Tweaks and minor bug fixes. Added purge buffer command.

- Added a purge buffer (and lock) command. This is an advanced option
to clear any queued blocks in the buffer in the event of system
position being lost or homed. These queued blocks will likely not move
correctly if not purged. In typical use, the purging command releases
the homing axes lock in case a user need to move the axes off their
hard limit switches, but position is not guaranteed. Homing is advised
immediately after.

- Created a system-wide sync current position function. Cleans up some
of the repetitive tasks in various places in the code that do the same
thing.

- Removed the clear all switches command '$S'. Not really needed and
helped clean up a sync call.

- Other minor tweaks. Readme updated slightly..

gcode.c

@@ -72,12 +72,6 @@ void gc_set_current_position(int32_t x, int32_t y, int32_t z)
   gc.position[Z_AXIS] = z/settings.steps_per_mm[Z_AXIS]; 
 }
 
-// Clears and zeros g-code parser position. Called by homing routine.
-void gc_clear_position()
-{
-  clear_vector(gc.position);
-}
-
 static float to_millimeters(float value) 
 {
   return(gc.inches_mode ? (value * MM_PER_INCH) : value);

gcode.h

@@ -106,7 +106,4 @@ uint8_t gc_execute_line(char *line);
 // Set g-code parser position. Input in steps.
 void gc_set_current_position(int32_t x, int32_t y, int32_t z); 
 
-// Clear g-code parser position
-void gc_clear_position();
-
 #endif

main.c

@@ -76,11 +76,13 @@ int main(void)
       limits_init();
       st_reset(); // Clear stepper subsystem variables.
 
-      // Set cleared gcode and planner positions to current system position, which is only
+      // Sync cleared gcode and planner positions to current system position, which is only
-      // cleared upon startup, not a reset/abort. If Grbl does not know or ensure its position,
+      // cleared upon startup, not a reset/abort. If Grbl does not know or can ensure its 
-      // a feedback message will be sent back to the user to let them know.
+      // position, a feedback message will be sent back to the user to let them know. Also,
-      gc_set_current_position(sys.position[X_AXIS],sys.position[Y_AXIS],sys.position[Z_AXIS]);
+      // if position is lost and homing is enabled, the axes motions will be locked, and 
-      plan_set_current_position(sys.position[X_AXIS],sys.position[Y_AXIS],sys.position[Z_AXIS]);
+      // user must either perform the homing cycle '$H' or purge the system locks '$P' to 
+      // resume.
+      sys_sync_current_position();
 
       // Reset system variables
       sys.abort = false;

motion_control.c

@@ -220,9 +220,9 @@ void mc_go_home()
   }
 
   // The machine should now be homed and machine zero has been located. Upon completion, 
-  // reset planner and system internal position vectors, but not gcode parser position yet.
+  // reset system position and sync internal position vectors.
-  plan_clear_position();
+  clear_vector_float(sys.position); // Set machine zero
-  clear_vector_float(sys.position);
+  sys_sync_current_position();
   
   // Pull-off all axes from limit switches before continuing motion. This provides some initial
   // clearance off the switches and should also help prevent them from falsely tripping when 
@@ -237,8 +237,8 @@ void mc_go_home()
   st_cycle_start(); // Move it. Nothing should be in the buffer except this motion. 
   plan_synchronize(); // Make sure the motion completes.
   
-  // Explicitly update the gcode parser position since it was circumvented by the pull-off maneuver.
+  // The gcode parser position was circumvented by the pull-off maneuver, so sync position vectors.
-  gc_set_current_position(sys.position[X_AXIS],sys.position[Y_AXIS],sys.position[Z_AXIS]);
+  sys_sync_current_position();
 
   // If hard limits feature enabled, re-enable hard limits interrupt after homing cycle.
   if (bit_istrue(settings.flags,BITFLAG_HARD_LIMIT_ENABLE)) { PCICR |= (1 << LIMIT_INT); }

nuts_bolts.c

@@ -19,8 +19,10 @@
   along with Grbl.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include "nuts_bolts.h"
 #include <util/delay.h>
+#include "nuts_bolts.h"
+#include "gcode.h"
+#include "planner.h"
 
 #define MAX_INT_DIGITS 8 // Maximum number of digits in int32 (and float)
 extern float __floatunsisf (unsigned long);
@@ -137,3 +139,10 @@ void delay_us(uint32_t us)
     }
   }
 }
+
+
+void sys_sync_current_position()
+{
+  plan_set_current_position(sys.position[X_AXIS],sys.position[Y_AXIS],sys.position[Z_AXIS]);
+  gc_set_current_position(sys.position[X_AXIS],sys.position[Y_AXIS],sys.position[Z_AXIS]);
+}

nuts_bolts.h

@@ -103,4 +103,7 @@ void delay_ms(uint16_t ms);
 // Delays variable-defined microseconds. Compiler compatibility fix for _delay_us().
 void delay_us(uint32_t us);
 
+// Syncs Grbl's gcode and planner position variables with the system position.
+void sys_sync_current_position();
+
 #endif

planner.c

@@ -482,12 +482,6 @@ void plan_set_current_position(int32_t x, int32_t y, int32_t z)
   pl.position[Z_AXIS] = z;
 }
 
-// Clear planner position vector. Called by homing routine.
-void plan_clear_position()
-{
-  clear_vector(pl.position);
-}
-
 // Re-initialize buffer plan with a partially completed block, assumed to exist at the buffer tail.
 // Called after a steppers have come to a complete stop for a feed hold and the cycle is stopped.
 void plan_cycle_reinitialize(int32_t step_events_remaining) 

planner.h

@@ -70,9 +70,6 @@ block_t *plan_get_current_block();
 // Reset the planner position vector (in steps)
 void plan_set_current_position(int32_t x, int32_t y, int32_t z);
 
-// Clear the planner position vector
-void plan_clear_position();
-
 // Reinitialize plan with a partially completed block
 void plan_cycle_reinitialize(int32_t step_events_remaining);
 

protocol.c

@@ -183,25 +183,33 @@ uint8_t protocol_execute_line(char *line)
       // block buffer without having the planner plan them. It would need to manage de/ac-celerations 
       // on its own carefully. This approach could be effective and possibly size/memory efficient.
       case 'S' : // Switch modes
+        if ( line[++char_counter] != 0 ) { return(STATUS_UNSUPPORTED_STATEMENT); }
         // Set helper_var as switch bitmask or clearing flag
         switch (line[++char_counter]) {
-          case 0 : helper_var = 0;  break;
+          case '0' : 
-          case '0' : helper_var = BITFLAG_CHECK_GCODE; break;
+            helper_var = BITFLAG_CHECK_GCODE; 
+            // Sync position vectors if check mode is being disabled. May be different after checking.
+            if (bit_istrue(gc.switches,helper_var)) { sys_sync_current_position(); }
+            break;
           case '1' : helper_var = BITFLAG_DRY_RUN; break;
           case '2' : helper_var = BITFLAG_BLOCK_DELETE; break;
           case '3' : helper_var = BITFLAG_SINGLE_BLOCK; break;
           case '4' : helper_var = BITFLAG_OPT_STOP; break;
           default : return(STATUS_INVALID_STATEMENT);
         }
-        if (helper_var) {
-          if ( line[++char_counter] != 0 ) { return(STATUS_UNSUPPORTED_STATEMENT); }
         gc.switches ^= helper_var;
         if (bit_istrue(gc.switches,helper_var)) { report_feedback_message(MESSAGE_SWITCH_ON); }
         else { report_feedback_message(MESSAGE_SWITCH_OFF); }
-        } else {
+        break;
-          gc.switches = helper_var; // Clear all switches
+      case 'P' : // Purge system
-          report_feedback_message(MESSAGE_SWITCHES_CLEARED);
+        if ( line[++char_counter] != 0 ) { return(STATUS_UNSUPPORTED_STATEMENT); }
+        if (sys.state == STATE_CYCLE) { return(STATUS_PURGE_CYCLE); } // Also prevents position error
+        plan_reset_buffer();
+        if (sys.state == STATE_LOST) { 
+          report_feedback_message(MESSAGE_PURGE_AXES_LOCK); 
+          sys_sync_current_position(); // Any motion commands during a lock can unsync position vectors.
         }
+        sys.state = STATE_IDLE;
         break;
       case 'N' : // Startup lines. 
         if ( line[++char_counter] == 0 ) { // Print startup lines

readme.textile

@@ -21,13 +21,13 @@ Grbl includes full acceleration management with look ahead. That means the contr
   - Re-factored g-code parser with robust error-checking.
   - 6 work coordinate systems (G54-G59), offsets(G92), and machine coordinate system support. Work coordinate systems are stored in EEPROM and persistent.
   - G10 L2 and L20 work coordinate settings support. L2 sets one or more axes values. L20 sets the current machine position to the specified work origin.
-  - Program stop(M0,M1,M2,M30) initial support.
+  - G28.1 and G30.1 set home position support. These set the internal EEPROM parameter values to the current machine position. (G28 and G30 no longer perform homing cycle, '$H' does. They move to these stored positions.)
+  - Program stop(M0,M1,M2,M30) support.
   - Coolant control(M7*,M8,M9) support. (M7 is a compile-time option).
   - System reset re-initializes grbl without resetting the Arduino and retains machine/home position and work coordinates.
   - Settings overhauled and dozens of new settings and internal commands are now available, when most were compile-time only.
   - New startup line setting. Allows users to store a custom g-code block into Grbl's startup routine. Executes immediately upon startup or reset. May be used to set g-code defaults like G20.
   - Misc bug fixes and removed deprecated acceleration enabled code.  
-  - Planned features: Axis acceleration and max speed individual settings, full-featured status reporting.
   - Advanced compile-time options: XON/XOFF flow control (limited support), direction and step pulse time delay, and up to 5 startup lines.
   
 

report.c

@@ -73,9 +73,11 @@ void report_status_message(uint8_t status_code)
       case STATUS_SETTING_READ_FAIL:
       printPgmString(PSTR("Failed to read EEPROM settings. Using defaults")); break;
       case STATUS_HOMING_ERROR:
-      printPgmString(PSTR("Grbl must be idle to home")); break;
+      printPgmString(PSTR("Must be idle to home")); break;
       case STATUS_ABORT_CYCLE:
-      printPgmString(PSTR("Abort during cycle")); break;
+      printPgmString(PSTR("Abort during cycle. Position may be lost")); break;
+      case STATUS_PURGE_CYCLE:
+      printPgmString(PSTR("Can't purge buffer during cycle")); break;
     }
     printPgmString(PSTR("\r\n"));
   }
@@ -95,15 +97,15 @@ void report_feedback_message(int8_t message_code)
     case MESSAGE_SYSTEM_ALARM:
     printPgmString(PSTR("ALARM: Check and reset Grbl")); break;
     case MESSAGE_POSITION_LOST:
-    printPgmString(PSTR("Position unknown. '$H' to home")); break;
+    printPgmString(PSTR("'$H' to home and enable axes")); break;
     case MESSAGE_HOMING_ENABLE:
     printPgmString(PSTR("WARNING: All limit switches must be installed before homing")); break;
     case MESSAGE_SWITCH_ON:
     printPgmString(PSTR("Switch enabled")); break;
     case MESSAGE_SWITCH_OFF:
     printPgmString(PSTR("Switch disabled")); break;    
-    case MESSAGE_SWITCHES_CLEARED:
+    case MESSAGE_PURGE_AXES_LOCK:
-    printPgmString(PSTR("Switches cleared")); break;
+    printPgmString(PSTR("WARNING: Motion lock disabled. Position unknown.")); break;
   }
   printPgmString(PSTR("]\r\n"));
 }
@@ -124,13 +126,13 @@ void report_grbl_help() {
                       "$N (print startup blocks)\r\n"
                       "$x=value (store Grbl setting)\r\n"
                       "$Nx=line (store startup block)\r\n"
-                      "$H (perform homing cycle)\r\n"
-                      "$S (clear all switches)\r\n"
                       "$S0 (toggle check gcode)\r\n"
                       "$S1 (toggle dry run)\r\n"
                       "$S2 (toggle block delete)\r\n"
                       "$S3 (toggle single block)\r\n"
                       "$S4 (toggle optional stop)\r\n"
+                      "$P (purge buffer and locks)\r\n"
+                      "$H (perform homing cycle)\r\n"
                       "~ (cycle start)\r\n"
                       "! (feed hold)\r\n"
                       "? (current position)\r\n"

report.h

@@ -36,6 +36,7 @@
 #define STATUS_SETTING_READ_FAIL 11
 #define STATUS_HOMING_ERROR 12
 #define STATUS_ABORT_CYCLE 13
+#define STATUS_PURGE_CYCLE 14
 
 // Define Grbl feedback message codes. Less than zero to distinguish message from error.
 #define MESSAGE_SYSTEM_ALARM -1
@@ -43,7 +44,7 @@
 #define MESSAGE_HOMING_ENABLE -3
 #define MESSAGE_SWITCH_ON -4
 #define MESSAGE_SWITCH_OFF -5
-#define MESSAGE_SWITCHES_CLEARED -6
+#define MESSAGE_PURGE_AXES_LOCK -6
 
 // Prints system status messages.
 void report_status_message(uint8_t status_code);