power panic: add readable flags and optimise ISR(INT4_vect)

Add more readable names for the EEPROM_UVLO values

Change in memory:
Flash: -14 bytes
SRAM: 0 bytes

Firmware/Marlin_main.cpp

@@ -1457,7 +1457,7 @@ void setup()
 		}
 		eeprom_write_byte((uint8_t*)EEPROM_TEMP_CAL_ACTIVE, 0);
 	}
-	eeprom_init_default_byte((uint8_t*)EEPROM_UVLO, 0);
+	eeprom_init_default_byte((uint8_t*)EEPROM_UVLO, NO_PENDING_RECOVERY);
 	eeprom_init_default_byte((uint8_t*)EEPROM_SD_SORT, 0);
 
 	//mbl_mode_init();
@@ -1578,7 +1578,7 @@ void setup()
     fw_crash_init();
 
 #ifdef UVLO_SUPPORT
-  if (eeprom_read_byte((uint8_t*)EEPROM_UVLO) != 0) { //previous print was terminated by UVLO
+  if (eeprom_read_byte((uint8_t*)EEPROM_UVLO) != NO_PENDING_RECOVERY) { //previous print was terminated by UVLO
       manage_heater(); // Update temperatures 
 #ifdef DEBUG_UVLO_AUTOMATIC_RECOVER 
 		printf_P(_N("Power panic detected!\nCurrent bed temp:%d\nSaved bed temp:%d\n"), (int)degBed(), eeprom_read_byte((uint8_t*)EEPROM_UVLO_TARGET_BED));
@@ -1596,7 +1596,7 @@ void setup()
           if ( lcd_show_fullscreen_message_yes_no_and_wait_P(_T(MSG_RECOVER_PRINT), false) == LCD_LEFT_BUTTON_CHOICE) {
               recover_print(0); 
           } else { 
-              eeprom_update_byte((uint8_t*)EEPROM_UVLO, 0); 
+              eeprom_update_byte((uint8_t*)EEPROM_UVLO, NO_PENDING_RECOVERY); 
               lcd_update_enable(true); 
               lcd_update(2); 
               lcd_setstatuspgm(MSG_WELCOME); 
@@ -4149,7 +4149,7 @@ void process_commands()
             printf_P(_N("E0:%d RPM\nPRN0:%d RPM\n"), 60*fan_speed[0], 60*fan_speed[1]);
         }
         else if (code_seen_P(PSTR("uvlo"))) { // PRUSA uvlo
-            eeprom_update_byte((uint8_t*)EEPROM_UVLO,0); 
+            eeprom_update_byte((uint8_t*)EEPROM_UVLO, NO_PENDING_RECOVERY); 
             enquecommand_P(MSG_M24); 
         }
 		else if (code_seen_P(PSTR("MMURES"))) // PRUSA MMURES
@@ -10660,7 +10660,7 @@ void restore_print_from_ram_and_continue(float e_move)
 // Cancel the state related to a currently saved print
 void cancel_saved_printing()
 {
-    eeprom_update_byte((uint8_t*)EEPROM_UVLO, 0);
+    eeprom_update_byte((uint8_t*)EEPROM_UVLO, NO_PENDING_RECOVERY);
     saved_start_position[0] = SAVED_START_POSITION_UNSET;
     saved_printing_type = PRINTING_TYPE_NONE;
     saved_printing = false;

Firmware/power_panic.cpp

@@ -196,7 +196,7 @@ void uvlo_() {
     // Note: Recovering a print from EEPROM currently assumes the user
     // is printing from an SD card, this is why this EEPROM byte is only set
     // when SD card print is detected
-    if(sd_print) eeprom_update_byte((uint8_t*)EEPROM_UVLO, 1);
+    if(sd_print) eeprom_update_byte((uint8_t*)EEPROM_UVLO, PENDING_RECOVERY);
 
     // Increment power failure counter
     eeprom_increment_byte((uint8_t*)EEPROM_POWER_COUNT);
@@ -268,7 +268,7 @@ static void uvlo_tiny() {
     }
 
     // Update the the "power outage" flag.
-    eeprom_update_byte((uint8_t*)EEPROM_UVLO,2);
+    eeprom_update_byte((uint8_t*)EEPROM_UVLO, PENDING_RECOVERY_RETRY);
 
     // Increment power failure counter
     eeprom_update_byte((uint8_t*)EEPROM_POWER_COUNT, eeprom_read_byte((uint8_t*)EEPROM_POWER_COUNT) + 1);
@@ -290,7 +290,7 @@ void setup_uvlo_interrupt() {
     EIMSK |= (1 << 4);
 
     // check if power was lost before we armed the interrupt
-    if(!(PINE & (1 << 4)) && eeprom_read_byte((uint8_t*)EEPROM_UVLO))
+    if(!(PINE & (1 << 4)) && eeprom_read_byte((uint8_t*)EEPROM_UVLO) != NO_PENDING_RECOVERY)
     {
         SERIAL_ECHOLNRPGM(MSG_INT4);
         uvlo_drain_reset();
@@ -300,9 +300,17 @@ void setup_uvlo_interrupt() {
 ISR(INT4_vect) {
     EIMSK &= ~(1 << 4); //disable INT4 interrupt to make sure that this code will be executed just once
     SERIAL_ECHOLNRPGM(MSG_INT4);
-    //fire normal uvlo only in case where EEPROM_UVLO is 0 or if IS_SD_PRINTING is 1.
+    if (eeprom_read_byte((uint8_t*)EEPROM_UVLO) == NO_PENDING_RECOVERY)
-     if(printer_active() && (!(eeprom_read_byte((uint8_t*)EEPROM_UVLO)))) uvlo_();
+    {
-     if(eeprom_read_byte((uint8_t*)EEPROM_UVLO)) uvlo_tiny();
+        if(printer_active()) {
+            uvlo_();
+        }
+    } else {
+        // There is already a pending recovery waiting. Power outage in this scenario
+        // arrives before we can fully recover the print. In that case call a 'tiny'
+        // version of uvlo_() which doesn't overwrite the print state already waiting in EEPROM
+        uvlo_tiny();
+    }
 }
 
 void recover_print(uint8_t automatic) {
@@ -315,7 +323,7 @@ void recover_print(uint8_t automatic) {
 
     // Lift the print head 25mm, first to avoid collisions with oozed material with the print,
     // and second also so one may remove the excess priming material.
-    if(eeprom_read_byte((uint8_t*)EEPROM_UVLO) == 1)
+    if(eeprom_read_byte((uint8_t*)EEPROM_UVLO) == PENDING_RECOVERY)
     {
         enquecommandf_P(PSTR("G1 Z%.3f F800"), current_position[Z_AXIS] + 25);
     }

Firmware/power_panic.h

@@ -1,5 +1,11 @@
 #pragma once
 
+enum PowerPanicFlag : uint8_t {
+    NO_PENDING_RECOVERY = 0,
+    PENDING_RECOVERY = 1, // First power panic, print state is saved in EEPROM
+    PENDING_RECOVERY_RETRY = 2, // Power outage occured during recovery, print is still saved in EEPROM
+};
+
 void uvlo_();
 void recover_print(uint8_t automatic); 
 void setup_uvlo_interrupt();