Comment, fix filament width sensor

Marlin/src/gcode/feature/filwidth/M404-M407.cpp

   }
 
   if (filwidth_delay_index[1] == -1) { // Initialize the ring buffer if not done since startup
-    const uint8_t temp_ratio = thermalManager.widthFil_to_size_ratio() - 100; // -100 to scale within a signed byte
+    const uint8_t temp_ratio = thermalManager.widthFil_to_size_ratio();
 
     for (uint8_t i = 0; i < COUNT(measurement_delay); ++i)
       measurement_delay[i] = temp_ratio;
   }
 
   filament_sensor = true;
-
-  //SERIAL_PROTOCOLPGM("Filament dia (measured mm):");
-  //SERIAL_PROTOCOL(filament_width_meas);
-  //SERIAL_PROTOCOLPGM("Extrusion ratio(%):");
-  //SERIAL_PROTOCOL(planner.flow_percentage[active_extruder]);
 }
 
 /**

Marlin/src/lcd/ultralcd_impl_DOGM.h

     strcpy(zstring, ftostr52sp(FIXFLOAT(LOGICAL_Z_POSITION(current_position[Z_AXIS]))));
     #if ENABLED(FILAMENT_LCD_DISPLAY)
       strcpy(wstring, ftostr12ns(filament_width_meas));
-      if (parser.volumetric_enabled)
-        strcpy(mstring, itostr3(100.0 * planner.volumetric_area_nominal / planner.volumetric_multiplier[FILAMENT_SENSOR_EXTRUDER_NUM]));
-      else
-        strcpy_P(mstring, PSTR("---"));
+      strcpy(mstring, itostr3(100.0 * (
+          parser.volumetric_enabled
+            ? planner.volumetric_area_nominal / planner.volumetric_multiplier[FILAMENT_SENSOR_EXTRUDER_NUM]
+            : planner.volumetric_multiplier[FILAMENT_SENSOR_EXTRUDER_NUM]
+        )
+      ));
     #endif
   }
 

Marlin/src/lcd/ultralcd_impl_HD44780.h

       lcd_printPGM(PSTR("Dia "));
       lcd.print(ftostr12ns(filament_width_meas));
       lcd_printPGM(PSTR(" V"));
-      if (parser.volumetric_enabled) {
-        lcd.print(itostr3(100.0 * planner.volumetric_area_nominal / planner.volumetric_multiplier[FILAMENT_SENSOR_EXTRUDER_NUM]));
-        lcd.write('%');
-      }
-      else
-        lcd_printPGM(PSTR("--- "));
+      lcd.print(itostr3(100.0 * (
+          parser.volumetric_enabled
+            ? planner.volumetric_area_nominal / planner.volumetric_multiplier[FILAMENT_SENSOR_EXTRUDER_NUM]
+            : planner.volumetric_multiplier[FILAMENT_SENSOR_EXTRUDER_NUM]
+        )
+      ));
+      lcd.write('%');
       return;
     }
 

Marlin/src/module/planner.cpp

   #endif
 }
 
+/**
+ * Get a volumetric multiplier from a filament diameter.
+ * This is the reciprocal of the circular cross-section area.
+ * Return 1.0 with volumetric off or a diameter of 0.0.
+ */
 inline float calculate_volumetric_multiplier(const float &diameter) {
   return (parser.volumetric_enabled && diameter) ? 1.0 / CIRCLE_AREA(diameter * 0.5) : 1.0;
 }
 
+/**
+ * Convert the filament sizes into volumetric multipliers.
+ * The multiplier converts a given E value into a length.
+ */
 void Planner::calculate_volumetric_multipliers() {
   for (uint8_t i = 0; i < COUNT(filament_size); i++) {
     volumetric_multiplier[i] = calculate_volumetric_multiplier(filament_size[i]);
   }
 }
 
+#if ENABLED(FILAMENT_WIDTH_SENSOR)
+  /**
+   * Convert the ratio value given by the filament width sensor
+   * into a volumetric multiplier. Conversion differs when using
+   * linear extrusion vs volumetric extrusion.
+   */
+  void Planner::calculate_volumetric_for_width_sensor(const int8_t encoded_ratio) {
+    // Reconstitute the nominal/measured ratio
+    const float nom_meas_ratio = 1.0 + 0.01 * encoded_ratio,
+                ratio_2 = sq(nom_meas_ratio);
+
+    volumetric_multiplier[FILAMENT_SENSOR_EXTRUDER_NUM] = parser.volumetric_enabled
+      ? ratio_2 / CIRCLE_AREA(filament_width_nominal * 0.5) // Volumetric uses a true volumetric multiplier
+      : ratio_2;                                            // Linear squares the ratio, which scales the volume
+
+    refresh_e_factor(FILAMENT_SENSOR_EXTRUDER_NUM);
+  }
+#endif
+
 #if PLANNER_LEVELING
   /**
    * rx, ry, rz - Cartesian positions in mm
         // If the index has changed (must have gone forward)...
         if (filwidth_delay_index[0] != filwidth_delay_index[1]) {
           filwidth_e_count = 0; // Reset the E movement counter
-          const uint8_t meas_sample = thermalManager.widthFil_to_size_ratio() - 100; // Subtract 100 to reduce magnitude - to store in a signed char
+          const uint8_t meas_sample = thermalManager.widthFil_to_size_ratio();
           do {
             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

Marlin/src/module/planner.h

     // Update multipliers based on new diameter measurements
     static void calculate_volumetric_multipliers();
 
+    #if ENABLED(FILAMENT_WIDTH_SENSOR)
+      void calculate_volumetric_for_width_sensor(const int8_t encoded_ratio);
+    #endif
+
     FORCE_INLINE static void set_filament_size(const uint8_t e, const float &v) {
       filament_size[e] = v;
       // make sure all extruders have some sane value for the filament size

Marlin/src/module/stepper.cpp

     // step_rate to timer interval
     const hal_timer_t interval = calc_timer_interval(acc_step_rate);
 
-    SPLIT(interval);  // split step into multiple ISRs if larger than  ENDSTOP_NOMINAL_OCR_VAL
+    SPLIT(interval);  // split step into multiple ISRs if larger than ENDSTOP_NOMINAL_OCR_VAL
     _NEXT_ISR(ocr_val);
 
     acceleration_time += interval;
     // step_rate to timer interval
     const hal_timer_t interval = calc_timer_interval(step_rate);
 
-    SPLIT(interval);  // split step into multiple ISRs if larger than  ENDSTOP_NOMINAL_OCR_VAL
+    SPLIT(interval);  // split step into multiple ISRs if larger than ENDSTOP_NOMINAL_OCR_VAL
     _NEXT_ISR(ocr_val);
     deceleration_time += interval;
 
 
     #endif
 
-    SPLIT(OCR1A_nominal);  // split step into multiple ISRs if larger than  ENDSTOP_NOMINAL_OCR_VAL
+    SPLIT(OCR1A_nominal);  // split step into multiple ISRs if larger than ENDSTOP_NOMINAL_OCR_VAL
     _NEXT_ISR(ocr_val);
     // ensure we're running at the correct step rate, even if we just came off an acceleration
     step_loops = step_loops_nominal;

Marlin/src/module/temperature.cpp

  *  - Apply filament width to the extrusion rate (may move)
  *  - Update the heated bed PID output value
  */
-
-/**
- * The following line SOMETIMES results in the dreaded "unable to find a register to spill in class 'POINTER_REGS'"
- * compile error.
- *    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);
- *
- * This is due to a bug in the C++ compiler used by the Arduino IDE from 1.6.10 to at least 1.8.1.
- *
- * The work around is to add the compiler flag "__attribute__((__optimize__("O2")))" to the declaration for manage_heater()
- */
-//void Temperature::manage_heater()  __attribute__((__optimize__("O2")));
 void Temperature::manage_heater() {
 
   if (!temp_meas_ready) return;
     }
   #endif
 
-  // Control the extruder rate based on the width sensor
   #if ENABLED(FILAMENT_WIDTH_SENSOR)
+    /**
+     * Filament Width Sensor dynamically sets the volumetric multiplier
+     * based on a delayed measurement of the filament diameter.
+     */
     if (filament_sensor) {
       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
       meas_shift_index = constrain(meas_shift_index, 0, MAX_MEASUREMENT_DELAY);
-
-      // Get the delayed info and add 100 to reconstitute to a percent of
-      // the nominal filament diameter then square it to get an area
-      const float vmroot = measurement_delay[meas_shift_index] * 0.01 + 1.0;
-      planner.volumetric_multiplier[FILAMENT_SENSOR_EXTRUDER_NUM] = vmroot <= 0.1 ? 0.01 : sq(vmroot);
-      planner.refresh_e_factor(FILAMENT_SENSOR_EXTRUDER_NUM);
+      calculate_volumetric_for_width_sensor(measurement_delay[meas_shift_index])
     }
   #endif // FILAMENT_WIDTH_SENSOR
 
     return current_raw_filwidth * 5.0 * (1.0 / 16383.0);
   }
 
-  // Convert raw Filament Width to a ratio
-  int Temperature::widthFil_to_size_ratio() {
-    float temp = filament_width_meas;
-    if (temp < MEASURED_LOWER_LIMIT) temp = filament_width_nominal;  // Assume a bad sensor reading
-    else NOMORE(temp, MEASURED_UPPER_LIMIT);
-    return filament_width_nominal / temp * 100;
+  /**
+   * Convert Filament Width (mm) to a simple ratio
+   * and reduce to an 8 bit value.
+   *
+   * A nominal width of 1.75 and measured width of 1.73
+   * gives (100 * 1.75 / 1.73) for a ratio of 101 and
+   * a return value of 1.
+   */
+  int8_t Temperature::widthFil_to_size_ratio() {
+    if (WITHIN(filament_width_meas, MEASURED_LOWER_LIMIT, MEASURED_UPPER_LIMIT))
+      return int(100.0 * filament_width_nominal / filament_width_meas) - 100;
+    return 0;
   }
 
 #endif

Marlin/src/module/temperature.h

     #endif
 
     #if ENABLED(FILAMENT_WIDTH_SENSOR)
-      static float analog2widthFil(); // Convert raw Filament Width to millimeters
-      static int widthFil_to_size_ratio(); // Convert raw Filament Width to an extrusion ratio
+      static float analog2widthFil();         // Convert raw Filament Width to millimeters
+      static int8_t widthFil_to_size_ratio(); // Convert Filament Width (mm) to an extrusion ratio
     #endif
 
-
     //high level conversion routines, for use outside of temperature.cpp
     //inline so that there is no performance decrease.
     //deg=degreeCelsius