Fixed long slope at deceleration issue. Moved things into config.h. New MINIMUM_PLANNER_SPEED parameter.

- The long standing issue of a long slope at deceleration is likely
fixed. The stepper program was not tracking and timing the end of
acceleration and start of deceleration exactly and now is fixed to
start and stop on time. Also, to ensure a better acceleration curve fit
used by the planner, the stepper program delays the start of the
accelerations by a half trapezoid tick to employ the midpoint rule. -
Settings version 3 migration (not fully tested, but should work) -
Added a MINIMUM_PLANNER_SPEED user-defined parameter to planner to let
a user change this if problems arise for some reason. - Moved all
user-definable #define parameters into config.h with clear comments on
what they do and recommendations of how to change them. - Minor
housekeeping.

config.h

@@ -3,6 +3,7 @@
   Part of Grbl
 
   Copyright (c) 2009-2011 Simen Svale Skogsrud
+  Copyright (c) 2011 Sungeun K. Jeon
 
   Grbl is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -21,6 +22,8 @@
 #ifndef config_h
 #define config_h
 
+// IMPORTANT: Any changes here requires a full re-compiling of the source code to propagate them.
+
 #define BAUD_RATE 9600
 
 // Updated default pin-assignments from 0.6 onwards 
@@ -55,12 +58,32 @@
 
 // The temporal resolution of the acceleration management subsystem. Higher number
 // give smoother acceleration but may impact performance
-// NOTE: Increasing this parameter will help remove the long slow motion bug at the end
-// of very fast de/ac-celerations. This is due to the increased resolution of the 
-// acceleration steps that more accurately predicted by the planner exact integration
-// of acceleration distance. An efficient solution to this bug is under investigation.
-// In general, setting this parameter is high as your system will allow is suggested.
-#define ACCELERATION_TICKS_PER_SECOND 40L
+// NOTE: Increasing this parameter will help any resolution related issues, especially with machines 
+// requiring very high accelerations and/or very fast feedrates. In general, this will reduce the 
+// error between how the planner plans the motions and how the stepper program actually performs them.
+// However, at some point, the resolution can be high enough, where the errors related to numerical 
+// round-off can be great enough to cause problems and/or it's too fast for the Arduino. The correct
+// value for this parameter is machine dependent, so it's advised to set this only as high as needed.
+// Approximate successful values can range from 30L to 100L or more.
+#define ACCELERATION_TICKS_PER_SECOND 50L
+
+// Minimum planner junction speed. Sets the default minimum speed the planner plans for at the end
+// of the buffer and all stops. This should not be much greater than zero and should only be changed
+// if unwanted behavior is observed on a user's machine when running at very slow speeds.
+#define MINIMUM_PLANNER_SPEED 0.0 // (mm/min)
+
+// Minimum stepper rate. Sets the absolute minimum stepper rate in the stepper program and never run
+// slower than this value, except when sleeping. This parameter overrides the minimum planner speed.
+// This is primarily used to guarantee that the end of a movement is always reached and not stop to
+// never reach its target. This parameter should always be greater than zero.
+#define MINIMUM_STEPS_PER_MINUTE 800 // (steps/min) - Integer value only
+
+// Number of arc generation iterations by small angle approximation before exact arc
+// trajectory correction. Value must be 1-255. This parameter maybe decreased if there are issues
+// with the accuracy of the arc generations. In general, the default value is more than enough for
+// the intended CNC applications of grbl, and should be on the order or greater than the size of
+// the buffer to help with the computational efficiency of generating arcs.
+#define N_ARC_CORRECTION 25 
 
 #endif
 
@@ -91,5 +114,4 @@
 // 
 // #define SPINDLE_DIRECTION_DDR DDRD
 // #define SPINDLE_DIRECTION_PORT PORTD
-// #define SPINDLE_DIRECTION_BIT 7
-
+// #define SPINDLE_DIRECTION_BIT 7