diff --git a/grbl/gcode.c b/grbl/gcode.c
new file mode 100644
index 0000000..57e31e5
--- /dev/null
+++ b/grbl/gcode.c
@@ -0,0 +1,1159 @@
+/*
+  gcode.c - rs274/ngc parser.
+  Part of Grbl
+
+  Copyright (c) 2011-2016 Sungeun K. Jeon for Gnea Research LLC
+  Copyright (c) 2009-2011 Simen Svale Skogsrud
+
+  Grbl is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  Grbl is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with Grbl.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "grbl.h"
+
+// NOTE: Max line number is defined by the g-code standard to be 99999. It seems to be an
+// arbitrary value, and some GUIs may require more. So we increased it based on a max safe
+// value when converting a float (7.2 digit precision)s to an integer.
+#define MAX_LINE_NUMBER 10000000
+#define MAX_TOOL_NUMBER 255 // Limited by max unsigned 8-bit value
+
+#define AXIS_COMMAND_NONE 0
+#define AXIS_COMMAND_NON_MODAL 1
+#define AXIS_COMMAND_MOTION_MODE 2
+#define AXIS_COMMAND_TOOL_LENGTH_OFFSET 3 // *Undefined but required
+
+// Declare gc extern struct
+parser_state_t gc_state;
+parser_block_t gc_block;
+
+#define FAIL(status) return(status);
+
+
+void gc_init()
+{
+  memset(&gc_state, 0, sizeof(parser_state_t));
+
+  // Load default G54 coordinate system.
+  if (!(settings_read_coord_data(gc_state.modal.coord_select,gc_state.coord_system))) {
+    report_status_message(STATUS_SETTING_READ_FAIL);
+  }
+}
+
+
+// Sets g-code parser position in mm. Input in steps. Called by the system abort and hard
+// limit pull-off routines.
+void gc_sync_position()
+{
+  system_convert_array_steps_to_mpos(gc_state.position,sys_position);
+}
+
+
+// Executes one line of 0-terminated G-Code. The line is assumed to contain only uppercase
+// characters and signed floating point values (no whitespace). Comments and block delete
+// characters have been removed. In this function, all units and positions are converted and
+// exported to grbl's internal functions in terms of (mm, mm/min) and absolute machine
+// coordinates, respectively.
+uint8_t gc_execute_line(char *line)
+{
+  /* -------------------------------------------------------------------------------------
+     STEP 1: Initialize parser block struct and copy current g-code state modes. The parser
+     updates these modes and commands as the block line is parser and will only be used and
+     executed after successful error-checking. The parser block struct also contains a block
+     values struct, word tracking variables, and a non-modal commands tracker for the new
+     block. This struct contains all of the necessary information to execute the block. */
+
+  memset(&gc_block, 0, sizeof(parser_block_t)); // Initialize the parser block struct.
+  memcpy(&gc_block.modal,&gc_state.modal,sizeof(gc_modal_t)); // Copy current modes
+
+  uint8_t axis_command = AXIS_COMMAND_NONE;
+  uint8_t axis_0, axis_1, axis_linear;
+  uint8_t coord_select = 0; // Tracks G10 P coordinate selection for execution
+
+  // Initialize bitflag tracking variables for axis indices compatible operations.
+  uint8_t axis_words = 0; // XYZ tracking
+  uint8_t ijk_words = 0; // IJK tracking
+
+  // Initialize command and value words and parser flags variables.
+  uint16_t command_words = 0; // Tracks G and M command words. Also used for modal group violations.
+  uint16_t value_words = 0; // Tracks value words.
+  uint8_t gc_parser_flags = GC_PARSER_NONE;
+
+  // Determine if the line is a jogging motion or a normal g-code block.
+  if (line[0] == '$') { // NOTE: `$J=` already parsed when passed to this function.
+    // Set G1 and G94 enforced modes to ensure accurate error checks.
+    gc_parser_flags |= GC_PARSER_JOG_MOTION;
+    gc_block.modal.motion = MOTION_MODE_LINEAR;
+    gc_block.modal.feed_rate = FEED_RATE_MODE_UNITS_PER_MIN;
+    #ifdef USE_LINE_NUMBERS
+      gc_block.values.n = JOG_LINE_NUMBER; // Initialize default line number reported during jog.
+    #endif
+  }
+
+  /* -------------------------------------------------------------------------------------
+     STEP 2: Import all g-code words in the block line. A g-code word is a letter followed by
+     a number, which can either be a 'G'/'M' command or sets/assigns a command value. Also,
+     perform initial error-checks for command word modal group violations, for any repeated
+     words, and for negative values set for the value words F, N, P, T, and S. */
+
+  uint8_t word_bit; // Bit-value for assigning tracking variables
+  uint8_t char_counter;
+  char letter;
+  float value;
+  uint8_t int_value = 0;
+  uint16_t mantissa = 0;
+  if (gc_parser_flags & GC_PARSER_JOG_MOTION) { char_counter = 3; } // Start parsing after `$J=`
+  else { char_counter = 0; }
+
+  while (line[char_counter] != 0) { // Loop until no more g-code words in line.
+
+    // Import the next g-code word, expecting a letter followed by a value. Otherwise, error out.
+    letter = line[char_counter];
+    if((letter < 'A') || (letter > 'Z')) { FAIL(STATUS_EXPECTED_COMMAND_LETTER); } // [Expected word letter]
+    char_counter++;
+    if (!read_float(line, &char_counter, &value)) { FAIL(STATUS_BAD_NUMBER_FORMAT); } // [Expected word value]
+
+    // Convert values to smaller uint8 significand and mantissa values for parsing this word.
+    // NOTE: Mantissa is multiplied by 100 to catch non-integer command values. This is more
+    // accurate than the NIST gcode requirement of x10 when used for commands, but not quite
+    // accurate enough for value words that require integers to within 0.0001. This should be
+    // a good enough comprimise and catch most all non-integer errors. To make it compliant,
+    // we would simply need to change the mantissa to int16, but this add compiled flash space.
+    // Maybe update this later.
+    int_value = trunc(value);
+    mantissa =  round(100*(value - int_value)); // Compute mantissa for Gxx.x commands.
+    // NOTE: Rounding must be used to catch small floating point errors.
+
+    // Check if the g-code word is supported or errors due to modal group violations or has
+    // been repeated in the g-code block. If ok, update the command or record its value.
+    switch(letter) {
+
+      /* 'G' and 'M' Command Words: Parse commands and check for modal group violations.
+         NOTE: Modal group numbers are defined in Table 4 of NIST RS274-NGC v3, pg.20 */
+
+      case 'G':
+        // Determine 'G' command and its modal group
+        switch(int_value) {
+          case 10: case 28: case 30: case 92:
+            // Check for G10/28/30/92 being called with G0/1/2/3/38 on same block.
+            // * G43.1 is also an axis command but is not explicitly defined this way.
+            if (mantissa == 0) { // Ignore G28.1, G30.1, and G92.1
+              if (axis_command) { FAIL(STATUS_GCODE_AXIS_COMMAND_CONFLICT); } // [Axis word/command conflict]
+              axis_command = AXIS_COMMAND_NON_MODAL;
+            }
+            // No break. Continues to next line.
+          case 4: case 53:
+            word_bit = MODAL_GROUP_G0;
+            gc_block.non_modal_command = int_value;
+            if ((int_value == 28) || (int_value == 30) || (int_value == 92)) {
+              if (!((mantissa == 0) || (mantissa == 10))) { FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND); }
+              gc_block.non_modal_command += mantissa;
+              mantissa = 0; // Set to zero to indicate valid non-integer G command.
+            }                
+            break;
+          case 0: case 1: case 2: case 3: case 38:
+            // Check for G0/1/2/3/38 being called with G10/28/30/92 on same block.
+            // * G43.1 is also an axis command but is not explicitly defined this way.
+            if (axis_command) { FAIL(STATUS_GCODE_AXIS_COMMAND_CONFLICT); } // [Axis word/command conflict]
+            axis_command = AXIS_COMMAND_MOTION_MODE;
+            // No break. Continues to next line.
+          case 80:
+            word_bit = MODAL_GROUP_G1;
+            gc_block.modal.motion = int_value;
+            if (int_value == 38){
+              if (!((mantissa == 20) || (mantissa == 30) || (mantissa == 40) || (mantissa == 50))) {
+                FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND); // [Unsupported G38.x command]
+              }
+              gc_block.modal.motion += (mantissa/10)+100;
+              mantissa = 0; // Set to zero to indicate valid non-integer G command.
+            }  
+            break;
+          case 17: case 18: case 19:
+            word_bit = MODAL_GROUP_G2;
+            gc_block.modal.plane_select = int_value - 17;
+            break;
+          case 90: case 91:
+            if (mantissa == 0) {
+              word_bit = MODAL_GROUP_G3;
+              gc_block.modal.distance = int_value - 90;
+            } else {
+              word_bit = MODAL_GROUP_G4;
+              if ((mantissa != 10) || (int_value == 90)) { FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND); } // [G90.1 not supported]
+              mantissa = 0; // Set to zero to indicate valid non-integer G command.
+              // Otherwise, arc IJK incremental mode is default. G91.1 does nothing.
+            }
+            break;
+          case 93: case 94:
+            word_bit = MODAL_GROUP_G5;
+            gc_block.modal.feed_rate = 94 - int_value;
+            break;
+          case 20: case 21:
+            word_bit = MODAL_GROUP_G6;
+            gc_block.modal.units = 21 - int_value;
+            break;
+          case 40:
+            word_bit = MODAL_GROUP_G7;
+            // NOTE: Not required since cutter radius compensation is always disabled. Only here
+            // to support G40 commands that often appear in g-code program headers to setup defaults.
+            // gc_block.modal.cutter_comp = CUTTER_COMP_DISABLE; // G40
+            break;
+          case 43: case 49:
+            word_bit = MODAL_GROUP_G8;
+            // NOTE: The NIST g-code standard vaguely states that when a tool length offset is changed,
+            // there cannot be any axis motion or coordinate offsets updated. Meaning G43, G43.1, and G49
+            // all are explicit axis commands, regardless if they require axis words or not.
+            if (axis_command) { FAIL(STATUS_GCODE_AXIS_COMMAND_CONFLICT); } // [Axis word/command conflict] }
+            axis_command = AXIS_COMMAND_TOOL_LENGTH_OFFSET;
+            if (int_value == 49) { // G49
+              gc_block.modal.tool_length = TOOL_LENGTH_OFFSET_CANCEL;
+            } else if (mantissa == 10) { // G43.1
+              gc_block.modal.tool_length = TOOL_LENGTH_OFFSET_ENABLE_DYNAMIC;
+            } else { FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND); } // [Unsupported G43.x command]
+            mantissa = 0; // Set to zero to indicate valid non-integer G command.
+            break;
+          case 54: case 55: case 56: case 57: case 58: case 59:
+            // NOTE: G59.x are not supported. (But their int_values would be 60, 61, and 62.)
+            word_bit = MODAL_GROUP_G12;
+            gc_block.modal.coord_select = int_value - 54; // Shift to array indexing.
+            break;
+          case 61:
+            word_bit = MODAL_GROUP_G13;
+            if (mantissa != 0) { FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND); } // [G61.1 not supported]
+            // gc_block.modal.control = CONTROL_MODE_EXACT_PATH; // G61
+            break;
+          default: FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND); // [Unsupported G command]
+        }
+        if (mantissa > 0) { FAIL(STATUS_GCODE_COMMAND_VALUE_NOT_INTEGER); } // [Unsupported or invalid Gxx.x command]
+        // Check for more than one command per modal group violations in the current block
+        // NOTE: Variable 'word_bit' is always assigned, if the command is valid.
+        if ( bit_istrue(command_words,bit(word_bit)) ) { FAIL(STATUS_GCODE_MODAL_GROUP_VIOLATION); }
+        command_words |= bit(word_bit);
+        break;
+
+      case 'M':
+
+        // Determine 'M' command and its modal group
+        if (mantissa > 0) { FAIL(STATUS_GCODE_COMMAND_VALUE_NOT_INTEGER); } // [No Mxx.x commands]
+        switch(int_value) {
+          case 0: case 1: case 2: case 30:
+            word_bit = MODAL_GROUP_M4;
+            switch(int_value) {
+              case 0: gc_block.modal.program_flow = PROGRAM_FLOW_PAUSED; break; // Program pause
+              case 1: break; // Optional stop not supported. Ignore.
+              default: gc_block.modal.program_flow = int_value; // Program end and reset
+            }
+            break;
+          case 3: case 4: case 5:
+            word_bit = MODAL_GROUP_M7;
+            switch(int_value) {
+              case 3: gc_block.modal.spindle = SPINDLE_ENABLE_CW; break;
+              case 4: gc_block.modal.spindle = SPINDLE_ENABLE_CCW; break;
+              case 5: gc_block.modal.spindle = SPINDLE_DISABLE; break;
+            }
+            break;
+          #ifdef ENABLE_M7
+            case 7: case 8: case 9:
+          #else
+            case 8: case 9:
+          #endif
+            word_bit = MODAL_GROUP_M8;
+            switch(int_value) {
+              #ifdef ENABLE_M7
+                case 7: gc_block.modal.coolant |= COOLANT_MIST_ENABLE; break;
+              #endif
+              case 8: gc_block.modal.coolant |= COOLANT_FLOOD_ENABLE; break;
+              case 9: gc_block.modal.coolant = COOLANT_DISABLE; break; // M9 disables both M7 and M8.
+            }
+            break;
+          #ifdef ENABLE_PARKING_OVERRIDE_CONTROL
+            case 56:
+              word_bit = MODAL_GROUP_M9;
+              gc_block.modal.override = OVERRIDE_PARKING_MOTION;
+              break;
+          #endif
+          default: FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND); // [Unsupported M command]
+        }
+
+        // Check for more than one command per modal group violations in the current block
+        // NOTE: Variable 'word_bit' is always assigned, if the command is valid.
+        if ( bit_istrue(command_words,bit(word_bit)) ) { FAIL(STATUS_GCODE_MODAL_GROUP_VIOLATION); }
+        command_words |= bit(word_bit);
+        break;
+
+      // NOTE: All remaining letters assign values.
+      default:
+
+        /* Non-Command Words: This initial parsing phase only checks for repeats of the remaining
+           legal g-code words and stores their value. Error-checking is performed later since some
+           words (I,J,K,L,P,R) have multiple connotations and/or depend on the issued commands. */
+        switch(letter){
+          // case 'A': // Not supported
+          // case 'B': // Not supported
+          // case 'C': // Not supported
+          // case 'D': // Not supported
+          case 'F': word_bit = WORD_F; gc_block.values.f = value; break;
+          // case 'H': // Not supported
+          case 'I': word_bit = WORD_I; gc_block.values.ijk[X_AXIS] = value; ijk_words |= (1<<X_AXIS); break;
+          case 'J': word_bit = WORD_J; gc_block.values.ijk[Y_AXIS] = value; ijk_words |= (1<<Y_AXIS); break;
+          case 'K': word_bit = WORD_K; gc_block.values.ijk[Z_AXIS] = value; ijk_words |= (1<<Z_AXIS); break;
+          case 'L': word_bit = WORD_L; gc_block.values.l = int_value; break;
+          case 'N': word_bit = WORD_N; gc_block.values.n = trunc(value); break;
+          case 'P': word_bit = WORD_P; gc_block.values.p = value; break;
+          // NOTE: For certain commands, P value must be an integer, but none of these commands are supported.
+          // case 'Q': // Not supported
+          case 'R': word_bit = WORD_R; gc_block.values.r = value; break;
+          case 'S': word_bit = WORD_S; gc_block.values.s = value; break;
+          case 'T': word_bit = WORD_T; 
+					  if (value > MAX_TOOL_NUMBER) { FAIL(STATUS_GCODE_MAX_VALUE_EXCEEDED); }
+            gc_block.values.t = int_value;
+						break;
+          case 'X': word_bit = WORD_X; gc_block.values.xyz[X_AXIS] = value; axis_words |= (1<<X_AXIS); break;
+          case 'Y': word_bit = WORD_Y; gc_block.values.xyz[Y_AXIS] = value; axis_words |= (1<<Y_AXIS); break;
+          case 'Z': word_bit = WORD_Z; gc_block.values.xyz[Z_AXIS] = value; axis_words |= (1<<Z_AXIS); break;
+          default: FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND);
+        }
+
+        // NOTE: Variable 'word_bit' is always assigned, if the non-command letter is valid.
+        if (bit_istrue(value_words,bit(word_bit))) { FAIL(STATUS_GCODE_WORD_REPEATED); } // [Word repeated]
+        // Check for invalid negative values for words F, N, P, T, and S.
+        // NOTE: Negative value check is done here simply for code-efficiency.
+        if ( bit(word_bit) & (bit(WORD_F)|bit(WORD_N)|bit(WORD_P)|bit(WORD_T)|bit(WORD_S)) ) {
+          if (value < 0.0) { FAIL(STATUS_NEGATIVE_VALUE); } // [Word value cannot be negative]
+        }
+        value_words |= bit(word_bit); // Flag to indicate parameter assigned.
+
+    }
+  }
+  // Parsing complete!
+
+
+  /* -------------------------------------------------------------------------------------
+     STEP 3: Error-check all commands and values passed in this block. This step ensures all of
+     the commands are valid for execution and follows the NIST standard as closely as possible.
+     If an error is found, all commands and values in this block are dumped and will not update
+     the active system g-code modes. If the block is ok, the active system g-code modes will be
+     updated based on the commands of this block, and signal for it to be executed.
+
+     Also, we have to pre-convert all of the values passed based on the modes set by the parsed
+     block. There are a number of error-checks that require target information that can only be
+     accurately calculated if we convert these values in conjunction with the error-checking.
+     This relegates the next execution step as only updating the system g-code modes and
+     performing the programmed actions in order. The execution step should not require any
+     conversion calculations and would only require minimal checks necessary to execute.
+  */
+
+  /* NOTE: At this point, the g-code block has been parsed and the block line can be freed.
+     NOTE: It's also possible, at some future point, to break up STEP 2, to allow piece-wise
+     parsing of the block on a per-word basis, rather than the entire block. This could remove
+     the need for maintaining a large string variable for the entire block and free up some memory.
+     To do this, this would simply need to retain all of the data in STEP 1, such as the new block
+     data struct, the modal group and value bitflag tracking variables, and axis array indices
+     compatible variables. This data contains all of the information necessary to error-check the
+     new g-code block when the EOL character is received. However, this would break Grbl's startup
+     lines in how it currently works and would require some refactoring to make it compatible.
+  */
+
+  // [0. Non-specific/common error-checks and miscellaneous setup]:
+
+  // Determine implicit axis command conditions. Axis words have been passed, but no explicit axis
+  // command has been sent. If so, set axis command to current motion mode.
+  if (axis_words) {
+    if (!axis_command) { axis_command = AXIS_COMMAND_MOTION_MODE; } // Assign implicit motion-mode
+  }
+
+  // Check for valid line number N value.
+  if (bit_istrue(value_words,bit(WORD_N))) {
+    // Line number value cannot be less than zero (done) or greater than max line number.
+    if (gc_block.values.n > MAX_LINE_NUMBER) { FAIL(STATUS_GCODE_INVALID_LINE_NUMBER); } // [Exceeds max line number]
+  }
+  // bit_false(value_words,bit(WORD_N)); // NOTE: Single-meaning value word. Set at end of error-checking.
+
+  // Track for unused words at the end of error-checking.
+  // NOTE: Single-meaning value words are removed all at once at the end of error-checking, because
+  // they are always used when present. This was done to save a few bytes of flash. For clarity, the
+  // single-meaning value words may be removed as they are used. Also, axis words are treated in the
+  // same way. If there is an explicit/implicit axis command, XYZ words are always used and are
+  // are removed at the end of error-checking.
+
+  // [1. Comments ]: MSG's NOT SUPPORTED. Comment handling performed by protocol.
+
+  // [2. Set feed rate mode ]: G93 F word missing with G1,G2/3 active, implicitly or explicitly. Feed rate
+  //   is not defined after switching to G94 from G93.
+  // NOTE: For jogging, ignore prior feed rate mode. Enforce G94 and check for required F word.
+  if (gc_parser_flags & GC_PARSER_JOG_MOTION) {
+    if (bit_isfalse(value_words,bit(WORD_F))) { FAIL(STATUS_GCODE_UNDEFINED_FEED_RATE); }
+    if (gc_block.modal.units == UNITS_MODE_INCHES) { gc_block.values.f *= MM_PER_INCH; }
+  } else {
+    if (gc_block.modal.feed_rate == FEED_RATE_MODE_INVERSE_TIME) { // = G93
+      // NOTE: G38 can also operate in inverse time, but is undefined as an error. Missing F word check added here.
+      if (axis_command == AXIS_COMMAND_MOTION_MODE) {
+        if ((gc_block.modal.motion != MOTION_MODE_NONE) && (gc_block.modal.motion != MOTION_MODE_SEEK)) {
+          if (bit_isfalse(value_words,bit(WORD_F))) { FAIL(STATUS_GCODE_UNDEFINED_FEED_RATE); } // [F word missing]
+        }
+      }
+      // NOTE: It seems redundant to check for an F word to be passed after switching from G94 to G93. We would
+      // accomplish the exact same thing if the feed rate value is always reset to zero and undefined after each
+      // inverse time block, since the commands that use this value already perform undefined checks. This would
+      // also allow other commands, following this switch, to execute and not error out needlessly. This code is
+      // combined with the above feed rate mode and the below set feed rate error-checking.
+
+      // [3. Set feed rate ]: F is negative (done.)
+      // - In inverse time mode: Always implicitly zero the feed rate value before and after block completion.
+      // NOTE: If in G93 mode or switched into it from G94, just keep F value as initialized zero or passed F word
+      // value in the block. If no F word is passed with a motion command that requires a feed rate, this will error
+      // out in the motion modes error-checking. However, if no F word is passed with NO motion command that requires
+      // a feed rate, we simply move on and the state feed rate value gets updated to zero and remains undefined.
+    } else { // = G94
+      // - In units per mm mode: If F word passed, ensure value is in mm/min, otherwise push last state value.
+      if (gc_state.modal.feed_rate == FEED_RATE_MODE_UNITS_PER_MIN) { // Last state is also G94
+        if (bit_istrue(value_words,bit(WORD_F))) {
+          if (gc_block.modal.units == UNITS_MODE_INCHES) { gc_block.values.f *= MM_PER_INCH; }
+        } else {
+          gc_block.values.f = gc_state.feed_rate; // Push last state feed rate
+        }
+      } // Else, switching to G94 from G93, so don't push last state feed rate. Its undefined or the passed F word value.
+    }
+  }
+  // bit_false(value_words,bit(WORD_F)); // NOTE: Single-meaning value word. Set at end of error-checking.
+
+  // [4. Set spindle speed ]: S is negative (done.)
+  if (bit_isfalse(value_words,bit(WORD_S))) { gc_block.values.s = gc_state.spindle_speed; }
+  // bit_false(value_words,bit(WORD_S)); // NOTE: Single-meaning value word. Set at end of error-checking.
+
+  // [5. Select tool ]: NOT SUPPORTED. Only tracks value. T is negative (done.) Not an integer. Greater than max tool value.
+  // bit_false(value_words,bit(WORD_T)); // NOTE: Single-meaning value word. Set at end of error-checking.
+
+  // [6. Change tool ]: N/A
+  // [7. Spindle control ]: N/A
+  // [8. Coolant control ]: N/A
+  // [9. Override control ]: Not supported except for a Grbl-only parking motion override control.
+  #ifdef ENABLE_PARKING_OVERRIDE_CONTROL
+    if (bit_istrue(command_words,bit(MODAL_GROUP_M9))) { // Already set as enabled in parser.
+      if (bit_istrue(value_words,bit(WORD_P))) {
+        if (gc_block.values.p == 0.0) { gc_block.modal.override = OVERRIDE_DISABLED; }
+        bit_false(value_words,bit(WORD_P));
+      }
+    }
+  #endif
+
+  // [10. Dwell ]: P value missing. P is negative (done.) NOTE: See below.
+  if (gc_block.non_modal_command == NON_MODAL_DWELL) {
+    if (bit_isfalse(value_words,bit(WORD_P))) { FAIL(STATUS_GCODE_VALUE_WORD_MISSING); } // [P word missing]
+    bit_false(value_words,bit(WORD_P));
+  }
+
+  // [11. Set active plane ]: N/A
+  switch (gc_block.modal.plane_select) {
+    case PLANE_SELECT_XY:
+      axis_0 = X_AXIS;
+      axis_1 = Y_AXIS;
+      axis_linear = Z_AXIS;
+      break;
+    case PLANE_SELECT_ZX:
+      axis_0 = Z_AXIS;
+      axis_1 = X_AXIS;
+      axis_linear = Y_AXIS;
+      break;
+    default: // case PLANE_SELECT_YZ:
+      axis_0 = Y_AXIS;
+      axis_1 = Z_AXIS;
+      axis_linear = X_AXIS;
+  }
+
+  // [12. Set length units ]: N/A
+  // Pre-convert XYZ coordinate values to millimeters, if applicable.
+  uint8_t idx;
+  if (gc_block.modal.units == UNITS_MODE_INCHES) {
+    for (idx=0; idx<N_AXIS; idx++) { // Axes indices are consistent, so loop may be used.
+      if (bit_istrue(axis_words,bit(idx)) ) {
+        gc_block.values.xyz[idx] *= MM_PER_INCH;
+      }
+    }
+  }
+
+  // [13. Cutter radius compensation ]: G41/42 NOT SUPPORTED. Error, if enabled while G53 is active.
+  // [G40 Errors]: G2/3 arc is programmed after a G40. The linear move after disabling is less than tool diameter.
+  //   NOTE: Since cutter radius compensation is never enabled, these G40 errors don't apply. Grbl supports G40
+  //   only for the purpose to not error when G40 is sent with a g-code program header to setup the default modes.
+
+  // [14. Cutter length compensation ]: G43 NOT SUPPORTED, but G43.1 and G49 are.
+  // [G43.1 Errors]: Motion command in same line.
+  //   NOTE: Although not explicitly stated so, G43.1 should be applied to only one valid
+  //   axis that is configured (in config.h). There should be an error if the configured axis
+  //   is absent or if any of the other axis words are present.
+  if (axis_command == AXIS_COMMAND_TOOL_LENGTH_OFFSET ) { // Indicates called in block.
+    if (gc_block.modal.tool_length == TOOL_LENGTH_OFFSET_ENABLE_DYNAMIC) {
+      if (axis_words ^ (1<<TOOL_LENGTH_OFFSET_AXIS)) { FAIL(STATUS_GCODE_G43_DYNAMIC_AXIS_ERROR); }
+    }
+  }
+
+  // [15. Coordinate system selection ]: *N/A. Error, if cutter radius comp is active.
+  // TODO: An EEPROM read of the coordinate data may require a buffer sync when the cycle
+  // is active. The read pauses the processor temporarily and may cause a rare crash. For
+  // future versions on processors with enough memory, all coordinate data should be stored
+  // in memory and written to EEPROM only when there is not a cycle active.
+  float block_coord_system[N_AXIS];
+  memcpy(block_coord_system,gc_state.coord_system,sizeof(gc_state.coord_system));
+  if ( bit_istrue(command_words,bit(MODAL_GROUP_G12)) ) { // Check if called in block
+    if (gc_block.modal.coord_select > N_COORDINATE_SYSTEM) { FAIL(STATUS_GCODE_UNSUPPORTED_COORD_SYS); } // [Greater than N sys]
+    if (gc_state.modal.coord_select != gc_block.modal.coord_select) {
+      if (!(settings_read_coord_data(gc_block.modal.coord_select,block_coord_system))) { FAIL(STATUS_SETTING_READ_FAIL); }
+    }
+  }
+
+  // [16. Set path control mode ]: N/A. Only G61. G61.1 and G64 NOT SUPPORTED.
+  // [17. Set distance mode ]: N/A. Only G91.1. G90.1 NOT SUPPORTED.
+  // [18. Set retract mode ]: NOT SUPPORTED.
+
+  // [19. Remaining non-modal actions ]: Check go to predefined position, set G10, or set axis offsets.
+  // NOTE: We need to separate the non-modal commands that are axis word-using (G10/G28/G30/G92), as these
+  // commands all treat axis words differently. G10 as absolute offsets or computes current position as
+  // the axis value, G92 similarly to G10 L20, and G28/30 as an intermediate target position that observes
+  // all the current coordinate system and G92 offsets.
+  switch (gc_block.non_modal_command) {
+    case NON_MODAL_SET_COORDINATE_DATA:
+      // [G10 Errors]: L missing and is not 2 or 20. P word missing. (Negative P value done.)
+      // [G10 L2 Errors]: R word NOT SUPPORTED. P value not 0 to nCoordSys(max 9). Axis words missing.
+      // [G10 L20 Errors]: P must be 0 to nCoordSys(max 9). Axis words missing.
+      if (!axis_words) { FAIL(STATUS_GCODE_NO_AXIS_WORDS) }; // [No axis words]
+      if (bit_isfalse(value_words,((1<<WORD_P)|(1<<WORD_L)))) { FAIL(STATUS_GCODE_VALUE_WORD_MISSING); } // [P/L word missing]
+      coord_select = trunc(gc_block.values.p); // Convert p value to int.
+      if (coord_select > N_COORDINATE_SYSTEM) { FAIL(STATUS_GCODE_UNSUPPORTED_COORD_SYS); } // [Greater than N sys]
+      if (gc_block.values.l != 20) {
+        if (gc_block.values.l == 2) {
+          if (bit_istrue(value_words,bit(WORD_R))) { FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND); } // [G10 L2 R not supported]
+        } else { FAIL(STATUS_GCODE_UNSUPPORTED_COMMAND); } // [Unsupported L]
+      }
+      bit_false(value_words,(bit(WORD_L)|bit(WORD_P)));
+
+      // Determine coordinate system to change and try to load from EEPROM.
+      if (coord_select > 0) { coord_select--; } // Adjust P1-P6 index to EEPROM coordinate data indexing.
+      else { coord_select = gc_block.modal.coord_select; } // Index P0 as the active coordinate system
+      
+      // NOTE: Store parameter data in IJK values. By rule, they are not in use with this command.
+      if (!settings_read_coord_data(coord_select,gc_block.values.ijk)) { FAIL(STATUS_SETTING_READ_FAIL); } // [EEPROM read fail]
+
+      // Pre-calculate the coordinate data changes.
+      for (idx=0; idx<N_AXIS; idx++) { // Axes indices are consistent, so loop may be used.
+        // Update axes defined only in block. Always in machine coordinates. Can change non-active system.
+        if (bit_istrue(axis_words,bit(idx)) ) {
+          if (gc_block.values.l == 20) {
+            // L20: Update coordinate system axis at current position (with modifiers) with programmed value
+            // WPos = MPos - WCS - G92 - TLO  ->  WCS = MPos - G92 - TLO - WPos
+            gc_block.values.ijk[idx] = gc_state.position[idx]-gc_state.coord_offset[idx]-gc_block.values.xyz[idx];
+            if (idx == TOOL_LENGTH_OFFSET_AXIS) { gc_block.values.ijk[idx] -= gc_state.tool_length_offset; }
+          } else {
+            // L2: Update coordinate system axis to programmed value.
+            gc_block.values.ijk[idx] = gc_block.values.xyz[idx];
+          }
+        } // Else, keep current stored value.
+      }
+      break;
+    case NON_MODAL_SET_COORDINATE_OFFSET:
+      // [G92 Errors]: No axis words.
+      if (!axis_words) { FAIL(STATUS_GCODE_NO_AXIS_WORDS); } // [No axis words]
+
+      // Update axes defined only in block. Offsets current system to defined value. Does not update when
+      // active coordinate system is selected, but is still active unless G92.1 disables it.
+      for (idx=0; idx<N_AXIS; idx++) { // Axes indices are consistent, so loop may be used.
+        if (bit_istrue(axis_words,bit(idx)) ) {
+          // WPos = MPos - WCS - G92 - TLO  ->  G92 = MPos - WCS - TLO - WPos
+          gc_block.values.xyz[idx] = gc_state.position[idx]-block_coord_system[idx]-gc_block.values.xyz[idx];
+          if (idx == TOOL_LENGTH_OFFSET_AXIS) { gc_block.values.xyz[idx] -= gc_state.tool_length_offset; }
+        } else {
+          gc_block.values.xyz[idx] = gc_state.coord_offset[idx];
+        }
+      }
+      break;
+
+    default:
+
+      // At this point, the rest of the explicit axis commands treat the axis values as the traditional
+      // target position with the coordinate system offsets, G92 offsets, absolute override, and distance
+      // modes applied. This includes the motion mode commands. We can now pre-compute the target position.
+      // NOTE: Tool offsets may be appended to these conversions when/if this feature is added.
+      if (axis_command != AXIS_COMMAND_TOOL_LENGTH_OFFSET ) { // TLO block any axis command.
+        if (axis_words) {
+          for (idx=0; idx<N_AXIS; idx++) { // Axes indices are consistent, so loop may be used to save flash space.
+            if ( bit_isfalse(axis_words,bit(idx)) ) {
+              gc_block.values.xyz[idx] = gc_state.position[idx]; // No axis word in block. Keep same axis position.
+            } else {
+              // Update specified value according to distance mode or ignore if absolute override is active.
+              // NOTE: G53 is never active with G28/30 since they are in the same modal group.
+              if (gc_block.non_modal_command != NON_MODAL_ABSOLUTE_OVERRIDE) {
+                // Apply coordinate offsets based on distance mode.
+                if (gc_block.modal.distance == DISTANCE_MODE_ABSOLUTE) {
+                  gc_block.values.xyz[idx] += block_coord_system[idx] + gc_state.coord_offset[idx];
+                  if (idx == TOOL_LENGTH_OFFSET_AXIS) { gc_block.values.xyz[idx] += gc_state.tool_length_offset; }
+                } else {  // Incremental mode
+                  gc_block.values.xyz[idx] += gc_state.position[idx];
+                }
+              }
+            }
+          }
+        }
+      }
+
+      // Check remaining non-modal commands for errors.
+      switch (gc_block.non_modal_command) {
+        case NON_MODAL_GO_HOME_0: // G28
+        case NON_MODAL_GO_HOME_1: // G30
+          // [G28/30 Errors]: Cutter compensation is enabled.
+          // Retreive G28/30 go-home position data (in machine coordinates) from EEPROM
+          // NOTE: Store parameter data in IJK values. By rule, they are not in use with this command.
+          if (gc_block.non_modal_command == NON_MODAL_GO_HOME_0) {
+            if (!settings_read_coord_data(SETTING_INDEX_G28,gc_block.values.ijk)) { FAIL(STATUS_SETTING_READ_FAIL); }
+          } else { // == NON_MODAL_GO_HOME_1
+            if (!settings_read_coord_data(SETTING_INDEX_G30,gc_block.values.ijk)) { FAIL(STATUS_SETTING_READ_FAIL); }
+          }
+          if (axis_words) {
+            // Move only the axes specified in secondary move.
+            for (idx=0; idx<N_AXIS; idx++) {
+              if (!(axis_words & (1<<idx))) { gc_block.values.ijk[idx] = gc_state.position[idx]; }
+            }
+          } else {
+            axis_command = AXIS_COMMAND_NONE; // Set to none if no intermediate motion.
+          }
+          break;
+        case NON_MODAL_SET_HOME_0: // G28.1
+        case NON_MODAL_SET_HOME_1: // G30.1
+          // [G28.1/30.1 Errors]: Cutter compensation is enabled.
+          // NOTE: If axis words are passed here, they are interpreted as an implicit motion mode.
+          break;
+        case NON_MODAL_RESET_COORDINATE_OFFSET:
+          // NOTE: If axis words are passed here, they are interpreted as an implicit motion mode.
+          break;
+        case NON_MODAL_ABSOLUTE_OVERRIDE:
+          // [G53 Errors]: G0 and G1 are not active. Cutter compensation is enabled.
+          // NOTE: All explicit axis word commands are in this modal group. So no implicit check necessary.
+          if (!(gc_block.modal.motion == MOTION_MODE_SEEK || gc_block.modal.motion == MOTION_MODE_LINEAR)) {
+            FAIL(STATUS_GCODE_G53_INVALID_MOTION_MODE); // [G53 G0/1 not active]
+          }
+          break;
+      }
+  }
+
+  // [20. Motion modes ]:
+  if (gc_block.modal.motion == MOTION_MODE_NONE) {
+    // [G80 Errors]: Axis word are programmed while G80 is active.
+    // NOTE: Even non-modal commands or TLO that use axis words will throw this strict error.
+    if (axis_words) { FAIL(STATUS_GCODE_AXIS_WORDS_EXIST); } // [No axis words allowed]
+
+  // Check remaining motion modes, if axis word are implicit (exist and not used by G10/28/30/92), or
+  // was explicitly commanded in the g-code block.
+  } else if ( axis_command == AXIS_COMMAND_MOTION_MODE ) {
+
+    if (gc_block.modal.motion == MOTION_MODE_SEEK) {
+      // [G0 Errors]: Axis letter not configured or without real value (done.)
+      // Axis words are optional. If missing, set axis command flag to ignore execution.
+      if (!axis_words) { axis_command = AXIS_COMMAND_NONE; }
+
+    // All remaining motion modes (all but G0 and G80), require a valid feed rate value. In units per mm mode,
+    // the value must be positive. In inverse time mode, a positive value must be passed with each block.
+    } else {
+      // Check if feed rate is defined for the motion modes that require it.
+      if (gc_block.values.f == 0.0) { FAIL(STATUS_GCODE_UNDEFINED_FEED_RATE); } // [Feed rate undefined]
+
+      switch (gc_block.modal.motion) {
+        case MOTION_MODE_LINEAR:
+          // [G1 Errors]: Feed rate undefined. Axis letter not configured or without real value.
+          // Axis words are optional. If missing, set axis command flag to ignore execution.
+          if (!axis_words) { axis_command = AXIS_COMMAND_NONE; }
+          break;
+        case MOTION_MODE_CW_ARC: 
+          gc_parser_flags |= GC_PARSER_ARC_IS_CLOCKWISE; // No break intentional.
+        case MOTION_MODE_CCW_ARC:
+          // [G2/3 Errors All-Modes]: Feed rate undefined.
+          // [G2/3 Radius-Mode Errors]: No axis words in selected plane. Target point is same as current.
+          // [G2/3 Offset-Mode Errors]: No axis words and/or offsets in selected plane. The radius to the current
+          //   point and the radius to the target point differs more than 0.002mm (EMC def. 0.5mm OR 0.005mm and 0.1% radius).
+          // [G2/3 Full-Circle-Mode Errors]: NOT SUPPORTED. Axis words exist. No offsets programmed. P must be an integer.
+          // NOTE: Both radius and offsets are required for arc tracing and are pre-computed with the error-checking.
+
+          if (!axis_words) { FAIL(STATUS_GCODE_NO_AXIS_WORDS); } // [No axis words]
+          if (!(axis_words & (bit(axis_0)|bit(axis_1)))) { FAIL(STATUS_GCODE_NO_AXIS_WORDS_IN_PLANE); } // [No axis words in plane]
+
+          // Calculate the change in position along each selected axis
+          float x,y;
+          x = gc_block.values.xyz[axis_0]-gc_state.position[axis_0]; // Delta x between current position and target
+          y = gc_block.values.xyz[axis_1]-gc_state.position[axis_1]; // Delta y between current position and target
+
+          if (value_words & bit(WORD_R)) { // Arc Radius Mode
+            bit_false(value_words,bit(WORD_R));
+            if (isequal_position_vector(gc_state.position, gc_block.values.xyz)) { FAIL(STATUS_GCODE_INVALID_TARGET); } // [Invalid target]
+
+            // Convert radius value to proper units.
+            if (gc_block.modal.units == UNITS_MODE_INCHES) { gc_block.values.r *= MM_PER_INCH; }
+            /*  We need to calculate the center of the circle that has the designated radius and passes
+                through both the current position and the target position. This method calculates the following
+                set of equations where [x,y] is the vector from current to target position, d == magnitude of
+                that vector, h == hypotenuse of the triangle formed by the radius of the circle, the distance to
+                the center of the travel vector. A vector perpendicular to the travel vector [-y,x] is scaled to the
+                length of h [-y/d*h, x/d*h] and added to the center of the travel vector [x/2,y/2] to form the new point
+                [i,j] at [x/2-y/d*h, y/2+x/d*h] which will be the center of our arc.
+
+                d^2 == x^2 + y^2
+                h^2 == r^2 - (d/2)^2
+                i == x/2 - y/d*h
+                j == y/2 + x/d*h
+
+                                                                     O <- [i,j]
+                                                                  -  |
+                                                        r      -     |
+                                                            -        |
+                                                         -           | h
+                                                      -              |
+                                        [0,0] ->  C -----------------+--------------- T  <- [x,y]
+                                                  | <------ d/2 ---->|
+
+                C - Current position
+                T - Target position
+                O - center of circle that pass through both C and T
+                d - distance from C to T
+                r - designated radius
+                h - distance from center of CT to O
+
+                Expanding the equations:
+
+                d -> sqrt(x^2 + y^2)
+                h -> sqrt(4 * r^2 - x^2 - y^2)/2
+                i -> (x - (y * sqrt(4 * r^2 - x^2 - y^2)) / sqrt(x^2 + y^2)) / 2
+                j -> (y + (x * sqrt(4 * r^2 - x^2 - y^2)) / sqrt(x^2 + y^2)) / 2
+
+                Which can be written:
+
+                i -> (x - (y * sqrt(4 * r^2 - x^2 - y^2))/sqrt(x^2 + y^2))/2
+                j -> (y + (x * sqrt(4 * r^2 - x^2 - y^2))/sqrt(x^2 + y^2))/2
+
+                Which we for size and speed reasons optimize to:
+
+                h_x2_div_d = sqrt(4 * r^2 - x^2 - y^2)/sqrt(x^2 + y^2)
+                i = (x - (y * h_x2_div_d))/2
+                j = (y + (x * h_x2_div_d))/2
+            */
+
+            // First, use h_x2_div_d to compute 4*h^2 to check if it is negative or r is smaller
+            // than d. If so, the sqrt of a negative number is complex and error out.
+            float h_x2_div_d = 4.0 * gc_block.values.r*gc_block.values.r - x*x - y*y;
+
+            if (h_x2_div_d < 0) { FAIL(STATUS_GCODE_ARC_RADIUS_ERROR); } // [Arc radius error]
+
+            // Finish computing h_x2_div_d.
+            h_x2_div_d = -sqrt(h_x2_div_d)/hypot_f(x,y); // == -(h * 2 / d)
+            // Invert the sign of h_x2_div_d if the circle is counter clockwise (see sketch below)
+            if (gc_block.modal.motion == MOTION_MODE_CCW_ARC) { h_x2_div_d = -h_x2_div_d; }
+
+            /* The counter clockwise circle lies to the left of the target direction. When offset is positive,
+               the left hand circle will be generated - when it is negative the right hand circle is generated.
+
+                                                                   T  <-- Target position
+
+                                                                   ^
+                        Clockwise circles with this center         |          Clockwise circles with this center will have
+                        will have > 180 deg of angular travel      |          < 180 deg of angular travel, which is a good thing!
+                                                         \         |          /
+            center of arc when h_x2_div_d is positive ->  x <----- | -----> x <- center of arc when h_x2_div_d is negative
+                                                                   |
+                                                                   |
+
+                                                                   C  <-- Current position
+            */
+            // Negative R is g-code-alese for "I want a circle with more than 180 degrees of travel" (go figure!),
+            // even though it is advised against ever generating such circles in a single line of g-code. By
+            // inverting the sign of h_x2_div_d the center of the circles is placed on the opposite side of the line of
+            // travel and thus we get the unadvisably long arcs as prescribed.
+            if (gc_block.values.r < 0) {
+                h_x2_div_d = -h_x2_div_d;
+                gc_block.values.r = -gc_block.values.r; // Finished with r. Set to positive for mc_arc
+            }
+            // Complete the operation by calculating the actual center of the arc
+            gc_block.values.ijk[axis_0] = 0.5*(x-(y*h_x2_div_d));
+            gc_block.values.ijk[axis_1] = 0.5*(y+(x*h_x2_div_d));
+
+          } else { // Arc Center Format Offset Mode
+            if (!(ijk_words & (bit(axis_0)|bit(axis_1)))) { FAIL(STATUS_GCODE_NO_OFFSETS_IN_PLANE); } // [No offsets in plane]
+            bit_false(value_words,(bit(WORD_I)|bit(WORD_J)|bit(WORD_K)));
+
+            // Convert IJK values to proper units.
+            if (gc_block.modal.units == UNITS_MODE_INCHES) {
+              for (idx=0; idx<N_AXIS; idx++) { // Axes indices are consistent, so loop may be used to save flash space.
+                if (ijk_words & bit(idx)) { gc_block.values.ijk[idx] *= MM_PER_INCH; }
+              }
+            }
+
+            // Arc radius from center to target
+            x -= gc_block.values.ijk[axis_0]; // Delta x between circle center and target
+            y -= gc_block.values.ijk[axis_1]; // Delta y between circle center and target
+            float target_r = hypot_f(x,y);
+
+            // Compute arc radius for mc_arc. Defined from current location to center.
+            gc_block.values.r = hypot_f(gc_block.values.ijk[axis_0], gc_block.values.ijk[axis_1]);
+
+            // Compute difference between current location and target radii for final error-checks.
+            float delta_r = fabs(target_r-gc_block.values.r);
+            if (delta_r > 0.005) {
+              if (delta_r > 0.5) { FAIL(STATUS_GCODE_INVALID_TARGET); } // [Arc definition error] > 0.5mm
+              if (delta_r > (0.001*gc_block.values.r)) { FAIL(STATUS_GCODE_INVALID_TARGET); } // [Arc definition error] > 0.005mm AND 0.1% radius
+            }
+          }
+          break;
+        case MOTION_MODE_PROBE_TOWARD_NO_ERROR: case MOTION_MODE_PROBE_AWAY_NO_ERROR:
+          gc_parser_flags |= GC_PARSER_PROBE_IS_NO_ERROR; // No break intentional.
+        case MOTION_MODE_PROBE_TOWARD: case MOTION_MODE_PROBE_AWAY:
+          if ((gc_block.modal.motion == MOTION_MODE_PROBE_AWAY) || 
+              (gc_block.modal.motion == MOTION_MODE_PROBE_AWAY_NO_ERROR)) { gc_parser_flags |= GC_PARSER_PROBE_IS_AWAY; }
+          // [G38 Errors]: Target is same current. No axis words. Cutter compensation is enabled. Feed rate
+          //   is undefined. Probe is triggered. NOTE: Probe check moved to probe cycle. Instead of returning
+          //   an error, it issues an alarm to prevent further motion to the probe. It's also done there to
+          //   allow the planner buffer to empty and move off the probe trigger before another probing cycle.
+          if (!axis_words) { FAIL(STATUS_GCODE_NO_AXIS_WORDS); } // [No axis words]
+          if (isequal_position_vector(gc_state.position, gc_block.values.xyz)) { FAIL(STATUS_GCODE_INVALID_TARGET); } // [Invalid target]
+          break;
+      }
+    }
+  }
+
+  // [21. Program flow ]: No error checks required.
+
+  // [0. Non-specific error-checks]: Complete unused value words check, i.e. IJK used when in arc
+  // radius mode, or axis words that aren't used in the block.
+  if (gc_parser_flags & GC_PARSER_JOG_MOTION) {
+    // Jogging only uses the F feed rate and XYZ value words. N is valid, but S and T are invalid.
+    bit_false(value_words,(bit(WORD_N)|bit(WORD_F)));
+  } else {
+    bit_false(value_words,(bit(WORD_N)|bit(WORD_F)|bit(WORD_S)|bit(WORD_T))); // Remove single-meaning value words.
+  }
+  if (axis_command) { bit_false(value_words,(bit(WORD_X)|bit(WORD_Y)|bit(WORD_Z))); } // Remove axis words.
+  if (value_words) { FAIL(STATUS_GCODE_UNUSED_WORDS); } // [Unused words]
+
+  /* -------------------------------------------------------------------------------------
+     STEP 4: EXECUTE!!
+     Assumes that all error-checking has been completed and no failure modes exist. We just
+     need to update the state and execute the block according to the order-of-execution.
+  */
+
+  // Initialize planner data struct for motion blocks.
+  plan_line_data_t plan_data;
+  plan_line_data_t *pl_data = &plan_data;
+  memset(pl_data,0,sizeof(plan_line_data_t)); // Zero pl_data struct
+
+  // Intercept jog commands and complete error checking for valid jog commands and execute.
+  // NOTE: G-code parser state is not updated, except the position to ensure sequential jog
+  // targets are computed correctly. The final parser position after a jog is updated in
+  // protocol_execute_realtime() when jogging completes or is canceled.
+  if (gc_parser_flags & GC_PARSER_JOG_MOTION) {
+    // Only distance and unit modal commands and G53 absolute override command are allowed.
+    // NOTE: Feed rate word and axis word checks have already been performed in STEP 3.
+    if (command_words & ~(bit(MODAL_GROUP_G3) | bit(MODAL_GROUP_G6) | bit(MODAL_GROUP_G0)) ) { FAIL(STATUS_INVALID_JOG_COMMAND) };
+    if (!(gc_block.non_modal_command == NON_MODAL_ABSOLUTE_OVERRIDE || gc_block.non_modal_command == NON_MODAL_NO_ACTION)) { FAIL(STATUS_INVALID_JOG_COMMAND); }
+
+    // Initialize planner data to current spindle and coolant modal state.
+    pl_data->spindle_speed = gc_state.spindle_speed;
+    plan_data.condition = (gc_state.modal.spindle | gc_state.modal.coolant);
+
+    uint8_t status = jog_execute(&plan_data, &gc_block);
+    if (status == STATUS_OK) { memcpy(gc_state.position, gc_block.values.xyz, sizeof(gc_block.values.xyz)); }
+    return(status);
+  }
+  
+  // If in laser mode, setup laser power based on current and past parser conditions.
+  if (bit_istrue(settings.flags,BITFLAG_LASER_MODE)) {
+    if ( !((gc_block.modal.motion == MOTION_MODE_LINEAR) || (gc_block.modal.motion == MOTION_MODE_CW_ARC) 
+        || (gc_block.modal.motion == MOTION_MODE_CCW_ARC)) ) {
+      gc_parser_flags |= GC_PARSER_LASER_DISABLE;
+    }
+
+    // Any motion mode with axis words is allowed to be passed from a spindle speed update. 
+    // NOTE: G1 and G0 without axis words sets axis_command to none. G28/30 are intentionally omitted.
+    // TODO: Check sync conditions for M3 enabled motions that don't enter the planner. (zero length).
+    if (axis_words && (axis_command == AXIS_COMMAND_MOTION_MODE)) { 
+      gc_parser_flags |= GC_PARSER_LASER_ISMOTION; 
+    } else {
+      // M3 constant power laser requires planner syncs to update the laser when changing between
+      // a G1/2/3 motion mode state and vice versa when there is no motion in the line.
+      if (gc_state.modal.spindle == SPINDLE_ENABLE_CW) {
+        if ((gc_state.modal.motion == MOTION_MODE_LINEAR) || (gc_state.modal.motion == MOTION_MODE_CW_ARC) 
+            || (gc_state.modal.motion == MOTION_MODE_CCW_ARC)) {
+          if (bit_istrue(gc_parser_flags,GC_PARSER_LASER_DISABLE)) { 
+            gc_parser_flags |= GC_PARSER_LASER_FORCE_SYNC; // Change from G1/2/3 motion mode.
+          }
+        } else {
+          // When changing to a G1 motion mode without axis words from a non-G1/2/3 motion mode.
+          if (bit_isfalse(gc_parser_flags,GC_PARSER_LASER_DISABLE)) { 
+            gc_parser_flags |= GC_PARSER_LASER_FORCE_SYNC;
+          }
+        } 
+      }
+    }
+  }
+
+  // [0. Non-specific/common error-checks and miscellaneous setup]:
+  // NOTE: If no line number is present, the value is zero.
+  gc_state.line_number = gc_block.values.n;
+  #ifdef USE_LINE_NUMBERS
+    pl_data->line_number = gc_state.line_number; // Record data for planner use.
+  #endif
+
+  // [1. Comments feedback ]:  NOT SUPPORTED
+
+  // [2. Set feed rate mode ]:
+  gc_state.modal.feed_rate = gc_block.modal.feed_rate;
+  if (gc_state.modal.feed_rate) { pl_data->condition |= PL_COND_FLAG_INVERSE_TIME; } // Set condition flag for planner use.
+
+  // [3. Set feed rate ]:
+  gc_state.feed_rate = gc_block.values.f; // Always copy this value. See feed rate error-checking.
+  pl_data->feed_rate = gc_state.feed_rate; // Record data for planner use.
+
+  // [4. Set spindle speed ]:
+  if ((gc_state.spindle_speed != gc_block.values.s) || bit_istrue(gc_parser_flags,GC_PARSER_LASER_FORCE_SYNC)) {
+    if (gc_state.modal.spindle != SPINDLE_DISABLE) { 
+      #ifdef VARIABLE_SPINDLE
+        if (bit_isfalse(gc_parser_flags,GC_PARSER_LASER_ISMOTION)) {
+          if (bit_istrue(gc_parser_flags,GC_PARSER_LASER_DISABLE)) {
+             spindle_sync(gc_state.modal.spindle, 0.0);
+          } else { spindle_sync(gc_state.modal.spindle, gc_block.values.s); }
+        }
+      #else
+        spindle_sync(gc_state.modal.spindle, 0.0);
+      #endif
+    }
+    gc_state.spindle_speed = gc_block.values.s; // Update spindle speed state.
+  }
+  // NOTE: Pass zero spindle speed for all restricted laser motions.
+  if (bit_isfalse(gc_parser_flags,GC_PARSER_LASER_DISABLE)) {
+    pl_data->spindle_speed = gc_state.spindle_speed; // Record data for planner use. 
+  } // else { pl_data->spindle_speed = 0.0; } // Initialized as zero already.
+  
+  // [5. Select tool ]: NOT SUPPORTED. Only tracks tool value.
+  gc_state.tool = gc_block.values.t;
+
+  // [6. Change tool ]: NOT SUPPORTED
+
+  // [7. Spindle control ]:
+  if (gc_state.modal.spindle != gc_block.modal.spindle) {
+    // Update spindle control and apply spindle speed when enabling it in this block.
+    // NOTE: All spindle state changes are synced, even in laser mode. Also, pl_data,
+    // rather than gc_state, is used to manage laser state for non-laser motions.
+    spindle_sync(gc_block.modal.spindle, pl_data->spindle_speed);
+    gc_state.modal.spindle = gc_block.modal.spindle;
+  }
+  pl_data->condition |= gc_state.modal.spindle; // Set condition flag for planner use.
+
+  // [8. Coolant control ]:
+  if (gc_state.modal.coolant != gc_block.modal.coolant) {
+    // NOTE: Coolant M-codes are modal. Only one command per line is allowed. But, multiple states
+    // can exist at the same time, while coolant disable clears all states.
+    coolant_sync(gc_block.modal.coolant);
+    gc_state.modal.coolant = gc_block.modal.coolant;
+  }
+  pl_data->condition |= gc_state.modal.coolant; // Set condition flag for planner use.
+
+  // [9. Override control ]: NOT SUPPORTED. Always enabled. Except for a Grbl-only parking control.
+  #ifdef ENABLE_PARKING_OVERRIDE_CONTROL
+    if (gc_state.modal.override != gc_block.modal.override) {
+      gc_state.modal.override = gc_block.modal.override;
+      mc_override_ctrl_update(gc_state.modal.override);
+    }
+  #endif
+
+  // [10. Dwell ]:
+  if (gc_block.non_modal_command == NON_MODAL_DWELL) { mc_dwell(gc_block.values.p); }
+
+  // [11. Set active plane ]:
+  gc_state.modal.plane_select = gc_block.modal.plane_select;
+
+  // [12. Set length units ]:
+  gc_state.modal.units = gc_block.modal.units;
+
+  // [13. Cutter radius compensation ]: G41/42 NOT SUPPORTED
+  // gc_state.modal.cutter_comp = gc_block.modal.cutter_comp; // NOTE: Not needed since always disabled.
+
+  // [14. Cutter length compensation ]: G43.1 and G49 supported. G43 NOT SUPPORTED.
+  // NOTE: If G43 were supported, its operation wouldn't be any different from G43.1 in terms
+  // of execution. The error-checking step would simply load the offset value into the correct
+  // axis of the block XYZ value array.
+  if (axis_command == AXIS_COMMAND_TOOL_LENGTH_OFFSET ) { // Indicates a change.
+    gc_state.modal.tool_length = gc_block.modal.tool_length;
+    if (gc_state.modal.tool_length == TOOL_LENGTH_OFFSET_CANCEL) { // G49
+      gc_block.values.xyz[TOOL_LENGTH_OFFSET_AXIS] = 0.0;
+    } // else G43.1
+    if ( gc_state.tool_length_offset != gc_block.values.xyz[TOOL_LENGTH_OFFSET_AXIS] ) {
+      gc_state.tool_length_offset = gc_block.values.xyz[TOOL_LENGTH_OFFSET_AXIS];
+      system_flag_wco_change();
+    }
+  }
+
+  // [15. Coordinate system selection ]:
+  if (gc_state.modal.coord_select != gc_block.modal.coord_select) {
+    gc_state.modal.coord_select = gc_block.modal.coord_select;
+    memcpy(gc_state.coord_system,block_coord_system,N_AXIS*sizeof(float));
+    system_flag_wco_change();
+  }
+
+  // [16. Set path control mode ]: G61.1/G64 NOT SUPPORTED
+  // gc_state.modal.control = gc_block.modal.control; // NOTE: Always default.
+
+  // [17. Set distance mode ]:
+  gc_state.modal.distance = gc_block.modal.distance;
+
+  // [18. Set retract mode ]: NOT SUPPORTED
+
+  // [19. Go to predefined position, Set G10, or Set axis offsets ]:
+  switch(gc_block.non_modal_command) {
+    case NON_MODAL_SET_COORDINATE_DATA:
+      settings_write_coord_data(coord_select,gc_block.values.ijk);
+      // Update system coordinate system if currently active.
+      if (gc_state.modal.coord_select == coord_select) {
+        memcpy(gc_state.coord_system,gc_block.values.ijk,N_AXIS*sizeof(float));
+        system_flag_wco_change();
+      }
+      break;
+    case NON_MODAL_GO_HOME_0: case NON_MODAL_GO_HOME_1:
+      // Move to intermediate position before going home. Obeys current coordinate system and offsets
+      // and absolute and incremental modes.
+      pl_data->condition |= PL_COND_FLAG_RAPID_MOTION; // Set rapid motion condition flag.
+      if (axis_command) { mc_line(gc_block.values.xyz, pl_data); }
+      mc_line(gc_block.values.ijk, pl_data);
+      memcpy(gc_state.position, gc_block.values.ijk, N_AXIS*sizeof(float));
+      break;
+    case NON_MODAL_SET_HOME_0:
+      settings_write_coord_data(SETTING_INDEX_G28,gc_state.position);
+      break;
+    case NON_MODAL_SET_HOME_1:
+      settings_write_coord_data(SETTING_INDEX_G30,gc_state.position);
+      break;
+    case NON_MODAL_SET_COORDINATE_OFFSET:
+      memcpy(gc_state.coord_offset,gc_block.values.xyz,sizeof(gc_block.values.xyz));
+      system_flag_wco_change();
+      break;
+    case NON_MODAL_RESET_COORDINATE_OFFSET:
+      clear_vector(gc_state.coord_offset); // Disable G92 offsets by zeroing offset vector.
+      system_flag_wco_change();
+      break;
+  }
+
+
+  // [20. Motion modes ]:
+  // NOTE: Commands G10,G28,G30,G92 lock out and prevent axis words from use in motion modes.
+  // Enter motion modes only if there are axis words or a motion mode command word in the block.
+  gc_state.modal.motion = gc_block.modal.motion;
+  if (gc_state.modal.motion != MOTION_MODE_NONE) {
+    if (axis_command == AXIS_COMMAND_MOTION_MODE) {
+      uint8_t gc_update_pos = GC_UPDATE_POS_TARGET;
+      if (gc_state.modal.motion == MOTION_MODE_LINEAR) {
+        mc_line(gc_block.values.xyz, pl_data);
+      } else if (gc_state.modal.motion == MOTION_MODE_SEEK) {
+        pl_data->condition |= PL_COND_FLAG_RAPID_MOTION; // Set rapid motion condition flag.
+        mc_line(gc_block.values.xyz, pl_data);
+      } else if ((gc_state.modal.motion == MOTION_MODE_CW_ARC) || (gc_state.modal.motion == MOTION_MODE_CCW_ARC)) {
+        mc_arc(gc_block.values.xyz, pl_data, gc_state.position, gc_block.values.ijk, gc_block.values.r,
+            axis_0, axis_1, axis_linear, bit_istrue(gc_parser_flags,GC_PARSER_ARC_IS_CLOCKWISE));
+      } else {
+        // NOTE: gc_block.values.xyz is returned from mc_probe_cycle with the updated position value. So
+        // upon a successful probing cycle, the machine position and the returned value should be the same.
+        #ifndef ALLOW_FEED_OVERRIDE_DURING_PROBE_CYCLES
+          pl_data->condition |= PL_COND_FLAG_NO_FEED_OVERRIDE;
+        #endif
+        gc_update_pos = mc_probe_cycle(gc_block.values.xyz, pl_data, gc_parser_flags);
+      }  
+     
+      // 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.
+      if (gc_update_pos == GC_UPDATE_POS_TARGET) {
+        memcpy(gc_state.position, gc_block.values.xyz, sizeof(gc_block.values.xyz)); // gc_state.position[] = gc_block.values.xyz[]
+      } else if (gc_update_pos == GC_UPDATE_POS_SYSTEM) {
+        gc_sync_position(); // gc_state.position[] = sys_position
+      } // == GC_UPDATE_POS_NONE
+    }     
+  }
+
+  // [21. Program flow ]:
+  // M0,M1,M2,M30: Perform non-running program flow actions. During a program pause, the buffer may
+  // refill and can only be resumed by the cycle start run-time command.
+  gc_state.modal.program_flow = gc_block.modal.program_flow;
+  if (gc_state.modal.program_flow) {
+    protocol_buffer_synchronize(); // Sync and finish all remaining buffered motions before moving on.
+    if (gc_state.modal.program_flow == PROGRAM_FLOW_PAUSED) {
+      if (sys.state != STATE_CHECK_MODE) {
+        system_set_exec_state_flag(EXEC_FEED_HOLD); // Use feed hold for program pause.
+        protocol_execute_realtime(); // Execute suspend.
+      }
+    } else { // == PROGRAM_FLOW_COMPLETED
+      // Upon program complete, only a subset of g-codes reset to certain defaults, according to
+      // LinuxCNC's program end descriptions and testing. Only modal groups [G-code 1,2,3,5,7,12]
+      // and [M-code 7,8,9] reset to [G1,G17,G90,G94,G40,G54,M5,M9,M48]. The remaining modal groups
+      // [G-code 4,6,8,10,13,14,15] and [M-code 4,5,6] and the modal words [F,S,T,H] do not reset.
+      gc_state.modal.motion = MOTION_MODE_LINEAR;
+      gc_state.modal.plane_select = PLANE_SELECT_XY;
+      gc_state.modal.distance = DISTANCE_MODE_ABSOLUTE;
+      gc_state.modal.feed_rate = FEED_RATE_MODE_UNITS_PER_MIN;
+      // gc_state.modal.cutter_comp = CUTTER_COMP_DISABLE; // Not supported.
+      gc_state.modal.coord_select = 0; // G54
+      gc_state.modal.spindle = SPINDLE_DISABLE;
+      gc_state.modal.coolant = COOLANT_DISABLE;
+      #ifdef ENABLE_PARKING_OVERRIDE_CONTROL
+        #ifdef DEACTIVATE_PARKING_UPON_INIT
+          gc_state.modal.override = OVERRIDE_DISABLED;
+        #else
+          gc_state.modal.override = OVERRIDE_PARKING_MOTION;
+        #endif
+      #endif
+
+      #ifdef RESTORE_OVERRIDES_AFTER_PROGRAM_END
+        sys.f_override = DEFAULT_FEED_OVERRIDE;
+        sys.r_override = DEFAULT_RAPID_OVERRIDE;
+        sys.spindle_speed_ovr = DEFAULT_SPINDLE_SPEED_OVERRIDE;
+      #endif
+
+      // Execute coordinate change and spindle/coolant stop.
+      if (sys.state != STATE_CHECK_MODE) {
+        if (!(settings_read_coord_data(gc_state.modal.coord_select,gc_state.coord_system))) { FAIL(STATUS_SETTING_READ_FAIL); }
+        system_flag_wco_change(); // Set to refresh immediately just in case something altered.
+        spindle_set_state(SPINDLE_DISABLE,0.0);
+        coolant_set_state(COOLANT_DISABLE);
+      }
+      report_feedback_message(MESSAGE_PROGRAM_END);
+    }
+    gc_state.modal.program_flow = PROGRAM_FLOW_RUNNING; // Reset program flow.
+  }
+
+  // TODO: % to denote start of program.
+
+  return(STATUS_OK);
+}
+
+
+/*
+  Not supported:
+
+  - Canned cycles
+  - Tool radius compensation
+  - A,B,C-axes
+  - Evaluation of expressions
+  - Variables
+  - Override control (TBD)
+  - Tool changes
+  - Switches
+
+   (*) Indicates optional parameter, enabled through config.h and re-compile
+   group 0 = {G92.2, G92.3} (Non modal: Cancel and re-enable G92 offsets)
+   group 1 = {G81 - G89} (Motion modes: Canned cycles)
+   group 4 = {M1} (Optional stop, ignored)
+   group 6 = {M6} (Tool change)
+   group 7 = {G41, G42} cutter radius compensation (G40 is supported)
+   group 8 = {G43} tool length offset (G43.1/G49 are supported)
+   group 8 = {M7*} enable mist coolant (* Compile-option)
+   group 9 = {M48, M49, M56*} enable/disable override switches (* Compile-option)
+   group 10 = {G98, G99} return mode canned cycles
+   group 13 = {G61.1, G64} path control mode (G61 is supported)
+*/