Further reduction when HOTENDS == 1

Marlin/Marlin_main.cpp

       SERIAL_PROTOCOL_F(thermalManager.degTargetBed(), 1);
     #endif
     #if HOTENDS > 1
-      for (int8_t e = 0; e < HOTENDS; ++e) {
+      HOTEND_LOOP() {
         SERIAL_PROTOCOLPGM(" T");
         SERIAL_PROTOCOL(e);
         SERIAL_PROTOCOLCHAR(':');
       SERIAL_PROTOCOL(thermalManager.getHeaterPower(target_extruder));
     #endif
     #if HOTENDS > 1
-      for (int8_t e = 0; e < HOTENDS; ++e) {
+      HOTEND_LOOP() {
         SERIAL_PROTOCOLPGM(" @");
         SERIAL_PROTOCOL(e);
         SERIAL_PROTOCOLCHAR(':');
         SERIAL_PROTOCOLPGM("C->");
         SERIAL_PROTOCOL_F(thermalManager.rawBedTemp() / OVERSAMPLENR, 0);
       #endif
-      for (int8_t cur_hotend = 0; cur_hotend < HOTENDS; ++cur_hotend) {
+      HOTEND_LOOP() {
         SERIAL_PROTOCOLPGM("  T");
-        SERIAL_PROTOCOL(cur_hotend);
+        SERIAL_PROTOCOL(e);
         SERIAL_PROTOCOLCHAR(':');
-        SERIAL_PROTOCOL_F(thermalManager.degHotend(cur_hotend), 1);
+        SERIAL_PROTOCOL_F(thermalManager.degHotend(e), 1);
         SERIAL_PROTOCOLPGM("C->");
-        SERIAL_PROTOCOL_F(thermalManager.rawHotendTemp(cur_hotend) / OVERSAMPLENR, 0);
+        SERIAL_PROTOCOL_F(thermalManager.rawHotendTemp(e) / OVERSAMPLENR, 0);
       }
     #endif
   }
 
     SERIAL_ECHO_START;
     SERIAL_ECHOPGM(MSG_HOTEND_OFFSET);
-    for (int e = 0; e < HOTENDS; e++) {
+    HOTEND_LOOP() {
       SERIAL_CHAR(' ');
       SERIAL_ECHO(hotend_offset[X_AXIS][e]);
       SERIAL_CHAR(',');
     float max_temp = 0.0;
     if (ELAPSED(millis(), next_status_led_update_ms)) {
       next_status_led_update_ms += 500; // Update every 0.5s
-      for (int8_t cur_hotend = 0; cur_hotend < HOTENDS; ++cur_hotend)
-        max_temp = max(max(max_temp, thermalManager.degHotend(cur_hotend)), thermalManager.degTargetHotend(cur_hotend));
+      HOTEND_LOOP() {
+        max_temp = max(max(max_temp, thermalManager.degHotend(e)), thermalManager.degTargetHotend(e));
+      }
       #if HAS_TEMP_BED
         max_temp = max(max(max_temp, thermalManager.degTargetBed()), thermalManager.degBed());
       #endif

Marlin/configuration_store.cpp

 
   #if ENABLED(PIDTEMP)
     #if ENABLED(PID_PARAMS_PER_HOTEND)
-      for (uint8_t e = 0; e < HOTENDS; e++)
+      HOTEND_LOOP
     #else
       int e = 0; UNUSED(e); // only need to write once
     #endif
     #if ENABLED(PIDTEMP)
       #if HOTENDS > 1
         if (forReplay) {
-          for (uint8_t i = 0; i < HOTENDS; i++) {
+          HOTEND_LOOP() {
             CONFIG_ECHO_START;
-            SERIAL_ECHOPAIR("  M301 E", i);
-            SERIAL_ECHOPAIR(" P", PID_PARAM(Kp, i));
-            SERIAL_ECHOPAIR(" I", unscalePID_i(PID_PARAM(Ki, i)));
-            SERIAL_ECHOPAIR(" D", unscalePID_d(PID_PARAM(Kd, i)));
+            SERIAL_ECHOPAIR("  M301 E", e);
+            SERIAL_ECHOPAIR(" P", PID_PARAM(Kp, e));
+            SERIAL_ECHOPAIR(" I", unscalePID_i(PID_PARAM(Ki, e)));
+            SERIAL_ECHOPAIR(" D", unscalePID_d(PID_PARAM(Kd, e)));
             #if ENABLED(PID_ADD_EXTRUSION_RATE)
-              SERIAL_ECHOPAIR(" C", PID_PARAM(Kc, i));
-              if (i == 0) SERIAL_ECHOPAIR(" L", lpq_len);
+              SERIAL_ECHOPAIR(" C", PID_PARAM(Kc, e));
+              if (e == 0) SERIAL_ECHOPAIR(" L", lpq_len);
             #endif
             SERIAL_EOL;
           }

Marlin/dogm_lcd_implementation.h

   #endif
 
   // Extruders
-  for (int i = 0; i < HOTENDS; i++) _draw_heater_status(5 + i * 25, i);
+  HOTEND_LOOP() _draw_heater_status(5 + e * 25, e);
 
   // Heated bed
   #if HOTENDS < 4 && HAS_TEMP_BED

Marlin/temperature.cpp

 
 void Temperature::updatePID() {
   #if ENABLED(PIDTEMP)
-    for (int e = 0; e < HOTENDS; e++) {
+    HOTEND_LOOP() {
       temp_iState_max[e] = (PID_INTEGRAL_DRIVE_MAX) / PID_PARAM(Ki, e);
       #if ENABLED(PID_ADD_EXTRUSION_RATE)
         last_position[e] = 0;
       EXTRUDER_3_AUTO_FAN_PIN == EXTRUDER_2_AUTO_FAN_PIN ? 2 : 3
     };
     uint8_t fanState = 0;
-    for (int f = 0; f < HOTENDS; f++) {
-      if (current_temperature[f] > EXTRUDER_AUTO_FAN_TEMPERATURE)
-        SBI(fanState, fanBit[f]);
+    HOTEND_LOOP() {
+      if (current_temperature[e] > EXTRUDER_AUTO_FAN_TEMPERATURE)
+        SBI(fanState, fanBit[e]);
     }
     uint8_t fanDone = 0;
-    for (int f = 0; f <= 3; f++) {
+    for (int8_t f = 0; f <= 3; f++) {
       int8_t pin = fanPin[f];
       if (pin >= 0 && !TEST(fanDone, fanBit[f])) {
         unsigned char newFanSpeed = TEST(fanState, fanBit[f]) ? EXTRUDER_AUTO_FAN_SPEED : 0;
 }
 
 void Temperature::max_temp_error(uint8_t e) {
-  _temp_error(e, PSTR(MSG_T_MAXTEMP), PSTR(MSG_ERR_MAXTEMP));
+  #if HOTENDS == 1
+    UNUSED(e);
+  #endif
+  _temp_error(HOTEND_INDEX, PSTR(MSG_T_MAXTEMP), PSTR(MSG_ERR_MAXTEMP));
 }
 void Temperature::min_temp_error(uint8_t e) {
-  _temp_error(e, PSTR(MSG_T_MINTEMP), PSTR(MSG_ERR_MINTEMP));
+  #if HOTENDS == 1
+    UNUSED(e);
+  #endif
+  _temp_error(HOTEND_INDEX, PSTR(MSG_T_MINTEMP), PSTR(MSG_ERR_MINTEMP));
 }
 
 float Temperature::get_pid_output(int e) {
   #endif
 
   // Loop through all hotends
-  for (uint8_t e = 0; e < HOTENDS; e++) {
+  HOTEND_LOOP() {
 
     #if ENABLED(THERMAL_PROTECTION_HOTENDS)
       thermal_runaway_protection(&thermal_runaway_state_machine[e], &thermal_runaway_timer[e], current_temperature[e], target_temperature[e], e, THERMAL_PROTECTION_PERIOD, THERMAL_PROTECTION_HYSTERESIS);
   #if ENABLED(HEATER_0_USES_MAX6675)
     current_temperature_raw[0] = read_max6675();
   #endif
-  for (uint8_t e = 0; e < HOTENDS; e++) {
+  HOTEND_LOOP() {
     current_temperature[e] = Temperature::analog2temp(current_temperature_raw[e], e);
   }
   current_temperature_bed = Temperature::analog2tempBed(current_temperature_bed_raw);
   #endif
 
   // Finish init of mult hotend arrays
-  for (int e = 0; e < HOTENDS; e++) {
+  HOTEND_LOOP() {
     // populate with the first value
     maxttemp[e] = maxttemp[0];
     #if ENABLED(PIDTEMP)
    * their target temperature by a configurable margin.
    * This is called when the temperature is set. (M104, M109)
    */
-  void Temperature::start_watching_heater(int e) {
-    if (degHotend(e) < degTargetHotend(e) - (WATCH_TEMP_INCREASE + TEMP_HYSTERESIS + 1)) {
-      watch_target_temp[e] = degHotend(e) + WATCH_TEMP_INCREASE;
-      watch_heater_next_ms[e] = millis() + (WATCH_TEMP_PERIOD) * 1000UL;
+  void Temperature::start_watching_heater(uint8_t e) {
+    #if HOTENDS == 1
+      UNUSED(e);
+    #endif
+    if (degHotend(HOTEND_INDEX) < degTargetHotend(HOTEND_INDEX) - (WATCH_TEMP_INCREASE + TEMP_HYSTERESIS + 1)) {
+      watch_target_temp[HOTEND_INDEX] = degHotend(HOTEND_INDEX) + WATCH_TEMP_INCREASE;
+      watch_heater_next_ms[HOTEND_INDEX] = millis() + (WATCH_TEMP_PERIOD) * 1000UL;
     }
     else
-      watch_heater_next_ms[e] = 0;
+      watch_heater_next_ms[HOTEND_INDEX] = 0;
   }
 #endif
 
 #endif // THERMAL_PROTECTION_HOTENDS || THERMAL_PROTECTION_BED
 
 void Temperature::disable_all_heaters() {
-  for (int i = 0; i < HOTENDS; i++) setTargetHotend(0, i);
+  HOTEND_LOOP() setTargetHotend(0, e);
   setTargetBed(0);
 
   // If all heaters go down then for sure our print job has stopped

Marlin/temperature.h

 #endif
 
 #if HOTENDS == 1
-  #define HOTEND_ARG 0
-  #define HOTEND_INDEX 0
-  #define EXTRUDER_ARG 0
+  #define HOTEND_LOOP() const uint8_t e = 0;
+  #define HOTEND_INDEX  0
+  #define EXTRUDER_IDX  0
 #else
-  #define HOTEND_ARG hotend
-  #define HOTEND_INDEX e
-  #define EXTRUDER_ARG active_extruder
+  #define HOTEND_LOOP() for (int8_t e = 0; e < HOTENDS; e++)
+  #define HOTEND_INDEX  e
+  #define EXTRUDER_IDX  active_extruder
 #endif
 
 class Temperature {
     //inline so that there is no performance decrease.
     //deg=degreeCelsius
 
-    static float degHotend(uint8_t hotend) {
+    static float degHotend(uint8_t e) {
       #if HOTENDS == 1
-        UNUSED(hotend);
+        UNUSED(e);
       #endif
-      return current_temperature[HOTEND_ARG];
+      return current_temperature[HOTEND_INDEX];
     }
     static float degBed() { return current_temperature_bed; }
 
     #if ENABLED(SHOW_TEMP_ADC_VALUES)
-    static float rawHotendTemp(uint8_t hotend) {
+    static float rawHotendTemp(uint8_t e) {
       #if HOTENDS == 1
-        UNUSED(hotend);
+        UNUSED(e);
       #endif
-      return current_temperature_raw[HOTEND_ARG];
+      return current_temperature_raw[HOTEND_INDEX];
     }
     static float rawBedTemp() { return current_temperature_bed_raw; }
     #endif
 
-    static float degTargetHotend(uint8_t hotend) {
+    static float degTargetHotend(uint8_t e) {
       #if HOTENDS == 1
-        UNUSED(hotend);
+        UNUSED(e);
       #endif
-      return target_temperature[HOTEND_ARG];
+      return target_temperature[HOTEND_INDEX];
     }
     static float degTargetBed() { return target_temperature_bed; }
 
     #if ENABLED(THERMAL_PROTECTION_HOTENDS) && WATCH_TEMP_PERIOD > 0
-      static void start_watching_heater(int e = 0);
+      static void start_watching_heater(uint8_t e = 0);
     #endif
 
     #if ENABLED(THERMAL_PROTECTION_BED) && WATCH_BED_TEMP_PERIOD > 0
       static void start_watching_bed();
     #endif
 
-    static void setTargetHotend(const float& celsius, uint8_t hotend) {
+    static void setTargetHotend(const float& celsius, uint8_t e) {
       #if HOTENDS == 1
-        UNUSED(hotend);
+        UNUSED(e);
       #endif
-      target_temperature[HOTEND_ARG] = celsius;
+      target_temperature[HOTEND_INDEX] = celsius;
       #if ENABLED(THERMAL_PROTECTION_HOTENDS) && WATCH_TEMP_PERIOD > 0
-        start_watching_heater(HOTEND_ARG);
+        start_watching_heater(HOTEND_INDEX);
       #endif
     }
 
       #endif
     }
 
-    static bool isHeatingHotend(uint8_t hotend) {
+    static bool isHeatingHotend(uint8_t e) {
       #if HOTENDS == 1
-        UNUSED(hotend);
+        UNUSED(e);
       #endif
-      return target_temperature[HOTEND_ARG] > current_temperature[HOTEND_ARG];
+      return target_temperature[HOTEND_INDEX] > current_temperature[HOTEND_INDEX];
     }
     static bool isHeatingBed() { return target_temperature_bed > current_temperature_bed; }
 
-    static bool isCoolingHotend(uint8_t hotend) {
+    static bool isCoolingHotend(uint8_t e) {
       #if HOTENDS == 1
-        UNUSED(hotend);
+        UNUSED(e);
       #endif
-      return target_temperature[HOTEND_ARG] < current_temperature[HOTEND_ARG];
+      return target_temperature[HOTEND_INDEX] < current_temperature[HOTEND_INDEX];
     }
     static bool isCoolingBed() { return target_temperature_bed < current_temperature_bed; }
 
       #if ENABLED(AUTOTEMP)
         if (planner.autotemp_enabled) {
           planner.autotemp_enabled = false;
-          if (degTargetHotend(EXTRUDER_ARG) > planner.autotemp_min)
-            setTargetHotend(0, EXTRUDER_ARG);
+          if (degTargetHotend(EXTRUDER_IDX) > planner.autotemp_min)
+            setTargetHotend(0, EXTRUDER_IDX);
         }
       #endif
     }