/* stepper.c - stepper motor driver: executes motion plans using stepper motors Part of Grbl Copyright (c) 2009-2011 Simen Svale Skogsrud Copyright (c) 2011-2012 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) // Stepper state variable. Contains running data and trapezoid variables. typedef struct { // Used by the bresenham line algorithm int32_t counter_x, // Counter variables for the bresenham line tracer counter_y, counter_z; uint32_t event_count; uint32_t step_events_completed; // The number of step events left in current motion // Used by the trapezoid generator uint32_t cycles_per_step_event; // The number of machine cycles between each step event 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 uint32_t trapezoid_adjusted_rate; // The current rate of step_events according to the trapezoid generator uint32_t min_safe_rate; // Minimum safe rate for full deceleration rate reduction step. Otherwise halves step_rate. } 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 static volatile uint8_t busy; // True when SIG_OUTPUT_COMPARE1A 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 // 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); // Set step pulse time. Ad hoc computation from oscilloscope. step_pulse_time = -(((settings.pulse_microseconds-2)*TICKS_PER_MICROSECOND) >> 3); // Enable steppers by resetting the stepper disable port STEPPERS_DISABLE_PORT &= ~(1<<STEPPERS_DISABLE_BIT); // Enable stepper driver interrupt TIMSK1 |= (1<<OCIE1A); } // Stepper shutdown void st_go_idle() { // 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. #ifdef STEPPER_IDLE_LOCK_TIME _delay_ms(STEPPER_IDLE_LOCK_TIME); #endif // Disable steppers by setting stepper disable STEPPERS_DISABLE_PORT |= (1<<STEPPERS_DISABLE_BIT); } // 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. inline static uint8_t iterate_trapezoid_cycle_counter() { st.trapezoid_tick_cycle_counter += st.cycles_per_step_event; if(st.trapezoid_tick_cycle_counter > CYCLES_PER_ACCELERATION_TICK) { st.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 = step_pulse_time; // 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) { if (!sys.feed_hold) { // During feed hold, do not update rate and trap counter. Keep decelerating. st.trapezoid_adjusted_rate = current_block->initial_rate; set_step_events_per_minute(st.trapezoid_adjusted_rate); // Initialize cycles_per_step_event st.trapezoid_tick_cycle_counter = CYCLES_PER_ACCELERATION_TICK/2; // Start halfway for midpoint rule. } st.min_safe_rate = current_block->rate_delta + (current_block->rate_delta >> 1); // 1.5 x rate_delta 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_completed = 0; } else { st_go_idle(); sys.cycle_start = false; bit_true(sys.execute,EXEC_CYCLE_STOP); // Flag main program for cycle end } } if (current_block != NULL) { // Execute step displacement profile by bresenham line algorithm out_bits = current_block->direction_bits; st.counter_x += current_block->steps_x; if (st.counter_x > 0) { out_bits |= (1<<X_STEP_BIT); st.counter_x -= st.event_count; if (out_bits & (1<<X_DIRECTION_BIT)) { sys.position[X_AXIS]--; } else { sys.position[X_AXIS]++; } } st.counter_y += current_block->steps_y; if (st.counter_y > 0) { out_bits |= (1<<Y_STEP_BIT); st.counter_y -= st.event_count; if (out_bits & (1<<Y_DIRECTION_BIT)) { sys.position[Y_AXIS]--; } else { sys.position[Y_AXIS]++; } } st.counter_z += current_block->steps_z; if (st.counter_z > 0) { out_bits |= (1<<Z_STEP_BIT); st.counter_z -= st.event_count; if (out_bits & (1<<Z_DIRECTION_BIT)) { sys.position[Z_AXIS]--; } else { sys.position[Z_AXIS]++; } } st.step_events_completed++; // Iterate step events // While in block steps, check for de/ac-celeration events and execute them accordingly. if (st.step_events_completed < current_block->step_event_count) { if (sys.feed_hold) { // Check for and execute feed hold by enforcing a steady deceleration from the moment of // execution. The rate of deceleration is limited by rate_delta and will never decelerate // faster or slower than in normal operation. If the distance required for the feed hold // deceleration spans more than one block, the initial rate of the following blocks are not // updated and deceleration is continued according to their corresponding rate_delta. // NOTE: The trapezoid tick cycle counter is not updated intentionally. This ensures that // the deceleration is smooth regardless of where the feed hold is initiated and if the // deceleration distance spans multiple blocks. if ( iterate_trapezoid_cycle_counter() ) { // If deceleration complete, set system flags and shutdown steppers. if (st.trapezoid_adjusted_rate <= current_block->rate_delta) { // Just go idle. Do not NULL current block. The bresenham algorithm variables must // remain intact to ensure the stepper path is exactly the same. Feed hold is still // active and is released after the buffer has been reinitialized. st_go_idle(); sys.cycle_start = false; bit_true(sys.execute,EXEC_CYCLE_STOP); // Flag main program that feed hold is complete. } else { st.trapezoid_adjusted_rate -= current_block->rate_delta; set_step_events_per_minute(st.trapezoid_adjusted_rate); } } } else { // 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 (st.step_events_completed < current_block->accelerate_until) { // Iterate cycle counter and check if speeds need to be increased. if ( iterate_trapezoid_cycle_counter() ) { st.trapezoid_adjusted_rate += current_block->rate_delta; if (st.trapezoid_adjusted_rate >= current_block->nominal_rate) { // Reached nominal rate a little early. Cruise at nominal rate until decelerate_after. st.trapezoid_adjusted_rate = current_block->nominal_rate; } set_step_events_per_minute(st.trapezoid_adjusted_rate); } } else if (st.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 (st.step_events_completed == current_block-> decelerate_after) { st.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 (st.trapezoid_adjusted_rate > st.min_safe_rate) { st.trapezoid_adjusted_rate -= current_block->rate_delta; } else { st.trapezoid_adjusted_rate >>= 1; // Bit shift divide by 2 } if (st.trapezoid_adjusted_rate < current_block->final_rate) { // Reached final rate a little early. Cruise to end of block at final rate. st.trapezoid_adjusted_rate = current_block->final_rate; } set_step_events_per_minute(st.trapezoid_adjusted_rate); } } } else { // No accelerations. Make sure we cruise exactly at the nominal rate. if (st.trapezoid_adjusted_rate != current_block->nominal_rate) { st.trapezoid_adjusted_rate = current_block->nominal_rate; set_step_events_per_minute(st.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. } // Reset and clear stepper subsystem variables void st_reset() { memset(&st, 0, sizeof(st)); set_step_events_per_minute(MINIMUM_STEPS_PER_MINUTE); 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; // 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); // Start in the idle state st_go_idle(); } // 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; } st.cycles_per_step_event = config_step_timer((TICKS_PER_MICROSECOND*1000000*60)/steps_per_minute); } // 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.cycle_start) { if (!sys.feed_hold) { sys.cycle_start = true; st_wake_up(); } } } // Execute a feed hold with deceleration, only during cycle. Called by main program. void st_feed_hold() { if (!sys.feed_hold) { if (sys.cycle_start) { sys.auto_start = false; // Disable planner auto start upon feed hold. sys.feed_hold = true; } } } // 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(current_block->step_event_count - st.step_events_completed); // Update initial rate and timers after feed hold. st.trapezoid_adjusted_rate = 0; // Resumes from rest set_step_events_per_minute(st.trapezoid_adjusted_rate); st.trapezoid_tick_cycle_counter = CYCLES_PER_ACCELERATION_TICK/2; // Start halfway for midpoint rule. st.step_events_completed = 0; } sys.feed_hold = false; // Release feed hold. Cycle is ready to re-start. }