
        }
      } else if (step_events_completed >= current_block->decelerate_after) {
        // Reset trapezoid tick cycle counter to make sure that the deceleration is performed the
        // same every time. Reset to CYCLES_PER_ACCELERATION_TICK/2 to follow the midpoint rule for
        // an accurate approximation of the deceleration curve.
        if (step_events_completed == current_block-> decelerate_after) {
          trapezoid_tick_cycle_counter = CYCLES_PER_ACCELERATION_TICK/2;
        } else {
          // Iterate cycle counter and check if speeds need to be reduced.
          if ( iterate_trapezoid_cycle_counter() ) {  
            // NOTE: We will only do a full speed reduction if the result is more than the minimum safe 
            // rate, initialized in trapezoid reset as 1.5 x rate_delta. Otherwise, reduce the speed by
            // half increments until finished. The half increments are guaranteed not to exceed the 
            // CNC acceleration limits, because they will never be greater than rate_delta. This catches
            // small errors that might leave steps hanging after the last trapezoid tick or a very slow
            // step rate at the end of a full stop deceleration in certain situations. The half rate 
            // reductions should only be called once or twice per block and create a nice smooth 
            // end deceleration.
            if (trapezoid_adjusted_rate > min_safe_rate) {
              trapezoid_adjusted_rate -= current_block->rate_delta;
            } else {
              trapezoid_adjusted_rate >>= 1; // Bit shift divide by 2
            }
            if (trapezoid_adjusted_rate < current_block->final_rate) {
              // Reached final rate a little early. Cruise to end of block at final rate.
              trapezoid_adjusted_rate = current_block->final_rate;
            }
            set_step_events_per_minute(trapezoid_adjusted_rate);
          }
        }
      } else {
        // No accelerations. Make sure we cruise exactly at the nominal rate.
        if (trapezoid_adjusted_rate != current_block->nominal_rate) {
          trapezoid_adjusted_rate = current_block->nominal_rate;
          set_step_events_per_minute(trapezoid_adjusted_rate);
        }
      }
            
    } else {   
      // If current block is finished, reset pointer 
      current_block = NULL;
      plan_discard_current_block();
    }
  }
 // out_bits ^= settings.invert_mask;  // Apply stepper invert mask    
  busy=false;
 }

 // This interrupt is set up by ISR_TIMER1_COMPAREA when it sets the motor port bits. It resets
 // the motor port after a short period (settings.pulse_microseconds) completing one step cycle.
 // TODO: It is possible for the serial interrupts to delay this interrupt by a few microseconds, if
 // they execute right before this interrupt. Not a big deal, but could use some TLC at some point.
 ISR(TIMER2_OVF_vect)
 {
  // Reset stepping pins (leave the direction pins)
 //  STEPPING_PORT = (STEPPING_PORT & ~STEP_MASK) | (settings.invert_mask & STEP_MASK); 
  TCCR2B = 0; // Disable Timer2 to prevent re-entering this interrupt when it's not needed. 
 }

 // Initialize and start the stepper motor subsystem
 void st_init()
 {
  // Configure directions of interface pins
 // STEPPING_DDR |= STEPPING_MASK;
 //  STEPPING_PORT = (STEPPING_PORT & ~STEPPING_MASK) | settings.invert_mask;
 //  STEPPERS_DISABLE_DDR |= 1<<STEPPERS_DISABLE_BIT;
  
  STEPPING_DDR_X  |= ALL_STEPPER_PINS_X;
  STEPPING_PORT_X |= ALL_STEPPER_PINS_X;
  STEPPING_DDR_Y  |= ALL_STEPPER_PINS_Y;
  STEPPING_PORT_Y |= ALL_STEPPER_PINS_Y;
  STEPPING_DDR_Z  |= ALL_STEPPER_PINS_Z;
  STEPPING_PORT_Z |= ALL_STEPPER_PINS_Z;


  // waveform generation = 0100 = CTC
  TCCR1B &= ~(1<<WGM13);
  TCCR1B |=  (1<<WGM12);
  TCCR1A &= ~(1<<WGM11); 
  TCCR1A &= ~(1<<WGM10);

  // output mode = 00 (disconnected)
  TCCR1A &= ~(3<<COM1A0); 
  TCCR1A &= ~(3<<COM1B0); 
 	
  // Configure Timer 2
  TCCR2A = 0; // Normal operation
  TCCR2B = 0; // Disable timer until needed.
  TIMSK2 |= (1<<TOIE2); // Enable Timer2 interrupt flag
  
  set_step_events_per_minute(MINIMUM_STEPS_PER_MINUTE);
  trapezoid_tick_cycle_counter = 0;
  current_block = NULL;
  busy = false;
  
  // Start in the idle state
  st_go_idle();
 }

 // Block until all buffered steps are executed
 void st_synchronize()
 {
  while(plan_get_current_block()) { sleep_mode(); }    
 }

 // Configures the prescaler and ceiling of timer 1 to produce the given rate as accurately as possible.
 // Returns the actual number of cycles per interrupt
 static uint32_t config_step_timer(uint32_t cycles)
 {
  uint16_t ceiling;
  uint16_t prescaler;
  uint32_t actual_cycles;
  if (cycles <= 0xffffL) {
    ceiling = cycles;
    prescaler = 0; // prescaler: 0
    actual_cycles = ceiling;
  } else if (cycles <= 0x7ffffL) {
    ceiling = cycles >> 3;
    prescaler = 1; // prescaler: 8
    actual_cycles = ceiling * 8L;
  } else if (cycles <= 0x3fffffL) {
    ceiling =  cycles >> 6;
    prescaler = 2; // prescaler: 64
    actual_cycles = ceiling * 64L;
  } else if (cycles <= 0xffffffL) {
    ceiling =  (cycles >> 8);
    prescaler = 3; // prescaler: 256
    actual_cycles = ceiling * 256L;
  } else if (cycles <= 0x3ffffffL) {
    ceiling = (cycles >> 10);
    prescaler = 4; // prescaler: 1024
    actual_cycles = ceiling * 1024L;    
  } else {
    // Okay, that was slower than we actually go. Just set the slowest speed
    ceiling = 0xffff;
    prescaler = 4;
    actual_cycles = 0xffff * 1024;
  }
  // Set prescaler
  TCCR1B = (TCCR1B & ~(0x07<<CS10)) | ((prescaler+1)<<CS10);
  // Set ceiling
  OCR1A = ceiling;
  return(actual_cycles);
 }

 static void set_step_events_per_minute(uint32_t steps_per_minute) 
 {
  if (steps_per_minute < MINIMUM_STEPS_PER_MINUTE) { steps_per_minute = MINIMUM_STEPS_PER_MINUTE; }
  cycles_per_step_event = config_step_timer((TICKS_PER_MICROSECOND*1000000*60)/steps_per_minute);
 }

 void st_go_home()
 {
  limits_go_home();  
  plan_set_current_position(0,0,0);
 }

 // Planner external interface to start stepper interrupt and execute the blocks in queue.
 void st_cycle_start() 
 {
  if (!cycle_start) {
    cycle_start = true;
    st_wake_up();
  }
 }
	/*
	config.h - compile time configuration
	Part of Grbl

	Copyright (c) 2009-2011 Simen Svale Skogsrud
	Copyright (c) 2011 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/>.
	*/

	#ifndef config_h
	#define config_h

	// IMPORTANT: Any changes here requires a full re-compiling of the source code to propagate them.

	#define BAUD_RATE 9600

	// Updated default pin-assignments from 0.6 onwards
	// (see bottom of file for a copy of the old config)

	#define STEPPERS_DISABLE_DDR DDRB
	#define STEPPERS_DISABLE_PORT PORTB
	#define STEPPERS_DISABLE_BIT 0

	//#define STEPPING_DDR DDRD
	//#define STEPPING_PORT PORTD
	#define X_STEP_BIT 2
	#define Y_STEP_BIT 3
	#define Z_STEP_BIT 4
	#define X_DIRECTION_BIT 5
	#define Y_DIRECTION_BIT 6
	#define Z_DIRECTION_BIT 7

	#define LIMIT_DDR DDRB
	#define LIMIT_PIN PINB
	#define X_LIMIT_BIT 1
	#define Y_LIMIT_BIT 2
	#define Z_LIMIT_BIT 3

	#define SPINDLE_ENABLE_DDR DDRB
	#define SPINDLE_ENABLE_PORT PORTB
	#define SPINDLE_ENABLE_BIT 4

	#define SPINDLE_DIRECTION_DDR DDRB
	#define SPINDLE_DIRECTION_PORT PORTB
	#define SPINDLE_DIRECTION_BIT 5

	// This parameter sets the delay time before disabling the steppers after the final block of movement.
	// A short delay ensures the steppers come to a complete stop and the residual inertial force in the
	// CNC axes don't cause the axes to drift off position. This is particularly important when manually
	// entering g-code into grbl, i.e. locating part zero or simple manual machining. If the axes drift,
	// grbl has no way to know this has happened, since stepper motors are open-loop control. Depending
	// on the machine, this parameter may need to be larger or smaller than the default time.
	// NOTE: If defined 0, the delay will not be compiled.
	#define STEPPER_IDLE_LOCK_TIME 25 // (milliseconds) - Integer >= 0

	// The temporal resolution of the acceleration management subsystem. Higher number give smoother
	// acceleration but may impact performance.
	// NOTE: Increasing this parameter will help any resolution related issues, especially with machines
	// requiring very high accelerations and/or very fast feedrates. In general, this will reduce the
	// error between how the planner plans the motions and how the stepper program actually performs them.
	// However, at some point, the resolution can be high enough, where the errors related to numerical
	// round-off can be great enough to cause problems and/or it's too fast for the Arduino. The correct
	// value for this parameter is machine dependent, so it's advised to set this only as high as needed.
	// Approximate successful values can range from 30L to 100L or more.
	#define ACCELERATION_TICKS_PER_SECOND 50L

	// Minimum planner junction speed. Sets the default minimum speed the planner plans for at the end
	// of the buffer and all stops. This should not be much greater than zero and should only be changed
	// if unwanted behavior is observed on a user's machine when running at very slow speeds.
	#define MINIMUM_PLANNER_SPEED 0.0 // (mm/min)

	// Minimum stepper rate. Sets the absolute minimum stepper rate in the stepper program and never runs
	// slower than this value, except when sleeping. This parameter overrides the minimum planner speed.
	// This is primarily used to guarantee that the end of a movement is always reached and not stop to
	// never reach its target. This parameter should always be greater than zero.
	#define MINIMUM_STEPS_PER_MINUTE 800 // (steps/min) - Integer value only

	// Number of arc generation iterations by small angle approximation before exact arc trajectory
	// correction. This parameter maybe decreased if there are issues with the accuracy of the arc
	// generations. In general, the default value is more than enough for the intended CNC applications
	// of grbl, and should be on the order or greater than the size of the buffer to help with the
	// computational efficiency of generating arcs.
	#define N_ARC_CORRECTION 25 // Integer (1-255)

	#endif

	// Pin-assignments from Grbl 0.5

	// #define STEPPERS_DISABLE_DDR DDRD
	// #define STEPPERS_DISABLE_PORT PORTD
	// #define STEPPERS_DISABLE_BIT 2
	//
	// #define STEPPING_DDR DDRC
	// #define STEPPING_PORT PORTC
	// #define X_STEP_BIT 0
	// #define Y_STEP_BIT 1
	// #define Z_STEP_BIT 2
	// #define X_DIRECTION_BIT 3
	// #define Y_DIRECTION_BIT 4
	// #define Z_DIRECTION_BIT 5
	//
	// #define LIMIT_DDR DDRD
	// #define LIMIT_PORT PORTD
	// #define X_LIMIT_BIT 3
	// #define Y_LIMIT_BIT 4
	// #define Z_LIMIT_BIT 5
	//
	// #define SPINDLE_ENABLE_DDR DDRD
	// #define SPINDLE_ENABLE_PORT PORTD
	// #define SPINDLE_ENABLE_BIT 6
	//
	// #define SPINDLE_DIRECTION_DDR DDRD
	// #define SPINDLE_DIRECTION_PORT PORTD
	// #define SPINDLE_DIRECTION_BIT 7
	/*
	limits.h - code pertaining to limit-switches and performing the homing cycle
	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 <util/delay.h>
	#include <avr/io.h>
	#include "stepper.h"
	#include "settings.h"
	#include "nuts_bolts.h"
	#include "config.h"

	void limits_init() {
	//LIMIT_DDR &= ~(LIMIT_MASK);
	}

	static void homing_cycle(bool x_axis, bool y_axis, bool z_axis, bool reverse_direction, uint32_t microseconds_per_pulse) {
	// First home the Z axis
	/* NOT SUPPORTED
	* uint32_t step_delay = microseconds_per_pulse - settings.pulse_microseconds;
	uint8_t out_bits = DIRECTION_MASK;
	uint8_t limit_bits;

	if (x_axis) { out_bits \|= (1<<X_STEP_BIT); }
	if (y_axis) { out_bits \|= (1<<Y_STEP_BIT); }
	if (z_axis) { out_bits \|= (1<<Z_STEP_BIT); }

	// Invert direction bits if this is a reverse homing_cycle
	if (reverse_direction) {
	out_bits ^= DIRECTION_MASK;
	}

	// Apply the global invert mask
	out_bits ^= settings.invert_mask;

	// Set direction pins
	STEPPING_PORT = (STEPPING_PORT & ~DIRECTION_MASK) \| (out_bits & DIRECTION_MASK);

	for(;;) {
	limit_bits = LIMIT_PIN;
	if (reverse_direction) {
	// Invert limit_bits if this is a reverse homing_cycle
	limit_bits ^= LIMIT_MASK;
	}
	if (x_axis && !(LIMIT_PIN & (1<<X_LIMIT_BIT))) {
	x_axis = false;
	out_bits ^= (1<<X_STEP_BIT);
	}
	if (y_axis && !(LIMIT_PIN & (1<<Y_LIMIT_BIT))) {
	y_axis = false;
	out_bits ^= (1<<Y_STEP_BIT);
	}
	if (z_axis && !(LIMIT_PIN & (1<<Z_LIMIT_BIT))) {
	z_axis = false;
	out_bits ^= (1<<Z_STEP_BIT);
	}
	// Check if we are done
	if(!(x_axis \|\| y_axis \|\| z_axis)) { return; }
	STEPPING_PORT \|= out_bits & STEP_MASK;
	delay_us(settings.pulse_microseconds);
	STEPPING_PORT ^= out_bits & STEP_MASK;
	delay_us(step_delay);
	}*/
	return;
	}

	static void approach_limit_switch(bool x, bool y, bool z) {
	homing_cycle(x, y, z, false, 100000);
	}

	static void leave_limit_switch(bool x, bool y, bool z) {
	homing_cycle(x, y, z, true, 500000);
	}

	void limits_go_home() {
	st_synchronize();
	// Store the current limit switch state
	uint8_t original_limit_state = LIMIT_PIN;
	approach_limit_switch(false, false, true); // First home the z axis
	approach_limit_switch(true, true, false); // Then home the x and y axis
	// Xor previous and current limit switch state to determine which were high then but have become
	// low now. These are the actual installed limit switches.
	uint8_t limit_switches_present = (original_limit_state ^ LIMIT_PIN) & LIMIT_MASK;
	// Now carefully leave the limit switches
	leave_limit_switch(
	limit_switches_present & (1<<X_LIMIT_BIT),
	limit_switches_present & (1<<Y_LIMIT_BIT),
	limit_switches_present & (1<<Z_LIMIT_BIT));
	}
	/*
	stepper.c - stepper motor driver: executes motion plans using stepper motors
	Part of Grbl

	Copyright (c) 2009-2011 Simen Svale Skogsrud
	Copyright (c) 2011 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/>.
	*/

	/* The timer calculations of this module informed by the 'RepRap cartesian firmware' by Zack Smith
	and Philipp Tiefenbacher. */

	#include "stepper.h"
	#include "config.h"
	#include "settings.h"
	#include <math.h>
	#include <stdlib.h>
	#include <util/delay.h>
	#include "nuts_bolts.h"
	#include <avr/interrupt.h>
	#include "planner.h"
	#include "limits.h"

	// Some useful constants
	#define STEP_MASK ((1<<X_STEP_BIT)\|(1<<Y_STEP_BIT)\|(1<<Z_STEP_BIT)) // All step bits
	#define DIRECTION_MASK ((1<<X_DIRECTION_BIT)\|(1<<Y_DIRECTION_BIT)\|(1<<Z_DIRECTION_BIT)) // All direction bits
	#define STEPPING_MASK (STEP_MASK \| DIRECTION_MASK) // All stepping-related bits (step/direction)

	#define TICKS_PER_MICROSECOND (F_CPU/1000000)
	#define CYCLES_PER_ACCELERATION_TICK ((TICKS_PER_MICROSECOND*1000000)/ACCELERATION_TICKS_PER_SECOND)

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

	// Variables used by The Stepper Driver Interrupt
	static uint8_t out_bits; // The next stepping-bits to be output
	static int32_t counter_x, // Counter variables for the bresenham line tracer
	counter_y,
	counter_z;
	static uint32_t step_events_completed; // The number of step events executed in the current block
	static volatile uint8_t busy; // true when SIG_OUTPUT_COMPARE1A is being serviced. Used to avoid retriggering that handler.

	// Variables used by the trapezoid generation
	static uint32_t cycles_per_step_event; // The number of machine cycles between each step event
	static uint32_t trapezoid_tick_cycle_counter; // The cycles since last trapezoid_tick. Used to generate ticks at a steady
	// pace without allocating a separate timer
	static uint32_t trapezoid_adjusted_rate; // The current rate of step_events according to the trapezoid generator
	static uint32_t min_safe_rate; // Minimum safe rate for full deceleration rate reduction step. Otherwise halves step_rate.
	static uint8_t cycle_start; // Cycle start flag to indicate program start and block processing.

	// __________________________
	// /\| \|\ _________________ ^
	// / \| \| \ /\| \|\ \|
	// / \| \| \ / \| \| \ 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 by block->rate_delta
	// during the 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 always +/- block->rate_delta and is applied at a constant rate following the midpoint rule
	// by the trapezoid generator, which is called ACCELERATION_TICKS_PER_SECOND times per second.

	static void set_step_events_per_minute(uint32_t steps_per_minute);

	// Stepper state initialization
	static void st_wake_up()
	{
	// Enable stepper driver interrupt
	TIMSK1 \|= (1<<OCIE1A);
	}

	// Stepper shutdown
	static void st_go_idle()
	{
	// Cycle finished. Set flag to false.
	cycle_start = false;
	// Disable stepper driver interrupt
	TIMSK1 &= ~(1<<OCIE1A);
	// Force stepper dwell to lock axes for a defined amount of time to ensure the axes come to a complete
	// stop and not drift from residual inertial forces at the end of the last movement.
	}

	// Initializes the trapezoid generator from the current block. Called whenever a new
	// block begins.
	static void trapezoid_generator_reset()
	{
	trapezoid_adjusted_rate = current_block->initial_rate;
	min_safe_rate = current_block->rate_delta + (current_block->rate_delta >> 1); // 1.5 x rate_delta
	trapezoid_tick_cycle_counter = CYCLES_PER_ACCELERATION_TICK/2; // Start halfway for midpoint rule.
	set_step_events_per_minute(trapezoid_adjusted_rate); // Initialize cycles_per_step_event
	}

	// This function determines an acceleration velocity change every CYCLES_PER_ACCELERATION_TICK by
	// keeping track of the number of elapsed cycles during a de/ac-celeration. The code assumes that
	// step_events occur significantly more often than the acceleration velocity iterations.
	static uint8_t iterate_trapezoid_cycle_counter()
	{
	trapezoid_tick_cycle_counter += cycles_per_step_event;
	if(trapezoid_tick_cycle_counter > CYCLES_PER_ACCELERATION_TICK) {
	trapezoid_tick_cycle_counter -= CYCLES_PER_ACCELERATION_TICK;
	return(true);
	} else {
	return(false);
	}
	}

	#define DIR_FORWARD (0)
	#define DIR_BACKWARD (1)

	#define STEPPER_X_A1 (0x01<<PINB0)
	#define STEPPER_X_A2 (0x01<<PINB1)
	#define STEPPER_X_B1 (0x01<<PINB2)
	#define STEPPER_X_B2 (0x01<<PINB3)

	#define STEPPER_Y_A1 (0x01<<PIND4)
	#define STEPPER_Y_A2 (0x01<<PIND5)
	#define STEPPER_Y_B1 (0x01<<PIND6)
	#define STEPPER_Y_B2 (0x01<<PIND7)

	#define STEPPER_Z_A1 (0x01<<PINC0)
	#define STEPPER_Z_A2 (0x01<<PINC1)
	#define STEPPER_Z_B1 (0x01<<PINC2)
	#define STEPPER_Z_B2 (0x01<<PINC3)

	#define STEPPING_PORT_Z PORTC
	#define STEPPING_PORT_Y PORTD
	#define STEPPING_PORT_X PORTB

	#define STEPPING_DDR_Z DDRC
	#define STEPPING_DDR_Y DDRD
	#define STEPPING_DDR_X DDRB

	//#define STEPPER_X_ENABLE (0x01<<25)
	//#define STEPPER_Y_ENABLE (0x01<<26)

	#define ALL_STEPPER_PINS_X (STEPPER_X_A1\|STEPPER_X_A2\|STEPPER_X_B1\|STEPPER_X_B2)
	#define ALL_STEPPER_PINS_Y (STEPPER_Y_A1\|STEPPER_Y_A2\|STEPPER_Y_B1\|STEPPER_Y_B2)
	#define ALL_STEPPER_PINS_Z (STEPPER_Z_A1 \|STEPPER_Z_A2\|STEPPER_Z_B1\|STEPPER_Z_B2)

	const int stepper_pins[3][4] = {
	{STEPPER_X_A1, STEPPER_X_A2, STEPPER_X_B1, STEPPER_X_B2},
	{STEPPER_Y_A1, STEPPER_Y_A2, STEPPER_Y_B1, STEPPER_Y_B2},
	{STEPPER_Z_A1, STEPPER_Z_A2, STEPPER_Z_B1, STEPPER_Z_B2},
	};

	void do_full_step(int direction, int axis)
	{
	static unsigned int crrnt_step[3] = {0,0,0};

	if(direction == DIR_FORWARD) {
	crrnt_step[axis] ++;
	if (crrnt_step[axis] >= 4)
	crrnt_step[axis] = 0;
	}
	else{
	if(crrnt_step[axis] == 0)
	crrnt_step[axis] = 4;
	crrnt_step[axis] --;
	}

	if(axis == X_AXIS) { // Z_AXIS is on a different I/O port
	switch(crrnt_step[axis]) {
	case 0:
	STEPPING_PORT_X &= ~(stepper_pins[axis][0]\|stepper_pins[axis][2]);
	STEPPING_PORT_X \|= stepper_pins[axis][3] \| stepper_pins[axis][1];
	break;
	case 1:
	STEPPING_PORT_X &= ~(stepper_pins[axis][1] \| stepper_pins[axis][2]);
	STEPPING_PORT_X \|= stepper_pins[axis][0] \| stepper_pins[axis][3];
	break;
	case 2:
	STEPPING_PORT_X &= ~(stepper_pins[axis][1] \| stepper_pins[axis][3]);
	STEPPING_PORT_X \|= stepper_pins[axis][2] \| stepper_pins[axis][0];
	break;
	case 3:
	STEPPING_PORT_X &= ~(stepper_pins[axis][0] \| stepper_pins[axis][3]);
	STEPPING_PORT_X \|= (stepper_pins[axis][1] \| stepper_pins[axis][2]);
	break;
	return;
	}
	}
	if(axis == Y_AXIS) {
	switch(crrnt_step[axis]) {
	case 0:
	STEPPING_PORT_Y &= ~(stepper_pins[axis][0]\|stepper_pins[axis][2]);
	STEPPING_PORT_Y \|= stepper_pins[axis][3] \| stepper_pins[axis][1];
	break;
	case 1:
	STEPPING_PORT_Y &= ~(stepper_pins[axis][1] \| stepper_pins[axis][2]);
	STEPPING_PORT_Y \|= stepper_pins[axis][0] \| stepper_pins[axis][3];
	break;
	case 2:
	STEPPING_PORT_Y &= ~(stepper_pins[axis][1] \| stepper_pins[axis][3]);
	STEPPING_PORT_Y \|= stepper_pins[axis][2] \| stepper_pins[axis][0];
	break;
	case 3:
	STEPPING_PORT_Y &= ~(stepper_pins[axis][0] \| stepper_pins[axis][3]);
	STEPPING_PORT_Y \|= (stepper_pins[axis][1] \| stepper_pins[axis][2]);
	break;
	return;
	}
	}
	if(axis == Z_AXIS) { // Z_AXIS is on a different I/O port
	switch(crrnt_step[axis]) {
	case 0:
	STEPPING_PORT_Z &= ~(stepper_pins[axis][0]\|stepper_pins[axis][2]);
	STEPPING_PORT_Z \|= stepper_pins[axis][3] \| stepper_pins[axis][1];
	break;
	case 1:
	STEPPING_PORT_Z &= ~(stepper_pins[axis][1] \| stepper_pins[axis][2]);
	STEPPING_PORT_Z \|= stepper_pins[axis][0] \| stepper_pins[axis][3];
	break;
	case 2:
	STEPPING_PORT_Z &= ~(stepper_pins[axis][1] \| stepper_pins[axis][3]);
	STEPPING_PORT_Z \|= stepper_pins[axis][2] \| stepper_pins[axis][0];
	break;
	case 3:
	STEPPING_PORT_Z &= ~(stepper_pins[axis][0] \| stepper_pins[axis][3]);
	STEPPING_PORT_Z \|= (stepper_pins[axis][1] \| stepper_pins[axis][2]);
	break;
	return;
	}
	}

	}

	// "The Stepper Driver Interrupt" - This timer interrupt is the workhorse of Grbl. It is executed at the rate set with
	// config_step_timer. It pops blocks from the block_buffer and executes them by pulsing the stepper pins appropriately.
	// It is supported by The Stepper Port Reset Interrupt which it uses to reset the stepper port after each pulse.
	// The bresenham line tracer algorithm controls all three stepper outputs simultaneously with these two interrupts.
	ISR(TIMER1_COMPA_vect)
	{
	if (busy) { return; } // The busy-flag is used to avoid reentering this interrupt

	/*
	// Set the direction pins a couple of nanoseconds before we step the steppers
	STEPPING_PORT = (STEPPING_PORT & ~DIRECTION_MASK) \| (out_bits & DIRECTION_MASK);
	// Then pulse the stepping pins
	STEPPING_PORT = (STEPPING_PORT & ~STEP_MASK) \| out_bits;
	// Enable step pulse reset timer so that The Stepper Port Reset Interrupt can reset the signal after
	// exactly settings.pulse_microseconds microseconds, independent of the main Timer1 prescaler.
	TCNT2 = -(((settings.pulse_microseconds-2)*TICKS_PER_MICROSECOND) >> 3); // Reload timer counter
	TCCR2B = (1<<CS21); // Begin timer2. Full speed, 1/8 prescaler
	*/

	if(out_bits & (1<<X_STEP_BIT)) {
	if(out_bits & (1<<X_DIRECTION_BIT)) {
	//do_half_step(DIR_FORWARD, X_AXIS);
	do_full_step(DIR_FORWARD, X_AXIS);
	} else {
	// do_half_step(DIR_BACKWARD, X_AXIS);
	do_full_step(DIR_BACKWARD, X_AXIS);
	}
	}
	if(out_bits & (1<<Y_STEP_BIT)) {
	if(out_bits & (1<<Y_DIRECTION_BIT)) {
	// do_half_step(DIR_FORWARD, Y_AXIS);
	do_full_step(DIR_FORWARD, Y_AXIS);
	} else {
	// do_half_step(DIR_BACKWARD, Y_AXIS);
	do_full_step(DIR_BACKWARD, Y_AXIS);
	}
	}
	if(out_bits & (1<<Z_STEP_BIT)) {
	if(out_bits & (1<<Z_DIRECTION_BIT)) {
	// do_half_step(DIR_FORWARD, Z_AXIS);
	do_full_step(DIR_FORWARD, Z_AXIS);
	} else {
	// do_half_step(DIR_BACKWARD, Z_AXIS);
	do_full_step(DIR_BACKWARD, Z_AXIS);
	}
	}


	busy = true;
	// Re-enable interrupts to allow ISR_TIMER2_OVERFLOW to trigger on-time and allow serial communications
	// regardless of time in this handler. The following code prepares the stepper driver for the next
	// step interrupt compare and will always finish before returning to the main program.
	sei();

	// If there is no current block, attempt to pop one from the buffer
	if (current_block == NULL) {
	// Anything in the buffer? If so, initialize next motion.
	current_block = plan_get_current_block();
	if (current_block != NULL) {
	trapezoid_generator_reset();
	counter_x = -(current_block->step_event_count >> 1);
	counter_y = counter_x;
	counter_z = counter_x;
	step_events_completed = 0;
	} else {
	st_go_idle();
	}
	}

	if (current_block != NULL) {
	// Execute step displacement profile by bresenham line algorithm
	out_bits = current_block->direction_bits;
	counter_x += current_block->steps_x;
	if (counter_x > 0) {
	out_bits \|= (1<<X_STEP_BIT);
	counter_x -= current_block->step_event_count;
	}
	counter_y += current_block->steps_y;
	if (counter_y > 0) {
	out_bits \|= (1<<Y_STEP_BIT);
	counter_y -= current_block->step_event_count;
	}
	counter_z += current_block->steps_z;
	if (counter_z > 0) {
	out_bits \|= (1<<Z_STEP_BIT);
	counter_z -= current_block->step_event_count;
	}

	step_events_completed++; // Iterate step events

	// While in block steps, check for de/ac-celeration events and execute them accordingly.
	if (step_events_completed < current_block->step_event_count) {
	// The trapezoid generator always checks step event location to ensure de/ac-celerations are
	// executed and terminated at exactly the right time. This helps prevent over/under-shooting
	// the target position and speed.
	// NOTE: By increasing the ACCELERATION_TICKS_PER_SECOND in config.h, the resolution of the
	// discrete velocity changes increase and accuracy can increase as well to a point. Numerical
	// round-off errors can effect this, if set too high. This is important to note if a user has
	// very high acceleration and/or feedrate requirements for their machine.
	if (step_events_completed < current_block->accelerate_until) {
	// Iterate cycle counter and check if speeds need to be increased.
	if ( iterate_trapezoid_cycle_counter() ) {
	trapezoid_adjusted_rate += current_block->rate_delta;
	if (trapezoid_adjusted_rate >= current_block->nominal_rate) {
	// Reached nominal rate a little early. Cruise at nominal rate until decelerate_after.
	trapezoid_adjusted_rate = current_block->nominal_rate;
	}
	set_step_events_per_minute(trapezoid_adjusted_rate);
	}
	} else if (step_events_completed >= current_block->decelerate_after) {
	// Reset trapezoid tick cycle counter to make sure that the deceleration is performed the
	// same every time. Reset to CYCLES_PER_ACCELERATION_TICK/2 to follow the midpoint rule for
	// an accurate approximation of the deceleration curve.
	if (step_events_completed == current_block-> decelerate_after) {
	trapezoid_tick_cycle_counter = CYCLES_PER_ACCELERATION_TICK/2;
	} else {
	// Iterate cycle counter and check if speeds need to be reduced.
	if ( iterate_trapezoid_cycle_counter() ) {
	// NOTE: We will only do a full speed reduction if the result is more than the minimum safe
	// rate, initialized in trapezoid reset as 1.5 x rate_delta. Otherwise, reduce the speed by
	// half increments until finished. The half increments are guaranteed not to exceed the
	// CNC acceleration limits, because they will never be greater than rate_delta. This catches
	// small errors that might leave steps hanging after the last trapezoid tick or a very slow
	// step rate at the end of a full stop deceleration in certain situations. The half rate
	// reductions should only be called once or twice per block and create a nice smooth
	// end deceleration.
	if (trapezoid_adjusted_rate > min_safe_rate) {
	trapezoid_adjusted_rate -= current_block->rate_delta;
	} else {
	trapezoid_adjusted_rate >>= 1; // Bit shift divide by 2
	}
	if (trapezoid_adjusted_rate < current_block->final_rate) {
	// Reached final rate a little early. Cruise to end of block at final rate.
	trapezoid_adjusted_rate = current_block->final_rate;
	}
	set_step_events_per_minute(trapezoid_adjusted_rate);
	}
	}
	} else {
	// No accelerations. Make sure we cruise exactly at the nominal rate.
	if (trapezoid_adjusted_rate != current_block->nominal_rate) {
	trapezoid_adjusted_rate = current_block->nominal_rate;
	set_step_events_per_minute(trapezoid_adjusted_rate);
	}
	}

	} else {
	// If current block is finished, reset pointer
	current_block = NULL;
	plan_discard_current_block();
	}
	}
	// out_bits ^= settings.invert_mask; // Apply stepper invert mask
	busy=false;
	}

	// This interrupt is set up by ISR_TIMER1_COMPAREA when it sets the motor port bits. It resets
	// the motor port after a short period (settings.pulse_microseconds) completing one step cycle.
	// TODO: It is possible for the serial interrupts to delay this interrupt by a few microseconds, if
	// they execute right before this interrupt. Not a big deal, but could use some TLC at some point.
	ISR(TIMER2_OVF_vect)
	{
	// Reset stepping pins (leave the direction pins)
	// STEPPING_PORT = (STEPPING_PORT & ~STEP_MASK) \| (settings.invert_mask & STEP_MASK);
	TCCR2B = 0; // Disable Timer2 to prevent re-entering this interrupt when it's not needed.
	}

	// Initialize and start the stepper motor subsystem
	void st_init()
	{
	// Configure directions of interface pins
	// STEPPING_DDR \|= STEPPING_MASK;
	// STEPPING_PORT = (STEPPING_PORT & ~STEPPING_MASK) \| settings.invert_mask;
	// STEPPERS_DISABLE_DDR \|= 1<<STEPPERS_DISABLE_BIT;

	STEPPING_DDR_X \|= ALL_STEPPER_PINS_X;
	STEPPING_PORT_X \|= ALL_STEPPER_PINS_X;
	STEPPING_DDR_Y \|= ALL_STEPPER_PINS_Y;
	STEPPING_PORT_Y \|= ALL_STEPPER_PINS_Y;
	STEPPING_DDR_Z \|= ALL_STEPPER_PINS_Z;
	STEPPING_PORT_Z \|= ALL_STEPPER_PINS_Z;


	// waveform generation = 0100 = CTC
	TCCR1B &= ~(1<<WGM13);
	TCCR1B \|= (1<<WGM12);
	TCCR1A &= ~(1<<WGM11);
	TCCR1A &= ~(1<<WGM10);

	// output mode = 00 (disconnected)
	TCCR1A &= ~(3<<COM1A0);
	TCCR1A &= ~(3<<COM1B0);

	// Configure Timer 2
	TCCR2A = 0; // Normal operation
	TCCR2B = 0; // Disable timer until needed.
	TIMSK2 \|= (1<<TOIE2); // Enable Timer2 interrupt flag

	set_step_events_per_minute(MINIMUM_STEPS_PER_MINUTE);
	trapezoid_tick_cycle_counter = 0;
	current_block = NULL;
	busy = false;

	// Start in the idle state
	st_go_idle();
	}

	// Block until all buffered steps are executed
	void st_synchronize()
	{
	while(plan_get_current_block()) { sleep_mode(); }
	}

	// Configures the prescaler and ceiling of timer 1 to produce the given rate as accurately as possible.
	// Returns the actual number of cycles per interrupt
	static uint32_t config_step_timer(uint32_t cycles)
	{
	uint16_t ceiling;
	uint16_t prescaler;
	uint32_t actual_cycles;
	if (cycles <= 0xffffL) {
	ceiling = cycles;
	prescaler = 0; // prescaler: 0
	actual_cycles = ceiling;
	} else if (cycles <= 0x7ffffL) {
	ceiling = cycles >> 3;
	prescaler = 1; // prescaler: 8
	actual_cycles = ceiling * 8L;
	} else if (cycles <= 0x3fffffL) {
	ceiling = cycles >> 6;
	prescaler = 2; // prescaler: 64
	actual_cycles = ceiling * 64L;
	} else if (cycles <= 0xffffffL) {
	ceiling = (cycles >> 8);
	prescaler = 3; // prescaler: 256
	actual_cycles = ceiling * 256L;
	} else if (cycles <= 0x3ffffffL) {
	ceiling = (cycles >> 10);
	prescaler = 4; // prescaler: 1024
	actual_cycles = ceiling * 1024L;
	} else {
	// Okay, that was slower than we actually go. Just set the slowest speed
	ceiling = 0xffff;
	prescaler = 4;
	actual_cycles = 0xffff * 1024;
	}
	// Set prescaler
	TCCR1B = (TCCR1B & ~(0x07<<CS10)) \| ((prescaler+1)<<CS10);
	// Set ceiling
	OCR1A = ceiling;
	return(actual_cycles);
	}

	static void set_step_events_per_minute(uint32_t steps_per_minute)
	{
	if (steps_per_minute < MINIMUM_STEPS_PER_MINUTE) { steps_per_minute = MINIMUM_STEPS_PER_MINUTE; }
	cycles_per_step_event = config_step_timer((TICKS_PER_MICROSECOND100000060)/steps_per_minute);
	}

	void st_go_home()
	{
	limits_go_home();
	plan_set_current_position(0,0,0);
	}

	// Planner external interface to start stepper interrupt and execute the blocks in queue.
	void st_cycle_start()
	{
	if (!cycle_start) {
	cycle_start = true;
	st_wake_up();
	}
	}