Cleaned up stepper and planner code.

- Added some compile-time error checking. Will add more in future
pushes to ensure settings are correct and within parameters that won't
break anything.

- Pushed some master branch changes with MEGA pin settings.

- Cleaned up planner code and comments to clarify some of the new
changes. Still much to do here.

- Cleaned up the new stepper code. May need to abstract some of the
segment buffer more to fix the feed holds (and integrate homing into
the main stepper routine). With what's planned, this should make the
stepper algorithm easier to attach other types of processes to it,
where it is now tightly integrated with the planner buffer and nothing
else.

config.h

@@ -49,9 +49,9 @@
 #define CMD_CYCLE_START '~'
 #define CMD_RESET 0x18 // ctrl-x
 
-// The "Stepper Driver Interrupt" employs the Pramod Ranade inverse time algorithm to manage the
-// Bresenham line stepping algorithm. The value ISR_TICKS_PER_SECOND is the frequency(Hz) at which
-// the Ranade algorithm ticks at. Recommended step frequencies are limited by the Ranade frequency by
+// The "Stepper Driver Interrupt" employs an inverse time algorithm to manage the Bresenham line 
+// stepping algorithm. The value ISR_TICKS_PER_SECOND is the frequency(Hz) at which the inverse time
+// algorithm ticks at. Recommended step frequencies are limited by the inverse time frequency by
 // approximately 0.75-0.9 * ISR_TICK_PER_SECOND. Meaning for 30kHz, the max step frequency is roughly
 // 22.5-27kHz, but 30kHz is still possible, just not optimal. An Arduino can safely complete a single
 // interrupt of the current stepper driver algorithm theoretically up to a frequency of 35-40kHz, but 
@@ -71,7 +71,7 @@
 // NOTE: Make sure this value is less than 256, when adjusting both dependent parameters.
 #define ISR_TICKS_PER_ACCELERATION_TICK (ISR_TICKS_PER_SECOND/ACCELERATION_TICKS_PER_SECOND)
 
-// The Ranade algorithm can use either floating point or long integers for its counters, but for 
+// The inverse time algorithm can use either floating point or long integers for its counters, but for 
 // integers the counter values must be scaled since these values can be very small (10^-6). This
 // multiplier value scales the floating point counter values for use in a long integer. Long integers
 // are finite so select the multiplier value high enough to avoid any numerical round-off issues and
@@ -82,10 +82,10 @@
 #define INV_TIME_MULTIPLIER 10000000.0
 
 // Minimum stepper rate for the "Stepper Driver Interrupt". Sets the absolute minimum stepper rate 
-// in the stepper program and never runs slower than this value. If the RANADE_MULTIPLIER value
+// in the stepper program and never runs slower than this value. If the INVE_TIME_MULTIPLIER value
 // changes, it will affect how this value works. So, if a zero is add/subtracted from the
-// RANADE_MULTIPLIER value, do the same to this value if you want to same response. 
-// NOTE: Compute by (desired_step_rate/60) * RANADE_MULTIPLIER/ISR_TICKS_PER_SECOND. (mm/min)
+// INV_TIME_MULTIPLIER value, do the same to this value if you want to same response. 
+// NOTE: Compute by (desired_step_rate/60) * INV_TIME_MULTIPLIER/ISR_TICKS_PER_SECOND. (mm/min)
 #define MINIMUM_STEP_RATE 1000L // Integer (mult*mm/isr_tic)
 
 // Minimum stepper rate. Only used by homing at this point. May be removed in later releases.
@@ -158,7 +158,7 @@
 // available RAM, like when re-compiling for a Mega or Sanguino. Or decrease if the Arduino
 // begins to crash due to the lack of available RAM or if the CPU is having trouble keeping
 // up with planning new incoming motions as they are executed. 
-// #define BLOCK_BUFFER_SIZE 17  // Uncomment to override default in planner.h.
+// #define BLOCK_BUFFER_SIZE 18  // Uncomment to override default in planner.h.
 
 // Line buffer size from the serial input stream to be executed. Also, governs the size of 
 // each of the startup blocks, as they are each stored as a string of this size. Make sure
@@ -193,4 +193,12 @@
 
 // TODO: Install compile-time option to send numeric status codes rather than strings.
 
+// ---------------------------------------------------------------------------------------
+// COMPILE-TIME ERROR CHECKING OF DEFINE VALUES:
+
+#if (ISR_TICKS_PER_ACCELERATION_TICK > 255)
+#error Parameters ACCELERATION_TICKS / ISR_TICKS must be < 256 to prevent integer overflow.
+#endif
+
+// ---------------------------------------------------------------------------------------
 #endif