Homing and feed hold bug fixes.

WARNING: Bugs may still exist. This branch is a work in progress and
will be pushed to the edge branch when at beta stability. Use at your
own risk.

- Homing freezing issue fixed. Had to do with the cycle stop flag being
set incorrectly after the homing cycles and before the pull-off
maneuver. Now resets the stepper motors before this can happen.

- Fixed an issue with a rare feed hold failure. Had to do with feed
hold ending exactly at the end of a block. The runtime protocol now
sets the QUEUED and IDLE states appropriately when this occurs. Still
need to clean this code up however, as it’s patched rather than written
well.

- Updated version build via $I command.

- Forgot to comment on a new feature for the last commit. Since steps
are integers and millimeters traveled are floats, the old step segment
generator ignored the step fraction differences in generating the
segment velocities. Didn’t see like it would be much of a big deal, but
there were instances that this would be a problem, especially for very
slow feed rates. The stepper algorithm now micro-adjusts the segment
velocities based on the step fractions not executed from the previous
segment. This ensures that Grbl generates the velocity profiles EXACTLY
and noticeably improves overall acceleration performance.

limits.c

@@ -190,15 +190,15 @@ void limits_go_home(uint8_t cycle_mask)
       if (sys.execute & EXEC_RESET) { protocol_execute_runtime(); return; }
     } while (STEP_MASK & axislock);
     
+    st_reset(); // Force disable steppers and reset step segment buffer. Ensure homing motion is cleared.
+    plan_reset(); // Reset planner buffer. Zero planner positions. Ensure homing motion is cleared.
+
     delay_ms(settings.homing_debounce_delay); // Delay to allow transient dynamics to dissipate.  
 
     // Reverse direction and reset homing rate for locate cycle(s).
     homing_rate = settings.homing_feed_rate;
     approach = !approach;
     
-    st_reset(); // Force disable steppers and reset step segment buffer. Ensure homing motion is cleared.
-    plan_reset(); // Reset planner buffer. Zero planner positions. Ensure homing motion is cleared.
-
   } while (n_cycle-- > 0);
     
   // The active cycle axes should now be homed and machine limits have been located. By 
@@ -230,7 +230,6 @@ void limits_go_home(uint8_t cycle_mask)
   // Initiate pull-off using main motion control routines. 
   // TODO : Clean up state routines so that this motion still shows homing state.
   sys.state = STATE_QUEUED;
-//   protocol_cycle_start();   
   sys.execute |= EXEC_CYCLE_START;
   protocol_execute_runtime();
   protocol_buffer_synchronize(); // Complete pull-off motion.

protocol.c

@@ -242,9 +242,8 @@ void protocol_execute_runtime()
     // cycle reinitializations. The stepper path should continue exactly as if nothing has happened.   
     // NOTE: EXEC_CYCLE_STOP is set by the stepper subsystem when a cycle or feed hold completes.
     if (rt_exec & EXEC_CYCLE_STOP) {
-      if (sys.state != STATE_QUEUED) {    
+      if ( plan_get_current_block() ) { sys.state = STATE_QUEUED; }
-        sys.state = STATE_IDLE;
+      else { sys.state = STATE_IDLE; }
-      }
       bit_false(sys.execute,EXEC_CYCLE_STOP);
     }
 

settings.h

@@ -26,7 +26,7 @@
 
 
 #define GRBL_VERSION "0.9c"
-#define GRBL_VERSION_BUILD "20140110"
+#define GRBL_VERSION_BUILD "20140215"
 
 // Version of the EEPROM data. Will be used to migrate existing data from older versions of Grbl
 // when firmware is upgraded. Always stored in byte 0 of eeprom

stepper.c

@@ -620,24 +620,6 @@ void st_prep_buffer()
     // Set new segment to point to the current segment data block.
     prep_segment->st_block_index = prep.st_block_index;
 
-
-    float mm_remaining = pl_block->millimeters;    
-    float minimum_mm = pl_block->millimeters-prep.req_mm_increment;
-    if (minimum_mm < 0.0) { minimum_mm = 0.0; }
-    if (sys.state == STATE_HOLD) {
-      if (minimum_mm < prep.mm_complete) { // NOTE: Exit condition
-        // Less than one step to decelerate to zero speed, but already very close. AMASS 
-        // requires full steps to execute. So, just bail.
-        prep.current_speed = 0.0;
-        prep.dt_remainder = 0.0;
-        prep.steps_remaining = ceil(pl_block->millimeters * prep.step_per_mm);
-        pl_block->millimeters = prep.steps_remaining/prep.step_per_mm; // Update with full steps.
-        plan_cycle_reinitialize();         
-        sys.state = STATE_QUEUED; 
-        return; // Segment not generated, but current step data still retained.
-      }
-    }
-
     /*------------------------------------------------------------------------------------
         Compute the average velocity of this new segment by determining the total distance
       traveled over the segment time DT_SEGMENT. The following code first attempts to create 
@@ -657,6 +639,10 @@ void st_prep_buffer()
     float time_var = dt_max; // Time worker variable
     float mm_var; // mm-Distance worker variable
     float speed_var; // Speed worker variable   
+    float mm_remaining = pl_block->millimeters;    
+    float minimum_mm = pl_block->millimeters-prep.req_mm_increment;
+    if (minimum_mm < 0.0) { minimum_mm = 0.0; }
+
     do {
       switch (prep.ramp_type) {
         case RAMP_ACCEL: 
@@ -729,6 +715,21 @@ void st_prep_buffer()
     float last_n_steps_remaining = ceil(prep.steps_remaining); // Round-up last steps remaining
     prep_segment->n_step = last_n_steps_remaining-n_steps_remaining; // Compute number of steps to execute.
     
+    // Bail if we are at the end of a feed hold and don't have a step to execute.
+    if (sys.state == STATE_HOLD) {
+      if (prep_segment->n_step == 0) {
+        // Less than one step to decelerate to zero speed, but already very close. AMASS 
+        // requires full steps to execute. So, just bail.
+        prep.current_speed = 0.0;
+        prep.dt_remainder = 0.0;
+        prep.steps_remaining = n_steps_remaining;
+        pl_block->millimeters = prep.steps_remaining/prep.step_per_mm; // Update with full steps.
+        plan_cycle_reinitialize();         
+        sys.state = STATE_QUEUED; 
+        return; // Segment not generated, but current step data still retained.
+      }
+    }
+
     // Compute segment step rate. Since steps are integers and mm distances traveled are not,
     // the end of every segment can have a partial step of varying magnitudes that are not 
     // executed, because the stepper ISR requires whole steps due to the AMASS algorithm. To