/*
  stepper.c - stepper motor driver: executes motion plans using stepper motors
  Part of Grbl

  Copyright (c) 2011-2013 Sungeun K. Jeon
  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 <avr/interrupt.h>
#include "stepper.h"
#include "config.h"
#include "settings.h"
#include "planner.h"

// Some useful constants
#define TICKS_PER_MICROSECOND (F_CPU/1000000)
#define CRUISE_RAMP 0
#define ACCEL_RAMP 1
#define DECEL_RAMP 2

// Stepper state variable. Contains running data and trapezoid variables.
typedef struct {
  // Used by the bresenham line algorithm
  int32_t counter[N_AXIS];  // Counter variables for the bresenham line tracer
  uint32_t event_count;     // Total event count. Retained for feed holds. 
  uint32_t step_events_remaining;  // Steps remaining in motion

  // Used by Pramod Ranade inverse time algorithm
  int32_t delta_d;     // Ranade distance traveled per interrupt tick
  int32_t d_counter;   // Ranade distance traveled since last step event
  uint8_t ramp_count; // Acceleration interrupt tick counter. 
  uint8_t ramp_type; // Ramp type variable.
  uint8_t execute_step; // Flags step execution for each interrupt.
  
} stepper_t;
static stepper_t st;
static block_t *current_block;  // A pointer to the block currently being traced

// Used by the stepper driver interrupt
static uint8_t step_pulse_time; // Step pulse reset time after step rise
static uint8_t out_bits;        // The next stepping-bits to be output

// NOTE: If the main interrupt is guaranteed to be complete before the next interrupt, then
// this blocking variable is no longer needed. Only here for safety reasons.
static volatile uint8_t busy;   // True when "Stepper Driver Interrupt" is being serviced. Used to avoid retriggering that handler.

//         __________________________
//        /|                        |\     _________________         ^
//       / |                        | \   /|               |\        |
//      /  |                        |  \ / |               | \       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
//  until reaching cruising speed block->nominal_rate, and/or until step_events_remaining reaches block->decelerate_after
//  after which it decelerates until the block is completed. The driver uses constant acceleration, which is applied as
//  +/- block->rate_delta velocity increments by the midpoint rule at each ACCELERATION_TICKS_PER_SECOND.


// Stepper state initialization. Cycle should only start if the st.cycle_start flag is
// enabled. Startup init and limits call this function but shouldn't start the cycle.
void st_wake_up() 
{
  // Enable steppers by resetting the stepper disable port
  if (bit_istrue(settings.flags,BITFLAG_INVERT_ST_ENABLE)) { 
    STEPPERS_DISABLE_PORT |= (1<<STEPPERS_DISABLE_BIT); 
  } else { 
    STEPPERS_DISABLE_PORT &= ~(1<<STEPPERS_DISABLE_BIT);
  }
  if (sys.state == STATE_CYCLE) {
    // Initialize stepper output bits
    out_bits = settings.invert_mask; 
    // Initialize step pulse timing from settings.
    step_pulse_time = -(((settings.pulse_microseconds-2)*TICKS_PER_MICROSECOND) >> 3);
    // Enable stepper driver interrupt
    st.execute_step = false;
    TCNT0 = 0; // Clear Timer2
    TIMSK0 |= (1<<OCIE0A); // Enable Timer0 Compare Match A interrupt
    TCCR0B = (1<<CS21); // Begin Timer0. Full speed, 1/8 prescaler
  }
}


// Stepper shutdown
void st_go_idle() 
{
  // Disable stepper driver interrupt. Allow Timer2 to finish. It will disable itself.
  TIMSK0 &= ~(1<<OCIE0A); // Disable Timer0 interrupt
  TCCR0B = 0; // Disable Timer0
  busy = false;

  // Disable steppers only upon system alarm activated or by user setting to not be kept enabled.
  if ((settings.stepper_idle_lock_time != 0xff) || bit_istrue(sys.execute,EXEC_ALARM)) {
    // 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.
    delay_ms(settings.stepper_idle_lock_time);
    if (bit_istrue(settings.flags,BITFLAG_INVERT_ST_ENABLE)) { 
      STEPPERS_DISABLE_PORT &= ~(1<<STEPPERS_DISABLE_BIT); 
    } else { 
      STEPPERS_DISABLE_PORT |= (1<<STEPPERS_DISABLE_BIT); 
    }   
  }
}


/* "The Stepper Driver Interrupt" - This timer interrupt is the workhorse of Grbl. It is based
   on the Pramod Ranade inverse time stepper algorithm, where a timer ticks at a constant
   frequency and uses time-distance counters to track when its the approximate time for any 
   step event. However, the Ranade algorithm, as described, is susceptible to numerical round-off,
   meaning that some axes steps may not execute/cause a phasing drift error between multiple axes.
     Grbl's algorithm differs by using a single Ranade-type time-distance counter to manage
   a Bresenham line algorithm for multi-axis step events, which ensures the number of steps for
   each axis are executed exactly and always in phase by inherent algorithm design. In other
   words, it uses a Bresenham within a Bresenham algorithm, where one tracks time(Ranade) and
   the other steps.
     This interrupt 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. */
// NOTE: Average time in this ISR is: 5 usec iterating timers only, 20-25 usec with step event, or
// 15 usec when popping a block. So, ensure Ranade frequency and step pulse times work with this.

ISR(TIMER0_COMPA_vect)
{
// SPINDLE_ENABLE_PORT ^= 1<<SPINDLE_ENABLE_BIT; // Debug: Used to time ISR
  
  // Pulse stepper port pins, if flagged. New block dir will always be set one timer tick 
  // before any step pulse due to algorithm design.
  if (st.execute_step) {
    st.execute_step = false;
    STEPPING_PORT = ( STEPPING_PORT & ~(DIRECTION_MASK | STEP_MASK) ) | out_bits;
    TCNT2 = step_pulse_time; // Reload Timer2 counter.
    TCCR2B = (1<<CS21); // Begin Timer2. Full speed, 1/8 prescaler
  }

// Assume that this takes less than 5 usec. If not, then this might not work on an 328p.
// Two sei() commands in two different interrupts will be hard to manage. If the main program
// can push fast enough, then this might be ok.
//   sei(); //  ??? The falling edge interrupt needs to fire before the rest of this executes.
    
    
/* 
1. Upon start, load segment/block.
   - Set direction bit for entire block early. This never changes.
   - Load Bresenham variables. Initialize their counters.
   - If using segments, counters cannot be updated, but this breaks the direction bit? No. Only set when block begins.

   (3) Generate step event. Can take up to an additional 10-15usec for the math.



Override idea: Main program can request the step event count from the stepper algorithm, which will
check for the request and write it to a safe variable for the main program. The main program will
then wait until the request is fulfilled via a flag. From there, the main program can determine
the safe point from which it can plan. This may require a snapshot of variables. Hopefully this 
won't take too much time in the interrupt.
*/    
    
  // Iterate inverse time counter. Triggers each Bresenham step event.
  if (st.delta_d < MINIMUM_STEP_RATE) { st.d_counter -= MINIMUM_STEP_RATE; }
  else { st.d_counter -= st.delta_d; }
  
  // Prepare Bresenham step event, when it's time to do so.
  if (st.d_counter < 0) {  
    st.d_counter += current_block->d_next;
    st.execute_step = true;
      
    // Configure next step
    out_bits = current_block->direction_bits; // Reset out_bits and reload direction bits
    
    // Execute step displacement profile by Bresenham line algorithm
    st.counter[X_AXIS] -= current_block->steps_x; // Doesn't change when set up.
    if (st.counter[X_AXIS] < 0) {
      out_bits |= (1<<X_STEP_BIT);
      st.counter[X_AXIS] += st.event_count;
      st.n_step[X_AXIS]; // Track number of steps
    }
    st.counter[Y_AXIS] -= current_block->steps_y;
    if (st.counter[Y_AXIS] < 0) {
      out_bits |= (1<<Y_STEP_BIT);
      st.counter[Y_AXIS] += st.event_count;
      st.n_step[Y_AXIS]++;
    }
    st.counter[Z_AXIS] -= current_block->steps_z;
    if (st.counter[Z_AXIS] < 0) {
      out_bits |= (1<<Z_STEP_BIT);
      st.counter[Z_AXIS] += st.event_count;
      st.n_step[Z_AXIS]++;      
    }

    // Check step events for trapezoid change or end of block.
    st.step_events_remaining--; // Decrement step events count
    if (st.step_events_remaining == 0) {
      // Load next line motion
    }

    out_bits ^= settings.invert_mask;  // Apply step port invert mask  
    
    
    
    
    // TIMSK2 |= (1<<OCIE2B); // Enable Timer2 Compare Match B interrupt
        
  }
// SPINDLE_ENABLE_PORT ^= 1<<SPINDLE_ENABLE_BIT;  
}


// This needs to complete and load before the next timer?
ISR(TIMER0_COMPB_vect)
{
  if (busy) { return; }
  busy = true;
  TIMSK0 &= ~(1<<OCIE0B); // Disable Timer2 Compare Match B interrupt
  sei();
  
  if (out_bits & (1<<X_DIRECTION_BIT)) { sys.position[X_AXIS]--; }
      else { sys.position[X_AXIS]++; }
    
          // If current block is finished, reset pointer 
      current_block = NULL;
      plan_discard_current_block();

  
    // 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) {
      // By algorithm design, the loading of the next block never coincides with a step event,
      // since there is always one inverse time tick before a step event occurs. This means
      // that the Bresenham counter math never is performed at the same time as the loading 
      // of a block, hence helping minimize total time spent in this interrupt. Also, this
      // allows the direction bits for the block to be always set one timer tick before the 
      // first step event.

      // Initialize direction bits for block      
      out_bits = current_block->direction_bits ^ settings.invert_mask;
      st.execute_step = true; // Set flag to set direction bits.
      
      // Initialize Bresenham variables
      st.counter_x = (current_block->step_event_count >> 1);
      st.counter_y = st.counter_x;
      st.counter_z = st.counter_x;
      st.event_count = current_block->step_event_count;
      st.step_events_remaining = st.event_count;
      
      // During feed hold, do not update inverse time counter, rate, or ramp type. Keep decelerating.
      if (sys.state == STATE_CYCLE) {
        // Initialize Ranade variables
        st.d_counter = current_block->d_next;  
        st.delta_d = current_block->initial_rate;
        st.ramp_count = ISR_TICKS_PER_ACCELERATION_TICK/2;
        
        // Initialize ramp type.
        if (st.step_events_remaining == current_block->decelerate_after) { st.ramp_type = DECEL_RAMP; }
        else if (st.delta_d == current_block->nominal_rate) { st.ramp_type = CRUISE_RAMP; }
        else { st.ramp_type = ACCEL_RAMP; }
      }
      
    } else {
      st_go_idle();
      bit_true(sys.execute,EXEC_CYCLE_STOP); // Flag main program for cycle end
      return; // Nothing to do but exit.
    }  
  } 
  
    // Adjust inverse time counter for ac/de-celerations
  if (st.ramp_type) {
    // Tick acceleration ramp counter
    st.ramp_count--;
    if (st.ramp_count == 0) {
      st.ramp_count = ISR_TICKS_PER_ACCELERATION_TICK; // Reload ramp counter
      if (st.ramp_type == ACCEL_RAMP) { // Adjust velocity for acceleration
        st.delta_d += current_block->rate_delta;
        if (st.delta_d >= current_block->nominal_rate) { // Reached cruise state.
          st.ramp_type = CRUISE_RAMP;
          st.delta_d = current_block->nominal_rate; // Set cruise velocity
        }
      } else if (st.ramp_type == DECEL_RAMP) { // Adjust velocity for deceleration
        if (st.delta_d > current_block->rate_delta) {
          st.delta_d -= current_block->rate_delta;
        } else {
          st.delta_d >>= 1; // Integer divide by 2 until complete. Also prevents overflow.
        }
      }
    }
  }
  
      
    // Check for feed hold state and execute accordingly.
    if (sys.state == STATE_HOLD) {
      if (st.ramp_type != DECEL_RAMP) {
        st.ramp_type = DECEL_RAMP;
        st.ramp_count = ISR_TICKS_PER_ACCELERATION_TICK/2; 
      } 
      if (st.delta_d <= current_block->rate_delta) {
        st_go_idle();
        bit_true(sys.execute,EXEC_CYCLE_STOP);
        return;
      }
    }
  
        if (st.ramp_type != DECEL_RAMP) {
        // Acceleration and cruise handled by ramping. Just check for deceleration.
        if (st.step_events_remaining <=  current_block->decelerate_after) {
          st.ramp_type = DECEL_RAMP;
          if (st.step_events_remaining == current_block->decelerate_after) {
            if (st.delta_d == current_block->nominal_rate) {
              st.ramp_count = ISR_TICKS_PER_ACCELERATION_TICK/2;  // Set ramp counter for trapezoid
            } else {
              st.ramp_count = ISR_TICKS_PER_ACCELERATION_TICK-st.ramp_count; // Set ramp counter for triangle
            }
          }
        }
      }
    } else {
  
  busy = false;
}


// The Stepper Port Reset Interrupt: Timer2 OVF interrupt handles the falling edge of the
// step pulse. This should always trigger before the next Timer0 COMPA interrupt and independently
// finish, if Timer0 is disabled after completing a move.
ISR(TIMER2_OVF_vect)
{
  STEPPING_PORT = (STEPPING_PORT & ~STEP_MASK) | (settings.invert_mask & STEP_MASK); 
  TCCR2B = 0; // Disable timer until needed.
}


// Reset and clear stepper subsystem variables
void st_reset()
{
  memset(&st, 0, sizeof(st));
  current_block = NULL;
  busy = false;
}


// 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;
	
  // Configure Timer 0
  TIMSK0 &= ~(1<<OCIE0A); // Disable Timer0 interrupt while configuring it
  TCCR0B = 0; // Disable Timer2 until needed
  TCNT0 = 0; // Clear Timer2 counter
  TCCR0A = (1<<WGM21);  // Set CTC mode
  OCR0A = (F_CPU/ISR_TICKS_PER_SECOND)/8 - 1; // Set Timer2 CTC rate

  // Configure Timer 2
  TIMSK2 &= ~(1<<TOIE2);
  TCCR2A = 0; // Normal operation
  TCCR2B = 0; // Disable Timer2 until needed
  TIMSK2 |= (1<<TOIE2); // Enable overflow interrupt
  
  // Start in the idle state, but first wake up to check for keep steppers enabled option.
  st_wake_up();
  st_go_idle();
}


// Planner external interface to start stepper interrupt and execute the blocks in queue. Called
// by the main program functions: planner auto-start and run-time command execution.
void st_cycle_start() 
{
  if (sys.state == STATE_QUEUED) {
    sys.state = STATE_CYCLE;
    st_wake_up();
  }
}


// Execute a feed hold with deceleration, only during cycle. Called by main program.
void st_feed_hold() 
{
  if (sys.state == STATE_CYCLE) {
    sys.state = STATE_HOLD;
    sys.auto_start = false; // Disable planner auto start upon feed hold.
  }
}


// Reinitializes the cycle plan and stepper system after a feed hold for a resume. Called by 
// runtime command execution in the main program, ensuring that the planner re-plans safely.
// NOTE: Bresenham algorithm variables are still maintained through both the planner and stepper
// cycle reinitializations. The stepper path should continue exactly as if nothing has happened.
// Only the planner de/ac-celerations profiles and stepper rates have been updated.
void st_cycle_reinitialize()
{
  if (current_block != NULL) {
    // Replan buffer from the feed hold stop location.
    plan_cycle_reinitialize(st.step_events_remaining);
    st.ramp_type = ACCEL_RAMP;
    st.ramp_count = ISR_TICKS_PER_ACCELERATION_TICK/2; 
    st.delta_d = 0;
    sys.state = STATE_QUEUED;
  } else {
    sys.state = STATE_IDLE;
  }
}