mmu: add DisableMMUInSettings

power_on should not be modifying
EEPROM_MMU_ENABLED. The code is never
executed unless it's already been set.

Only disable EEPROM_MMU_ENABLED through Buttons::DisableMMU

Change in memory:
Flash: -18 bytes
SRAM: 0 bytes

Firmware/mmu2.cpp

@@ -69,7 +69,7 @@ void MMU2::Start() {
 
 void MMU2::Stop() {
     StopKeepPowered();
-    PowerOff(); // This also disables the MMU in the EEPROM.
+    PowerOff();
 }
 
 void MMU2::StopKeepPowered() {
@@ -125,11 +125,9 @@ void MMU2::TriggerResetPin() {
 void MMU2::PowerCycle() {
     // cut the power to the MMU and after a while restore it
     // Sadly, MK3/S/+ cannot do this
-    // NOTE: the below will toggle the EEPROM var. Should we
-    // assert this function is never called in the MK3 FW? Do we even care?
-    PowerOff();
+    Stop();
     safe_delay_keep_alive(1000);
-    PowerOn();
+    Start();
 }
 
 void MMU2::PowerOff() {
@@ -735,7 +733,8 @@ void MMU2::CheckUserInput() {
         // ... but mmu2_power.cpp knows this and triggers a soft-reset instead.
         break;
     case Buttons::DisableMMU:
-        Stop(); // Poweroff handles updating the EEPROM shutoff.
+        Stop();
+        DisableMMUInSettings();
         break;
     case Buttons::StopPrint:
         // @@TODO not sure if we shall handle this high level operation at this spot

Firmware/mmu2_power.cpp

@@ -4,7 +4,6 @@
 #include "fastio.h"
 #include <util/delay.h>
 #include "mmu2.h"
-#include "eeprom.h"
 
 namespace MMU2 {
 
@@ -16,13 +15,10 @@ void power_on() {
     SET_OUTPUT(MMU_RST_PIN); // setup reset pin
 #endif //MMU_HWRESET
 
-    eeprom_update_byte((uint8_t *)EEPROM_MMU_ENABLED, true);
-
     reset();
 }
 
 void power_off() {
-    eeprom_update_byte((uint8_t *)EEPROM_MMU_ENABLED, false);
 }
 
 void reset() {

Firmware/mmu2_reporting.cpp

@@ -1,4 +1,5 @@
 #include <avr/pgmspace.h>
+#include "eeprom.h"
 #include "mmu2.h"
 #include "mmu2_log.h"
 #include "mmu2_reporting.h"
@@ -344,6 +345,11 @@ void TryLoadUnloadReporter::DumpToSerial(){
     MMU2_ECHO_MSGLN(buf);
 }
 
+/// Disables MMU in EEPROM
+void DisableMMUInSettings() {
+    eeprom_update_byte((uint8_t *)EEPROM_MMU_ENABLED, false);
+}
+
 void IncrementLoadFails(){
     eeprom_increment_byte((uint8_t *)EEPROM_MMU_LOAD_FAIL);
     eeprom_increment_word((uint16_t *)EEPROM_MMU_LOAD_FAIL_TOT);

Firmware/mmu2_reporting.h

@@ -84,6 +84,9 @@ bool MMUAvailable();
 /// Global Enable/Disable use MMU (to be stored in EEPROM)
 bool UseMMU();
 
+/// Disables MMU in EEPROM
+void DisableMMUInSettings();
+
 /// Increments EEPROM cell - number of failed loads into the nozzle
 /// Note: technically, this is not an MMU error but an error of the printer.
 void IncrementLoadFails();