From b9428bf0876944e163bc83a00f6dabbb48e8b472 Mon Sep 17 00:00:00 2001
From: FBN <62633887+fBn0523@users.noreply.github.com>
Date: Fri, 16 Sep 2022 07:02:08 +0800
Subject: [PATCH] =?UTF-8?q?=F0=9F=9A=B8=20More=20automatic=20MMU2=20load?=
 =?UTF-8?q?=20(#24750,=20#24770)?=
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---
 Marlin/src/feature/mmu/mmu2.cpp | 31 ++++++++++++++++++++++++++-----
 Marlin/src/feature/mmu/mmu2.h   |  1 +
 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/Marlin/src/feature/mmu/mmu2.cpp b/Marlin/src/feature/mmu/mmu2.cpp
index a4718b53d9..54553a4f2d 100644
--- a/Marlin/src/feature/mmu/mmu2.cpp
+++ b/Marlin/src/feature/mmu/mmu2.cpp
@@ -585,7 +585,7 @@ static void mmu2_not_responding() {
       command(MMU_CMD_T0 + index);
       manage_response(true, true);
       mmu_continue_loading();
-      command(MMU_CMD_C0);
+      //command(MMU_CMD_C0);
       extruder = index;
       active_extruder = 0;
 
@@ -653,13 +653,34 @@ static void mmu2_not_responding() {
   }
 
   void MMU2::mmu_continue_loading() {
+    // Try to load the filament a limited number of times
+    bool fil_present = 0;
     for (uint8_t i = 0; i < MMU_LOADING_ATTEMPTS_NR; i++) {
-      DEBUG_ECHOLNPGM("Additional load attempt #", i);
-      if (FILAMENT_PRESENT()) break;
+      DEBUG_ECHOLNPGM("Load attempt #", i + 1);
+
+      // Done as soon as filament is present
+      fil_present = FILAMENT_PRESENT();
+      if (fil_present) break;
+
+      // Attempt to load the filament, 1mm at a time, for 3s
       command(MMU_CMD_C0);
+      stepper.enable_extruder();
+      const millis_t expire_ms = millis() + 3000;
+      do {
+        current_position.e += 1;
+        line_to_current_position(MMU_LOAD_FEEDRATE);
+        planner.synchronize();
+        // When (T0 rx->ok) load is ready, but in fact it did not load
+        // successfully or an overload created pressure in the extruder.
+        // Send (C0) to load more and move E_AXIS a little to release pressure.
+        if ((fil_present = FILAMENT_PRESENT())) MMU2_COMMAND("A");
+      } while (!fil_present && PENDING(millis(), expire_ms));
+      stepper.disable_extruder();
       manage_response(true, true);
     }
-    if (!FILAMENT_PRESENT()) {
+
+    // Was the filament still missing in the last check?
+    if (!fil_present) {
       DEBUG_ECHOLNPGM("Filament never reached sensor, runout");
       filament_runout();
     }
@@ -682,7 +703,7 @@ static void mmu2_not_responding() {
       command(MMU_CMD_T0 + index);
       manage_response(true, true);
       command(MMU_CMD_C0);
-      extruder = index; //filament change is finished
+      extruder = index; // Filament change is finished
       active_extruder = 0;
       stepper.enable_extruder();
       SERIAL_ECHO_MSG(STR_ACTIVE_EXTRUDER, extruder);
diff --git a/Marlin/src/feature/mmu/mmu2.h b/Marlin/src/feature/mmu/mmu2.h
index 7d3d9ec4df..18d6d38a35 100644
--- a/Marlin/src/feature/mmu/mmu2.h
+++ b/Marlin/src/feature/mmu/mmu2.h
@@ -86,6 +86,7 @@ private:
   #endif
 
   #if ENABLED(MMU_EXTRUDER_SENSOR)
+    #define MMU_LOAD_FEEDRATE 19.02f // (mm/s)
     static void mmu_continue_loading();
   #endif