Limit pin internal pull-resistors enabled. Re-wrote read_double() function. Correctly changed all 'double's to 'float's.

- Limit pin internal pull-resistors now enabled. Normal high operation.
This will be the standard going forward.

- Updated all of the 'double' variable types to 'float' to reflect what
happens when compiled for the Arduino. Also done for compatibility
reasons to @jgeisler0303 's Grbl simulator code.

- G-code parser will now ignore 'E' exponent values, since they are
reserved g-code characters for some machines. Thanks @csdexter!

- The read_double() function was re-written and optimized for use in
Grbl. The strtod() avr lib was removed.

config.h

@@ -42,6 +42,7 @@
 
 #define LIMIT_DDR       DDRB
 #define LIMIT_PIN       PINB
+#define LIMIT_PORT      PORTB
 #define X_LIMIT_BIT     1  // Uno Digital Pin 9
 #define Y_LIMIT_BIT     2  // Uno Digital Pin 10
 #define Z_LIMIT_BIT     3  // Uno Digital Pin 11
@@ -175,7 +176,5 @@
 
 //  Limit step rate for homing
 #define LIMIT_DEBOUNCE 50  // Limit switch debounce delay (in ms)
-// #define LIMIT_INVERT_MASK 0 //
-// #define LIMIT_NORMAL_HIGH 1 // Normal low 0 or normal high 1
 
 #endif

gcode.c

@@ -77,8 +77,8 @@ typedef struct {
   uint8_t program_flow;            // {M0, M1, M2, M30}
   int8_t spindle_direction;        // 1 = CW, -1 = CCW, 0 = Stop {M3, M4, M5}
   uint8_t coolant_mode;            // 0 = Disable, 1 = Flood Enable {M8, M9}
-  double feed_rate, seek_rate;     // Millimeters/second
+  float feed_rate, seek_rate;     // Millimeters/second
-  double position[3];              // Where the interpreter considers the tool to be at this point in the code
+  float position[3];              // Where the interpreter considers the tool to be at this point in the code
   uint8_t tool;
   uint16_t spindle_speed;          // RPM/100
   uint8_t plane_axis_0, 
@@ -89,7 +89,7 @@ static parser_state_t gc;
 
 #define FAIL(status) gc.status_code = status;
 
-static int next_statement(char *letter, double *double_ptr, char *line, uint8_t *char_counter);
+static int next_statement(char *letter, float *float_ptr, char *line, uint8_t *char_counter);
 
 static void select_plane(uint8_t axis_0, uint8_t axis_1, uint8_t axis_2) 
 {
@@ -120,7 +120,7 @@ void gc_clear_position()
   clear_vector(gc.position);
 }
 
-static float to_millimeters(double value) 
+static float to_millimeters(float value) 
 {
   return(gc.inches_mode ? (value * MM_PER_INCH) : value);
 }
@@ -133,17 +133,17 @@ uint8_t gc_execute_line(char *line)
 {
   uint8_t char_counter = 0;  
   char letter;
-  double value;
+  float value;
   int int_value;
   
   uint16_t modal_group_words = 0;  // Bitflag variable to track and check modal group words in block
   uint8_t axis_words = 0;          // Bitflag to track which XYZ(ABC) parameters exist in block
 
-  double inverse_feed_rate = -1; // negative inverse_feed_rate means no inverse_feed_rate specified
+  float inverse_feed_rate = -1; // negative inverse_feed_rate means no inverse_feed_rate specified
   uint8_t absolute_override = false; // true(1) = absolute motion for this block only {G53}
   uint8_t non_modal_action = NON_MODAL_NONE; // Tracks the actions of modal group 0 (non-modal)
   
-  double target[3], offset[3];  
+  float target[3], offset[3];  
   clear_vector(target); // XYZ(ABC) axes parameters.
   clear_vector(offset); // IJK Arc offsets are incremental. Value of zero indicates no change.
     
@@ -248,11 +248,12 @@ uint8_t gc_execute_line(char *line)
   /* Pass 2: Parameters. All units converted according to current block commands. Position 
      parameters are converted and flagged to indicate a change. These can have multiple connotations
      for different commands. Each will be converted to their proper value upon execution. */
-  double p = 0, r = 0;
+  float p = 0, r = 0;
   uint8_t l = 0;
   char_counter = 0;
   while(next_statement(&letter, &value, line, &char_counter)) {
     switch(letter) {
+      case 'G': case 'M': break; // Ignore command statements
       case 'F': 
         if (value <= 0) { FAIL(STATUS_INVALID_COMMAND); } // Must be greater than zero
         if (gc.inverse_feed_rate_mode) {
@@ -276,6 +277,7 @@ uint8_t gc_execute_line(char *line)
       case 'X': target[X_AXIS] = to_millimeters(value); bit_true(axis_words,bit(X_AXIS)); break;
       case 'Y': target[Y_AXIS] = to_millimeters(value); bit_true(axis_words,bit(Y_AXIS)); break;
       case 'Z': target[Z_AXIS] = to_millimeters(value); bit_true(axis_words,bit(Z_AXIS)); break;
+      default: FAIL(STATUS_UNSUPPORTED_STATEMENT);
     }
   }
   
@@ -342,7 +344,6 @@ uint8_t gc_execute_line(char *line)
         mc_line(target[X_AXIS], target[Y_AXIS], target[Z_AXIS], settings.default_seek_rate, false);
       }
       mc_go_home(); 
-//      clear_vector(gc.position); // Assumes home is at [0,0,0]
       axis_words = 0; // Axis words used. Lock out from motion modes by clearing flags.
       break;      
     case NON_MODAL_SET_COORDINATE_OFFSET:
@@ -473,11 +474,11 @@ uint8_t gc_execute_line(char *line)
             */
             
             // Calculate the change in position along each selected axis
-            double x = target[gc.plane_axis_0]-gc.position[gc.plane_axis_0];
+            float x = target[gc.plane_axis_0]-gc.position[gc.plane_axis_0];
-            double y = target[gc.plane_axis_1]-gc.position[gc.plane_axis_1];
+            float y = target[gc.plane_axis_1]-gc.position[gc.plane_axis_1];
             
             clear_vector(offset);
-            double h_x2_div_d = -sqrt(4 * r*r - x*x - y*y)/hypot(x,y); // == -(h * 2 / d)
+            float h_x2_div_d = -sqrt(4 * r*r - x*x - y*y)/hypot(x,y); // == -(h * 2 / d)
             // If r is smaller than d, the arc is now traversing the complex plane beyond the reach of any
             // real CNC, and thus - for practical reasons - we will terminate promptly:
             if(isnan(h_x2_div_d)) { FAIL(STATUS_FLOATING_POINT_ERROR); return(gc.status_code); }
@@ -535,7 +536,7 @@ uint8_t gc_execute_line(char *line)
     // As far as the parser is concerned, the position is now == target. In reality the
     // motion control system might still be processing the action and the real tool position
     // in any intermediate location.
-    memcpy(gc.position, target, sizeof(double)*3); // gc.position[] = target[];
+    memcpy(gc.position, target, sizeof(float)*3); // gc.position[] = target[];
   }
   
   // M0,M1,M2,M30: Perform non-running program flow actions. During a program pause, the buffer may 
@@ -556,7 +557,7 @@ uint8_t gc_execute_line(char *line)
 // Parses the next statement and leaves the counter on the first character following
 // the statement. Returns 1 if there was a statements, 0 if end of string was reached
 // or there was an error (check state.status_code).
-static int next_statement(char *letter, double *double_ptr, char *line, uint8_t *char_counter) 
+static int next_statement(char *letter, float *float_ptr, char *line, uint8_t *char_counter) 
 {
   if (line[*char_counter] == 0) {
     return(0); // No more statements
@@ -568,7 +569,7 @@ static int next_statement(char *letter, double *double_ptr, char *line, uint8_t
     return(0);
   }
   (*char_counter)++;
-  if (!read_double(line, char_counter, double_ptr)) {
+  if (!read_float(line, char_counter, float_ptr)) {
     FAIL(STATUS_BAD_NUMBER_FORMAT); 
     return(0);
   };

limits.c

@@ -35,18 +35,19 @@
 
 void limits_init() 
 {
-  LIMIT_DDR &= ~(LIMIT_MASK);
+  LIMIT_DDR &= ~(LIMIT_MASK); // Input pin
+  LIMIT_PORT |= (LIMIT_MASK); // Enable internal pull-up resistors for normal high
 }
 
 // Moves all specified axes in same specified direction (positive=true, negative=false)
 // and at the homing rate. Homing is a special motion case, where there is only an 
 // acceleration followed by abrupt asynchronous stops by each axes reaching their limit 
-// switch independently. Instead of showhorning homing cycles into the main stepper 
+// switch independently. Instead of shoehorning homing cycles into the main stepper 
 // algorithm and overcomplicate things, a stripped-down, lite version of the stepper 
 // algorithm is written here. This also lets users hack and tune this code freely for
 // their own particular needs without affecting the rest of Grbl.
 // NOTE: Only the abort runtime command can interrupt this process.
-static void homing_cycle(bool x_axis, bool y_axis, bool z_axis, int8_t pos_dir, double homing_rate) 
+static void homing_cycle(bool x_axis, bool y_axis, bool z_axis, int8_t pos_dir, float homing_rate) 
 {
   // Determine governing axes with finest step resolution per distance for the Bresenham
   // algorithm. This solves the issue when homing multiple axes that have different 
@@ -67,7 +68,7 @@ static void homing_cycle(bool x_axis, bool y_axis, bool z_axis, int8_t pos_dir,
   // used in the main planner to account for distance traveled when moving multiple axes.
   // NOTE: When axis acceleration independence is installed, this will be updated to move
   // all axes at their maximum acceleration and rate.
-  double ds = step_event_count/sqrt(x_axis+y_axis+z_axis);
+  float ds = step_event_count/sqrt(x_axis+y_axis+z_axis);
 
   // Compute the adjusted step rate change with each acceleration tick. (in step/min/acceleration_tick)
   uint32_t delta_rate = ceil( ds*settings.acceleration/(60*ACCELERATION_TICKS_PER_SECOND));
@@ -180,5 +181,5 @@ void limits_go_home()
     limit_switches_present & (1<<X_LIMIT_BIT), 
     limit_switches_present & (1<<Y_LIMIT_BIT),
     limit_switches_present & (1<<Z_LIMIT_BIT));
-  delay_ms(LIMIT_DEBOUNCE); // Delay to debounce signal before leaving limit switches    
+  delay_ms(LIMIT_DEBOUNCE); // Delay to debounce signal before exiting routine
 }

main.c

@@ -62,7 +62,7 @@ int main(void)
       // releases will auto-reset the machine position back to [0,0,0] if an abort is used while 
       // grbl is moving the machine.
       int32_t last_position[3];
-      double last_coord_system[N_COORDINATE_SYSTEM][3];
+      float last_coord_system[N_COORDINATE_SYSTEM][3];
       memcpy(last_position, sys.position, sizeof(sys.position)); // last_position[] = sys.position[]
       memcpy(last_coord_system, sys.coord_system, sizeof(sys.coord_system)); // last_coord_system[] = sys.coord_system[]
 

motion_control.c

@@ -45,7 +45,7 @@
 // However, this keeps the memory requirements lower since it doesn't have to call and hold two 
 // plan_buffer_lines in memory. Grbl only has to retain the original line input variables during a
 // backlash segment(s).
-void mc_line(double x, double y, double z, double feed_rate, uint8_t invert_feed_rate)
+void mc_line(float x, float y, float z, float feed_rate, uint8_t invert_feed_rate)
 {
   // TODO: Backlash compensation may be installed here. Only need direction info to track when
   // to insert a backlash line motion(s) before the intended line motion. Requires its own
@@ -80,23 +80,23 @@ void mc_line(double x, double y, double z, double feed_rate, uint8_t invert_feed
 // for vector transformation direction.
 // The arc is approximated by generating a huge number of tiny, linear segments. The length of each 
 // segment is configured in settings.mm_per_arc_segment.  
-void mc_arc(double *position, double *target, double *offset, uint8_t axis_0, uint8_t axis_1, 
+void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8_t axis_1, 
-  uint8_t axis_linear, double feed_rate, uint8_t invert_feed_rate, double radius, uint8_t isclockwise)
+  uint8_t axis_linear, float feed_rate, uint8_t invert_feed_rate, float radius, uint8_t isclockwise)
 {      
-  double center_axis0 = position[axis_0] + offset[axis_0];
+  float center_axis0 = position[axis_0] + offset[axis_0];
-  double center_axis1 = position[axis_1] + offset[axis_1];
+  float center_axis1 = position[axis_1] + offset[axis_1];
-  double linear_travel = target[axis_linear] - position[axis_linear];
+  float linear_travel = target[axis_linear] - position[axis_linear];
-  double r_axis0 = -offset[axis_0];  // Radius vector from center to current location
+  float r_axis0 = -offset[axis_0];  // Radius vector from center to current location
-  double r_axis1 = -offset[axis_1];
+  float r_axis1 = -offset[axis_1];
-  double rt_axis0 = target[axis_0] - center_axis0;
+  float rt_axis0 = target[axis_0] - center_axis0;
-  double rt_axis1 = target[axis_1] - center_axis1;
+  float rt_axis1 = target[axis_1] - center_axis1;
   
   // CCW angle between position and target from circle center. Only one atan2() trig computation required.
-  double angular_travel = atan2(r_axis0*rt_axis1-r_axis1*rt_axis0, r_axis0*rt_axis0+r_axis1*rt_axis1);
+  float angular_travel = atan2(r_axis0*rt_axis1-r_axis1*rt_axis0, r_axis0*rt_axis0+r_axis1*rt_axis1);
   if (angular_travel < 0) { angular_travel += 2*M_PI; }
   if (isclockwise) { angular_travel -= 2*M_PI; }
   
-  double millimeters_of_travel = hypot(angular_travel*radius, fabs(linear_travel));
+  float millimeters_of_travel = hypot(angular_travel*radius, fabs(linear_travel));
   if (millimeters_of_travel == 0.0) { return; }
   uint16_t segments = floor(millimeters_of_travel/settings.mm_per_arc_segment);
   // Multiply inverse feed_rate to compensate for the fact that this movement is approximated
@@ -104,8 +104,8 @@ void mc_arc(double *position, double *target, double *offset, uint8_t axis_0, ui
   // all segments.
   if (invert_feed_rate) { feed_rate *= segments; }
  
-  double theta_per_segment = angular_travel/segments;
+  float theta_per_segment = angular_travel/segments;
-  double linear_per_segment = linear_travel/segments;
+  float linear_per_segment = linear_travel/segments;
   
   /* Vector rotation by transformation matrix: r is the original vector, r_T is the rotated vector,
      and phi is the angle of rotation. Based on the solution approach by Jens Geisler.
@@ -133,13 +133,13 @@ void mc_arc(double *position, double *target, double *offset, uint8_t axis_0, ui
      This is important when there are successive arc motions. 
   */
   // Vector rotation matrix values
-  double cos_T = 1-0.5*theta_per_segment*theta_per_segment; // Small angle approximation
+  float cos_T = 1-0.5*theta_per_segment*theta_per_segment; // Small angle approximation
-  double sin_T = theta_per_segment;
+  float sin_T = theta_per_segment;
   
-  double arc_target[3];
+  float arc_target[3];
-  double sin_Ti;
+  float sin_Ti;
-  double cos_Ti;
+  float cos_Ti;
-  double r_axisi;
+  float r_axisi;
   uint16_t i;
   int8_t count = 0;
 
@@ -179,7 +179,7 @@ void mc_arc(double *position, double *target, double *offset, uint8_t axis_0, ui
 
 
 // Execute dwell in seconds.
-void mc_dwell(double seconds) 
+void mc_dwell(float seconds) 
 {
    uint16_t i = floor(1000/DWELL_TIME_STEP*seconds);
    plan_synchronize();
@@ -200,5 +200,5 @@ void mc_go_home()
   // Upon completion, reset all internal position vectors (g-code parser, planner, system)
   gc_clear_position();
   plan_clear_position();
-  clear_vector_double(sys.position);
+  clear_vector_float(sys.position);
 }

motion_control.h

@@ -28,17 +28,17 @@
 // Execute linear motion in absolute millimeter coordinates. Feed rate given in millimeters/second
 // unless invert_feed_rate is true. Then the feed_rate means that the motion should be completed in
 // (1 minute)/feed_rate time.
-void mc_line(double x, double y, double z, double feed_rate, uint8_t invert_feed_rate);
+void mc_line(float x, float y, float z, float feed_rate, uint8_t invert_feed_rate);
 
 // Execute an arc in offset mode format. position == current xyz, target == target xyz, 
 // offset == offset from current xyz, axis_XXX defines circle plane in tool space, axis_linear is
 // the direction of helical travel, radius == circle radius, isclockwise boolean. Used
 // for vector transformation direction.
-void mc_arc(double *position, double *target, double *offset, uint8_t axis_0, uint8_t axis_1,
+void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8_t axis_1,
-  uint8_t axis_linear, double feed_rate, uint8_t invert_feed_rate, double radius, uint8_t isclockwise);
+  uint8_t axis_linear, float feed_rate, uint8_t invert_feed_rate, float radius, uint8_t isclockwise);
   
 // Dwell for a specific number of seconds
-void mc_dwell(double seconds);
+void mc_dwell(float seconds);
 
 // Send the tool home (not implemented)
 void mc_go_home();

nuts_bolts.c

@@ -24,20 +24,92 @@
 #include <stdlib.h>
 #include <util/delay.h>
 
-int read_double(char *line, uint8_t *char_counter, double *double_ptr)                  
+#define MAX_INT_DIGITS 8 // Maximum number of digits in int32 (and float)
-{
+extern float __floatunsisf (unsigned long);
-  char *start = line + *char_counter;
-  char *end;
-  
-  *double_ptr = strtod(start, &end);
-  if(end == start) { 
-    return(false); 
-  };
 
-  *char_counter = end - line;
+// Extracts a floating point value from a string. The following code is based loosely on
+// the avr-libc strtod() function by Michael Stumpf and Dmitry Xmelkov and many freely
+// available conversion method examples, but has been highly optimized for Grbl. For known
+// CNC applications, the typical decimal value is expected to be in the range of E0 to E-4.
+// Scientific notation is officially not supported by g-code, and the 'E' character may
+// be a g-code word on some CNC systems. So, 'E' notation will not be recognized. 
+// NOTE: Thanks to Radu-Eosif Mihailescu for identifying the issues with using strtod().
+int read_float(char *line, uint8_t *char_counter, float *float_ptr)                  
+{
+  char *ptr = line + *char_counter;
+  unsigned char c;
+    
+  // Grab first character and increment pointer. No spaces assumed in line.
+  c = *ptr++;
+  
+  // Capture initial positive/minus character
+  bool isnegative = false;
+  if (c == '-') {
+    isnegative = true;
+    c = *ptr++;
+  } else if (c == '+') {
+    c = *ptr++;
+  }
+  
+  // Extract number into fast integer. Track decimal in terms of exponent value.
+  uint32_t intval = 0;
+  int8_t exp = 0;
+  uint8_t ndigit = 0;
+  bool isdecimal = false;
+  while(1) {
+    c -= '0';
+    if (c <= 9) {
+      ndigit++;
+      if (ndigit <= MAX_INT_DIGITS) {
+        if (isdecimal) { exp--; }
+        intval = (((intval << 2) + intval) << 1) + c; // intval*10 + c
+      } else {
+        if (!(isdecimal)) { exp++; }  // Drop overflow digits
+      }
+    } else if (c == (('.'-'0') & 0xff)  &&  !(isdecimal)) {
+      isdecimal = true;
+    } else {
+      break;
+    }
+    c = *ptr++;
+  }
+  
+  // Return if no digits have been read.
+  if (!ndigit) { return(false); };
+  
+  // Convert integer into floating point.
+  float fval;
+  fval = __floatunsisf(intval);
+  
+  // Apply decimal. Should perform no more than two floating point multiplications for the
+  // expected range of E0 to E-4.
+  if (fval != 0) {
+    while (exp <= -2) {
+      fval *= 0.01; 
+      exp += 2;
+    }
+    if (exp < 0) { 
+      fval *= 0.1; 
+    } else if (exp > 0) {
+      do {
+        fval *= 10.0;
+      } while (--exp > 0);
+    } 
+  }
+
+  // Assign floating point value with correct sign.    
+  if (isnegative) {
+    *float_ptr = -fval;
+  } else {
+    *float_ptr = fval;
+  }
+
+  *char_counter = ptr - line - 1; // Set char_counter to next statement
+  
   return(true);
 }
 
+
 // Delays variable defined milliseconds. Compiler compatibility fix for _delay_ms(),
 // which only accepts constants in future compiler releases.
 void delay_ms(uint16_t ms) 
@@ -45,6 +117,7 @@ void delay_ms(uint16_t ms)
   while ( ms-- ) { _delay_ms(1); }
 }
 
+
 // Delays variable defined microseconds. Compiler compatibility fix for _delay_us(),
 // which only accepts constants in future compiler releases. Written to perform more 
 // efficiently with larger delays, as the counter adds parasitic time in each iteration.

nuts_bolts.h

@@ -38,7 +38,7 @@
 
 // Useful macros
 #define clear_vector(a) memset(a, 0, sizeof(a))
-#define clear_vector_double(a) memset(a, 0.0, sizeof(a))
+#define clear_vector_float(a) memset(a, 0.0, sizeof(a))
 #define max(a,b) (((a) > (b)) ? (a) : (b))
 #define min(a,b) (((a) < (b)) ? (a) : (b))
 
@@ -74,10 +74,10 @@ typedef struct {
                                  // NOTE: This may need to be a volatile variable, if problems arise. 
 
   uint8_t coord_select;          // Active work coordinate system number. Default: 0=G54.
-  double coord_system[N_COORDINATE_SYSTEM][3]; // Work coordinate systems (G54+). Stores offset from
+  float coord_system[N_COORDINATE_SYSTEM][3]; // Work coordinate systems (G54+). Stores offset from
   															 // absolute machine position in mm.
                                  // Rows: Work system number (0=G54,1=G55,...5=G59), Columns: XYZ Offsets
-  double coord_offset[3];        // Retains the G92 coordinate offset (work coordinates) relative to
+  float coord_offset[3];        // Retains the G92 coordinate offset (work coordinates) relative to
                                  // machine zero in mm.
                           
   volatile uint8_t cycle_start;  // Cycle start flag. Set by stepper subsystem or main program. 
@@ -86,9 +86,9 @@ typedef struct {
 extern system_t sys;
 
 // Read a floating point value from a string. Line points to the input buffer, char_counter 
-// is the indexer pointing to the current character of the line, while double_ptr is 
+// is the indexer pointing to the current character of the line, while float_ptr is 
 // a pointer to the result variable. Returns true when it succeeds
-int read_double(char *line, uint8_t *char_counter, double *double_ptr);
+int read_float(char *line, uint8_t *char_counter, float *float_ptr);
 
 // Delays variable-defined milliseconds. Compiler compatibility fix for _delay_ms().
 void delay_ms(uint16_t ms);

planner.c

@@ -46,8 +46,8 @@ typedef struct {
   int32_t position[3];             // The planner position of the tool in absolute steps. Kept separate
                                    // from g-code position for movements requiring multiple line motions,
                                    // i.e. arcs, canned cycles, and backlash compensation.
-  double previous_unit_vec[3];     // Unit vector of previous path line segment
+  float previous_unit_vec[3];     // Unit vector of previous path line segment
-  double previous_nominal_speed;   // Nominal speed of previous path line segment
+  float previous_nominal_speed;   // Nominal speed of previous path line segment
 } planner_t;
 static planner_t pl;
 
@@ -72,7 +72,7 @@ static uint8_t prev_block_index(uint8_t block_index)
 
 // Calculates the distance (not time) it takes to accelerate from initial_rate to target_rate using the 
 // given acceleration:
-static double estimate_acceleration_distance(double initial_rate, double target_rate, double acceleration) 
+static float estimate_acceleration_distance(float initial_rate, float target_rate, float acceleration) 
 {
   return( (target_rate*target_rate-initial_rate*initial_rate)/(2*acceleration) );
 }
@@ -91,7 +91,7 @@ static double estimate_acceleration_distance(double initial_rate, double target_
 // you started at speed initial_rate and accelerated until this point and want to end at the final_rate after
 // a total travel of distance. This can be used to compute the intersection point between acceleration and
 // deceleration in the cases where the trapezoid has no plateau (i.e. never reaches maximum speed)
-static double intersection_distance(double initial_rate, double final_rate, double acceleration, double distance) 
+static float intersection_distance(float initial_rate, float final_rate, float acceleration, float distance) 
 {
   return( (2*acceleration*distance-initial_rate*initial_rate+final_rate*final_rate)/(4*acceleration) );
 }
@@ -102,7 +102,7 @@ static double intersection_distance(double initial_rate, double final_rate, doub
 // NOTE: sqrt() reimplimented here from prior version due to improved planner logic. Increases speed
 // in time critical computations, i.e. arcs or rapid short lines from curves. Guaranteed to not exceed
 // BLOCK_BUFFER_SIZE calls per planner cycle.
-static double max_allowable_speed(double acceleration, double target_velocity, double distance) 
+static float max_allowable_speed(float acceleration, float target_velocity, float distance) 
 {
   return( sqrt(target_velocity*target_velocity-2*acceleration*distance) );
 }
@@ -162,7 +162,7 @@ static void planner_forward_pass_kernel(block_t *previous, block_t *current, blo
   // If nominal length is true, max junction speed is guaranteed to be reached. No need to recheck.  
   if (!previous->nominal_length_flag) {
     if (previous->entry_speed < current->entry_speed) {
-      double entry_speed = min( current->entry_speed,
+      float entry_speed = min( current->entry_speed,
         max_allowable_speed(-settings.acceleration,previous->entry_speed,previous->millimeters) );
 
       // Check for junction speed change
@@ -205,7 +205,7 @@ static void planner_forward_pass()
 // The factors represent a factor of braking and must be in the range 0.0-1.0.
 // This converts the planner parameters to the data required by the stepper controller.
 // NOTE: Final rates must be computed in terms of their respective blocks.
-static void calculate_trapezoid_for_block(block_t *block, double entry_factor, double exit_factor) 
+static void calculate_trapezoid_for_block(block_t *block, float entry_factor, float exit_factor) 
 {  
   block->initial_rate = ceil(block->nominal_rate*entry_factor); // (step/min)
   block->final_rate = ceil(block->nominal_rate*exit_factor); // (step/min)
@@ -347,7 +347,7 @@ void plan_synchronize()
 // All position data passed to the planner must be in terms of machine position to keep the planner 
 // independent of any coordinate system changes and offsets, which are handled by the g-code parser.
 // NOTE: Assumes buffer is available. Buffer checks are handled at a higher level by motion_control.
-void plan_buffer_line(double x, double y, double z, double feed_rate, uint8_t invert_feed_rate) 
+void plan_buffer_line(float x, float y, float z, float feed_rate, uint8_t invert_feed_rate) 
 {
   // Prepare to set up new block
   block_t *block = &block_buffer[block_buffer_head];
@@ -374,17 +374,17 @@ void plan_buffer_line(double x, double y, double z, double feed_rate, uint8_t in
   if (block->step_event_count == 0) { return; };
   
   // Compute path vector in terms of absolute step target and current positions
-  double delta_mm[3];
+  float delta_mm[3];
   delta_mm[X_AXIS] = (target[X_AXIS]-pl.position[X_AXIS])/settings.steps_per_mm[X_AXIS];
   delta_mm[Y_AXIS] = (target[Y_AXIS]-pl.position[Y_AXIS])/settings.steps_per_mm[Y_AXIS];
   delta_mm[Z_AXIS] = (target[Z_AXIS]-pl.position[Z_AXIS])/settings.steps_per_mm[Z_AXIS];
   block->millimeters = sqrt(delta_mm[X_AXIS]*delta_mm[X_AXIS] + delta_mm[Y_AXIS]*delta_mm[Y_AXIS] + 
                             delta_mm[Z_AXIS]*delta_mm[Z_AXIS]);
-  double inverse_millimeters = 1.0/block->millimeters;  // Inverse millimeters to remove multiple divides	
+  float inverse_millimeters = 1.0/block->millimeters;  // Inverse millimeters to remove multiple divides	
   
   // Calculate speed in mm/minute for each axis. No divide by zero due to previous checks.
   // NOTE: Minimum stepper speed is limited by MINIMUM_STEPS_PER_MINUTE in stepper.c
-  double inverse_minute;
+  float inverse_minute;
   if (!invert_feed_rate) {
     inverse_minute = feed_rate * inverse_millimeters;
   } else {
@@ -404,7 +404,7 @@ void plan_buffer_line(double x, double y, double z, double feed_rate, uint8_t in
         settings.acceleration / (60 * ACCELERATION_TICKS_PER_SECOND )); // (step/min/acceleration_tick)
 
   // Compute path unit vector                            
-  double unit_vec[3];
+  float unit_vec[3];
 
   unit_vec[X_AXIS] = delta_mm[X_AXIS]*inverse_millimeters;
   unit_vec[Y_AXIS] = delta_mm[Y_AXIS]*inverse_millimeters;
@@ -419,13 +419,13 @@ void plan_buffer_line(double x, double y, double z, double feed_rate, uint8_t in
   // path width or max_jerk in the previous grbl version. This approach does not actually deviate 
   // from path, but used as a robust way to compute cornering speeds, as it takes into account the
   // nonlinearities of both the junction angle and junction velocity.
-  double vmax_junction = MINIMUM_PLANNER_SPEED; // Set default max junction speed
+  float vmax_junction = MINIMUM_PLANNER_SPEED; // Set default max junction speed
 
   // Skip first block or when previous_nominal_speed is used as a flag for homing and offset cycles.
   if ((block_buffer_head != block_buffer_tail) && (pl.previous_nominal_speed > 0.0)) {
     // Compute cosine of angle between previous and current path. (prev_unit_vec is negative)
     // NOTE: Max junction velocity is computed without sin() or acos() by trig half angle identity.
-    double cos_theta = - pl.previous_unit_vec[X_AXIS] * unit_vec[X_AXIS] 
+    float cos_theta = - pl.previous_unit_vec[X_AXIS] * unit_vec[X_AXIS] 
                        - pl.previous_unit_vec[Y_AXIS] * unit_vec[Y_AXIS] 
                        - pl.previous_unit_vec[Z_AXIS] * unit_vec[Z_AXIS] ;
                          
@@ -435,7 +435,7 @@ void plan_buffer_line(double x, double y, double z, double feed_rate, uint8_t in
       // Skip and avoid divide by zero for straight junctions at 180 degrees. Limit to min() of nominal speeds.
       if (cos_theta > -0.95) {
         // Compute maximum junction velocity based on maximum acceleration and junction deviation
-        double sin_theta_d2 = sqrt(0.5*(1.0-cos_theta)); // Trig half angle identity. Always positive.
+        float sin_theta_d2 = sqrt(0.5*(1.0-cos_theta)); // Trig half angle identity. Always positive.
         vmax_junction = min(vmax_junction,
           sqrt(settings.acceleration * settings.junction_deviation * sin_theta_d2/(1.0-sin_theta_d2)) );
       }
@@ -444,7 +444,7 @@ void plan_buffer_line(double x, double y, double z, double feed_rate, uint8_t in
   block->max_entry_speed = vmax_junction;
   
   // Initialize block entry speed. Compute based on deceleration to user-defined MINIMUM_PLANNER_SPEED.
-  double v_allowable = max_allowable_speed(-settings.acceleration,MINIMUM_PLANNER_SPEED,block->millimeters);
+  float v_allowable = max_allowable_speed(-settings.acceleration,MINIMUM_PLANNER_SPEED,block->millimeters);
   block->entry_speed = min(vmax_junction, v_allowable);
 
   // Initialize planner efficiency flags

planner.h

@@ -34,10 +34,10 @@ typedef struct {
   int32_t  step_event_count;          // The number of step events required to complete this block
 
   // Fields used by the motion planner to manage acceleration
-  double nominal_speed;               // The nominal speed for this block in mm/min  
+  float nominal_speed;               // The nominal speed for this block in mm/min  
-  double entry_speed;                 // Entry speed at previous-current block junction in mm/min
+  float entry_speed;                 // Entry speed at previous-current block junction in mm/min
-  double max_entry_speed;             // Maximum allowable junction entry speed in mm/min
+  float max_entry_speed;             // Maximum allowable junction entry speed in mm/min
-  double millimeters;                 // The total travel of this block in mm
+  float millimeters;                 // The total travel of this block in mm
   uint8_t recalculate_flag;           // Planner flag to recalculate trapezoids on entry junction
   uint8_t nominal_length_flag;        // Planner flag for nominal speed always reached
 
@@ -57,7 +57,7 @@ void plan_init();
 // Add a new linear movement to the buffer. x, y and z is the signed, absolute target position in 
 // millimaters. Feed rate specifies the speed of the motion. If feed rate is inverted, the feed
 // rate is taken to mean "frequency" and would complete the operation in 1/feed_rate minutes.
-void plan_buffer_line(double x, double y, double z, double feed_rate, uint8_t invert_feed_rate);
+void plan_buffer_line(float x, float y, float z, float feed_rate, uint8_t invert_feed_rate);
 
 // Called when the current block is no longer needed. Discards the block and makes the memory
 // availible for new blocks.

print.c

@@ -105,7 +105,7 @@ void printInteger(long n)
   print_uint32_base10(n);
 }
 
-void printFloat(double n)
+void printFloat(float n)
 {
   if (n < 0) {
     serial_write('-');

print.h

@@ -33,6 +33,6 @@ void printInteger(long n);
 
 void print_uint8_base2(uint8_t n);
 
-void printFloat(double n);
+void printFloat(float n);
 
 #endif

protocol.c

@@ -245,7 +245,7 @@ void protocol_process()
           // Enable comments flag and ignore all characters until ')' or EOL.
           iscomment = true;
         } else if (char_counter >= LINE_BUFFER_SIZE-1) {
-          // Throw away any characters beyond the end of the line buffer
+          // Throw away any characters beyond the end of the line buffer          
         } else if (c >= 'a' && c <= 'z') { // Upcase lowercase
           line[char_counter++] = c-'a'+'A';
         } else {

settings.c

@@ -33,13 +33,13 @@ settings_t settings;
 
 // Version 1 outdated settings record
 typedef struct {
-  double steps_per_mm[3];
+  float steps_per_mm[3];
   uint8_t microsteps;
   uint8_t pulse_microseconds;
-  double default_feed_rate;
+  float default_feed_rate;
-  double default_seek_rate;
+  float default_seek_rate;
   uint8_t invert_mask;
-  double mm_per_arc_segment;
+  float mm_per_arc_segment;
 } settings_v1_t;
 
 // Default settings (used when resetting eeprom-settings)
@@ -89,20 +89,20 @@ void settings_dump() {
 // Parameter lines are on the form '$4=374.3' or '$' to dump current settings
 uint8_t settings_execute_line(char *line) {
   uint8_t char_counter = 1;
-  double parameter, value;
+  float parameter, value;
   if(line[0] != '$') { 
     return(STATUS_UNSUPPORTED_STATEMENT); 
   }
   if(line[char_counter] == 0) { 
     settings_dump(); return(STATUS_OK); 
   }
-  if(!read_double(line, &char_counter, &parameter)) {
+  if(!read_float(line, &char_counter, &parameter)) {
     return(STATUS_BAD_NUMBER_FORMAT);
   };
   if(line[char_counter++] != '=') { 
     return(STATUS_UNSUPPORTED_STATEMENT); 
   }
-  if(!read_double(line, &char_counter, &value)) {
+  if(!read_float(line, &char_counter, &value)) {
     return(STATUS_BAD_NUMBER_FORMAT);
   }
   if(line[char_counter] != 0) { 
@@ -158,7 +158,7 @@ int read_settings() {
 }
 
 // A helper method to set settings from command line
-void settings_store_setting(int parameter, double value) {
+void settings_store_setting(int parameter, float value) {
   switch(parameter) {
     case 0: case 1: case 2:
     if (value <= 0.0) {

settings.h

@@ -33,15 +33,15 @@
 
 // Current global settings (persisted in EEPROM from byte 1 onwards)
 typedef struct {
-  double steps_per_mm[3];
+  float steps_per_mm[3];
   uint8_t microsteps;
   uint8_t pulse_microseconds;
-  double default_feed_rate;
+  float default_feed_rate;
-  double default_seek_rate;
+  float default_seek_rate;
   uint8_t invert_mask;
-  double mm_per_arc_segment;
+  float mm_per_arc_segment;
-  double acceleration;
+  float acceleration;
-  double junction_deviation;
+  float junction_deviation;
 } settings_t;
 extern settings_t settings;
 
@@ -55,6 +55,6 @@ void settings_dump();
 uint8_t settings_execute_line(char *line);
 
 // A helper method to set new settings from command line
-void settings_store_setting(int parameter, double value);
+void settings_store_setting(int parameter, float value);
 
 #endif

stepper.c

@@ -304,8 +304,10 @@ ISR(TIMER1_COMPA_vect)
 
 // This interrupt is set up by ISR_TIMER1_COMPAREA when it sets the motor port bits. It resets
 // the motor port after a short period (settings.pulse_microseconds) completing one step cycle.
-// TODO: It is possible for the serial interrupts to delay this interrupt by a few microseconds, if
+// NOTE: Interrupt collisions between the serial and stepper interrupts can cause delays by
-// they execute right before this interrupt. Not a big deal, but could use some TLC at some point.
+// a few microseconds, if they execute right before one another. Not a big deal, but can
+// cause issues at high step rates if another high frequency asynchronous interrupt is 
+// added to Grbl.
 ISR(TIMER2_OVF_vect)
 {
   // Reset stepping pins (leave the direction pins)
@@ -355,12 +357,11 @@ void st_init()
   // Configure Timer 2
   TCCR2A = 0; // Normal operation
   TCCR2B = 0; // Disable timer until needed.
-  TIMSK2 |= (1<<TOIE2);      
+  TIMSK2 |= (1<<TOIE2); // Enable Timer2 Overflow interrupt     
-  
   #ifdef STEP_PULSE_DELAY
     TIMSK2 |= (1<<OCIE2A); // Enable Timer2 Compare Match A interrupt
   #endif
-  
+
   // Start in the idle state
   st_go_idle();
 }
@@ -452,5 +453,3 @@ void st_cycle_reinitialize()
   }
   sys.feed_hold = false; // Release feed hold. Cycle is ready to re-start.
 }
-
-