/*
  stepper.c - stepper motor interface
  Part of Grbl

  Copyright (c) 2009 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/>.
*/

/* The timer calculations of this module informed by the 'RepRap cartesian firmware' by Zack Smith
   and Philipp Tiefenbacher. The circle buffer implementation gleaned from the wiring_serial library 
   by David A. Mellis */

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

#include "wiring_serial.h"

#define LINE_BUFFER_SIZE 10

struct Line {
  uint32_t steps_x, steps_y, steps_z;
  int32_t maximum_steps;
  uint8_t direction_bits;
  uint32_t rate;
};

struct Line line_buffer[LINE_BUFFER_SIZE]; // A buffer for step instructions
volatile int line_buffer_head = 0;
volatile int line_buffer_tail = 0;

// Variables used by SIG_OUTPUT_COMPARE1A
uint8_t out_bits; // The next stepping-bits to be output
struct Line *current_line; // A pointer to the line currently being traced
volatile int32_t counter_x, counter_y, counter_z; // counter variables for the bresenham line tracer
uint32_t iterations; // The number of iterations left to complete the current_line
volatile busy; // TRUE when SIG_OUTPUT_COMPARE1A is being serviced. Used to avoid retriggering that handler.

void config_step_timer(uint32_t microseconds);

// 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.
void st_buffer_line(int32_t steps_x, int32_t steps_y, int32_t steps_z, uint32_t microseconds) {
  // Calculate the buffer head after we push this byte
	int next_buffer_head = (line_buffer_head + 1) % LINE_BUFFER_SIZE;	
	// If the buffer is full: good! That means we are well ahead of the robot. 
	// Nap until there is room in the buffer.
  while(line_buffer_tail == next_buffer_head) { sleep_mode(); }
  // Setup line record
  struct Line *line = &line_buffer[line_buffer_head];
  line->steps_x = labs(steps_x);
  line->steps_y = labs(steps_y);
  line->steps_z = labs(steps_z);  
  line->maximum_steps = max(line->steps_x, max(line->steps_y, line->steps_z));
  // Bail if this is a zero-length line
  if (line->maximum_steps == 0) { return; };
  line->rate = microseconds/line->maximum_steps;
  uint8_t direction_bits = 0;
  if (steps_x < 0) { direction_bits |= (1<<X_DIRECTION_BIT); }
  if (steps_y < 0) { direction_bits |= (1<<Y_DIRECTION_BIT); }
  if (steps_z < 0) { direction_bits |= (1<<Z_DIRECTION_BIT); }
  line->direction_bits = direction_bits;
  // Move buffer head
  line_buffer_head = next_buffer_head;
  // enable stepper interrupt
	TIMSK1 |= (1<<OCIE1A);
}

// This timer interrupt is executed at the rate set with config_step_timer. It pops one instruction from
// the line_buffer, executes it. Then it starts timer2 in order to reset the motor port after
// five microseconds.
SIGNAL(SIG_OUTPUT_COMPARE1A)
{
  if(busy){ return; } // The busy-flag is used to avoid reentering this interrupt
  
  PORTD |= (1<<3);
  // Set the direction pins a cuple 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;
  // Reset step pulse reset timer so that SIG_OVERFLOW2 can reset the signal after
  // exactly STEP_PULSE_MICROSECONDS microseconds.
  TCNT2 = -(((STEP_PULSE_MICROSECONDS-2)*TICKS_PER_MICROSECOND)/8);

  busy = TRUE;
  sei(); // Re enable interrupts (normally disabled while inside an interrupt handler)
  // We re-enable interrupts in order for SIG_OVERFLOW2 to be able to be triggered 
  // at exactly the right time even if we occasionally spend a lot of time inside this handler.
    
  // If there is no current line, attempt to pop one from the buffer
  if (current_line == NULL) {
    PORTD &= ~(1<<4);
    // Anything in the buffer?
    if (line_buffer_head != line_buffer_tail) {
      PORTD ^= (1<<5);
      // Retrieve a new line and get ready to step it
      current_line = &line_buffer[line_buffer_tail]; 
      config_step_timer(current_line->rate);
      counter_x = -(current_line->maximum_steps >> 1);
      counter_y = counter_x;
      counter_z = counter_x;
      iterations = current_line->maximum_steps;
    } else {
      // disable this interrupt until there is something to handle
    	TIMSK1 &= ~(1<<OCIE1A);
      PORTD |= (1<<4);          
    }    
  } 

  if (current_line != NULL) {
    out_bits = current_line->direction_bits;
    counter_x += current_line->steps_x;
    if (counter_x > 0) {
      out_bits |= (1<<X_STEP_BIT);
      counter_x -= current_line->maximum_steps;
    }
    counter_y += current_line->steps_y;
    if (counter_y > 0) {
      out_bits |= (1<<Y_STEP_BIT);
      counter_y -= current_line->maximum_steps;
    }
    counter_z += current_line->steps_z;
    if (counter_z > 0) {
      out_bits |= (1<<Z_STEP_BIT);
      counter_z -= current_line->maximum_steps;
    }
    // If current line is finished, reset pointer 
    iterations -= 1;
    if (iterations <= 0) {
      current_line = NULL;
      // move the line buffer tail to the next instruction
      line_buffer_tail = (line_buffer_tail + 1) % LINE_BUFFER_SIZE;      
    }
  } else {
    out_bits = 0;
  }
  out_bits ^= STEPPING_INVERT_MASK;
  busy=FALSE;
  PORTD &= ~(1<<3);  
}

// This interrupt is set up by SIG_OUTPUT_COMPARE1A when it sets the motor port bits. It resets
// the motor port after a short period (STEP_PULSE_MICROSECONDS) completing one step cycle.
SIGNAL(SIG_OVERFLOW2)
{
  // reset stepping pins (leave the direction pins)
  STEPPING_PORT = (STEPPING_PORT & ~STEP_MASK) | (STEPPING_INVERT_MASK & STEP_MASK); 
}

// 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); //| STEPPING_INVERT_MASK;
  LIMIT_DDR &= ~(LIMIT_MASK);
  STEPPERS_ENABLE_DDR |= 1<<STEPPERS_ENABLE_BIT;
  
	// 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 = (1<<CS21); // Full speed, 1/8 prescaler
  TIMSK2 |= (1<<TOIE2);      
  
  // Just ste the step_timer to something serviceably lazy
  config_step_timer(20000);
  // set enable pin     
  STEPPERS_ENABLE_PORT |= 1<<STEPPERS_ENABLE_BIT;
  
  sei();
}

// Block until all buffered steps are executed
void st_synchronize()
{
  while(line_buffer_tail != line_buffer_head) { sleep_mode(); }    
}

// Cancel all buffered steps
void st_flush()
{
  cli();
  line_buffer_tail = line_buffer_head;
  current_line = NULL;
  sei();
}

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

void st_go_home()
{
  // Todo: Perform the homing cycle
}