Commenting updates. Minor bug fix with exit of soft limit event.

limits.c

@@ -190,7 +190,7 @@ 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.
+    st_reset(); // Immediately force kill steppers and reset step segment buffer.
     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.  
@@ -255,7 +255,7 @@ void limits_soft_check(float *target)
         do {
           protocol_execute_runtime();
           if (sys.abort) { return; }
-        } while (sys.state == STATE_HOLD);
+        } while ( sys.state != STATE_IDLE || sys.state != STATE_QUEUED);
       }
       
       mc_reset(); // Issue system reset and ensure spindle and coolant are shutdown.

motion_control.c

@@ -48,16 +48,19 @@ void mc_line(float *target, float feed_rate, uint8_t invert_feed_rate)
   // If in check gcode mode, prevent motion by blocking planner. Soft limits still work.
   if (sys.state == STATE_CHECK_MODE) { return; }
     
-  // 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
+  // NOTE: Backlash compensation may be installed here. It will need direction info to track when
+  // to insert a backlash line motion(s) before the intended line motion and will require its own
   // plan_check_full_buffer() and check for system abort loop. Also for position reporting 
-  // backlash steps will need to be also tracked. Not sure what the best strategy is for this,
-  // i.e. keep the planner independent and do the computations in the status reporting, or let
-  // the planner handle the position corrections. The latter may get complicated.
-  // TODO: Backlash comp positioning values may need to be kept at a system level, i.e. tracking 
-  // true position after a feed hold in the middle of a backlash move. The difficulty is in making 
-  // sure that the stepper subsystem and planner are working in sync, and the status report 
-  // position also takes this into account.
+  // backlash steps will need to be also tracked, which will need to be kept at a system level.
+  // There are likely some other things that will need to be tracked as well. However, we feel
+  // that backlash compensation should NOT be handled by Grbl itself, because there are a myriad
+  // of ways to implement it and can be effective or ineffective for different CNC machines. This
+  // would be better handled by the interface as a post-processor task, where the original g-code
+  // is translated and inserts backlash motions that best suits the machine. 
+  // NOTE: Perhaps as a middle-ground, all that needs to be sent is a flag or special command that
+  // indicates to Grbl what is a backlash compensation motion, so that Grbl executes the move but
+  // doesn't update the machine position values. Since the position values used by the g-code
+  // parser and planner are separate from the system machine positions, this is doable.
 
   // If the buffer is full: good! That means we are well ahead of the robot. 
   // Remain in this loop until there is room in the buffer.

stepper.c

@@ -541,7 +541,7 @@ void st_prep_buffer()
         // Initialize segment buffer data for generating the segments.
         prep.steps_remaining = pl_block->step_event_count;
         prep.step_per_mm = prep.steps_remaining/pl_block->millimeters;
-        prep.req_mm_increment = REQ_MM_INCREMENT_SCALAR*pl_block->millimeters/prep.steps_remaining;
+        prep.req_mm_increment = REQ_MM_INCREMENT_SCALAR/prep.step_per_mm;
         
         prep.dt_remainder = 0.0; // Reset for new planner block
 
@@ -639,8 +639,8 @@ 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;
+    float mm_remaining = pl_block->millimeters; // New segment distance from end of block.
+    float minimum_mm = mm_remaining-prep.req_mm_increment; // Guarantee at least one step.
     if (minimum_mm < 0.0) { minimum_mm = 0.0; }
 
     do {
@@ -691,7 +691,9 @@ void st_prep_buffer()
       if (dt < dt_max) { time_var = dt_max - dt; } // **Incomplete** At ramp junction.
       else {
         if (mm_remaining > minimum_mm) { // Check for very slow segments with zero steps.
-          dt_max += DT_SEGMENT; // Increase segment time to ensure at least one step in segment.
+          // Increase segment time to ensure at least one step in segment. Override and loop
+          // through distance calculations until minimum_mm or mm_complete.
+          dt_max += DT_SEGMENT;
           time_var = dt_max - dt;
         } else { 
           break; // **Complete** Exit loop. Segment execution time maxed.
@@ -716,8 +718,9 @@ void st_prep_buffer()
     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) {
+      if (sys.state == STATE_HOLD) {
+
         // 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;
@@ -776,7 +779,11 @@ void st_prep_buffer()
       }
     #endif
 
-    // Determine end of segment conditions. Setup initial conditions for next segment.
+    // Segment complete! Increment segment buffer indices.
+    segment_buffer_head = segment_next_head;
+    if ( ++segment_next_head == SEGMENT_BUFFER_SIZE ) { segment_next_head = 0; }
+
+    // Setup initial conditions for next segment.
     if (mm_remaining > prep.mm_complete) { 
       // Normal operation. Block incomplete. Distance remaining in block to be executed.
       pl_block->millimeters = mm_remaining;      
@@ -793,6 +800,7 @@ void st_prep_buffer()
         plan_cycle_reinitialize(); 
         sys.state = STATE_QUEUED; // End cycle.        
 
+        return; // Bail!
 // TODO: Try to move QUEUED setting into cycle re-initialize.
 
       } else { // End of planner block
@@ -802,12 +810,6 @@ void st_prep_buffer()
       }
     }
 
-    // New step segment initialization completed. Increment segment buffer indices.
-    segment_buffer_head = segment_next_head;
-    if ( ++segment_next_head == SEGMENT_BUFFER_SIZE ) { segment_next_head = 0; }
-
-    if (sys.state == STATE_QUEUED) { return; } // Bail if hold completes    
-
 // int32_t blength = segment_buffer_head - segment_buffer_tail;
 // if (blength < 0) { blength += SEGMENT_BUFFER_SIZE; } 
 // printInteger(blength);

system.c

@@ -150,7 +150,7 @@ uint8_t system_execute_line(char *line)
             } else {
               report_build_info(line);
             }
-          } else { // Store startup line
+          } else { // Store startup line [IDLE/ALARM]
             if(line[char_counter++] != '=') { return(STATUS_UNSUPPORTED_STATEMENT); }
             helper_var = char_counter; // Set helper variable as counter to start of user info line.
             do {
@@ -169,7 +169,7 @@ uint8_t system_execute_line(char *line)
               }
             }
             break;
-          } else { // Store startup line
+          } else { // Store startup line [IDLE Only] Prevents motion during ALARM.
             if (sys.state != STATE_IDLE) { return(STATUS_IDLE_ERROR); } // Store only when idle.
             helper_var = true;  // Set helper_var to flag storing method. 
             // No break. Continues into default: to read remaining command characters.

system.h

@@ -59,12 +59,12 @@
 // of Grbl to manage each without overlapping. It is also used as a messaging flag for
 // critical events.
 #define STATE_IDLE       0      // Must be zero. No flags.
-#define STATE_QUEUED     bit(0) // Indicates buffered blocks, awaiting cycle start.
-#define STATE_CYCLE      bit(1) // Cycle is running
-#define STATE_HOLD       bit(2) // Executing feed hold
-#define STATE_HOMING     bit(3) // Performing homing cycle
-#define STATE_ALARM      bit(4) // In alarm state. Locks out all g-code processes. Allows settings access.
-#define STATE_CHECK_MODE bit(5) // G-code check mode. Locks out planner and motion only.
+#define STATE_ALARM      bit(0) // In alarm state. Locks out all g-code processes. Allows settings access.
+#define STATE_CHECK_MODE bit(1) // G-code check mode. Locks out planner and motion only.
+#define STATE_HOMING     bit(2) // Performing homing cycle
+#define STATE_QUEUED     bit(3) // Indicates buffered blocks, awaiting cycle start.
+#define STATE_CYCLE      bit(4) // Cycle is running
+#define STATE_HOLD       bit(5) // Executing feed hold
 // #define STATE_JOG     bit(6) // Jogging mode is unique like homing.
 
 // Define global system variables