stepcompress: Implement a step+dir+step filter

Some stepper motor drivers do not respond well to rapid "step +
direction change + step" events.  In particular, it is believed this
can cause "over current" events on the tmc2208 drivers when they are
in "stealthchop" mode.  Detect these events and remove them from the
generated step times.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/chelper/itersolve.c

@@ -13,6 +13,11 @@
 #include "stepcompress.h" // queue_append_start
 #include "trapq.h" // struct move
 
+
+/****************************************************************
+ * Main iterative solver
+ ****************************************************************/
+
 struct timepos {
     double time, position;
 };
@@ -66,7 +71,7 @@ itersolve_gen_steps_range(struct stepper_kinematics *sk, struct move *m
     double start = move_start - m->print_time, end = move_end - m->print_time;
     struct timepos last = { start, sk->commanded_pos }, low = last, high = last;
     double seek_time_delta = SEEK_TIME_RESET;
-    int sdir = !!stepcompress_get_step_dir(sk->sc), is_dir_change = 0;
+    int sdir = stepcompress_get_step_dir(sk->sc), is_dir_change = 0;
     for (;;) {
         double diff = high.position - last.position, dist = sdir ? diff : -diff;
         if (dist >= half_step) {
@@ -90,6 +95,9 @@ itersolve_gen_steps_range(struct stepper_kinematics *sk, struct move *m
             if (low.time < high.time)
                 // The existing search range is still valid
                 continue;
+        } else if (dist > 0.) {
+            // Avoid rollback if stepper fully reaches target position
+            stepcompress_commit(sk->sc);
         } else if (unlikely(dist < -(half_step + .000000001))) {
             // Found direction change
             is_dir_change = 1;
@@ -127,6 +135,11 @@ itersolve_gen_steps_range(struct stepper_kinematics *sk, struct move *m
     return 0;
 }
 
+
+/****************************************************************
+ * Interface functions
+ ****************************************************************/
+
 // Check if a move is likely to cause movement on a stepper
 static inline int
 check_active(struct stepper_kinematics *sk, struct move *m)

klippy/chelper/stepcompress.c

@@ -38,6 +38,9 @@ struct stepcompress {
     struct list_head msg_queue;
     uint32_t queue_step_msgid, set_next_step_dir_msgid, oid;
     int sdir, invert_sdir;
+    // Step+dir+step filter
+    uint64_t next_step_clock;
+    int next_step_dir;
 };
 
 
@@ -270,7 +273,7 @@ stepcompress_get_oid(struct stepcompress *sc)
 int
 stepcompress_get_step_dir(struct stepcompress *sc)
 {
-    return sc->sdir;
+    return sc->next_step_dir;
 }
 
 // Determine the "print time" of the last_step_clock
@@ -293,7 +296,7 @@ stepcompress_set_time(struct stepcompress *sc
 
 // Convert previously scheduled steps into commands for the mcu
 static int
-stepcompress_flush(struct stepcompress *sc, uint64_t move_clock)
+queue_flush(struct stepcompress *sc, uint64_t move_clock)
 {
     if (sc->queue_pos >= sc->queue_next)
         return 0;
@@ -346,7 +349,7 @@ set_next_step_dir(struct stepcompress *sc, int sdir)
     if (sc->sdir == sdir)
         return 0;
     sc->sdir = sdir;
-    int ret = stepcompress_flush(sc, UINT64_MAX);
+    int ret = queue_flush(sc, UINT64_MAX);
     if (ret)
         return ret;
     uint32_t msg[3] = {
@@ -361,26 +364,30 @@ set_next_step_dir(struct stepcompress *sc, int sdir)
 // Maximium clock delta between messages in the queue
 #define CLOCK_DIFF_MAX (3<<28)
 
-// Slow path for stepcompress_append()
+// Slow path for queue_append() - handle next step far in future
 static int
-queue_append_slow(struct stepcompress *sc, double rel_sc)
+queue_append_far(struct stepcompress *sc)
 {
-    uint64_t abs_step_clock = (uint64_t)rel_sc + sc->last_step_clock;
-    if (abs_step_clock >= sc->last_step_clock + CLOCK_DIFF_MAX) {
-        // Avoid integer overflow on steps far in the future
-        int ret = stepcompress_flush(sc, abs_step_clock - CLOCK_DIFF_MAX + 1);
+    uint64_t step_clock = sc->next_step_clock;
+    sc->next_step_clock = 0;
+    int ret = queue_flush(sc, step_clock - CLOCK_DIFF_MAX + 1);
     if (ret)
         return ret;
-
-        if (abs_step_clock >= sc->last_step_clock + CLOCK_DIFF_MAX)
-            return stepcompress_flush_far(sc, abs_step_clock);
+    if (step_clock >= sc->last_step_clock + CLOCK_DIFF_MAX)
+        return stepcompress_flush_far(sc, step_clock);
+    *sc->queue_next++ = step_clock;
+    return 0;
 }
 
+// Slow path for queue_append() - expand the internal queue storage
+static int
+queue_append_extend(struct stepcompress *sc)
+{
     if (sc->queue_next - sc->queue_pos > 65535 + 2000) {
         // No point in keeping more than 64K steps in memory
         uint32_t flush = (*(sc->queue_next-65535)
                           - (uint32_t)sc->last_step_clock);
-        int ret = stepcompress_flush(sc, sc->last_step_clock + flush);
+        int ret = queue_flush(sc, sc->last_step_clock + flush);
         if (ret)
             return ret;
     }
@@ -405,29 +412,81 @@ queue_append_slow(struct stepcompress *sc, double rel_sc)
         sc->queue_next = sc->queue + in_use;
     }
 
-    *sc->queue_next++ = abs_step_clock;
+    *sc->queue_next++ = sc->next_step_clock;
+    sc->next_step_clock = 0;
     return 0;
 }
 
 // Add a step time to the queue (flushing the queue if needed)
-inline int
-stepcompress_append(struct stepcompress *sc, int sdir
-                    , double print_time, double step_time)
+static int
+queue_append(struct stepcompress *sc)
 {
-    if (unlikely(sdir != sc->sdir)) {
-        int ret = set_next_step_dir(sc, sdir);
+    if (unlikely(sc->next_step_dir != sc->sdir)) {
+        int ret = set_next_step_dir(sc, sc->next_step_dir);
         if (ret)
             return ret;
     }
+    if (unlikely(sc->next_step_clock >= sc->last_step_clock + CLOCK_DIFF_MAX))
+        return queue_append_far(sc);
+    if (unlikely(sc->queue_next >= sc->queue_end))
+        return queue_append_extend(sc);
+    *sc->queue_next++ = sc->next_step_clock;
+    sc->next_step_clock = 0;
+    return 0;
+}
+
+#define SDS_FILTER_TIME .000750
+
+// Add next step time
+int
+stepcompress_append(struct stepcompress *sc, int sdir
+                    , double print_time, double step_time)
+{
+    // Calculate step clock
     double offset = print_time - sc->last_step_print_time;
     double rel_sc = (step_time + offset) * sc->mcu_freq;
-    if (unlikely(sc->queue_next >= sc->queue_end
-                 || rel_sc >= (double)CLOCK_DIFF_MAX))
-        // Slow path to handle queue expansion and integer overflow
-        return queue_append_slow(sc, rel_sc);
-    *sc->queue_next++ = (uint32_t)sc->last_step_clock + (uint32_t)rel_sc;
+    uint64_t step_clock = sc->last_step_clock + (uint64_t)rel_sc;
+    // Flush previous pending step (if any)
+    if (sc->next_step_clock) {
+        if (unlikely(sdir != sc->next_step_dir)) {
+            double diff = step_clock - sc->next_step_clock;
+            if (diff < SDS_FILTER_TIME * sc->mcu_freq) {
+                // Rollback last step to avoid rapid step+dir+step
+                sc->next_step_clock = 0;
+                sc->next_step_dir = sdir;
                 return 0;
             }
+        }
+        int ret = queue_append(sc);
+        if (ret)
+            return ret;
+    }
+    // Store this step as the next pending step
+    sc->next_step_clock = step_clock;
+    sc->next_step_dir = sdir;
+    return 0;
+}
+
+// Commit next pending step (ie, do not allow a rollback)
+int
+stepcompress_commit(struct stepcompress *sc)
+{
+    if (sc->next_step_clock)
+        return queue_append(sc);
+    return 0;
+}
+
+// Flush pending steps
+static int
+stepcompress_flush(struct stepcompress *sc, uint64_t move_clock)
+{
+    if (sc->next_step_clock && move_clock >= sc->next_step_clock) {
+        int ret = queue_append(sc);
+        if (ret)
+            return ret;
+    }
+    return queue_flush(sc, move_clock);
+}
 
 // Reset the internal state of the stepcompress object
 int __visible

klippy/chelper/stepcompress.h

@@ -14,6 +14,7 @@ uint32_t stepcompress_get_oid(struct stepcompress *sc);
 int stepcompress_get_step_dir(struct stepcompress *sc);
 int stepcompress_append(struct stepcompress *sc, int sdir
                         , double print_time, double step_time);
+int stepcompress_commit(struct stepcompress *sc);
 int stepcompress_reset(struct stepcompress *sc, uint64_t last_step_clock);
 int stepcompress_queue_msg(struct stepcompress *sc, uint32_t *data, int len);
 

klippy/toolhead.py

@@ -1,6 +1,6 @@
 # Code for coordinating events on the printer toolhead
 #
-# Copyright (C) 2016-2019  Kevin O'Connor <kevin@koconnor.net>
+# Copyright (C) 2016-2020  Kevin O'Connor <kevin@koconnor.net>
 #
 # This file may be distributed under the terms of the GNU GPLv3 license.
 import math, logging, importlib
@@ -183,6 +183,7 @@ class MoveQueue:
 
 MIN_KIN_TIME = 0.100
 MOVE_BATCH_TIME = 0.500
+SDS_CHECK_TIME = 0.001 # step+dir+step filter in stepcompress.c
 
 DRIP_SEGMENT_TIME = 0.050
 DRIP_TIME = 0.100
@@ -236,7 +237,7 @@ class ToolHead:
         self.print_stall = 0
         self.drip_completion = None
         # Kinematic step generation scan window time tracking
-        self.kin_flush_delay = 0.
+        self.kin_flush_delay = SDS_CHECK_TIME
         self.kin_flush_times = []
         self.last_kin_flush_time = self.last_kin_move_time = 0.
         # Setup iterative solver
@@ -512,7 +513,7 @@ class ToolHead:
             self.kin_flush_times.pop(self.kin_flush_times.index(old_delay))
         if delay:
             self.kin_flush_times.append(delay)
-        new_delay = max(self.kin_flush_times + [0.])
+        new_delay = max(self.kin_flush_times + [SDS_CHECK_TIME])
         self.kin_flush_delay = new_delay
     def register_lookahead_callback(self, callback):
         last_move = self.move_queue.get_last()