Clean up MMU2 code (#20794)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/src/feature/mmu/mmu2.cpp

 
     case -1:
       if (rx_start()) {
+        prev_P0_request = millis();   // Initialize finda sensor timeout
+
         DEBUG_ECHOLNPGM("MMU => 'start'");
         DEBUG_ECHOLNPGM("MMU <= 'S1'");
 
         // if (finda_runout_valid) DEBUG_ECHOLNPAIR_F("MMU <= 'P0'\nMMU => ", finda, 6);
 
         if (!finda && finda_runout_valid) filament_runout();
-        if (cmd == 0) ready = true;
+        if (cmd == MMU_CMD_NONE) ready = true;
         state = 1;
       }
       else if (ELAPSED(millis(), prev_request + MMU_P0_TIMEOUT)) // Resend request after timeout (3s)
       #endif
 
       if (rx_ok()) {
-        // Response to C0 mmu command in MMU2S model
-        bool can_reset = true;
         #if HAS_PRUSA_MMU2S
-          if (!mmu2s_triggered && last_cmd == MMU_CMD_C0) {
-            can_reset = false;
+          // Respond to C0 MMU command in MMU2S model
+          const bool keep_trying = !mmu2s_triggered && last_cmd == MMU_CMD_C0;
+          if (keep_trying) {
             // MMU ok received but filament sensor not triggered, retrying...
             DEBUG_ECHOLNPGM("MMU => 'ok' (filament not present in gears)");
             DEBUG_ECHOLNPGM("MMU <= 'C0' (keep trying)");
             MMU2_COMMAND("C0");
           }
+        #else
+          constexpr bool keep_trying = false;
         #endif
-        if (can_reset) {
+
+        if (!keep_trying) {
           DEBUG_ECHOLNPGM("MMU => 'ok'");
           ready = true;
           state = 1;
  */
 bool MMU2::rx_start() {
   // check for start message
-  if (rx_str_P(PSTR("start\n"))) {
-    prev_P0_request = millis();
-    return true;
-  }
-  return false;
+  return rx_str_P(PSTR("start\n"));
 }
 
 /**
 
   while (MMU2_SERIAL.available()) {
     rx_buffer[i++] = MMU2_SERIAL.read();
-    rx_buffer[i] = '\0';
 
     if (i == sizeof(rx_buffer) - 1) {
       DEBUG_ECHOLNPGM("rx buffer overrun");
       break;
     }
   }
+  rx_buffer[i] = '\0';
 
   uint8_t len = strlen_P(str);
 
   clear_rx_buffer();
   uint8_t len = strlen_P(str);
   LOOP_L_N(i, len) MMU2_SERIAL.write(pgm_read_byte(str++));
-  rx_buffer[0] = '\0';
   prev_request = millis();
 }
 
   clear_rx_buffer();
   uint8_t len = sprintf_P(tx_buffer, format, argument);
   LOOP_L_N(i, len) MMU2_SERIAL.write(tx_buffer[i]);
-  rx_buffer[0] = '\0';
   prev_request = millis();
 }
 
   clear_rx_buffer();
   uint8_t len = sprintf_P(tx_buffer, format, argument1, argument2);
   LOOP_L_N(i, len) MMU2_SERIAL.write(tx_buffer[i]);
-  rx_buffer[0] = '\0';
   prev_request = millis();
 }
 
 
         case 'c': {
           while (!thermalManager.wait_for_hotend(active_extruder, false)) safe_delay(100);
-          execute_extruder_sequence((const E_Step *)load_to_nozzle_sequence, COUNT(load_to_nozzle_sequence));
+          load_to_nozzle();
         } break;
       }
 
 }
 
 /**
- * Wait for response and deal with timeout if nexcessary
+ * Wait for response and deal with timeout if necessary
  */
 void MMU2::manage_response(const bool move_axes, const bool turn_off_nozzle) {
 
 // Load filament into MMU2
 void MMU2::load_filament(const uint8_t index) {
   if (!enabled) return;
+
   command(MMU_CMD_L0 + index);
   manage_response(false, false);
   BUZZ(200, 404);
     return false;
   }
 
+  DISABLE_AXIS_E0();
   command(MMU_CMD_T0 + index);
   manage_response(true, true);
 
  * filament to nozzle.
  */
 void MMU2::load_to_nozzle() {
-  if (!enabled) return;
   execute_extruder_sequence((const E_Step *)load_to_nozzle_sequence, COUNT(load_to_nozzle_sequence));
 }
 
     return false;
   }
 
-  filament_ramming();
+  // Unload sequence to optimize shape of the tip of the unloaded filament
+  execute_extruder_sequence((const E_Step *)ramming_sequence, sizeof(ramming_sequence) / sizeof(E_Step));
 
   command(MMU_CMD_U0);
   manage_response(false, true);
   return true;
 }
 
-/**
- * Unload sequence to optimize shape of the tip of the unloaded filament
- */
-void MMU2::filament_ramming() {
-  execute_extruder_sequence((const E_Step *)ramming_sequence, sizeof(ramming_sequence) / sizeof(E_Step));
-}
-
 void MMU2::execute_extruder_sequence(const E_Step * sequence, int steps) {
 
   planner.synchronize();

Marlin/src/feature/mmu/mmu2.h

   static void manage_response(const bool move_axes, const bool turn_off_nozzle);
 
   static void load_to_nozzle();
-  static void filament_ramming();
   static void execute_extruder_sequence(const E_Step * sequence, int steps);
 
   static void filament_runout();

Marlin/src/lcd/menu/menu_mmu2.cpp

 // Load Filament
 //
 
-void _mmu2_load_filamentToNozzle(uint8_t index) {
+inline void action_mmu2_load_filament_to_nozzle(const uint8_t tool) {
   ui.reset_status();
   ui.return_to_status();
-  ui.status_printf_P(0,  GET_TEXT(MSG_MMU2_LOADING_FILAMENT), int(index + 1));
-  if (mmu2.load_filament_to_nozzle(index)) ui.reset_status();
-}
-
-inline void action_mmu2_load_filament_to_nozzle(const uint8_t tool) {
-  _mmu2_load_filamentToNozzle(tool);
+  ui.status_printf_P(0,  GET_TEXT(MSG_MMU2_LOADING_FILAMENT), int(tool + 1));
+  if (mmu2.load_filament_to_nozzle(tool))
+    ui.reset_status();
   ui.return_to_status();
 }
 
   START_MENU();
   BACK_ITEM(MSG_MMU2_MENU);
   ACTION_ITEM(MSG_MMU2_ALL, action_mmu2_load_all);
-  LOOP_L_N(i, 5) ACTION_ITEM_N(i, MSG_MMU2_FILAMENT_N, []{ _mmu2_load_filament(MenuItemBase::itemIndex); });
+  LOOP_L_N(i, EXTRUDERS) ACTION_ITEM_N(i, MSG_MMU2_FILAMENT_N, []{ _mmu2_load_filament(MenuItemBase::itemIndex); });
   END_MENU();
 }
 
 void menu_mmu2_load_to_nozzle() {
   START_MENU();
   BACK_ITEM(MSG_MMU2_MENU);
-  LOOP_L_N(i, 5) ACTION_ITEM_N(i, MSG_MMU2_FILAMENT_N, []{ action_mmu2_load_filament_to_nozzle(MenuItemBase::itemIndex); });
+  LOOP_L_N(i, EXTRUDERS) ACTION_ITEM_N(i, MSG_MMU2_FILAMENT_N, []{ action_mmu2_load_filament_to_nozzle(MenuItemBase::itemIndex); });
   END_MENU();
 }
 
 void menu_mmu2_eject_filament() {
   START_MENU();
   BACK_ITEM(MSG_MMU2_MENU);
-  LOOP_L_N(i, 5) ACTION_ITEM_N(i, MSG_MMU2_FILAMENT_N, []{ _mmu2_eject_filament(MenuItemBase::itemIndex); });
+  LOOP_L_N(i, EXTRUDERS) ACTION_ITEM_N(i, MSG_MMU2_FILAMENT_N, []{ _mmu2_eject_filament(MenuItemBase::itemIndex); });
   END_MENU();
 }
 
   #if LCD_HEIGHT > 2
     STATIC_ITEM(MSG_MMU2_CHOOSE_FILAMENT_HEADER, SS_DEFAULT|SS_INVERT);
   #endif
-  LOOP_L_N(i, 5) ACTION_ITEM_N(i, MSG_MMU2_FILAMENT_N, []{ action_mmu2_chosen(MenuItemBase::itemIndex); });
+  LOOP_L_N(i, EXTRUDERS) ACTION_ITEM_N(i, MSG_MMU2_FILAMENT_N, []{ action_mmu2_chosen(MenuItemBase::itemIndex); });
   END_MENU();
 }