🔧 Chamber Fan index option (#23262)

Marlin/Configuration_adv.h

@@ -186,7 +186,8 @@
 
   //#define CHAMBER_FAN               // Enable a fan on the chamber
   #if ENABLED(CHAMBER_FAN)
-    #define CHAMBER_FAN_MODE 2        // Fan control mode: 0=Static; 1=Linear increase when temp is higher than target; 2=V-shaped curve; 3=similar to 1 but fan is always on.
+    //#define CHAMBER_FAN_INDEX   2   // Index of a fan to repurpose as the chamber fan. (Default: first unused fan)
+    #define CHAMBER_FAN_MODE      2   // Fan control mode: 0=Static; 1=Linear increase when temp is higher than target; 2=V-shaped curve; 3=similar to 1 but fan is always on.
     #if CHAMBER_FAN_MODE == 0
       #define CHAMBER_FAN_BASE  255   // Chamber fan PWM (0-255)
     #elif CHAMBER_FAN_MODE == 1

Marlin/src/inc/SanityCheck.h

@@ -2272,8 +2272,8 @@ static_assert(Y_MAX_LENGTH >= Y_BED_SIZE, "Movement bounds (Y_MIN_POS, Y_MAX_POS
   #error "LASER_COOLANT_FLOW_METER requires FLOWMETER_PIN and LASER_FEATURE."
 #endif
 
-#if ENABLED(CHAMBER_FAN) && !(defined(CHAMBER_FAN_MODE) && WITHIN(CHAMBER_FAN_MODE, 0, 2))
+#if ENABLED(CHAMBER_FAN) && !(defined(CHAMBER_FAN_MODE) && WITHIN(CHAMBER_FAN_MODE, 0, 3))
-  #error "CHAMBER_FAN_MODE must be between 0 and 2."
+  #error "CHAMBER_FAN_MODE must be between 0 and 3."
 #endif
 
 #if ENABLED(CHAMBER_VENT)

Marlin/src/inc/Warnings.cpp

@@ -524,6 +524,10 @@
   #endif
 #endif
 
+#if ENABLED(CHAMBER_FAN) && !defined(CHAMBER_FAN_INDEX)
+  #warning "Auto-assigned CHAMBER_FAN_INDEX to the first free FAN pin."
+#endif
+
 #if IS_LEGACY_TFT
   #warning "Don't forget to update your TFT settings in Configuration.h."
 #endif

Marlin/src/module/temperature.cpp

@@ -865,7 +865,9 @@ int16_t Temperature::getHeaterPower(const heater_id_t heater_id) {
     #define INIT_CHAMBER_AUTO_FAN_PIN(P) SET_OUTPUT(P)
   #endif
 
-  #define CHAMBER_FAN_INDEX HOTENDS
+  #ifndef CHAMBER_FAN_INDEX
+    #define CHAMBER_FAN_INDEX HOTENDS
+  #endif
 
   void Temperature::update_autofans() {
     #define _EFAN(B,A) _EFANOVERLAP(A,B) ? B :