extruder: Support disassociating a stepper from all extruders

Support SYNC_STEPPER_TO_EXTRUDER commands with an EXTRUDER parameter
set to an empty string.

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

docs/Config_Reference.md

@@ -1835,8 +1835,9 @@ more information.
 ```
 [extruder_stepper my_extra_stepper]
 #extruder: extruder
-#   The extruder this stepper is synchronized to. The default is
-#   "extruder".
+#   The extruder this stepper is synchronized to. If this is set to an
+#   empty string then the stepper will not be synchronized to an
+#   extruder. The default is "extruder".
 #step_pin:
 #dir_pin:
 #enable_pin:

docs/G-Codes.md

@@ -186,7 +186,9 @@ The following standard commands are supported:
   command will cause the given extruder STEPPER (as specified in an
   [extruder](Config_Reference#extruder) or
   [extruder stepper](Config_Reference#extruder_stepper) config
-  section) to become synchronized to the given EXTRUDER.
+  section) to become synchronized to the given EXTRUDER. If EXTRUDER
+  is an empty string then the stepper will not be synchronized to an
+  extruder.
 - `SET_STEPPER_ENABLE STEPPER=<config_name> ENABLE=[0|1]`: Enable or
   disable only the given stepper. This is a diagnostic and debugging
   tool and must be used with care. Disabling an axis motor does not

klippy/kinematics/extruder.py

@@ -44,12 +44,15 @@ class ExtruderStepper:
         mcu_pos = self.stepper.get_past_mcu_position(print_time)
         return self.stepper.mcu_to_commanded_position(mcu_pos)
     def sync_to_extruder(self, extruder_name):
+        toolhead = self.printer.lookup_object('toolhead')
+        toolhead.flush_step_generation()
+        if not extruder_name:
+            self.stepper.set_trapq(None)
+            return
         extruder = self.printer.lookup_object(extruder_name, None)
         if extruder is None or not isinstance(extruder, PrinterExtruder):
             raise self.printer.command_error("'%s' is not a valid extruder."
                                              % (extruder_name,))
-        toolhead = self.printer.lookup_object('toolhead')
-        toolhead.flush_step_generation()
         self.stepper.set_position([extruder.last_position, 0., 0.])
         self.stepper.set_trapq(extruder.get_trapq())
     def _set_pressure_advance(self, pressure_advance, smooth_time):

test/klippy/extruders.test

@@ -15,3 +15,32 @@ G1 X25 Y25 E7.5
 # Update step_distance
 SET_EXTRUDER_STEP_DISTANCE EXTRUDER=extruder DISTANCE=.005
 G1 X30 Y30 E8.0
+
+# Disable extruder stepper motor
+SYNC_STEPPER_TO_EXTRUDER STEPPER=extruder EXTRUDER=
+G1 X35 Y35 E8.5
+
+# Disable my_extra_stepper stepper motor
+SYNC_STEPPER_TO_EXTRUDER STEPPER=my_extra_stepper EXTRUDER=
+G1 X40 Y40 E9.0
+
+# Enable extruder stepper motor
+SYNC_STEPPER_TO_EXTRUDER STEPPER=extruder EXTRUDER=extruder
+G1 X45 Y45 E9.5
+
+# Switch to just my_extra_stepper stepper motor
+SYNC_STEPPER_TO_EXTRUDER STEPPER=extruder EXTRUDER=
+SYNC_STEPPER_TO_EXTRUDER STEPPER=my_extra_stepper EXTRUDER=extruder
+G1 X50 Y50 E10.0
+
+# Test pressure advance move
+SET_PRESSURE_ADVANCE EXTRUDER=my_extra_stepper ADVANCE=0.020
+G1 X55 Y55 E0
+G1 X55 Y55 E0.5
+G1 X60 Y60 E1.1
+G1 X50 Y50
+SET_PRESSURE_ADVANCE EXTRUDER=extruder ADVANCE=0.025
+G1 X55 Y55 E1.5
+G1 X50 Y50
+G1 X55 Y55 E2.0
+G1 X50 Y50