diff --git a/serial.c b/serial.c
index 57cacc8..ee22333 100755
--- a/serial.c
+++ b/serial.c
@@ -91,7 +91,11 @@ void serial_write(uint8_t data) {
 }
 
 // Data Register Empty Interrupt handler
+#ifdef __AVR_ATmega644P__
+ISR(USART0_UDRE_vect)
+#else
 ISR(USART_UDRE_vect)
+#endif
 {
   // Temporary tx_buffer_tail (to optimize for volatile)
   uint8_t tail = tx_buffer_tail;
@@ -140,7 +144,11 @@ uint8_t serial_read()
   }
 }
 
+#ifdef __AVR_ATmega644P__
+ISR(USART0_RX_vect)
+#else
 ISR(USART_RX_vect)
+#endif
 {
   uint8_t data = UDR0;
   uint8_t next_head;
diff --git a/settings.c b/settings.c
index d1d42e2..5b1ef2e 100644
--- a/settings.c
+++ b/settings.c
@@ -1,223 +1,222 @@
-/*
-  settings.c - eeprom configuration handling 
-  Part of Grbl
-
-  Copyright (c) 2009-2011 Simen Svale Skogsrud
-  Copyright (c) 2011-2012 Sungeun K. Jeon  
-
-  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 <avr/io.h>
-#include "protocol.h"
-#include "report.h"
-#include "stepper.h"
-#include "nuts_bolts.h"
-#include "settings.h"
-#include "eeprom.h"
-
-settings_t settings;
-
-// Version 4 outdated settings record
-typedef struct {
-  float steps_per_mm[3];
-  uint8_t microsteps;
-  uint8_t pulse_microseconds;
-  float default_feed_rate;
-  float default_seek_rate;
-  uint8_t invert_mask;
-  float mm_per_arc_segment;
-  float acceleration;
-  float junction_deviation;
-} settings_v4_t;
-
-
-// Method to store startup lines into EEPROM
-void settings_store_startup_line(uint8_t n, char *line)
-{
-  uint16_t addr = n*(LINE_BUFFER_SIZE+1)+EEPROM_ADDR_STARTUP_BLOCK;
-  memcpy_to_eeprom_with_checksum(addr,(char*)line, LINE_BUFFER_SIZE);
-}
-
-// Method to store coord data parameters into EEPROM
-void settings_write_coord_data(uint8_t coord_select, float *coord_data)
-{  
-  uint16_t addr = coord_select*(sizeof(float)*N_AXIS+1) + EEPROM_ADDR_PARAMETERS;
-  memcpy_to_eeprom_with_checksum(addr,(char*)coord_data, sizeof(float)*N_AXIS);
-}  
-
-// Method to store Grbl global settings struct and version number into EEPROM
-void write_global_settings() 
-{
-  eeprom_put_char(0, SETTINGS_VERSION);
-  memcpy_to_eeprom_with_checksum(EEPROM_ADDR_GLOBAL, (char*)&settings, sizeof(settings_t));
-}
-
-// Method to reset Grbl global settings back to defaults. 
-void settings_reset(bool reset_all) {
-  // Reset all settings or only the migration settings to the new version.
-  if (reset_all) {
-    settings.steps_per_mm[X_AXIS] = DEFAULT_X_STEPS_PER_MM;
-    settings.steps_per_mm[Y_AXIS] = DEFAULT_Y_STEPS_PER_MM;
-    settings.steps_per_mm[Z_AXIS] = DEFAULT_Z_STEPS_PER_MM;
-    settings.pulse_microseconds = DEFAULT_STEP_PULSE_MICROSECONDS;
-    settings.default_feed_rate = DEFAULT_FEEDRATE;
-    settings.default_seek_rate = DEFAULT_RAPID_FEEDRATE;
-    settings.acceleration = DEFAULT_ACCELERATION;
-    settings.mm_per_arc_segment = DEFAULT_MM_PER_ARC_SEGMENT;
-    settings.invert_mask = DEFAULT_STEPPING_INVERT_MASK;
-    settings.junction_deviation = DEFAULT_JUNCTION_DEVIATION;
-  }
-  // New settings since last version
-  settings.flags = 0;
-  if (DEFAULT_REPORT_INCHES) { settings.flags |= BITFLAG_REPORT_INCHES; }
-  if (DEFAULT_AUTO_START) { settings.flags |= BITFLAG_AUTO_START; }
-  if (DEFAULT_INVERT_ST_ENABLE) { settings.flags |= BITFLAG_INVERT_ST_ENABLE; }
-  if (DEFAULT_HARD_LIMIT_ENABLE) { settings.flags |= BITFLAG_HARD_LIMIT_ENABLE; }
-  if (DEFAULT_HOMING_ENABLE) { settings.flags |= BITFLAG_HOMING_ENABLE; }
-  settings.homing_dir_mask = DEFAULT_HOMING_DIR_MASK;
-  settings.homing_feed_rate = DEFAULT_HOMING_FEEDRATE;
-  settings.homing_seek_rate = DEFAULT_HOMING_RAPID_FEEDRATE;
-  settings.homing_debounce_delay = DEFAULT_HOMING_DEBOUNCE_DELAY;
-  settings.homing_pulloff = DEFAULT_HOMING_PULLOFF;
-  settings.stepper_idle_lock_time = DEFAULT_STEPPER_IDLE_LOCK_TIME;
-  settings.decimal_places = DEFAULT_DECIMAL_PLACES;
-  settings.n_arc_correction = DEFAULT_N_ARC_CORRECTION;
-  write_global_settings();
-}
-
-// Reads startup line from EEPROM. Updated pointed line string data.
-uint8_t settings_read_startup_line(uint8_t n, char *line)
-{
-  uint16_t addr = n*(LINE_BUFFER_SIZE+1)+EEPROM_ADDR_STARTUP_BLOCK;
-  if (!(memcpy_from_eeprom_with_checksum((char*)line, addr, LINE_BUFFER_SIZE))) {
-    // Reset line with default value
-    // TODO: Need to come up with a method to do this.
-    line[0] = 0;
-    settings_store_startup_line(n, line);
-    return(false);
-  } else {
-    return(true);
-  }
-}
-
-// Read selected coordinate data from EEPROM. Updates pointed coord_data value.
-uint8_t settings_read_coord_data(uint8_t coord_select, float *coord_data)
-{
-  uint16_t addr = coord_select*(sizeof(float)*N_AXIS+1) + EEPROM_ADDR_PARAMETERS;
-  if (!(memcpy_from_eeprom_with_checksum((char*)coord_data, addr, sizeof(float)*N_AXIS))) {
-    // Reset with default zero vector
-    clear_vector_float(coord_data); 
-    settings_write_coord_data(coord_select,coord_data);
-    return(false);
-  } else {
-    return(true);
-  }
-}  
-
-// Reads Grbl global settings struct from EEPROM.
-uint8_t read_global_settings() {
-  // Check version-byte of eeprom
-  uint8_t version = eeprom_get_char(0);
-  
-  if (version == SETTINGS_VERSION) {
-    // Read settings-record and check checksum
-    if (!(memcpy_from_eeprom_with_checksum((char*)&settings, EEPROM_ADDR_GLOBAL, sizeof(settings_t)))) {
-      return(false);
-    }
-  } else {
-    if (version <= 4) {
-      // Migrate from settings version 4 to current version.
-      if (!(memcpy_from_eeprom_with_checksum((char*)&settings, 1, sizeof(settings_v4_t)))) {
-        return(false);
-      }     
-      settings_reset(false); // Old settings ok. Write new settings only.
-    } else {      
-      return(false);
-    }
-  }
-  return(true);
-}
-
-
-// A helper method to set settings from command line
-uint8_t settings_store_global_setting(int parameter, float value) {
-  switch(parameter) {
-    case 0: case 1: case 2:
-      if (value <= 0.0) { return(STATUS_SETTING_VALUE_NEG); } 
-      settings.steps_per_mm[parameter] = value; break;
-    case 3: 
-      if (value < 3) { return(STATUS_SETTING_STEP_PULSE_MIN); }
-      settings.pulse_microseconds = round(value); break;
-    case 4: settings.default_feed_rate = value; break;
-    case 5: settings.default_seek_rate = value; break;
-    case 6: settings.invert_mask = trunc(value); break;
-    case 7: settings.stepper_idle_lock_time = round(value); break;
-    case 8: settings.acceleration = value*60*60; break; // Convert to mm/min^2 for grbl internal use.
-    case 9: settings.junction_deviation = fabs(value); break;
-    case 10: settings.mm_per_arc_segment = value; break;
-    case 11: settings.n_arc_correction = round(value); break;
-    case 12: settings.decimal_places = round(value); break;
-    case 13:
-      if (value) { settings.flags |= BITFLAG_REPORT_INCHES; }
-      else { settings.flags &= ~BITFLAG_REPORT_INCHES; }
-      break;
-    case 14: // Reboot to ensure change
-      if (value) { settings.flags |= BITFLAG_AUTO_START; }
-      else { settings.flags &= ~BITFLAG_AUTO_START; }
-      break;
-    case 15: // Reboot to ensure change
-       if (value) { settings.flags |= BITFLAG_INVERT_ST_ENABLE; }
-       else { settings.flags &= ~BITFLAG_INVERT_ST_ENABLE; }
-      break;
-    case 16: // Reboot to ensure change
-      if (value) { settings.flags |= BITFLAG_HARD_LIMIT_ENABLE; }
-      else { settings.flags &= ~BITFLAG_HARD_LIMIT_ENABLE; }
-      break;
-    case 17:
-      if (value) { 
-        settings.flags |= BITFLAG_HOMING_ENABLE;
-        sys.state = STATE_ALARM;
-        report_feedback_message(MESSAGE_HOMING_ALARM);
-      } else { settings.flags &= ~BITFLAG_HOMING_ENABLE; }
-      break;
-    case 18: settings.homing_dir_mask = trunc(value); break;
-    case 19: settings.homing_feed_rate = value; break;
-    case 20: settings.homing_seek_rate = value; break;
-    case 21: settings.homing_debounce_delay = round(value); break;
-    case 22: settings.homing_pulloff = value; break;
-    default: 
-      return(STATUS_INVALID_STATEMENT);
-  }
-  write_global_settings();
-  return(STATUS_OK);
-}
-
-// Initialize the config subsystem
-void settings_init() {
-  if(!read_global_settings()) {
-    report_status_message(STATUS_SETTING_READ_FAIL);
-    settings_reset(true);
-    report_grbl_settings();
-  }
-  // Read all parameter data into a dummy variable. If error, reset to zero, otherwise do nothing.
-  float coord_data[N_AXIS];
-  uint8_t i;
-  for (i=0; i<=SETTING_INDEX_NCOORD; i++) {
-    if (!settings_read_coord_data(i, coord_data)) {
-      report_status_message(STATUS_SETTING_READ_FAIL);
-    }
-  }
-  // NOTE: Startup lines are handled and called by protocol_init().
-}
+/*
+  settings.c - eeprom configuration handling 
+  Part of Grbl
+
+  Copyright (c) 2009-2011 Simen Svale Skogsrud
+  Copyright (c) 2011-2012 Sungeun K. Jeon  
+
+  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 <avr/io.h>
+#include "protocol.h"
+#include "report.h"
+#include "stepper.h"
+#include "nuts_bolts.h"
+#include "settings.h"
+#include "eeprom.h"
+
+settings_t settings;
+
+// Version 4 outdated settings record
+typedef struct {
+  float steps_per_mm[3];
+  uint8_t microsteps;
+  uint8_t pulse_microseconds;
+  float default_feed_rate;
+  float default_seek_rate;
+  uint8_t invert_mask;
+  float mm_per_arc_segment;
+  float acceleration;
+  float junction_deviation;
+} settings_v4_t;
+
+
+// Method to store startup lines into EEPROM
+void settings_store_startup_line(uint8_t n, char *line)
+{
+  uint16_t addr = n*(LINE_BUFFER_SIZE+1)+EEPROM_ADDR_STARTUP_BLOCK;
+  memcpy_to_eeprom_with_checksum(addr,(char*)line, LINE_BUFFER_SIZE);
+}
+
+// Method to store coord data parameters into EEPROM
+void settings_write_coord_data(uint8_t coord_select, float *coord_data)
+{  
+  uint16_t addr = coord_select*(sizeof(float)*N_AXIS+1) + EEPROM_ADDR_PARAMETERS;
+  memcpy_to_eeprom_with_checksum(addr,(char*)coord_data, sizeof(float)*N_AXIS);
+}  
+
+// Method to store Grbl global settings struct and version number into EEPROM
+void write_global_settings() 
+{
+  eeprom_put_char(0, SETTINGS_VERSION);
+  memcpy_to_eeprom_with_checksum(EEPROM_ADDR_GLOBAL, (char*)&settings, sizeof(settings_t));
+}
+
+// Method to reset Grbl global settings back to defaults. 
+void settings_reset(bool reset_all) {
+  // Reset all settings or only the migration settings to the new version.
+  if (reset_all) {
+    settings.steps_per_mm[X_AXIS] = DEFAULT_X_STEPS_PER_MM;
+    settings.steps_per_mm[Y_AXIS] = DEFAULT_Y_STEPS_PER_MM;
+    settings.steps_per_mm[Z_AXIS] = DEFAULT_Z_STEPS_PER_MM;
+    settings.pulse_microseconds = DEFAULT_STEP_PULSE_MICROSECONDS;
+    settings.default_feed_rate = DEFAULT_FEEDRATE;
+    settings.default_seek_rate = DEFAULT_RAPID_FEEDRATE;
+    settings.acceleration = DEFAULT_ACCELERATION;
+    settings.mm_per_arc_segment = DEFAULT_MM_PER_ARC_SEGMENT;
+    settings.invert_mask = DEFAULT_STEPPING_INVERT_MASK;
+    settings.junction_deviation = DEFAULT_JUNCTION_DEVIATION;
+  }
+  // New settings since last version
+  settings.flags = 0;
+  if (DEFAULT_REPORT_INCHES) { settings.flags |= BITFLAG_REPORT_INCHES; }
+  if (DEFAULT_AUTO_START) { settings.flags |= BITFLAG_AUTO_START; }
+  if (DEFAULT_INVERT_ST_ENABLE) { settings.flags |= BITFLAG_INVERT_ST_ENABLE; }
+  if (DEFAULT_HARD_LIMIT_ENABLE) { settings.flags |= BITFLAG_HARD_LIMIT_ENABLE; }
+  if (DEFAULT_HOMING_ENABLE) { settings.flags |= BITFLAG_HOMING_ENABLE; }
+  settings.homing_dir_mask = DEFAULT_HOMING_DIR_MASK;
+  settings.homing_feed_rate = DEFAULT_HOMING_FEEDRATE;
+  settings.homing_seek_rate = DEFAULT_HOMING_RAPID_FEEDRATE;
+  settings.homing_debounce_delay = DEFAULT_HOMING_DEBOUNCE_DELAY;
+  settings.homing_pulloff = DEFAULT_HOMING_PULLOFF;
+  settings.stepper_idle_lock_time = DEFAULT_STEPPER_IDLE_LOCK_TIME;
+  settings.decimal_places = DEFAULT_DECIMAL_PLACES;
+  settings.n_arc_correction = DEFAULT_N_ARC_CORRECTION;
+  write_global_settings();
+}
+
+// Reads startup line from EEPROM. Updated pointed line string data.
+uint8_t settings_read_startup_line(uint8_t n, char *line)
+{
+  uint16_t addr = n*(LINE_BUFFER_SIZE+1)+EEPROM_ADDR_STARTUP_BLOCK;
+  if (!(memcpy_from_eeprom_with_checksum((char*)line, addr, LINE_BUFFER_SIZE))) {
+    // Reset line with default value
+    line[0] = 0;
+    settings_store_startup_line(n, line);
+    return(false);
+  } else {
+    return(true);
+  }
+}
+
+// Read selected coordinate data from EEPROM. Updates pointed coord_data value.
+uint8_t settings_read_coord_data(uint8_t coord_select, float *coord_data)
+{
+  uint16_t addr = coord_select*(sizeof(float)*N_AXIS+1) + EEPROM_ADDR_PARAMETERS;
+  if (!(memcpy_from_eeprom_with_checksum((char*)coord_data, addr, sizeof(float)*N_AXIS))) {
+    // Reset with default zero vector
+    clear_vector_float(coord_data); 
+    settings_write_coord_data(coord_select,coord_data);
+    return(false);
+  } else {
+    return(true);
+  }
+}  
+
+// Reads Grbl global settings struct from EEPROM.
+uint8_t read_global_settings() {
+  // Check version-byte of eeprom
+  uint8_t version = eeprom_get_char(0);
+  
+  if (version == SETTINGS_VERSION) {
+    // Read settings-record and check checksum
+    if (!(memcpy_from_eeprom_with_checksum((char*)&settings, EEPROM_ADDR_GLOBAL, sizeof(settings_t)))) {
+      return(false);
+    }
+  } else {
+    if (version <= 4) {
+      // Migrate from settings version 4 to current version.
+      if (!(memcpy_from_eeprom_with_checksum((char*)&settings, 1, sizeof(settings_v4_t)))) {
+        return(false);
+      }     
+      settings_reset(false); // Old settings ok. Write new settings only.
+    } else {      
+      return(false);
+    }
+  }
+  return(true);
+}
+
+
+// A helper method to set settings from command line
+uint8_t settings_store_global_setting(int parameter, float value) {
+  switch(parameter) {
+    case 0: case 1: case 2:
+      if (value <= 0.0) { return(STATUS_SETTING_VALUE_NEG); } 
+      settings.steps_per_mm[parameter] = value; break;
+    case 3: 
+      if (value < 3) { return(STATUS_SETTING_STEP_PULSE_MIN); }
+      settings.pulse_microseconds = round(value); break;
+    case 4: settings.default_feed_rate = value; break;
+    case 5: settings.default_seek_rate = value; break;
+    case 6: settings.invert_mask = trunc(value); break;
+    case 7: settings.stepper_idle_lock_time = round(value); break;
+    case 8: settings.acceleration = value*60*60; break; // Convert to mm/min^2 for grbl internal use.
+    case 9: settings.junction_deviation = fabs(value); break;
+    case 10: settings.mm_per_arc_segment = value; break;
+    case 11: settings.n_arc_correction = round(value); break;
+    case 12: settings.decimal_places = round(value); break;
+    case 13:
+      if (value) { settings.flags |= BITFLAG_REPORT_INCHES; }
+      else { settings.flags &= ~BITFLAG_REPORT_INCHES; }
+      break;
+    case 14: // Reboot to ensure change
+      if (value) { settings.flags |= BITFLAG_AUTO_START; }
+      else { settings.flags &= ~BITFLAG_AUTO_START; }
+      break;
+    case 15: // Reboot to ensure change
+       if (value) { settings.flags |= BITFLAG_INVERT_ST_ENABLE; }
+       else { settings.flags &= ~BITFLAG_INVERT_ST_ENABLE; }
+      break;
+    case 16: // Reboot to ensure change
+      if (value) { settings.flags |= BITFLAG_HARD_LIMIT_ENABLE; }
+      else { settings.flags &= ~BITFLAG_HARD_LIMIT_ENABLE; }
+      break;
+    case 17:
+      if (value) { 
+        settings.flags |= BITFLAG_HOMING_ENABLE;
+        sys.state = STATE_ALARM;
+        report_feedback_message(MESSAGE_HOMING_ALARM);
+      } else { settings.flags &= ~BITFLAG_HOMING_ENABLE; }
+      break;
+    case 18: settings.homing_dir_mask = trunc(value); break;
+    case 19: settings.homing_feed_rate = value; break;
+    case 20: settings.homing_seek_rate = value; break;
+    case 21: settings.homing_debounce_delay = round(value); break;
+    case 22: settings.homing_pulloff = value; break;
+    default: 
+      return(STATUS_INVALID_STATEMENT);
+  }
+  write_global_settings();
+  return(STATUS_OK);
+}
+
+// Initialize the config subsystem
+void settings_init() {
+  if(!read_global_settings()) {
+    report_status_message(STATUS_SETTING_READ_FAIL);
+    settings_reset(true);
+    report_grbl_settings();
+  }
+  // Read all parameter data into a dummy variable. If error, reset to zero, otherwise do nothing.
+  float coord_data[N_AXIS];
+  uint8_t i;
+  for (i=0; i<=SETTING_INDEX_NCOORD; i++) {
+    if (!settings_read_coord_data(i, coord_data)) {
+      report_status_message(STATUS_SETTING_READ_FAIL);
+    }
+  }
+  // NOTE: Startup lines are handled and called by main.c at the end of initialization.
+}