Merge pull request #4721 from thinkyhead/rc_temperature_isr_comments

Rc temperature isr comments

Marlin/enum.h

   DEBUG_ERRORS        = _BV(2), ///< Not implemented
   DEBUG_DRYRUN        = _BV(3), ///< Ignore temperature setting and E movement commands
   DEBUG_COMMUNICATION = _BV(4), ///< Not implemented
-  DEBUG_LEVELING      = _BV(5)  ///< Print detailed output for homing and leveling
+  DEBUG_LEVELING      = _BV(5), ///< Print detailed output for homing and leveling
+  DEBUG_ALL           = 0xFF
 };
 
 enum EndstopEnum {

Marlin/planner.cpp

        dy = target[Y_AXIS] - position[Y_AXIS],
        dz = target[Z_AXIS] - position[Z_AXIS];
 
+  /*
+  SERIAL_ECHO_START;
+  SERIAL_ECHOPAIR("Planner X:", x);
+  SERIAL_ECHOPAIR(" (", dx);
+  SERIAL_ECHOPAIR(") Y:", y);
+  SERIAL_ECHOPAIR(" (", dy);
+  SERIAL_ECHOPAIR(") Z:", z);
+  SERIAL_ECHOPAIR(" (", dz);
+  SERIAL_ECHOLNPGM(")");
+  //*/
+
   // DRYRUN ignores all temperature constraints and assures that the extruder is instantly satisfied
   if (DEBUGGING(DRYRUN))
     position[E_AXIS] = target[E_AXIS];

Marlin/temperature.cpp

 }
 
 /**
- * Timer 0 is shared with millies
+ * Timer 0 is shared with millies so don't change the prescaler.
+ *
+ * This ISR uses the compare method so it runs at the base
+ * frequency (16 MHz / 256 = 62500 Hz), but at the TCNT0 set
+ * in OCR0B above (128 or halfway between OVFs).
+ *
  *  - Manage PWM to all the heaters and fan
  *  - Update the raw temperature values
  *  - Check new temperature values for MIN/MAX errors
       #endif
     #endif
 
+    // 488.28 Hz (or 1:976.56, 2:1953.12, 3:3906.25, 4:7812.5, 5:7812.5 6:15625, 6:15625 7:31250)
     pwm_count += _BV(SOFT_PWM_SCALE);
     pwm_count &= 0x7f;
 
     /**
      * SLOW PWM HEATERS
      *
-     * for heaters drived by relay
+     * For relay-driven heaters
      */
     #ifndef MIN_STATE_TIME
       #define MIN_STATE_TIME 16 // MIN_STATE_TIME * 65.5 = time in milliseconds