Tweak Filament Width variables

Marlin/Marlin.h

 #endif
 
 #if ENABLED(FILAMENT_WIDTH_SENSOR)
-  extern float filament_width_nominal;  //holds the theoretical filament diameter i.e., 3.00 or 1.75
-  extern bool filament_sensor;  //indicates that filament sensor readings should control extrusion
-  extern float filament_width_meas; //holds the filament diameter as accurately measured
-  extern int8_t measurement_delay[];  //ring buffer to delay measurement
-  extern int filwidth_delay_index1, filwidth_delay_index2;  //ring buffer index. used by planner, temperature, and main code
-  extern int meas_delay_cm; //delay distance
+  extern bool filament_sensor;         // Flag that filament sensor readings should control extrusion
+  extern float filament_width_nominal, // Theoretical filament diameter i.e., 3.00 or 1.75
+               filament_width_meas;    // Measured filament diameter
+  extern int8_t measurement_delay[];   // Ring buffer to delay measurement
+  extern int filwidth_delay_index[2];  // Ring buffer indexes. Used by planner, temperature, and main code
+  extern int meas_delay_cm;            // Delay distance
 #endif
 
 #if ENABLED(FILAMENT_CHANGE_FEATURE)

Marlin/Marlin_main.cpp

 #endif
 
 #if ENABLED(FILAMENT_WIDTH_SENSOR)
-  //Variables for Filament Sensor input
-  float filament_width_nominal = DEFAULT_NOMINAL_FILAMENT_DIA;  //Set nominal filament width, can be changed with M404
   bool filament_sensor = false;  //M405 turns on filament_sensor control, M406 turns it off
-  float filament_width_meas = DEFAULT_MEASURED_FILAMENT_DIA; //Stores the measured filament diameter
-  int8_t measurement_delay[MAX_MEASUREMENT_DELAY + 1]; //ring buffer to delay measurement  store extruder factor after subtracting 100
-  int filwidth_delay_index1 = 0;  //index into ring buffer
-  int filwidth_delay_index2 = -1;  //index into ring buffer - set to -1 on startup to indicate ring buffer needs to be initialized
+  float filament_width_nominal = DEFAULT_NOMINAL_FILAMENT_DIA,  // Nominal filament width. Change with M404
+        filament_width_meas = DEFAULT_MEASURED_FILAMENT_DIA;    // Measured filament diameter
+  int8_t measurement_delay[MAX_MEASUREMENT_DELAY + 1]; // Ring buffer to delayed measurement. Store extruder factor after subtracting 100
+  int filwidth_delay_index[2] = { 0, -1 };  // Indexes into ring buffer
   int meas_delay_cm = MEASUREMENT_DELAY_CM;  //distance delay setting
 #endif
 
     if (code_seen('D')) meas_delay_cm = code_value_int();
     NOMORE(meas_delay_cm, MAX_MEASUREMENT_DELAY);
 
-    if (filwidth_delay_index2 == -1) { // Initialize the ring buffer if not done since startup
+    if (filwidth_delay_index[1] == -1) { // Initialize the ring buffer if not done since startup
       int temp_ratio = thermalManager.widthFil_to_size_ratio();
 
       for (uint8_t i = 0; i < COUNT(measurement_delay); ++i)
         measurement_delay[i] = temp_ratio - 100;  // Subtract 100 to scale within a signed byte
 
-      filwidth_delay_index1 = filwidth_delay_index2 = 0;
+      filwidth_delay_index[0] = filwidth_delay_index[1] = 0;
     }
 
     filament_sensor = true;

Marlin/planner.cpp

     static float filwidth_e_count = 0, filwidth_delay_dist = 0;
 
     //FMM update ring buffer used for delay with filament measurements
-    if (extruder == FILAMENT_SENSOR_EXTRUDER_NUM && filwidth_delay_index2 >= 0) {  //only for extruder with filament sensor and if ring buffer is initialized
+    if (extruder == FILAMENT_SENSOR_EXTRUDER_NUM && filwidth_delay_index[1] >= 0) {  //only for extruder with filament sensor and if ring buffer is initialized
 
       const int MMD_CM = MAX_MEASUREMENT_DELAY + 1, MMD_MM = MMD_CM * 10;
 
         while (filwidth_delay_dist >= MMD_MM) filwidth_delay_dist -= MMD_MM;
 
         // Convert into an index into the measurement array
-        filwidth_delay_index1 = (int)(filwidth_delay_dist * 0.1 + 0.0001);
+        filwidth_delay_index[0] = (int)(filwidth_delay_dist * 0.1 + 0.0001);
 
         // If the index has changed (must have gone forward)...
-        if (filwidth_delay_index1 != filwidth_delay_index2) {
+        if (filwidth_delay_index[0] != filwidth_delay_index[1]) {
           filwidth_e_count = 0; // Reset the E movement counter
           int8_t meas_sample = thermalManager.widthFil_to_size_ratio() - 100; // Subtract 100 to reduce magnitude - to store in a signed char
           do {
-            filwidth_delay_index2 = (filwidth_delay_index2 + 1) % MMD_CM; // The next unused slot
-            measurement_delay[filwidth_delay_index2] = meas_sample;       // Store the measurement
-          } while (filwidth_delay_index1 != filwidth_delay_index2);       // More slots to fill?
+            filwidth_delay_index[1] = (filwidth_delay_index[1] + 1) % MMD_CM; // The next unused slot
+            measurement_delay[filwidth_delay_index[1]] = meas_sample;         // Store the measurement
+          } while (filwidth_delay_index[0] != filwidth_delay_index[1]);       // More slots to fill?
         }
       }
     }

Marlin/temperature.cpp

   // Control the extruder rate based on the width sensor
   #if ENABLED(FILAMENT_WIDTH_SENSOR)
     if (filament_sensor) {
-      meas_shift_index = filwidth_delay_index1 - meas_delay_cm;
+      meas_shift_index = filwidth_delay_index[0] - meas_delay_cm;
       if (meas_shift_index < 0) meas_shift_index += MAX_MEASUREMENT_DELAY + 1;  //loop around buffer if needed
 
       // Get the delayed info and add 100 to reconstitute to a percent of