Fix, improve Linear Advance (#24533)

Author: tombrazier

Marlin/src/module/planner.cpp

@@ -788,7 +788,7 @@ void Planner::calculate_trapezoid_for_block(block_t * const block, const_float_t
   NOLESS(initial_rate, uint32_t(MINIMAL_STEP_RATE));
   NOLESS(final_rate, uint32_t(MINIMAL_STEP_RATE));
 
-  #if ENABLED(S_CURVE_ACCELERATION)
+  #if EITHER(S_CURVE_ACCELERATION, LIN_ADVANCE)
     // If we have some plateau time, the cruise rate will be the nominal rate
     uint32_t cruise_rate = block->nominal_rate;
   #endif
@@ -820,7 +820,7 @@ void Planner::calculate_trapezoid_for_block(block_t * const block, const_float_t
       accelerate_steps = _MIN(uint32_t(_MAX(accelerate_steps_float, 0)), block->step_event_count);
       decelerate_steps = block->step_event_count - accelerate_steps;
 
-      #if ENABLED(S_CURVE_ACCELERATION)
+      #if EITHER(S_CURVE_ACCELERATION, LIN_ADVANCE)
         // We won't reach the cruising rate. Let's calculate the speed we will reach
         cruise_rate = final_speed(initial_rate, accel, accelerate_steps);
       #endif
@@ -849,6 +849,14 @@ void Planner::calculate_trapezoid_for_block(block_t * const block, const_float_t
   #endif
   block->final_rate = final_rate;
 
+  #if ENABLED(LIN_ADVANCE)
+    if (block->la_advance_rate) {
+      const float comp = extruder_advance_K[block->extruder] * block->steps.e / block->step_event_count;
+      block->max_adv_steps = cruise_rate * comp;
+      block->final_adv_steps = final_rate * comp;
+    }
+  #endif
+
   #if ENABLED(LASER_POWER_TRAP)
     /**
      * Laser Trapezoid Calculations
@@ -899,75 +907,76 @@ void Planner::calculate_trapezoid_for_block(block_t * const block, const_float_t
   #endif // LASER_POWER_TRAP
 }
 
-/*                            PLANNER SPEED DEFINITION
-                                     +--------+   <- current->nominal_speed
-                                    /          \
-         current->entry_speed ->   +            \
-                                   |             + <- next->entry_speed (aka exit speed)
-                                   +-------------+
-                                       time -->
-
-  Recalculates the motion plan according to the following basic guidelines:
-
-    1. Go over every feasible block sequentially in reverse order and calculate the junction speeds
-        (i.e. current->entry_speed) such that:
-      a. No junction speed exceeds the pre-computed maximum junction speed limit or nominal speeds of
-         neighboring blocks.
-      b. A block entry speed cannot exceed one reverse-computed from its exit speed (next->entry_speed)
-         with a maximum allowable deceleration over the block travel distance.
-      c. The last (or newest appended) block is planned from a complete stop (an exit speed of zero).
-    2. Go over every block in chronological (forward) order and dial down junction speed values if
-      a. The exit speed exceeds the one forward-computed from its entry speed with the maximum allowable
-         acceleration over the block travel distance.
-
-  When these stages are complete, the planner will have maximized the velocity profiles throughout the all
-  of the planner blocks, where every block is operating at its maximum allowable acceleration limits. In
-  other words, for all of the blocks in the planner, the plan is optimal and no further speed improvements
-  are possible. If a new block is added to the buffer, the plan is recomputed according to the said
-  guidelines for a new optimal plan.
-
-  To increase computational efficiency of these guidelines, a set of planner block pointers have been
-  created to indicate stop-compute points for when the planner guidelines cannot logically make any further
-  changes or improvements to the plan when in normal operation and new blocks are streamed and added to the
-  planner buffer. For example, if a subset of sequential blocks in the planner have been planned and are
-  bracketed by junction velocities at their maximums (or by the first planner block as well), no new block
-  added to the planner buffer will alter the velocity profiles within them. So we no longer have to compute
-  them. Or, if a set of sequential blocks from the first block in the planner (or a optimal stop-compute
-  point) are all accelerating, they are all optimal and can not be altered by a new block added to the
-  planner buffer, as this will only further increase the plan speed to chronological blocks until a maximum
-  junction velocity is reached. However, if the operational conditions of the plan changes from infrequently
-  used feed holds or feedrate overrides, the stop-compute pointers will be reset and the entire plan is
-  recomputed as stated in the general guidelines.
-
-  Planner buffer index mapping:
-  - block_buffer_tail: Points to the beginning of the planner buffer. First to be executed or being executed.
-  - block_buffer_head: Points to the buffer block after the last block in the buffer. Used to indicate whether
-      the buffer is full or empty. As described for standard ring buffers, this block is always empty.
-  - block_buffer_planned: Points to the first buffer block after the last optimally planned block for normal
-      streaming operating conditions. Use for planning optimizations by avoiding recomputing parts of the
-      planner buffer that don't change with the addition of a new block, as describe above. In addition,
-      this block can never be less than block_buffer_tail and will always be pushed forward and maintain
-      this requirement when encountered by the Planner::release_current_block() routine during a cycle.
-
-  NOTE: Since the planner only computes on what's in the planner buffer, some motions with many short
-        segments (e.g., complex curves) may seem to move slowly. This is because there simply isn't
-        enough combined distance traveled in the entire buffer to accelerate up to the nominal speed and
-        then decelerate to a complete stop at the end of the buffer, as stated by the guidelines. If this
-        happens and becomes an annoyance, there are a few simple solutions:
-
-    - Maximize the machine acceleration. The planner will be able to compute higher velocity profiles
-      within the same combined distance.
-
-    - Maximize line motion(s) distance per block to a desired tolerance. The more combined distance the
-      planner has to use, the faster it can go.
-
-    - Maximize the planner buffer size. This also will increase the combined distance for the planner to
-      compute over. It also increases the number of computations the planner has to perform to compute an
-      optimal plan, so select carefully.
-
-    - Use G2/G3 arcs instead of many short segments. Arcs inform the planner of a safe exit speed at the
-      end of the last segment, which alleviates this problem.
-*/
+/**
+ *                              PLANNER SPEED DEFINITION
+ *                                     +--------+   <- current->nominal_speed
+ *                                    /          \
+ *         current->entry_speed ->   +            \
+ *                                   |             + <- next->entry_speed (aka exit speed)
+ *                                   +-------------+
+ *                                       time -->
+ *
+ *  Recalculates the motion plan according to the following basic guidelines:
+ *
+ *    1. Go over every feasible block sequentially in reverse order and calculate the junction speeds
+ *        (i.e. current->entry_speed) such that:
+ *      a. No junction speed exceeds the pre-computed maximum junction speed limit or nominal speeds of
+ *         neighboring blocks.
+ *      b. A block entry speed cannot exceed one reverse-computed from its exit speed (next->entry_speed)
+ *         with a maximum allowable deceleration over the block travel distance.
+ *      c. The last (or newest appended) block is planned from a complete stop (an exit speed of zero).
+ *    2. Go over every block in chronological (forward) order and dial down junction speed values if
+ *      a. The exit speed exceeds the one forward-computed from its entry speed with the maximum allowable
+ *         acceleration over the block travel distance.
+ *
+ *  When these stages are complete, the planner will have maximized the velocity profiles throughout the all
+ *  of the planner blocks, where every block is operating at its maximum allowable acceleration limits. In
+ *  other words, for all of the blocks in the planner, the plan is optimal and no further speed improvements
+ *  are possible. If a new block is added to the buffer, the plan is recomputed according to the said
+ *  guidelines for a new optimal plan.
+ *
+ *  To increase computational efficiency of these guidelines, a set of planner block pointers have been
+ *  created to indicate stop-compute points for when the planner guidelines cannot logically make any further
+ *  changes or improvements to the plan when in normal operation and new blocks are streamed and added to the
+ *  planner buffer. For example, if a subset of sequential blocks in the planner have been planned and are
+ *  bracketed by junction velocities at their maximums (or by the first planner block as well), no new block
+ *  added to the planner buffer will alter the velocity profiles within them. So we no longer have to compute
+ *  them. Or, if a set of sequential blocks from the first block in the planner (or a optimal stop-compute
+ *  point) are all accelerating, they are all optimal and can not be altered by a new block added to the
+ *  planner buffer, as this will only further increase the plan speed to chronological blocks until a maximum
+ *  junction velocity is reached. However, if the operational conditions of the plan changes from infrequently
+ *  used feed holds or feedrate overrides, the stop-compute pointers will be reset and the entire plan is
+ *  recomputed as stated in the general guidelines.
+ *
+ *  Planner buffer index mapping:
+ *  - block_buffer_tail: Points to the beginning of the planner buffer. First to be executed or being executed.
+ *  - block_buffer_head: Points to the buffer block after the last block in the buffer. Used to indicate whether
+ *      the buffer is full or empty. As described for standard ring buffers, this block is always empty.
+ *  - block_buffer_planned: Points to the first buffer block after the last optimally planned block for normal
+ *      streaming operating conditions. Use for planning optimizations by avoiding recomputing parts of the
+ *      planner buffer that don't change with the addition of a new block, as describe above. In addition,
+ *      this block can never be less than block_buffer_tail and will always be pushed forward and maintain
+ *      this requirement when encountered by the Planner::release_current_block() routine during a cycle.
+ *
+ *  NOTE: Since the planner only computes on what's in the planner buffer, some motions with many short
+ *        segments (e.g., complex curves) may seem to move slowly. This is because there simply isn't
+ *        enough combined distance traveled in the entire buffer to accelerate up to the nominal speed and
+ *        then decelerate to a complete stop at the end of the buffer, as stated by the guidelines. If this
+ *        happens and becomes an annoyance, there are a few simple solutions:
+ *
+ *    - Maximize the machine acceleration. The planner will be able to compute higher velocity profiles
+ *      within the same combined distance.
+ *
+ *    - Maximize line motion(s) distance per block to a desired tolerance. The more combined distance the
+ *      planner has to use, the faster it can go.
+ *
+ *    - Maximize the planner buffer size. This also will increase the combined distance for the planner to
+ *      compute over. It also increases the number of computations the planner has to perform to compute an
+ *      optimal plan, so select carefully.
+ *
+ *    - Use G2/G3 arcs instead of many short segments. Arcs inform the planner of a safe exit speed at the
+ *      end of the last segment, which alleviates this problem.
+ */
 
 // The kernel called by recalculate() when scanning the plan from last to first entry.
 void Planner::reverse_pass_kernel(block_t * const current, const block_t * const next
@@ -1211,13 +1220,6 @@ void Planner::recalculate_trapezoids(TERN_(HINTS_SAFE_EXIT_SPEED, const_float_t
             // NOTE: Entry and exit factors always > 0 by all previous logic operations.
             const float nomr = 1.0f / block->nominal_speed;
             calculate_trapezoid_for_block(block, current_entry_speed * nomr, next_entry_speed * nomr);
-            #if ENABLED(LIN_ADVANCE)
-              if (block->use_advance_lead) {
-                const float comp = block->e_D_ratio * extruder_advance_K[active_extruder] * settings.axis_steps_per_mm[E_AXIS];
-                block->max_adv_steps = block->nominal_speed * comp;
-                block->final_adv_steps = next_entry_speed * comp;
-              }
-            #endif
           }
 
           // Reset current only to ensure next trapezoid is computed - The
@@ -1251,13 +1253,6 @@ void Planner::recalculate_trapezoids(TERN_(HINTS_SAFE_EXIT_SPEED, const_float_t
 
       const float nomr = 1.0f / block->nominal_speed;
       calculate_trapezoid_for_block(block, current_entry_speed * nomr, next_entry_speed * nomr);
-      #if ENABLED(LIN_ADVANCE)
-        if (block->use_advance_lead) {
-          const float comp = block->e_D_ratio * extruder_advance_K[active_extruder] * settings.axis_steps_per_mm[E_AXIS];
-          block->max_adv_steps = block->nominal_speed * comp;
-          block->final_adv_steps = next_entry_speed * comp;
-        }
-      #endif
     }
 
     // Reset block to ensure its trapezoid is computed - The stepper is free to use
@@ -2502,13 +2497,15 @@ bool Planner::_populate_block(
   // Compute and limit the acceleration rate for the trapezoid generator.
   const float steps_per_mm = block->step_event_count * inverse_millimeters;
   uint32_t accel;
+  #if ENABLED(LIN_ADVANCE)
+    bool use_advance_lead = false;
+  #endif
   if (NUM_AXIS_GANG(
          !block->steps.a, && !block->steps.b, && !block->steps.c,
       && !block->steps.i, && !block->steps.j, && !block->steps.k,
       && !block->steps.u, && !block->steps.v, && !block->steps.w)
   ) {                                                             // Is this a retract / recover move?
     accel = CEIL(settings.retract_acceleration * steps_per_mm);   // Convert to: acceleration steps/sec^2
-    TERN_(LIN_ADVANCE, block->use_advance_lead = false);          // No linear advance for simple retract/recover
   }
   else {
     #define LIMIT_ACCEL_LONG(AXIS,INDX) do{ \
@@ -2535,33 +2532,29 @@ bool Planner::_populate_block(
       /**
        * Use LIN_ADVANCE for blocks if all these are true:
        *
-       * esteps             : This is a print move, because we checked for A, B, C steps before.
+       * esteps                       : This is a print move, because we checked for A, B, C steps before.
        *
-       * extruder_advance_K[active_extruder] : There is an advance factor set for this extruder.
+       * extruder_advance_K[extruder] : There is an advance factor set for this extruder.
        *
-       * de > 0             : Extruder is running forward (e.g., for "Wipe while retracting" (Slic3r) or "Combing" (Cura) moves)
+       * de > 0                       : Extruder is running forward (e.g., for "Wipe while retracting" (Slic3r) or "Combing" (Cura) moves)
        */
-      block->use_advance_lead =  esteps
-                              && extruder_advance_K[active_extruder]
-                              && de > 0;
-
-      if (block->use_advance_lead) {
-        block->e_D_ratio = (target_float.e - position_float.e) /
-          #if IS_KINEMATIC
-            block->millimeters
-          #else
+      use_advance_lead = esteps && extruder_advance_K[extruder] && de > 0;
+
+      if (use_advance_lead) {
+        float e_D_ratio = (target_float.e - position_float.e) /
+          TERN(IS_KINEMATIC, block->millimeters,
             SQRT(sq(target_float.x - position_float.x)
                + sq(target_float.y - position_float.y)
                + sq(target_float.z - position_float.z))
-          #endif
-        ;
+          );
 
         // Check for unusual high e_D ratio to detect if a retract move was combined with the last print move due to min. steps per segment. Never execute this with advance!
         // This assumes no one will use a retract length of 0mm < retr_length < ~0.2mm and no one will print 100mm wide lines using 3mm filament or 35mm wide lines using 1.75mm filament.
-        if (block->e_D_ratio > 3.0f)
-          block->use_advance_lead = false;
+        if (e_D_ratio > 3.0f)
+          use_advance_lead = false;
         else {
-          const uint32_t max_accel_steps_per_s2 = MAX_E_JERK(extruder) / (extruder_advance_K[active_extruder] * block->e_D_ratio) * steps_per_mm;
+          // Scale E acceleration so that it will be possible to jump to the advance speed.
+          const uint32_t max_accel_steps_per_s2 = MAX_E_JERK(extruder) / (extruder_advance_K[extruder] * e_D_ratio) * steps_per_mm;
           if (TERN0(LA_DEBUG, accel > max_accel_steps_per_s2))
             SERIAL_ECHOLNPGM("Acceleration limited.");
           NOMORE(accel, max_accel_steps_per_s2);
@@ -2593,13 +2586,21 @@ bool Planner::_populate_block(
     block->acceleration_rate = (uint32_t)(accel * (float(1UL << 24) / (STEPPER_TIMER_RATE)));
   #endif
   #if ENABLED(LIN_ADVANCE)
-    if (block->use_advance_lead) {
-      block->advance_speed = (STEPPER_TIMER_RATE) / (extruder_advance_K[active_extruder] * block->e_D_ratio * block->acceleration * settings.axis_steps_per_mm[E_AXIS_N(extruder)]);
+    block->la_advance_rate = 0;
+    block->la_scaling = 0;
+
+    if (use_advance_lead) {
+      // the Bresenham algorithm will convert this step rate into extruder steps
+      block->la_advance_rate = extruder_advance_K[extruder] * block->acceleration_steps_per_s2;
+
+      // reduce LA ISR frequency by calling it only often enough to ensure that there will
+      // never be more than four extruder steps per call
+      for (uint32_t dividend = block->steps.e << 1; dividend <= (block->step_event_count >> 2); dividend <<= 1)
+        block->la_scaling++;
+
       #if ENABLED(LA_DEBUG)
-        if (extruder_advance_K[active_extruder] * block->e_D_ratio * block->acceleration * 2 < block->nominal_speed * block->e_D_ratio)
-          SERIAL_ECHOLNPGM("More than 2 steps per eISR loop executed.");
-        if (block->advance_speed < 200)
-          SERIAL_ECHOLNPGM("eISR running at > 10kHz.");
+        if (block->la_advance_rate >> block->la_scaling > 10000)
+          SERIAL_ECHOLNPGM("eISR running at > 10kHz: ", block->la_advance_rate);
       #endif
     }
   #endif

Marlin/src/module/planner.h

@@ -239,11 +239,10 @@ typedef struct PlannerBlock {
 
   // Advance extrusion
   #if ENABLED(LIN_ADVANCE)
-    bool use_advance_lead;
-    uint16_t advance_speed,                 // STEP timer value for extruder speed offset ISR
-             max_adv_steps,                 // max. advance steps to get cruising speed pressure (not always nominal_speed!)
-             final_adv_steps;               // advance steps due to exit speed
-    float e_D_ratio;
+    uint32_t la_advance_rate;               // The rate at which steps are added whilst accelerating
+    uint8_t  la_scaling;                    // Scale ISR frequency down and step frequency up by 2 ^ la_scaling
+    uint16_t max_adv_steps,                 // Max advance steps to get cruising speed pressure
+             final_adv_steps;               // Advance steps for exit speed pressure
   #endif
 
   uint32_t nominal_rate,                    // The nominal step rate for this block in step_events/sec
@@ -1018,7 +1017,7 @@ class Planner {
       return target_velocity_sqr - 2 * accel * distance;
     }
 
-    #if ENABLED(S_CURVE_ACCELERATION)
+    #if EITHER(S_CURVE_ACCELERATION, LIN_ADVANCE)
       /**
        * Calculate the speed reached given initial speed, acceleration and distance
        */