Safe Z homing for Power Loss Recovery (#16909)

Marlin/Configuration_adv.h

   #if ENABLED(POWER_LOSS_RECOVERY)
     #define PLR_ENABLED_DEFAULT   false // Power Loss Recovery enabled by default. (Set with 'M413 Sn' & M500)
     //#define BACKUP_POWER_SUPPLY       // Backup power / UPS to move the steppers on power loss
-    //#define POWER_LOSS_RECOVER_ZHOME  // Z homing is needed for proper recovery. 99.9% of the time this should be disabled!
     //#define POWER_LOSS_ZRAISE       2 // (mm) Z axis raise on resume (on power loss with UPS)
     //#define POWER_LOSS_PIN         44 // Pin to detect power loss. Set to -1 to disable default pin on boards without module.
     //#define POWER_LOSS_STATE     HIGH // State of pin indicating power loss
     // Without a POWER_LOSS_PIN the following option helps reduce wear on the SD card,
     // especially with "vase mode" printing. Set too high and vases cannot be continued.
     #define POWER_LOSS_MIN_Z_CHANGE 0.05 // (mm) Minimum Z change before saving power-loss data
+
+    // Enable if Z homing is needed for proper recovery. 99.9% of the time this should be disabled!
+    //#define POWER_LOSS_RECOVER_ZHOME
+    #if ENABLED(POWER_LOSS_RECOVER_ZHOME)
+      //#define POWER_LOSS_ZHOME_POS { 0, 0 } // Safe XY position to home Z while avoiding objects on the bed
+    #endif
   #endif
 
   /**

Marlin/src/feature/powerloss.cpp

     // Home safely with no Z raise
     gcode.process_subcommands_now_P(PSTR(
       "G28R0"                               // No raise during G28
-      #if IS_CARTESIAN && DISABLED(POWER_LOSS_RECOVER_ZHOME)
+      #if IS_CARTESIAN && (DISABLED(POWER_LOSS_RECOVER_ZHOME) || defined(POWER_LOSS_ZHOME_POS))
         "XY"                                // Don't home Z on Cartesian unless overridden
       #endif
     ));
 
   #endif
 
-  // Pretend that all axes are homed
+  #ifdef POWER_LOSS_ZHOME_POS
+    // If defined move to a safe Z homing position that avoids the print
+    constexpr xy_pos_t homepos = POWER_LOSS_ZHOME_POS;
+    sprintf_P(cmd, PSTR("G1 X%s Y%s F1000\nG28Z", dtostrf(homepos.x, 1, 3, str_1), dtostrf(homepos.y, 1, 3, str_2)));
+    gcode.process_subcommands_now(cmd);
+  #endif
+
+  // Ensure that all axes are marked as homed
   set_all_homed();
 
   #if ENABLED(POWER_LOSS_RECOVER_ZHOME)
-    // Z has been homed so restore Z to ZsavedPos + POWER_LOSS_ZRAISE
+    // 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));
     gcode.process_subcommands_now(cmd);
   #endif
 
   // Additional purge if configured
   #if POWER_LOSS_PURGE_LEN
-    sprintf_P(cmd, PSTR("G1 E%d F200"), (POWER_LOSS_PURGE_LEN) + (POWER_LOSS_RETRACT_LEN));
+    sprintf_P(cmd, PSTR("G1 E%d F3000"), (POWER_LOSS_PURGE_LEN) + (POWER_LOSS_RETRACT_LEN));
     gcode.process_subcommands_now(cmd);
   #endif
 
   // Move back to the saved Z
   dtostrf(info.current_position.z, 1, 3, str_1);
   #if Z_HOME_DIR > 0 || ENABLED(POWER_LOSS_RECOVER_ZHOME)
-    sprintf_P(cmd, PSTR("G1 Z%s F200"), str_1);
+    sprintf_P(cmd, PSTR("G1 Z%s F500"), str_1);
   #else
     gcode.process_subcommands_now_P(PSTR("G1 Z0 F200"));
     sprintf_P(cmd, PSTR("G92.9 Z%s"), str_1);

Marlin/src/inc/SanityCheck.h

  * Allen Key
  * Deploying the Allen Key probe uses big moves in z direction. Too dangerous for an unhomed z-axis.
  */
-#if BOTH(Z_PROBE_ALLEN_KEY, Z_MIN_PROBE_USES_Z_MIN_ENDSTOP_PIN) && (Z_HOME_DIR < 0)
+#if BOTH(Z_PROBE_ALLEN_KEY, Z_MIN_PROBE_USES_Z_MIN_ENDSTOP_PIN) && Z_HOME_DIR < 0
   #error "You can't home to a Z min endstop with a Z_PROBE_ALLEN_KEY."
 #endif
 
   #endif
 #endif
 
-#if ENABLED(BACKUP_POWER_SUPPLY) && !PIN_EXISTS(POWER_LOSS)
-  #error "BACKUP_POWER_SUPPLY requires a POWER_LOSS_PIN."
-#endif
-
-#if BOTH(POWER_LOSS_PULLUP, POWER_LOSS_PULLDOWN)
-  #error "You can't enable POWER_LOSS_PULLUP and POWER_LOSS_PULLDOWN at the same time."
+#if ENABLED(POWER_LOSS_RECOVERY)
+  #if ENABLED(BACKUP_POWER_SUPPLY) && !PIN_EXISTS(POWER_LOSS)
+    #error "BACKUP_POWER_SUPPLY requires a POWER_LOSS_PIN."
+  #elif BOTH(POWER_LOSS_RECOVER_ZHOME, Z_SAFE_HOMING)
+    #error "POWER_LOSS_RECOVER_ZHOME cannot be used with Z_SAFE_HOMING."
+  #elif BOTH(POWER_LOSS_PULLUP, POWER_LOSS_PULLDOWN)
+    #error "You can't enable POWER_LOSS_PULLUP and POWER_LOSS_PULLDOWN at the same time."
+  #elif BOTH(IS_CARTESIAN, POWER_LOSS_RECOVER_ZHOME) && Z_HOME_DIR < 0 && !defined(POWER_LOSS_ZHOME_POS)
+    #error "POWER_LOSS_RECOVER_ZHOME requires POWER_LOSS_ZHOME_POS for a Cartesian that homes to ZMIN."
+  #endif
 #endif
 
 #if ENABLED(Z_STEPPER_AUTO_ALIGN)

Marlin/src/module/probe.cpp

    *  - If a preheat input is higher than the current target, raise the target temperature.
    *  - If a preheat input is higher than the current temperature, wait for stabilization.
    */
-  void Probe::preheat_for_probing(const uint16_t hotend_temp, const uint16_t bed_temp) {
+  void Probe::preheat_for_probing(const int16_t hotend_temp, const int16_t bed_temp) {
     #if HAS_HOTEND && (PROBING_NOZZLE_TEMP || LEVELING_NOZZLE_TEMP)
       #define WAIT_FOR_NOZZLE_HEAT
     #endif
     DEBUG_ECHOPGM("Preheating ");
 
     #if ENABLED(WAIT_FOR_NOZZLE_HEAT)
-      const uint16_t hotendPreheat = hotend_temp > thermalManager.degTargetHotend(0) ? hotend_temp : 0;
+      const int16_t hotendPreheat = hotend_temp > thermalManager.degTargetHotend(0) ? hotend_temp : 0;
       if (hotendPreheat) {
         DEBUG_ECHOPAIR("hotend (", hotendPreheat, ")");
         thermalManager.setTargetHotend(hotendPreheat, 0);
       }
     #elif ENABLED(WAIT_FOR_BED_HEAT)
-      constexpr uint16_t hotendPreheat = 0;
+      constexpr int16_t hotendPreheat = 0;
     #endif
 
     #if ENABLED(WAIT_FOR_BED_HEAT)
-      const uint16_t bedPreheat = bed_temp > thermalManager.degTargetBed() ? bed_temp : 0;
+      const int16_t bedPreheat = bed_temp > thermalManager.degTargetBed() ? bed_temp : 0;
       if (bedPreheat) {
         if (hotendPreheat) DEBUG_ECHOPGM(" and ");
         DEBUG_ECHOPAIR("bed (", bedPreheat, ")");

Marlin/src/module/probe.h

     static xyz_pos_t offset;
 
     #if EITHER(PREHEAT_BEFORE_PROBING, PREHEAT_BEFORE_LEVELING)
-      static void preheat_for_probing(const uint16_t hotend_temp, const uint16_t bed_temp);
+      static void preheat_for_probing(const int16_t hotend_temp, const int16_t bed_temp);
     #endif
 
     static bool set_deployed(const bool deploy);

buildroot/tests/rambo-tests

 opt_add HEATER_CHAMBER_PIN 45
 opt_set GRID_MAX_POINTS_X 16
 opt_set FANMUX0_PIN 53
-opt_disable USE_WATCHDOG
+opt_set Z_HOME_DIR 1
+opt_enable USE_ZMAX_PLUG
+opt_disable USE_ZMIN_PLUG Z_MIN_PROBE_USES_Z_MIN_ENDSTOP_PIN USE_WATCHDOG
 opt_enable REPRAP_DISCOUNT_SMART_CONTROLLER LCD_PROGRESS_BAR LCD_PROGRESS_BAR_TEST \
-           FIX_MOUNTED_PROBE Z_SAFE_HOMING CODEPENDENT_XY_HOMING PIDTEMPBED PROBE_TEMP_COMPENSATION \
+           FIX_MOUNTED_PROBE CODEPENDENT_XY_HOMING PIDTEMPBED PROBE_TEMP_COMPENSATION \
            PREHEAT_BEFORE_PROBING PROBING_HEATERS_OFF PROBING_FANS_OFF PROBING_STEPPERS_OFF WAIT_FOR_BED_HEATER \
            EEPROM_SETTINGS SDSUPPORT SD_REPRINT_LAST_SELECTED_FILE BINARY_FILE_TRANSFER \
            BLINKM PCA9533 PCA9632 RGB_LED RGB_LED_R_PIN RGB_LED_G_PIN RGB_LED_B_PIN LED_CONTROL_MENU \
            SKEW_CORRECTION SKEW_CORRECTION_FOR_Z SKEW_CORRECTION_GCODE \
            BACKLASH_COMPENSATION BACKLASH_GCODE BAUD_RATE_GCODE BEZIER_CURVE_SUPPORT \
            FWRETRACT ARC_P_CIRCLES CNC_WORKSPACE_PLANES CNC_COORDINATE_SYSTEMS \
-           PSU_CONTROL AUTO_POWER_CONTROL POWER_LOSS_RECOVERY POWER_LOSS_PIN POWER_LOSS_STATE \
+           PSU_CONTROL AUTO_POWER_CONTROL POWER_LOSS_RECOVERY POWER_LOSS_PIN POWER_LOSS_STATE POWER_LOSS_RECOVER_ZHOME \
            SLOW_PWM_HEATERS THERMAL_PROTECTION_CHAMBER LIN_ADVANCE EXTRA_LIN_ADVANCE_K \
            HOST_ACTION_COMMANDS HOST_PROMPT_SUPPORT PINS_DEBUGGING MAX7219_DEBUG M114_DETAIL
 opt_add DEBUG_POWER_LOSS_RECOVERY