From 56dd15c0ad7e9d41725511744866aa9c2e46c495 Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Fri, 2 Dec 2016 22:40:18 -0600
Subject: [PATCH 01/11] Use SET_INPUT for PS_ON_PIN in kill

---
 Marlin/Marlin_main.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index c02c02c7466..1599c7ba5b2 100755
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -9950,7 +9950,7 @@ void kill(const char* lcd_msg) {
   disable_all_steppers();
 
   #if HAS_POWER_SWITCH
-    pinMode(PS_ON_PIN, INPUT);
+    SET_INPUT(PS_ON_PIN);
   #endif
 
   suicide();

From ee50928eee74757d9d1fd33467b6ef1ee244b907 Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Sun, 27 Nov 2016 21:07:23 -0600
Subject: [PATCH 02/11] Make LOGICAL and RAW position macros ternary-compatible

---
 Marlin/Marlin.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Marlin/Marlin.h b/Marlin/Marlin.h
index 58d56cdbfe1..0c3511ad7ca 100644
--- a/Marlin/Marlin.h
+++ b/Marlin/Marlin.h
@@ -294,8 +294,8 @@ void update_software_endstops(AxisEnum axis);
 extern float soft_endstop_min[XYZ];
 extern float soft_endstop_max[XYZ];
 
-#define LOGICAL_POSITION(POS, AXIS) (POS + home_offset[AXIS] + position_shift[AXIS])
-#define RAW_POSITION(POS, AXIS)     (POS - home_offset[AXIS] - position_shift[AXIS])
+#define LOGICAL_POSITION(POS, AXIS) ((POS) + home_offset[AXIS] + position_shift[AXIS])
+#define RAW_POSITION(POS, AXIS)     ((POS) - home_offset[AXIS] - position_shift[AXIS])
 #define LOGICAL_X_POSITION(POS)     LOGICAL_POSITION(POS, X_AXIS)
 #define LOGICAL_Y_POSITION(POS)     LOGICAL_POSITION(POS, Y_AXIS)
 #define LOGICAL_Z_POSITION(POS)     LOGICAL_POSITION(POS, Z_AXIS)

From 053fb55af60a3b9bec7d2e65740e666e42917d42 Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Mon, 7 Nov 2016 00:18:44 -0600
Subject: [PATCH 03/11] Fix modes ordering in prepare_move_to_destination_dualx

---
 Marlin/Marlin_main.cpp | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index 1599c7ba5b2..da69727f1a4 100755
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -9223,23 +9223,6 @@ void set_current_from_steppers_for_axis(const AxisEnum axis) {
       switch (dual_x_carriage_mode) {
         case DXC_FULL_CONTROL_MODE:
           break;
-        case DXC_DUPLICATION_MODE:
-          if (active_extruder == 0) {
-            // move duplicate extruder into correct duplication position.
-            planner.set_position_mm(
-              LOGICAL_X_POSITION(inactive_extruder_x_pos),
-              current_position[Y_AXIS],
-              current_position[Z_AXIS],
-              current_position[E_AXIS]
-            );
-            planner.buffer_line(current_position[X_AXIS] + duplicate_extruder_x_offset,
-                             current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], planner.max_feedrate_mm_s[X_AXIS], 1);
-            SYNC_PLAN_POSITION_KINEMATIC();
-            stepper.synchronize();
-            extruder_duplication_enabled = true;
-            active_extruder_parked = false;
-          }
-          break;
         case DXC_AUTO_PARK_MODE:
           if (current_position[E_AXIS] == destination[E_AXIS]) {
             // This is a travel move (with no extrusion)
@@ -9259,6 +9242,23 @@ void set_current_from_steppers_for_axis(const AxisEnum axis) {
           planner.buffer_line(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], planner.max_feedrate_mm_s[Z_AXIS], active_extruder);
           active_extruder_parked = false;
           break;
+        case DXC_DUPLICATION_MODE:
+          if (active_extruder == 0) {
+            // move duplicate extruder into correct duplication position.
+            planner.set_position_mm(
+              LOGICAL_X_POSITION(inactive_extruder_x_pos),
+              current_position[Y_AXIS],
+              current_position[Z_AXIS],
+              current_position[E_AXIS]
+            );
+            planner.buffer_line(current_position[X_AXIS] + duplicate_extruder_x_offset,
+                             current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], planner.max_feedrate_mm_s[X_AXIS], 1);
+            SYNC_PLAN_POSITION_KINEMATIC();
+            stepper.synchronize();
+            extruder_duplication_enabled = true;
+            active_extruder_parked = false;
+          }
+          break;
       }
     }
     return true;

From 41278c1e8b24b01cf01511631ec4afad5124281e Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Mon, 7 Nov 2016 00:20:19 -0600
Subject: [PATCH 04/11] Apply LOGICAL_POSITION to home positions on Dual X

---
 Marlin/Marlin_main.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index da69727f1a4..d4cb4a027d4 100755
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -1318,11 +1318,11 @@ bool get_target_extruder_from_command(int code) {
     else
       /**
        * In dual carriage mode the extruder offset provides an override of the
-       * second X-carriage offset when homed - otherwise X2_HOME_POS is used.
-       * This allow soft recalibration of the second extruder offset position
+       * second X-carriage position when homed - otherwise X2_HOME_POS is used.
+       * This allows soft recalibration of the second extruder home position
        * without firmware reflash (through the M218 command).
        */
-      return (hotend_offset[X_AXIS][1] > 0) ? hotend_offset[X_AXIS][1] : X2_HOME_POS;
+      return LOGICAL_X_POSITION(hotend_offset[X_AXIS][1] > 0 ? hotend_offset[X_AXIS][1] : X2_HOME_POS);
   }
 
   static int x_home_dir(int extruder) {

From fe96f74db193eda4af5798f1aef25f3e2ae4a66b Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Mon, 7 Nov 2016 00:20:59 -0600
Subject: [PATCH 05/11] Use const arguments in Dual X helper functions

---
 Marlin/Marlin_main.cpp | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index d4cb4a027d4..ef31136cfb9 100755
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -1312,7 +1312,7 @@ bool get_target_extruder_from_command(int code) {
 
   static DualXMode dual_x_carriage_mode = DEFAULT_DUAL_X_CARRIAGE_MODE;
 
-  static float x_home_pos(int extruder) {
+  static float x_home_pos(const int extruder) {
     if (extruder == 0)
       return LOGICAL_X_POSITION(base_home_pos(X_AXIS));
     else
@@ -1325,9 +1325,7 @@ bool get_target_extruder_from_command(int code) {
       return LOGICAL_X_POSITION(hotend_offset[X_AXIS][1] > 0 ? hotend_offset[X_AXIS][1] : X2_HOME_POS);
   }
 
-  static int x_home_dir(int extruder) {
-    return (extruder == 0) ? X_HOME_DIR : X2_HOME_DIR;
-  }
+  static int x_home_dir(const int extruder) { return extruder ? X2_HOME_DIR : X_HOME_DIR; }
 
   static float inactive_extruder_x_pos = X2_MAX_POS; // used in mode 0 & 1
   static bool active_extruder_parked = false;        // used in mode 1 & 2

From 54109dfaec881477e151b5905515b155ab2dafc1 Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Mon, 7 Nov 2016 00:33:12 -0600
Subject: [PATCH 06/11] Reduce code size for Dual X un-park

---
 Marlin/Marlin_main.cpp | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index ef31136cfb9..dafaf4a3ec3 100755
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -9233,11 +9233,17 @@ void set_current_from_steppers_for_axis(const AxisEnum axis) {
               return false;
             }
           }
-          delayed_move_time = 0;
           // unpark extruder: 1) raise, 2) move into starting XY position, 3) lower
-          planner.buffer_line(raised_parked_position[X_AXIS], raised_parked_position[Y_AXIS], raised_parked_position[Z_AXIS], current_position[E_AXIS], planner.max_feedrate_mm_s[Z_AXIS], active_extruder);
-          planner.buffer_line(current_position[X_AXIS], current_position[Y_AXIS], raised_parked_position[Z_AXIS], current_position[E_AXIS], PLANNER_XY_FEEDRATE(), active_extruder);
-          planner.buffer_line(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], planner.max_feedrate_mm_s[Z_AXIS], active_extruder);
+          for (uint8_t i = 0; i < 3; i++)
+            planner.buffer_line(
+              i == 0 ? raised_parked_position[X_AXIS] : current_position[X_AXIS],
+              i == 0 ? raised_parked_position[Y_AXIS] : current_position[Y_AXIS],
+              i == 2 ? current_position[Z_AXIS] : raised_parked_position[Z_AXIS],
+              current_position[E_AXIS],
+              i == 1 ? PLANNER_XY_FEEDRATE() : planner.max_feedrate_mm_s[Z_AXIS],
+              active_extruder
+            );
+          delayed_move_time = 0;
           active_extruder_parked = false;
           break;
         case DXC_DUPLICATION_MODE:

From 0e15b4f434cee8df7738cd790b29f2957a368e0a Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Mon, 7 Nov 2016 00:23:39 -0600
Subject: [PATCH 07/11] Dual X set_axis_is_at_home can use x_home_pos for both

---
 Marlin/Marlin_main.cpp | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index dafaf4a3ec3..e043228f22f 100755
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -1432,12 +1432,8 @@ static void set_axis_is_at_home(AxisEnum axis) {
   update_software_endstops(axis);
 
   #if ENABLED(DUAL_X_CARRIAGE)
-    if (axis == X_AXIS && (active_extruder != 0 || dual_x_carriage_mode == DXC_DUPLICATION_MODE)) {
-      if (active_extruder != 0)
-        current_position[X_AXIS] = x_home_pos(active_extruder);
-      else
-        current_position[X_AXIS] = LOGICAL_X_POSITION(base_home_pos(X_AXIS));
-      update_software_endstops(X_AXIS);
+    if (axis == X_AXIS && (active_extruder == 1 || dual_x_carriage_mode == DXC_DUPLICATION_MODE)) {
+      current_position[X_AXIS] = x_home_pos(active_extruder);
       return;
     }
   #endif

From ca24af7d5dc9f6a8c1584007c85f418d7ad61895 Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Mon, 7 Nov 2016 00:24:39 -0600
Subject: [PATCH 08/11] Dual X with home_z_safely is not parked

---
 Marlin/Marlin_main.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index e043228f22f..c853d2117ce 100755
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -3253,6 +3253,12 @@ inline void gcode_G4() {
       #if ENABLED(DEBUG_LEVELING_FEATURE)
         if (DEBUGGING(LEVELING)) DEBUG_POS("Z_SAFE_HOMING", destination);
       #endif
+
+      // This causes the carriage on Dual X to unpark
+      #if ENABLED(DUAL_X_CARRIAGE)
+        active_extruder_parked = false;
+      #endif
+
       do_blocking_move_to_xy(destination[X_AXIS], destination[Y_AXIS]);
       HOMEAXIS(Z);
     }

From b20405db316db9ac4788ac27d3fce286b0a77f11 Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Mon, 7 Nov 2016 02:46:16 -0600
Subject: [PATCH 09/11] Only DXC_AUTO_PARK_MODE should auto-move in tool_change

---
 Marlin/Marlin_main.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index c853d2117ce..cdb8e62df35 100755
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -7525,6 +7525,9 @@ void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool n
             if (DEBUGGING(LEVELING)) DEBUG_POS("New Extruder", current_position);
           #endif
 
+          // Only when auto-parking are carriages safe to move
+          if (dual_x_carriage_mode != DXC_AUTO_PARK_MODE) no_move = true;
+
           switch (dual_x_carriage_mode) {
             case DXC_FULL_CONTROL_MODE:
               current_position[X_AXIS] = LOGICAL_X_POSITION(inactive_extruder_x_pos);

From 4217e9653e4f5dae457948f7e10da0a80eedd7a1 Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Mon, 7 Nov 2016 00:21:45 -0600
Subject: [PATCH 10/11] Adjust park code in tool_change

---
 Marlin/Marlin_main.cpp | 76 +++++++++++++++++++++++++++---------------
 1 file changed, 50 insertions(+), 26 deletions(-)

diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index cdb8e62df35..7fbc4f6c2f0 100755
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -1416,6 +1416,7 @@ static void set_home_offset(AxisEnum axis, float v) {
  * current_position to home, because neither X nor Y is at home until
  * both are at home. Z can however be homed individually.
  *
+ * Callers must sync the planner position after calling this!
  */
 static void set_axis_is_at_home(AxisEnum axis) {
   #if ENABLED(DEBUG_LEVELING_FEATURE)
@@ -3246,10 +3247,12 @@ inline void gcode_G4() {
           #endif
         )
     ) {
+
       #if HOMING_Z_WITH_PROBE
         destination[X_AXIS] -= X_PROBE_OFFSET_FROM_EXTRUDER;
         destination[Y_AXIS] -= Y_PROBE_OFFSET_FROM_EXTRUDER;
       #endif
+
       #if ENABLED(DEBUG_LEVELING_FEATURE)
         if (DEBUGGING(LEVELING)) DEBUG_POS("Z_SAFE_HOMING", destination);
       #endif
@@ -3407,20 +3410,31 @@ inline void gcode_G28() {
 
     // Home X
     if (home_all_axis || homeX) {
+
       #if ENABLED(DUAL_X_CARRIAGE)
-        int tmp_extruder = active_extruder;
-        active_extruder = !active_extruder;
+
+        // Always home the 2nd (right) extruder first
+        active_extruder = 1;
         HOMEAXIS(X);
+
+        // Remember this extruder's position for later tool change
         inactive_extruder_x_pos = RAW_X_POSITION(current_position[X_AXIS]);
-        active_extruder = tmp_extruder;
+
+        // Home the 1st (left) extruder
+        active_extruder = 0;
         HOMEAXIS(X);
-        // reset state used by the different modes
+
+        // Consider the active extruder to be parked
         memcpy(raised_parked_position, current_position, sizeof(raised_parked_position));
         delayed_move_time = 0;
         active_extruder_parked = true;
+
       #else
+
         HOMEAXIS(X);
+
       #endif
+
       #if ENABLED(DEBUG_LEVELING_FEATURE)
         if (DEBUGGING(LEVELING)) DEBUG_POS("> homeX", current_position);
       #endif
@@ -7446,10 +7460,8 @@ inline void invalid_extruder_error(const uint8_t &e) {
 void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool no_move/*=false*/) {
   #if ENABLED(MIXING_EXTRUDER) && MIXING_VIRTUAL_TOOLS > 1
 
-    if (tmp_extruder >= MIXING_VIRTUAL_TOOLS) {
-      invalid_extruder_error(tmp_extruder);
-      return;
-    }
+    if (tmp_extruder >= MIXING_VIRTUAL_TOOLS)
+      return invalid_extruder_error(tmp_extruder);
 
     // T0-Tnnn: Switch virtual tool by changing the mix
     for (uint8_t j = 0; j < MIXING_STEPPERS; j++)
@@ -7459,10 +7471,8 @@ void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool n
 
     #if HOTENDS > 1
 
-      if (tmp_extruder >= EXTRUDERS) {
-        invalid_extruder_error(tmp_extruder);
-        return;
-      }
+      if (tmp_extruder >= EXTRUDERS)
+        return invalid_extruder_error(tmp_extruder);
 
       float old_feedrate_mm_s = feedrate_mm_s;
 
@@ -7490,22 +7500,28 @@ void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool n
             }
           #endif
 
-          if (dual_x_carriage_mode == DXC_AUTO_PARK_MODE && IsRunning() &&
-              (delayed_move_time || current_position[X_AXIS] != x_home_pos(active_extruder))
+          const float xhome = x_home_pos(active_extruder);
+          if (dual_x_carriage_mode == DXC_AUTO_PARK_MODE
+              && IsRunning()
+              && (delayed_move_time || current_position[X_AXIS] != xhome)
           ) {
+            float raised_z = current_position[Z_AXIS] + TOOLCHANGE_PARK_ZLIFT;
+            #if ENABLED(max_software_endstops)
+              NOMORE(raised_z, soft_endstop_max[Z_AXIS]);
+            #endif
             #if ENABLED(DEBUG_LEVELING_FEATURE)
               if (DEBUGGING(LEVELING)) {
-                SERIAL_ECHOPAIR("Raise to ", current_position[Z_AXIS] + TOOLCHANGE_PARK_ZLIFT); SERIAL_EOL;
-                SERIAL_ECHOPAIR("MoveX to ", x_home_pos(active_extruder)); SERIAL_EOL;
-                SERIAL_ECHOPAIR("Lower to ", current_position[Z_AXIS]); SERIAL_EOL;
+                SERIAL_ECHOLNPAIR("Raise to ", raised_z);
+                SERIAL_ECHOLNPAIR("MoveX to ", xhome);
+                SERIAL_ECHOLNPAIR("Lower to ", current_position[Z_AXIS]);
               }
             #endif
             // Park old head: 1) raise 2) move to park position 3) lower
             for (uint8_t i = 0; i < 3; i++)
               planner.buffer_line(
-                i == 0 ? current_position[X_AXIS] : x_home_pos(active_extruder),
+                i == 0 ? current_position[X_AXIS] : xhome,
                 current_position[Y_AXIS],
-                current_position[Z_AXIS] + (i == 2 ? 0 : TOOLCHANGE_PARK_ZLIFT),
+                i == 2 ? current_position[Z_AXIS] : raised_z,
                 current_position[E_AXIS],
                 planner.max_feedrate_mm_s[i == 1 ? X_AXIS : Z_AXIS],
                 active_extruder
@@ -7513,9 +7529,11 @@ void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool n
             stepper.synchronize();
           }
 
-          // apply Y & Z extruder offset (x offset is already used in determining home pos)
+          // Apply Y & Z extruder offset (X offset is used as home pos with Dual X)
           current_position[Y_AXIS] -= hotend_offset[Y_AXIS][active_extruder] - hotend_offset[Y_AXIS][tmp_extruder];
           current_position[Z_AXIS] -= hotend_offset[Z_AXIS][active_extruder] - hotend_offset[Z_AXIS][tmp_extruder];
+
+          // Activate the new extruder
           active_extruder = tmp_extruder;
 
           // This function resets the max/min values - the current position may be overwritten below.
@@ -7530,7 +7548,9 @@ void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool n
 
           switch (dual_x_carriage_mode) {
             case DXC_FULL_CONTROL_MODE:
+              // New current position is the position of the activated extruder
               current_position[X_AXIS] = LOGICAL_X_POSITION(inactive_extruder_x_pos);
+              // Save the inactive extruder's position (from the old current_position)
               inactive_extruder_x_pos = RAW_X_POSITION(destination[X_AXIS]);
               break;
             case DXC_AUTO_PARK_MODE:
@@ -7544,7 +7564,10 @@ void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool n
               delayed_move_time = 0;
               break;
             case DXC_DUPLICATION_MODE:
-              active_extruder_parked = (active_extruder == 0); // this triggers the second extruder to move into the duplication position
+              // If the new extruder is the left one, set it "parked"
+              // This triggers the second extruder to move into the duplication position
+              active_extruder_parked = (active_extruder == 0);
+
               if (active_extruder_parked)
                 current_position[X_AXIS] = LOGICAL_X_POSITION(inactive_extruder_x_pos);
               else
@@ -7569,9 +7592,7 @@ void tool_change(const uint8_t tmp_extruder, const float fr_mm_s/*=0.0*/, bool n
             float z_diff = hotend_offset[Z_AXIS][active_extruder] - hotend_offset[Z_AXIS][tmp_extruder],
                   z_raise = 0.3 + (z_diff > 0.0 ? z_diff : 0.0);
 
-            set_destination_to_current();
-
-            // Always raise by some amount
+            // Always raise by some amount (destination copied from current_position earlier)
             destination[Z_AXIS] += z_raise;
             planner.buffer_line_kinematic(destination, planner.max_feedrate_mm_s[Z_AXIS], active_extruder);
             stepper.synchronize();
@@ -9260,8 +9281,11 @@ void set_current_from_steppers_for_axis(const AxisEnum axis) {
               current_position[Z_AXIS],
               current_position[E_AXIS]
             );
-            planner.buffer_line(current_position[X_AXIS] + duplicate_extruder_x_offset,
-                             current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], planner.max_feedrate_mm_s[X_AXIS], 1);
+            planner.buffer_line(
+              current_position[X_AXIS] + duplicate_extruder_x_offset,
+              current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS],
+              planner.max_feedrate_mm_s[X_AXIS], 1
+            );
             SYNC_PLAN_POSITION_KINEMATIC();
             stepper.synchronize();
             extruder_duplication_enabled = true;

From c47e07d129106b513c0787555139e9fe82527138 Mon Sep 17 00:00:00 2001
From: Scott Lahteine <sourcetree@thinkyhead.com>
Date: Sat, 3 Dec 2016 00:27:10 -0600
Subject: [PATCH 11/11] Fix Dual X software endstops

---
 Marlin/Marlin_main.cpp | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/Marlin/Marlin_main.cpp b/Marlin/Marlin_main.cpp
index 7fbc4f6c2f0..4e7a1b8f318 100755
--- a/Marlin/Marlin_main.cpp
+++ b/Marlin/Marlin_main.cpp
@@ -1349,25 +1349,33 @@ void update_software_endstops(AxisEnum axis) {
   float offs = LOGICAL_POSITION(0, axis);
 
   #if ENABLED(DUAL_X_CARRIAGE)
+    bool did_update = false;
     if (axis == X_AXIS) {
+
+      // In Dual X mode hotend_offset[X] is T1's home position
       float dual_max_x = max(hotend_offset[X_AXIS][1], X2_MAX_POS);
+
       if (active_extruder != 0) {
+        // T1 can move from X2_MIN_POS to X2_MAX_POS or X2 home position (whichever is larger)
         soft_endstop_min[X_AXIS] = X2_MIN_POS + offs;
         soft_endstop_max[X_AXIS] = dual_max_x + offs;
-        return;
       }
       else if (dual_x_carriage_mode == DXC_DUPLICATION_MODE) {
+        // In Duplication Mode, T0 can move as far left as X_MIN_POS
+        // but not so far to the right that T1 would move past the end
         soft_endstop_min[X_AXIS] = base_min_pos(X_AXIS) + offs;
         soft_endstop_max[X_AXIS] = min(base_max_pos(X_AXIS), dual_max_x - duplicate_extruder_x_offset) + offs;
-        return;
+      }
+      else {
+        // In other modes, T0 can move from X_MIN_POS to X_MAX_POS
+        soft_endstop_min[axis] = base_min_pos(axis) + offs;
+        soft_endstop_max[axis] = base_max_pos(axis) + offs;
       }
     }
-    else
-  #endif
-  {
+  #else
     soft_endstop_min[axis] = base_min_pos(axis) + offs;
     soft_endstop_max[axis] = base_max_pos(axis) + offs;
-  }
+  #endif
 
   #if ENABLED(DEBUG_LEVELING_FEATURE)
     if (DEBUGGING(LEVELING)) {