power panic: implement partial back up in RAM

A partial backup is needed in scenarios where the extruder may be
parked after a print is saved. For example during a blocking wait for the user in M600
Or during a MMU error screen.

A sudden power panic at this point would previously save the parked position
into EEPROM. When the print is recovered it would print in mid air.

Firmware/Marlin.h

@@ -391,6 +391,8 @@ extern void print_mesh_bed_leveling_table();
 void save_print_file_state();
 void restore_print_file_state();
 void save_planner_global_state();
+void refresh_print_state_in_ram();
+void clear_print_state_in_ram();
 extern void stop_and_save_print_to_ram(float z_move, float e_move);
 void restore_extruder_temperature_from_ram();
 extern void restore_print_from_ram_and_continue(float e_move);
@@ -402,6 +404,7 @@ extern void cancel_saved_printing();
 #define SAVED_START_POSITION_UNSET X_COORD_INVALID
 extern float saved_start_position[NUM_AXIS];
 extern uint16_t saved_segment_idx;
+extern bool isPartialBackupAvailable;
 
 
 //estimated time to end of the print

Firmware/Marlin_main.cpp

@@ -247,6 +247,7 @@ const char echomagic[] PROGMEM = "echo:";
 float saved_start_position[NUM_AXIS] = {SAVED_START_POSITION_UNSET, 0, 0, 0};
 
 uint16_t saved_segment_idx = 0;
+bool isPartialBackupAvailable;
 
 // storing estimated time to end of print counted by slicer
 uint8_t print_percent_done_normal = PRINT_PERCENT_DONE_INIT;
@@ -7624,6 +7625,10 @@ Sigma_Exit:
     {
     st_synchronize();
 
+    // In case a power panic happens while waiting for the user
+    // take a partial back up of print state into RAM (current position, etc.)
+    refresh_print_state_in_ram();
+
     float x_position = FILAMENTCHANGE_XPOS;
     float y_position = FILAMENTCHANGE_YPOS;
     float z_shift = MIN_Z_FOR_SWAP;
@@ -10479,6 +10484,29 @@ void save_planner_global_state() {
     }
 }
 
+/// Take a backup of the current state of variables
+/// e.g. feedrate, Z-axis position etc.
+/// This function should backup variables which may be lost
+/// For example a power panic in M600 or during MMU error
+void refresh_print_state_in_ram()
+{
+    if (saved_printing) return;
+    memcpy(saved_pos, current_position, sizeof(saved_pos));
+    saved_feedmultiply2 = feedmultiply; //save feedmultiply
+    saved_extruder_temperature = (uint16_t)degTargetHotend(active_extruder);
+    saved_bed_temperature = (uint8_t)degTargetBed();
+    saved_extruder_relative_mode = axis_relative_modes & E_AXIS_MASK;
+    saved_fan_speed = fanSpeed;
+    isPartialBackupAvailable = true;
+}
+
+void clear_print_state_in_ram()
+{
+    // Set flag to false in order to avoid using
+    // the saved values during power panic
+    isPartialBackupAvailable = false;
+}
+
 //! @brief Immediately stop print moves
 //!
 //! Immediately stop print moves, save current extruder temperature and position to RAM.

Firmware/mmu2.cpp

@@ -627,6 +627,10 @@ void MMU2::SaveAndPark(bool move_axes) {
         Disable_E0();
         planner_synchronize();
 
+        // In case a power panic happens while waiting for the user
+        // take a partial back up of print state into RAM (current position, etc.)
+        refresh_print_state_in_ram();
+
         if (move_axes) {
             mmu_print_saved |= SavedState::ParkExtruder;
             resume_position = planner_current_position(); // save current pos
@@ -681,6 +685,11 @@ void MMU2::ResumeUnpark() {
         // Move Z_AXIS to saved position
         motion_do_blocking_move_to_z(resume_position.xyz[2], feedRate_t(NOZZLE_PARK_Z_FEEDRATE));
 
+        // From this point forward, power panic should not use
+        // the partial backup in RAM since the extruder is no
+        // longer in parking position
+        clear_print_state_in_ram();
+
         mmu_print_saved &= ~(SavedState::ParkExtruder);
     }
 }

Firmware/power_panic.cpp

@@ -66,12 +66,14 @@ void uvlo_() {
     tmc2130_set_current_r(E_AXIS, 20);
 #endif //TMC2130
 
-    if (!sd_print_saved_in_ram)
+    if (!sd_print_saved_in_ram && !isPartialBackupAvailable)
     {
         saved_bed_temperature = target_temperature_bed;
         saved_extruder_temperature = target_temperature[active_extruder];
         saved_extruder_relative_mode = axis_relative_modes & E_AXIS_MASK;
         saved_fan_speed = fanSpeed;
+        memcpy(saved_pos, current_position, sizeof(saved_pos));
+        if (pos_invalid) saved_pos[X_AXIS] = X_COORD_INVALID;
     }
 
     // Stop all heaters before continuing
@@ -84,9 +86,6 @@ void uvlo_() {
 
         // save the global state at planning time
         save_planner_global_state();
-
-        memcpy(saved_pos, current_position, sizeof(saved_pos));
-        if (pos_invalid) saved_pos[X_AXIS] = X_COORD_INVALID;
     }
 
     // From this point on and up to the print recovery, Z should not move during X/Y travels and