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/*
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()
{
// Initialize stepper output bits
out_bits = (0) ^ (settings.invert_mask);
// Enable steppers by resetting the stepper disable port
STEPPERS_DISABLE_PORT &= ~(1<<STEPPERS_DISABLE_BIT);
// 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.
#if STEPPER_IDLE_LOCK_TIME
_delay_ms(STEPPER_IDLE_LOCK_TIME);
#endif
// Disable steppers by setting stepper disable
STEPPERS_DISABLE_PORT |= (1<<STEPPERS_DISABLE_BIT);
}
// 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);
}
}
// "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
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;
// 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();
}
}
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