Pause and PLR refinements

- Move `pause_print` argument `unload_length` after `show_lcd` so it's next to `DXC_ARGS`.
- Tweak the position and conditions of PLR save in `resume_print`.
- Add `Nozzle::park_mode_0_height` accessor to get the raised Z height.
- Remove extraneous `recovery.save` from `dwin.cpp`.
- Move PLR `info.volumetric...` to `flag`.
- Remove some G-code spaces in PLR code
- Document `pause.h` function declarations.

Marlin/src/feature/pause.cpp

   );
 
   #if !BOTH(FILAMENT_UNLOAD_ALL_EXTRUDERS, MIXING_EXTRUDER)
-    constexpr float mix_multiplier = 1.0;
+    constexpr float mix_multiplier = 1.0f;
   #endif
 
   if (!ensure_safe_temperature(false, mode)) {
  */
 uint8_t did_pause_print = 0;
 
-bool pause_print(const_float_t retract, const xyz_pos_t &park_point, const_float_t unload_length/*=0*/, const bool show_lcd/*=false*/ DXC_ARGS) {
+bool pause_print(const_float_t retract, const xyz_pos_t &park_point, const bool show_lcd/*=false*/, const_float_t unload_length/*=0*/ DXC_ARGS) {
   DEBUG_SECTION(pp, "pause_print", true);
   DEBUG_ECHOLNPAIR("... park.x:", park_point.x, " y:", park_point.y, " z:", park_point.z, " unloadlen:", unload_length, " showlcd:", show_lcd DXC_SAY);
 
 
   // Pause the print job and timer
   #if ENABLED(SDSUPPORT)
-    if (IS_SD_PRINTING()) {
+    const bool was_sd_printing = IS_SD_PRINTING();
+    if (was_sd_printing) {
       card.pauseSDPrint();
       ++did_pause_print; // Indicate SD pause also
     }
     unscaled_e_move(retract, PAUSE_PARK_RETRACT_FEEDRATE);
   }
 
-  // Park the nozzle by moving up by z_lift and then moving to (x_pos, y_pos)
+  // Park the nozzle by doing a Minimum Z Raise followed by an XY Move
   if (!axes_should_home())
     nozzle.park(0, park_point);
 
   // Set extruder to saved position
   planner.set_e_position_mm((destination.e = current_position.e = resume_position.e));
 
-  // Write PLR now to update the z axis value
-  TERN_(POWER_LOSS_RECOVERY, if (recovery.enabled) recovery.save(true));
-
   ui.pause_show_message(PAUSE_MESSAGE_STATUS);
 
   #ifdef ACTION_ON_RESUMED
 
   TERN_(HOST_PROMPT_SUPPORT, host_prompt_open(PROMPT_INFO, PSTR("Resuming"), DISMISS_STR));
 
+  // Resume the print job timer if it was running
+  if (print_job_timer.isPaused()) print_job_timer.start();
+
   #if ENABLED(SDSUPPORT)
-    if (did_pause_print) { card.startFileprint(); --did_pause_print; }
+    if (did_pause_print) {
+      --did_pause_print;
+      card.startFileprint();
+      // Write PLR now to update the z axis value
+      TERN_(POWER_LOSS_RECOVERY, if (recovery.enabled) recovery.save(true));
+    }
   #endif
 
   #if ENABLED(ADVANCED_PAUSE_FANS_PAUSE) && HAS_FAN
 
   TERN_(HAS_FILAMENT_SENSOR, runout.reset());
 
-  // Resume the print job timer if it was running
-  if (print_job_timer.isPaused()) print_job_timer.start();
-
   TERN_(HAS_STATUS_MESSAGE, ui.reset_status());
   TERN_(HAS_LCD_MENU, ui.return_to_status());
 }

Marlin/src/feature/pause.h

   #define DXC_SAY
 #endif
 
-bool pause_print(const_float_t retract, const xyz_pos_t &park_point, const_float_t unload_length=0, const bool show_lcd=false DXC_PARAMS);
+// Pause the print. If unload_length is set, do a Filament Unload
+bool pause_print(
+  const_float_t   retract,                                    // (mm) Retraction length
+  const xyz_pos_t &park_point,                                // Parking XY Position and Z Raise
+  const bool      show_lcd=false,                             // Set LCD status messages?
+  const_float_t   unload_length=0                             // (mm) Filament Change Unload Length - 0 to skip
+  DXC_PARAMS                                                  // Dual-X-Carriage extruder index
+);
 
-void wait_for_confirmation(const bool is_reload=false, const int8_t max_beep_count=0 DXC_PARAMS);
+void wait_for_confirmation(
+  const bool      is_reload=false,                            // Reload Filament? (otherwise Resume Print)
+  const int8_t    max_beep_count=0                            // Beep alert for attention
+  DXC_PARAMS                                                  // Dual-X-Carriage extruder index
+);
 
-void resume_print(const_float_t slow_load_length=0, const_float_t fast_load_length=0, const_float_t extrude_length=ADVANCED_PAUSE_PURGE_LENGTH,
-                    const int8_t max_beep_count=0, const celsius_t targetTemp=0 DXC_PARAMS);
+void resume_print(
+  const_float_t   slow_load_length=0,                         // (mm) Slow Load Length for finishing move
+  const_float_t   fast_load_length=0,                         // (mm) Fast Load Length for initial move
+  const_float_t   extrude_length=ADVANCED_PAUSE_PURGE_LENGTH, // (mm) Purge length
+  const int8_t    max_beep_count=0,                           // Beep alert for attention
+  const celsius_t targetTemp=0                                // (°C) A target temperature for the hotend
+  DXC_PARAMS                                                  // Dual-X-Carriage extruder index
+);
 
-bool load_filament(const_float_t slow_load_length=0, const_float_t fast_load_length=0, const_float_t extrude_length=0, const int8_t max_beep_count=0,
-                    const bool show_lcd=false, const bool pause_for_user=false, const PauseMode mode=PAUSE_MODE_PAUSE_PRINT DXC_PARAMS);
+bool load_filament(
+  const_float_t   slow_load_length=0,                         // (mm) Slow Load Length for finishing move
+  const_float_t   fast_load_length=0,                         // (mm) Fast Load Length for initial move
+  const_float_t   extrude_length=0,                           // (mm) Purge length
+  const int8_t    max_beep_count=0,                           // Beep alert for attention
+  const bool      show_lcd=false,                             // Set LCD status messages?
+  const bool      pause_for_user=false,                       // Pause for user before returning?
+  const PauseMode mode=PAUSE_MODE_PAUSE_PRINT                 // Pause Mode to apply
+  DXC_PARAMS                                                  // Dual-X-Carriage extruder index
+);
 
-bool unload_filament(const_float_t unload_length, const bool show_lcd=false, const PauseMode mode=PAUSE_MODE_PAUSE_PRINT
+bool unload_filament(
+  const_float_t   unload_length,                              // (mm) Filament Unload Length - 0 to skip
+  const bool      show_lcd=false,                             // Set LCD status messages?
+  const PauseMode mode=PAUSE_MODE_PAUSE_PRINT                 // Pause Mode to apply
   #if BOTH(FILAMENT_UNLOAD_ALL_EXTRUDERS, MIXING_EXTRUDER)
-    , const_float_t mix_multiplier=1.0
+    , const_float_t mix_multiplier=1.0f                       // Extrusion multiplier (for a Mixing Extruder)
   #endif
 );
 

Marlin/src/feature/powerloss.cpp

  */
 void PrintJobRecovery::save(const bool force/*=false*/, const float zraise/*=0*/) {
 
+  // We don't check IS_SD_PRINTING here so a save may occur during a pause
+
   #if SAVE_INFO_INTERVAL_MS > 0
     static millis_t next_save_ms; // = 0
     millis_t ms = millis();
     #endif
 
     #if DISABLED(NO_VOLUMETRICS)
-      info.volumetric_enabled = parser.volumetric_enabled;
+      info.flag.volumetric_enabled = parser.volumetric_enabled;
       #if HAS_MULTI_EXTRUDER
         for (int8_t e = 0; e < EXTRUDERS; e++) info.filament_size[e] = planner.filament_size[e];
       #else
     }
   #endif
 
-  // Reset E, raise Z, home XY...
+  //
+  // Home the axes that can safely be homed, and
+  // establish the current position as best we can
+  //
   #if Z_HOME_DIR > 0
 
-    // If Z homing goes to max, just reset E and home all
+    // If Z homing goes to max...
     gcode.process_subcommands_now_P(PSTR(
-      "G92.9 E0\n"
-      "G28R0"
+      "G92.9 E0\n"                          // Reset E to 0
+      "G28R0"                               // Home all axes (no raise)
     ));
 
   #else // "G92.9 E0 ..."
 
   #endif
 
-  #ifdef POWER_LOSS_ZHOME_POS
-    // If defined move to a safe Z homing position that avoids the print
+  #if ENABLED(POWER_LOSS_RECOVER_ZHOME) && defined(POWER_LOSS_ZHOME_POS)
+    // Move to a safe XY position where Z can home while avoiding the print.
+    // If Z_SAFE_HOMING is enabled, its position must also be outside the print area!
     constexpr xy_pos_t p = POWER_LOSS_ZHOME_POS;
-    sprintf_P(cmd, PSTR("G1 X%s Y%s F1000\nG28Z"), dtostrf(p.x, 1, 3, str_1), dtostrf(p.y, 1, 3, str_2));
+    sprintf_P(cmd, PSTR("G1X%sY%sF1000\nG28Z"), dtostrf(p.x, 1, 3, str_1), dtostrf(p.y, 1, 3, str_2));
     gcode.process_subcommands_now(cmd);
   #endif
 
-  // Ensure that all axes are marked as homed
+  // Mark all axes as having been homed (no effect on current_position)
   set_all_homed();
 
   #if ENABLED(POWER_LOSS_RECOVER_ZHOME)
-    // Now move to ZsavedPos + POWER_LOSS_ZRAISE
-    sprintf_P(cmd, PSTR("G1 F500 Z%s"), dtostrf(info.current_position.z + POWER_LOSS_ZRAISE, 1, 3, str_1));
+    // Z was homed. Now move Z back up to the saved Z height, plus the POWER_LOSS_ZRAISE.
+    sprintf_P(cmd, PSTR("G1Z%sF500"), dtostrf(info.current_position.z + POWER_LOSS_ZRAISE, 1, 3, str_1));
     gcode.process_subcommands_now(cmd);
   #endif
 
   #if DISABLED(NO_VOLUMETRICS)
     #if HAS_MULTI_EXTRUDER
       for (int8_t e = 0; e < EXTRUDERS; e++) {
-        sprintf_P(cmd, PSTR("M200 T%i D%s"), e, dtostrf(info.filament_size[e], 1, 3, str_1));
+        sprintf_P(cmd, PSTR("M200T%iD%s"), e, dtostrf(info.filament_size[e], 1, 3, str_1));
         gcode.process_subcommands_now(cmd);
       }
-      if (!info.volumetric_enabled) {
-        sprintf_P(cmd, PSTR("M200 T%i D0"), info.active_extruder);
+      if (!info.flag.volumetric_enabled) {
+        sprintf_P(cmd, PSTR("M200T%iD0"), info.active_extruder);
         gcode.process_subcommands_now(cmd);
       }
     #else
-      if (info.volumetric_enabled) {
-        sprintf_P(cmd, PSTR("M200 D%s"), dtostrf(info.filament_size[0], 1, 3, str_1));
+      if (info.flag.volumetric_enabled) {
+        sprintf_P(cmd, PSTR("M200D%s"), dtostrf(info.filament_size[0], 1, 3, str_1));
         gcode.process_subcommands_now(cmd);
       }
     #endif
     FANS_LOOP(i) {
       const int f = info.fan_speed[i];
       if (f) {
-        sprintf_P(cmd, PSTR("M106 P%i S%i"), i, f);
+        sprintf_P(cmd, PSTR("M106P%iS%i"), i, f);
         gcode.process_subcommands_now(cmd);
       }
     }
   #endif
 
-  // Restore retract and hop state
+  // Restore retract and hop state from an active `G10` command
   #if ENABLED(FWRETRACT)
     LOOP_L_N(e, EXTRUDERS) {
       if (info.retract[e] != 0.0) {
     // Restore leveling state before 'G92 Z' to ensure
     // the Z stepper count corresponds to the native Z.
     if (info.fade || info.flag.leveling) {
-      sprintf_P(cmd, PSTR("M420 S%i Z%s"), int(info.flag.leveling), dtostrf(info.fade, 1, 1, str_1));
+      sprintf_P(cmd, PSTR("M420S%cZ%s"), '0' + (char)info.flag.leveling, dtostrf(info.fade, 1, 1, str_1));
       gcode.process_subcommands_now(cmd);
     }
   #endif
   #endif
 
   // Un-retract if there was a retract at outage
-  #if POWER_LOSS_RETRACT_LEN
+  #if ENABLED(BACKUP_POWER_SUPPLY) && POWER_LOSS_RETRACT_LEN > 0
     gcode.process_subcommands_now_P(PSTR("G1 E" STRINGIFY(POWER_LOSS_RETRACT_LEN) " F3000"));
   #endif
 
-  // Additional purge if configured
+  // Additional purge on resume if configured
   #if POWER_LOSS_PURGE_LEN
     sprintf_P(cmd, PSTR("G1 E%d F3000"), (POWER_LOSS_PURGE_LEN) + (POWER_LOSS_RETRACT_LEN));
     gcode.process_subcommands_now(cmd);

Marlin/src/feature/powerloss.h

   #endif
 
   #if DISABLED(NO_VOLUMETRICS)
-    bool volumetric_enabled;
     float filament_size[EXTRUDERS];
   #endif
 
     bool dryrun:1;                // M111 S8
     bool allow_cold_extrusion:1;  // M302 P1
     #if ENABLED(HAS_LEVELING)
-      bool leveling:1;
+      bool leveling:1;            // M420 S
+    #endif
+    #if DISABLED(NO_VOLUMETRICS)
+      bool volumetric_enabled:1;  // M200 S D
     #endif
   } flag;
 

Marlin/src/gcode/feature/pause/M125.cpp

 
   TERN_(POWER_LOSS_RECOVERY, if (recovery.enabled) recovery.save(true));
 
-  if (pause_print(retract, park_point, 0, show_lcd)) {
+  if (pause_print(retract, park_point, show_lcd, 0)) {
     if (ENABLED(EXTENSIBLE_UI) || !sd_printing || show_lcd) {
       wait_for_confirmation(false, 0);
       resume_print(0, 0, -retract, 0);

Marlin/src/gcode/feature/pause/M600.cpp

     #endif
   );
 
-  if (pause_print(retract, park_point, unload_length, true DXC_PASS)) {
+  if (pause_print(retract, park_point, true, unload_length DXC_PASS)) {
     #if ENABLED(MMU2_MENUS)
       mmu2_M600();
       resume_print(slow_load_length, fast_load_length, 0, beep_count DXC_PASS);

Marlin/src/lcd/dwin/e3v2/dwin.cpp

       if (HMI_flag.select_flag) {
         HMI_flag.pause_action = true;
         ICON_Continue();
-        #if ENABLED(POWER_LOSS_RECOVERY)
-          if (recovery.enabled) recovery.save(true);
-        #endif
         queue.inject_P(PSTR("M25"));
       }
       else {

Marlin/src/libs/nozzle.cpp

 
 #if ENABLED(NOZZLE_PARK_FEATURE)
 
+  float Nozzle::park_mode_0_height(const_float_t park_z) {
+    // Apply a minimum raise, if specified. Use park.z as a minimum height instead.
+    return _MAX(park_z,                       // Minimum height over 0 based on input
+      _MIN(Z_MAX_POS,                         // Maximum height is fixed
+        #ifdef NOZZLE_PARK_Z_RAISE_MIN
+          NOZZLE_PARK_Z_RAISE_MIN +           // Minimum raise...
+        #endif
+        current_position.z                    // ...over current position
+      )
+    );
+  }
+
   void Nozzle::park(const uint8_t z_action, const xyz_pos_t &park/*=NOZZLE_PARK_POINT*/) {
     constexpr feedRate_t fr_xy = NOZZLE_PARK_XY_FEEDRATE, fr_z = NOZZLE_PARK_Z_FEEDRATE;
 
         do_blocking_move_to_z(_MIN(current_position.z + park.z, Z_MAX_POS), fr_z);
         break;
 
-      default: {
-        // Apply a minimum raise, overriding G27 Z
-        const float min_raised_z =_MIN(Z_MAX_POS, current_position.z
-          #ifdef NOZZLE_PARK_Z_RAISE_MIN
-            + NOZZLE_PARK_Z_RAISE_MIN
-          #endif
-        );
-        do_blocking_move_to_z(_MAX(park.z, min_raised_z), fr_z);
-      } break;
+      default: // Raise by NOZZLE_PARK_Z_RAISE_MIN, use park.z as a minimum height
+        do_blocking_move_to_z(park_mode_0_height(park.z), fr_z);
+        break;
     }
 
     do_blocking_move_to_xy(

Marlin/src/libs/nozzle.h

 
   #if ENABLED(NOZZLE_PARK_FEATURE)
 
+    static float park_mode_0_height(const_float_t park_z) _Os;
     static void park(const uint8_t z_action, const xyz_pos_t &park=NOZZLE_PARK_POINT) _Os;
 
   #endif