Major g-code parser overhaul. 100%* compliant. Other related updates.

- Completely overhauled the g-code parser. It’s now 100%* compliant. (*
may have some bugs). Being compliant, here are some of the major
differences.

- SMALLER and JUST AS FAST! A number of optimizations were found that
sped things up and allowed for the more thorough error-checking to be
installed without a speed hit. Trimmed a lot of ‘fat’ in the parser and
still was able to make it significantly smaller than it was.

- No default feed rate setting! Removed completely! This doesn’t exist
in the g-code standard. So, it now errors out whenever it’s undefined
for motions that require it (G1/2/3/38.2).

- Any g-code parser error expunges the ENTIRE block. This means all
information is lost and not passed on to the running state. Before some
of the states would remain, which could have led to some problems.

- If the g-code block passes all of the error-checks, the g-code state
is updated and all motions are executed according to the order of
execution.

- Changes in spindle speed, when already running, will update the
output pin accordingly. This fixes a bug, where it wouldn’t update the
speed.

- Update g-code parser error reporting. Errors now return detailed
information of what exact went wrong. The most common errors return a
short text description. For less common errors, the parser reports
‘Invalid gcode ID:20’, where 20 is a error ID. A list of error code IDs
and their descriptions will be documented for user reference elsewhere
to save flash space.

- Other notable changes:

- Added a print integer routine for uint8 variables. This saved
significant flash space by switching from a heavier universal print
integer routine.

- Saved some flash space with our own short hypotenuse calculation

- Some arc computation flash and memory optimizations.

motion_control.c

@@ -97,16 +97,15 @@ void mc_line(float *target, float feed_rate, uint8_t invert_feed_rate)
 // of each segment is configured in settings.arc_tolerance, which is defined to be the maximum normal
 // distance from segment to the circle when the end points both lie on the circle.
 #ifdef USE_LINE_NUMBERS
-void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8_t axis_1, 
-  uint8_t axis_linear, float feed_rate, uint8_t invert_feed_rate, float radius, uint8_t isclockwise, int32_t line_number)
+void mc_arc(float *position, float *target, float *offset, float radius, float feed_rate, 
+  uint8_t invert_feed_rate, uint8_t axis_0, uint8_t axis_1, uint8_t axis_linear, int32_t line_number)
 #else
-void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8_t axis_1, 
-  uint8_t axis_linear, float feed_rate, uint8_t invert_feed_rate, float radius, uint8_t isclockwise)
+void mc_arc(float *position, float *target, float *offset, float radius, float feed_rate,
+  uint8_t invert_feed_rate, uint8_t axis_0, uint8_t axis_1, uint8_t axis_linear)
 #endif
-{      
+{
   float center_axis0 = position[axis_0] + offset[axis_0];
   float center_axis1 = position[axis_1] + offset[axis_1];
-  float linear_travel = target[axis_linear] - position[axis_linear];
   float r_axis0 = -offset[axis_0];  // Radius vector from center to current location
   float r_axis1 = -offset[axis_1];
   float rt_axis0 = target[axis_0] - center_axis0;
@@ -114,7 +113,7 @@ void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8
   
   // CCW angle between position and target from circle center. Only one atan2() trig computation required.
   float angular_travel = atan2(r_axis0*rt_axis1-r_axis1*rt_axis0, r_axis0*rt_axis0+r_axis1*rt_axis1);
-  if (isclockwise) { // Correct atan2 output per direction
+  if (gc_state.modal.motion == MOTION_MODE_CW_ARC) { // Correct atan2 output per direction
     if (angular_travel >= 0) { angular_travel -= 2*M_PI; }
   } else {
     if (angular_travel <= 0) { angular_travel += 2*M_PI; }
@@ -123,10 +122,8 @@ void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8
   // NOTE: Segment end points are on the arc, which can lead to the arc diameter being smaller by up to
   // (2x) settings.arc_tolerance. For 99% of users, this is just fine. If a different arc segment fit
   // is desired, i.e. least-squares, midpoint on arc, just change the mm_per_arc_segment calculation.
-  // Computes: mm_per_arc_segment = sqrt(4*arc_tolerance*(2*radius-arc_tolerance)),
-  //           segments = millimeters_of_travel/mm_per_arc_segment
-  float millimeters_of_travel = hypot(angular_travel*radius, fabs(linear_travel));
-  uint16_t segments = floor(0.5*millimeters_of_travel/
+  // For the intended uses of Grbl, this value shouldn't exceed 2000 for the strictest of cases.
+  uint16_t segments = floor(fabs(0.5*angular_travel*radius)/
                           sqrt(settings.arc_tolerance*(2*radius - settings.arc_tolerance)) );
   
   if (segments) { 
@@ -136,7 +133,7 @@ void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8
     if (invert_feed_rate) { feed_rate *= segments; }
    
     float theta_per_segment = angular_travel/segments;
-    float linear_per_segment = linear_travel/segments;
+    float linear_per_segment = (target[axis_linear] - position[axis_linear])/segments;
 
     /* Vector rotation by transformation matrix: r is the original vector, r_T is the rotated vector,
        and phi is the angle of rotation. Solution approach by Jens Geisler.
@@ -166,17 +163,13 @@ void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8
     float sin_T = theta_per_segment*0.16666667*(cos_T + 4.0);
     cos_T *= 0.5;
 
-    float arc_target[N_AXIS];
     float sin_Ti;
     float cos_Ti;
     float r_axisi;
     uint16_t i;
     uint8_t count = 0;
   
-    // Initialize the linear axis
-    arc_target[axis_linear] = position[axis_linear];
-  
-    for (i = 1; i<segments; i++) { // Increment (segments-1)
+    for (i = 1; i<segments; i++) { // Increment (segments-1).
       
       if (count < N_ARC_CORRECTION) {
         // Apply vector rotation matrix. ~40 usec
@@ -184,7 +177,7 @@ void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8
         r_axis0 = r_axis0*cos_T - r_axis1*sin_T;
         r_axis1 = r_axisi;
         count++;
-      } else {
+      } else {      
         // Arc correction to radius vector. Computed only every N_ARC_CORRECTION increments. ~375 usec
         // Compute exact location by applying transformation matrix from initial radius vector(=-offset).
         cos_Ti = cos(i*theta_per_segment);
@@ -195,14 +188,14 @@ void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8
       }
   
       // Update arc_target location
-      arc_target[axis_0] = center_axis0 + r_axis0;
-      arc_target[axis_1] = center_axis1 + r_axis1;
-      arc_target[axis_linear] += linear_per_segment;
+      position[axis_0] = center_axis0 + r_axis0;
+      position[axis_1] = center_axis1 + r_axis1;
+      position[axis_linear] += linear_per_segment;
       
       #ifdef USE_LINE_NUMBERS
-      mc_line(arc_target, feed_rate, invert_feed_rate, line_number);
+      mc_line(position, feed_rate, invert_feed_rate, line_number);
       #else
-      mc_line(arc_target, feed_rate, invert_feed_rate);
+      mc_line(position, feed_rate, invert_feed_rate);
       #endif
       
       // Bail mid-circle on system abort. Runtime command check already performed by mc_line.
@@ -221,6 +214,8 @@ void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8
 // Execute dwell in seconds.
 void mc_dwell(float seconds) 
 {
+   if (sys.state != STATE_CHECK_MODE) { return; }
+   
    uint16_t i = floor(1000/DWELL_TIME_STEP*seconds);
    protocol_buffer_synchronize();
    delay_ms(floor(1000*seconds-i*DWELL_TIME_STEP)); // Delay millisecond remainder.
@@ -290,7 +285,7 @@ void mc_probe_cycle(float *target, float feed_rate, uint8_t invert_feed_rate)
   mc_line(target, feed_rate, invert_feed_rate);
   #endif
 
-  //TODO - make sure the probe isn't already closed
+  // NOTE: Parser error-checking ensures the probe isn't already closed/triggered.
   sys.probe_state = PROBE_ACTIVE;
 
   sys.execute |= EXEC_CYCLE_START;
@@ -328,7 +323,7 @@ void mc_probe_cycle(float *target, float feed_rate, uint8_t invert_feed_rate)
   // Gcode parser position was circumvented by the this routine, so sync position now.
   gc_sync_position();
 
-  //TODO - ouput a mandatory status update with the probe position.  What if another was recently sent?
+  // Output the probe position as message.
   report_probe_parameters();
 }