Removed interrupt nesting in the stepper ISR.

Add serial checkRx in stepper ISR.
Copied HardwareSerial to MarlinSerial (Needed for checkRx).

Marlin/Configuration.h

@@ -232,7 +232,7 @@ const bool Z_ENDSTOPS_INVERTING = true; // set to true to invert the logic of th
 
 // minimum time in microseconds that a movement needs to take if the buffer is emptied.   Increase this number if you see blobs while printing high speed & high detail.  It will slowdown on the detailed stuff.
 #define DEFAULT_MINSEGMENTTIME        20000   // Obsolete delete this
-#define DEFAULT_XYJERK                30.0    // (mm/sec)
+#define DEFAULT_XYJERK                20.0    // (mm/sec)
 #define DEFAULT_ZJERK                 0.4     // (mm/sec)
 
 

Marlin/EEPROMwrite.h

@@ -4,6 +4,7 @@
 #include "Marlin.h"
 #include "planner.h"
 #include "temperature.h"
+
 #include <EEPROM.h>
 
 template <class T> int EEPROM_writeAnything(int &ee, const T& value)

Marlin/Marlin.h

@@ -3,10 +3,12 @@
 
 // Tonokip RepRap firmware rewrite based off of Hydra-mmm firmware.
 // Licence: GPL
+#define  HardwareSerial_h // trick to disable the standard HWserial
 #include <WProgram.h>
 #include "fastio.h"
 #include <avr/pgmspace.h>
 #include "Configuration.h"
+#include "MarlinSerial.h"
 
 //#define SERIAL_ECHO(x) Serial << "echo: " << x;
 //#define SERIAL_ECHOLN(x) Serial << "echo: "<<x<<endl;
@@ -17,10 +19,10 @@
 
 
 
-#define SERIAL_PROTOCOL(x) Serial.print(x);
+#define SERIAL_PROTOCOL(x) MSerial.print(x);
 #define SERIAL_PROTOCOLPGM(x) serialprintPGM(PSTR(x));
-#define SERIAL_PROTOCOLLN(x) {Serial.print(x);Serial.write('\n');}
+#define SERIAL_PROTOCOLLN(x) {MSerial.print(x);MSerial.write('\n');}
-#define SERIAL_PROTOCOLLNPGM(x) {serialprintPGM(PSTR(x));Serial.write('\n');}
+#define SERIAL_PROTOCOLLNPGM(x) {serialprintPGM(PSTR(x));MSerial.write('\n');}
 
 const char errormagic[] PROGMEM ="Error:";
 const char echomagic[] PROGMEM ="echo:";
@@ -46,7 +48,7 @@ inline void serialprintPGM(const char *str)
   char ch=pgm_read_byte(str);
   while(ch)
   {
-    Serial.write(ch);
+    MSerial.write(ch);
     ch=pgm_read_byte(++str);
   }
 }

Marlin/Marlin.pde

@@ -176,6 +176,7 @@ static unsigned long stoptime=0;
 
 static uint8_t tmp_extruder;
 
+
 //===========================================================================
 //=============================ROUTINES=============================
 //===========================================================================
@@ -199,13 +200,6 @@ extern "C"{
   }
 }
 
-
-
-
-
-
-
-
 //adds an command to the main command buffer
 //thats really done in a non-safe way.
 //needs overworking someday
@@ -226,7 +220,7 @@ void enquecommand(const char *cmd)
 
 void setup()
 { 
-  Serial.begin(BAUDRATE);
+  MSerial.begin(BAUDRATE);
   SERIAL_ECHO_START;
   SERIAL_ECHOLNPGM(VERSION_STRING);
   SERIAL_PROTOCOLLNPGM("start");
@@ -289,15 +283,14 @@ void loop()
   manage_heater();
   manage_inactivity(1);
   checkHitEndstops();
-  checkStepperErrors();
   LCD_STATUS;
 }
 
 
 inline void get_command() 
 { 
-  while( Serial.available() > 0  && buflen < BUFSIZE) {
+  while( MSerial.available() > 0  && buflen < BUFSIZE) {
-    serial_char = Serial.read();
+    serial_char = MSerial.read();
     if(serial_char == '\n' || serial_char == '\r' || serial_char == ':' || serial_count >= (MAX_CMD_SIZE - 1) ) 
     {
       if(!serial_count) return; //if empty line
@@ -1039,7 +1032,7 @@ inline void process_commands()
 void FlushSerialRequestResend()
 {
   //char cmdbuffer[bufindr][100]="Resend:";
-  Serial.flush();
+  MSerial.flush();
   SERIAL_PROTOCOLPGM("Resend:");
   SERIAL_PROTOCOLLN(gcode_LastN + 1);
   ClearToSend();
@@ -1088,7 +1081,7 @@ void prepare_move()
     if (destination[Z_AXIS] > Z_MAX_LENGTH) destination[Z_AXIS] = Z_MAX_LENGTH;
   }
 
-  plan_buffer_line(destination[X_AXIS], destination[Y_AXIS], destination[Z_AXIS], destination[E_AXIS], feedrate*feedmultiply/60/100.0);
+  plan_buffer_line(destination[X_AXIS], destination[Y_AXIS], destination[Z_AXIS], destination[E_AXIS], feedrate*feedmultiply/60/100.0, active_extruder);
   for(int8_t i=0; i < NUM_AXIS; i++) {
     current_position[i] = destination[i];
   }
@@ -1098,7 +1091,7 @@ void prepare_arc_move(char isclockwise) {
   float r = hypot(offset[X_AXIS], offset[Y_AXIS]); // Compute arc radius for mc_arc
 
   // Trace the arc
-  mc_arc(current_position, destination, offset, X_AXIS, Y_AXIS, Z_AXIS, feedrate*feedmultiply/60/100.0, r, isclockwise);
+  mc_arc(current_position, destination, offset, X_AXIS, Y_AXIS, Z_AXIS, feedrate*feedmultiply/60/100.0, r, isclockwise, active_extruder);
   
   // 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
@@ -1108,10 +1101,6 @@ void prepare_arc_move(char isclockwise) {
   }
 }
 
-
-
-
-
 void manage_inactivity(byte debug) 
 { 
   if( (millis()-previous_millis_cmd) >  max_inactive_time ) 

Marlin/MarlinSerial.cpp

@@ -0,0 +1,213 @@
+/*
+  HardwareSerial.cpp - Hardware serial library for Wiring
+  Copyright (c) 2006 Nicholas Zambetti.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+  
+  Modified 23 November 2006 by David A. Mellis
+  Modified 28 September 2010 by Mark Sproul
+*/
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <inttypes.h>
+#include "wiring.h"
+#include "wiring_private.h"
+
+// this next line disables the entire HardwareSerial.cpp, 
+// this is so I can support Attiny series and any other chip without a uart
+#if defined(UBRRH) || defined(UBRR0H) || defined(UBRR1H) || defined(UBRR2H) || defined(UBRR3H)
+
+#include "MarlinSerial.h"
+
+// Define constants and variables for buffering incoming serial data.  We're
+// using a ring buffer (I think), in which rx_buffer_head is the index of the
+// location to which to write the next incoming character and rx_buffer_tail
+// is the index of the location from which to read.
+#define RX_BUFFER_SIZE 128
+
+struct ring_buffer
+{
+  unsigned char buffer[RX_BUFFER_SIZE];
+  int head;
+  int tail;
+};
+
+#if defined(UBRRH) || defined(UBRR0H)
+  ring_buffer rx_buffer  =  { { 0 }, 0, 0 };
+#endif
+
+
+inline void store_char(unsigned char c, ring_buffer *rx_buffer)
+{
+  int i = (unsigned int)(rx_buffer->head + 1) % RX_BUFFER_SIZE;
+
+  // if we should be storing the received character into the location
+  // just before the tail (meaning that the head would advance to the
+  // current location of the tail), we're about to overflow the buffer
+  // and so we don't write the character or advance the head.
+  if (i != rx_buffer->tail) {
+    rx_buffer->buffer[rx_buffer->head] = c;
+    rx_buffer->head = i;
+  }
+}
+
+
+//#elif defined(SIG_USART_RECV)
+#if defined(USART0_RX_vect)
+  // fixed by Mark Sproul this is on the 644/644p
+  //SIGNAL(SIG_USART_RECV)
+  SIGNAL(USART0_RX_vect)
+  {
+  #if defined(UDR0)
+    unsigned char c  =  UDR0;
+  #elif defined(UDR)
+    unsigned char c  =  UDR;  //  atmega8, atmega32
+  #else
+    #error UDR not defined
+  #endif
+    store_char(c, &rx_buffer);
+  }
+#endif
+
+// Constructors ////////////////////////////////////////////////////////////////
+
+MarlinSerial::MarlinSerial(ring_buffer *rx_buffer,
+  volatile uint8_t *ubrrh, volatile uint8_t *ubrrl,
+  volatile uint8_t *ucsra, volatile uint8_t *ucsrb,
+  volatile uint8_t *udr,
+  uint8_t rxen, uint8_t txen, uint8_t rxcie, uint8_t udre, uint8_t u2x)
+{
+  _rx_buffer = rx_buffer;
+  _ubrrh = ubrrh;
+  _ubrrl = ubrrl;
+  _ucsra = ucsra;
+  _ucsrb = ucsrb;
+  _udr = udr;
+  _rxen = rxen;
+  _txen = txen;
+  _rxcie = rxcie;
+  _udre = udre;
+  _u2x = u2x;
+}
+
+// Public Methods //////////////////////////////////////////////////////////////
+
+void MarlinSerial::begin(long baud)
+{
+  uint16_t baud_setting;
+  bool use_u2x = true;
+
+#if F_CPU == 16000000UL
+  // hardcoded exception for compatibility with the bootloader shipped
+  // with the Duemilanove and previous boards and the firmware on the 8U2
+  // on the Uno and Mega 2560.
+  if (baud == 57600) {
+    use_u2x = false;
+  }
+#endif
+  
+  if (use_u2x) {
+    *_ucsra = 1 << _u2x;
+    baud_setting = (F_CPU / 4 / baud - 1) / 2;
+  } else {
+    *_ucsra = 0;
+    baud_setting = (F_CPU / 8 / baud - 1) / 2;
+  }
+
+  // assign the baud_setting, a.k.a. ubbr (USART Baud Rate Register)
+  *_ubrrh = baud_setting >> 8;
+  *_ubrrl = baud_setting;
+
+  sbi(*_ucsrb, _rxen);
+  sbi(*_ucsrb, _txen);
+  sbi(*_ucsrb, _rxcie);
+}
+
+void MarlinSerial::end()
+{
+  cbi(*_ucsrb, _rxen);
+  cbi(*_ucsrb, _txen);
+  cbi(*_ucsrb, _rxcie);  
+}
+
+int MarlinSerial::available(void)
+{
+  return (unsigned int)(RX_BUFFER_SIZE + _rx_buffer->head - _rx_buffer->tail) % RX_BUFFER_SIZE;
+}
+
+int MarlinSerial::peek(void)
+{
+  if (_rx_buffer->head == _rx_buffer->tail) {
+    return -1;
+  } else {
+    return _rx_buffer->buffer[_rx_buffer->tail];
+  }
+}
+
+int MarlinSerial::read(void)
+{
+  // if the head isn't ahead of the tail, we don't have any characters
+  if (_rx_buffer->head == _rx_buffer->tail) {
+    return -1;
+  } else {
+    unsigned char c = _rx_buffer->buffer[_rx_buffer->tail];
+    _rx_buffer->tail = (unsigned int)(_rx_buffer->tail + 1) % RX_BUFFER_SIZE;
+    return c;
+  }
+}
+
+void MarlinSerial::flush()
+{
+  // don't reverse this or there may be problems if the RX interrupt
+  // occurs after reading the value of rx_buffer_head but before writing
+  // the value to rx_buffer_tail; the previous value of rx_buffer_head
+  // may be written to rx_buffer_tail, making it appear as if the buffer
+  // don't reverse this or there may be problems if the RX interrupt
+  // occurs after reading the value of rx_buffer_head but before writing
+  // the value to rx_buffer_tail; the previous value of rx_buffer_head
+  // may be written to rx_buffer_tail, making it appear as if the buffer
+  // were full, not empty.
+  _rx_buffer->head = _rx_buffer->tail;
+}
+
+void MarlinSerial::write(uint8_t c)
+{
+  while (!((*_ucsra) & (1 << _udre)))
+    ;
+
+  *_udr = c;
+}
+
+void MarlinSerial::checkRx()
+{
+  if((UCSR0A & (1<<RXC0)) != 0) {
+    unsigned char c  =  UDR0;
+    store_char(c, &rx_buffer);
+  }
+}
+
+// Preinstantiate Objects //////////////////////////////////////////////////////
+
+#if defined(UBRR0H) && defined(UBRR0L)
+  MarlinSerial MSerial(&rx_buffer, &UBRR0H, &UBRR0L, &UCSR0A, &UCSR0B, &UDR0, RXEN0, TXEN0, RXCIE0, UDRE0, U2X0);
+#else
+  #error no serial port defined  (port 0)
+#endif
+
+
+#endif // whole file
+

Marlin/MarlinSerial.h

@@ -0,0 +1,66 @@
+/*
+  HardwareSerial.h - Hardware serial library for Wiring
+  Copyright (c) 2006 Nicholas Zambetti.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library 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
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+
+  Modified 28 September 2010 by Mark Sproul
+*/
+
+#ifndef MarlinSerial_h
+#define MarlinSerial_h
+
+#include <inttypes.h>
+
+#include "Stream.h"
+
+struct ring_buffer;
+
+class MarlinSerial : public Stream
+{
+  private:
+    ring_buffer *_rx_buffer;
+    volatile uint8_t *_ubrrh;
+    volatile uint8_t *_ubrrl;
+    volatile uint8_t *_ucsra;
+    volatile uint8_t *_ucsrb;
+    volatile uint8_t *_udr;
+    uint8_t _rxen;
+    uint8_t _txen;
+    uint8_t _rxcie;
+    uint8_t _udre;
+    uint8_t _u2x;
+  public:
+    MarlinSerial(ring_buffer *rx_buffer,
+      volatile uint8_t *ubrrh, volatile uint8_t *ubrrl,
+      volatile uint8_t *ucsra, volatile uint8_t *ucsrb,
+      volatile uint8_t *udr,
+      uint8_t rxen, uint8_t txen, uint8_t rxcie, uint8_t udre, uint8_t u2x);
+    void begin(long);
+    void end();
+    virtual int available(void);
+    virtual int peek(void);
+    virtual int read(void);
+    virtual void flush(void);
+    virtual void write(uint8_t);
+    virtual void checkRx(void);
+    using Print::write; // pull in write(str) and write(buf, size) from Print
+};
+
+#if defined(UBRRH) || defined(UBRR0H)
+  extern MarlinSerial MSerial;
+#endif
+
+#endif

Marlin/Sd2Card.cpp

@@ -18,6 +18,7 @@
  * <http://www.gnu.org/licenses/>.
  */
 #if ARDUINO < 100
+#define  HardwareSerial_h // trick to disable the standard HWserial
 #include <WProgram.h>
 #else  // ARDUINO
 #include <Arduino.h>

Marlin/SdBaseFile.cpp

@@ -306,7 +306,7 @@ void SdBaseFile::getpos(fpos_t* pos) {
  * LS_R - Recursive list of subdirectories.
  */
 void SdBaseFile::ls(uint8_t flags) {
-  ls(&Serial, flags, 0);
+  ls(&MSerial, flags, 0);
 }
 //------------------------------------------------------------------------------
 /** List directory contents.
@@ -949,7 +949,7 @@ int SdBaseFile::peek() {
  */
 void SdBaseFile::printDirName(const dir_t& dir,
   uint8_t width, bool printSlash) {
-  printDirName(&Serial, dir, width, printSlash);
+  printDirName(&MSerial, dir, width, printSlash);
 }
 //------------------------------------------------------------------------------
 /** %Print the name field of a directory entry in 8.3 format.
@@ -993,7 +993,7 @@ static void print2u(Print* pr, uint8_t v) {
  * \param[in] fatDate The date field from a directory entry.
  */
 void SdBaseFile::printFatDate(uint16_t fatDate) {
-  printFatDate(&Serial, fatDate);
+  printFatDate(&MSerial, fatDate);
 }
 //------------------------------------------------------------------------------
 /** %Print a directory date field.
@@ -1018,7 +1018,7 @@ void SdBaseFile::printFatDate(Print* pr, uint16_t fatDate) {
  * \param[in] fatTime The time field from a directory entry.
  */
 void SdBaseFile::printFatTime(uint16_t fatTime) {
-  printFatTime(&Serial, fatTime);
+  printFatTime(&MSerial, fatTime);
 }
 //------------------------------------------------------------------------------
 /** %Print a directory time field.
@@ -1044,7 +1044,7 @@ void SdBaseFile::printFatTime(Print* pr, uint16_t fatTime) {
 bool SdBaseFile::printName() {
   char name[13];
   if (!getFilename(name)) return false;
-  Serial.print(name);
+  MSerial.print(name);
   return true;
 }
 //------------------------------------------------------------------------------

Marlin/SdBaseFile.h

@@ -25,7 +25,9 @@
  */
 #include <avr/pgmspace.h>
 #if ARDUINO < 100
+#define  HardwareSerial_h // trick to disable the standard HWserial
 #include <WProgram.h>
+#include "MarlinSerial.h"
 #else  // ARDUINO
 #include <Arduino.h>
 #endif  // ARDUINO

Marlin/SdFatUtil.cpp

@@ -62,7 +62,7 @@ void SdFatUtil::println_P(Print* pr, PGM_P str) {
  * \param[in] str Pointer to string stored in flash memory.
  */
 void SdFatUtil::SerialPrint_P(PGM_P str) {
-  print_P(&Serial, str);
+  print_P(&MSerial, str);
 }
 //------------------------------------------------------------------------------
 /** %Print a string in flash memory to Serial followed by a CR/LF.
@@ -70,5 +70,5 @@ void SdFatUtil::SerialPrint_P(PGM_P str) {
  * \param[in] str Pointer to string stored in flash memory.
  */
 void SdFatUtil::SerialPrintln_P(PGM_P str) {
-  println_P(&Serial, str);
+  println_P(&MSerial, str);
 }

Marlin/SdFatUtil.h

@@ -25,7 +25,9 @@
  */
 #include <avr/pgmspace.h>
 #if ARDUINO < 100
+#define  HardwareSerial_h // trick to disable the standard HWserial
 #include <WProgram.h>
+#include "MarlinSerial.h"
 #else  // ARDUINO
 #include <Arduino.h>
 #endif  // ARDUINO

Marlin/motion_control.cpp

@@ -27,7 +27,7 @@
 // The arc is approximated by generating a huge number of tiny, linear segments. The length of each 
 // segment is configured in settings.mm_per_arc_segment.  
 void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8_t axis_1, 
-  uint8_t axis_linear, float feed_rate, float radius, uint8_t isclockwise)
+  uint8_t axis_linear, float feed_rate, float radius, uint8_t isclockwise, uint8_t extruder)
 {      
   //   int acceleration_manager_was_enabled = plan_is_acceleration_manager_enabled();
   //   plan_set_acceleration_manager_enabled(false); // disable acceleration management for the duration of the arc
@@ -123,11 +123,11 @@ void mc_arc(float *position, float *target, float *offset, uint8_t axis_0, uint8
     arc_target[axis_1] = center_axis1 + r_axis1;
     arc_target[axis_linear] += linear_per_segment;
     arc_target[E_AXIS] += extruder_per_segment;
-    plan_buffer_line(arc_target[X_AXIS], arc_target[Y_AXIS], arc_target[Z_AXIS], arc_target[E_AXIS], feed_rate);
+    plan_buffer_line(arc_target[X_AXIS], arc_target[Y_AXIS], arc_target[Z_AXIS], arc_target[E_AXIS], feed_rate, extruder);
     
   }
   // Ensure last segment arrives at target location.
-  plan_buffer_line(target[X_AXIS], target[Y_AXIS], target[Z_AXIS], target[E_AXIS], feed_rate);
+  plan_buffer_line(target[X_AXIS], target[Y_AXIS], target[Z_AXIS], target[E_AXIS], feed_rate, extruder);
 
   //   plan_set_acceleration_manager_enabled(acceleration_manager_was_enabled);
 }

Marlin/motion_control.h

@@ -27,6 +27,6 @@
 // the direction of helical travel, radius == circle radius, isclockwise boolean. Used
 // for vector transformation direction.
 void mc_arc(float *position, float *target, float *offset, unsigned char axis_0, unsigned char axis_1,
-  unsigned char axis_linear, float feed_rate, float radius, unsigned char isclockwise);
+  unsigned char axis_linear, float feed_rate, float radius, unsigned char isclockwise, uint8_t extruder);
   
 #endif

Marlin/planner.cpp

@@ -451,7 +451,7 @@ float junction_deviation = 0.1;
 // Add a new linear movement to the buffer. steps_x, _y and _z is the absolute position in 
 // mm. Microseconds specify how many microseconds the move should take to perform. To aid acceleration
 // calculation the caller must also provide the physical length of the line in millimeters.
-void plan_buffer_line(const float &x, const float &y, const float &z, const float &e,  float feed_rate)
+void plan_buffer_line(const float &x, const float &y, const float &z, const float &e,  float feed_rate, const uint8_t &extruder)
 {
   // Calculate the buffer head after we push this byte
   int next_buffer_head = next_block_index(block_buffer_head);
@@ -532,7 +532,7 @@ void plan_buffer_line(const float &x, const float &y, const float &z, const floa
   // slow down when de buffer starts to empty, rather than wait at the corner for a buffer refill
   int moves_queued=(block_buffer_head-block_buffer_tail + BLOCK_BUFFER_SIZE) & (BLOCK_BUFFER_SIZE - 1);
   
-  if(moves_queued < (BLOCK_BUFFER_SIZE * 0.5)) feed_rate = feed_rate*moves_queued / (BLOCK_BUFFER_SIZE * 0.5); 
+  if(moves_queued < (BLOCK_BUFFER_SIZE * 0.5) && moves_queued > 1) feed_rate = feed_rate*moves_queued / (BLOCK_BUFFER_SIZE * 0.5); 
 #endif
 
 /*

Marlin/planner.h

@@ -66,7 +66,7 @@ void plan_init();
 
 // Add a new linear movement to the buffer. x, y and z is the signed, absolute target position in 
 // millimaters. Feed rate specifies the speed of the motion.
-void plan_buffer_line(const float &x, const float &y, const float &z, const float &e, float feed_rate);
+void plan_buffer_line(const float &x, const float &y, const float &z, const float &e, float feed_rate, const uint8_t &extruder);
 
 // Set position. Used for G92 instructions.
 void plan_set_position(const float &x, const float &y, const float &z, const float &e);

Marlin/stepper.cpp

@@ -52,7 +52,7 @@ static long counter_x,       // Counter variables for the bresenham line tracer
             counter_y, 
             counter_z,       
             counter_e;
-static unsigned long step_events_completed; // The number of step events executed in the current block
+volatile static unsigned long step_events_completed; // The number of step events executed in the current block
 #ifdef ADVANCE
   static long advance_rate, advance, final_advance = 0;
   static short old_advance = 0;
@@ -63,6 +63,7 @@ static long acceleration_time, deceleration_time;
 //static unsigned long accelerate_until, decelerate_after, acceleration_rate, initial_rate, final_rate, nominal_rate;
 static unsigned short acc_step_rate; // needed for deccelaration start point
 static char step_loops;
+static unsigned short OCR1A_nominal;
 
 volatile long endstops_trigsteps[3]={0,0,0};
 volatile long endstops_stepsTotal,endstops_stepsDone;
@@ -77,10 +78,6 @@ static bool old_y_max_endstop=false;
 static bool old_z_min_endstop=false;
 static bool old_z_max_endstop=false;
 
-static bool busy_error=false;
-unsigned short OCR1A_error=12345;
-unsigned short OCR1A_nominal;
-
 volatile long count_position[NUM_AXIS] = { 0, 0, 0, 0};
 volatile char count_direction[NUM_AXIS] = { 1, 1, 1, 1};
 
@@ -164,15 +161,6 @@ asm volatile ( \
 #define ENABLE_STEPPER_DRIVER_INTERRUPT()  TIMSK1 |= (1<<OCIE1A)
 #define DISABLE_STEPPER_DRIVER_INTERRUPT() TIMSK1 &= ~(1<<OCIE1A)
 
-void checkStepperErrors()
-{
-  if(busy_error) {
-    SERIAL_ERROR_START
-    SERIAL_ERROR(OCR1A_error);
-    SERIAL_ERRORLNPGM(" ISR overtaking itself.");
-    busy_error = false;
-  }
-}
 
 void checkHitEndstops()
 {
@@ -255,7 +243,7 @@ inline unsigned short calc_timer(unsigned short step_rate) {
     timer = (unsigned short)pgm_read_word_near(table_address);
     timer -= (((unsigned short)pgm_read_word_near(table_address+2) * (unsigned char)(step_rate & 0x0007))>>3);
   }
-  if(timer < 100) { timer = 100; Serial.print("Steprate to high : "); Serial.println(step_rate); }//(20kHz this should never happen)
+  if(timer < 100) { timer = 100; MSerial.print("Steprate to high : "); MSerial.println(step_rate); }//(20kHz this should never happen)
   return timer;
 }
 
@@ -278,16 +266,6 @@ inline void trapezoid_generator_reset() {
 // It pops blocks from the block_buffer and executes them by pulsing the stepper pins appropriately. 
 ISR(TIMER1_COMPA_vect)
 {    
-  if(busy){ 
-    OCR1A_error = OCR1A;
-    busy_error = true;
-    OCR1A = 30000;
-    return; 
-  } // The busy-flag is used to avoid reentering this interrupt
-
-  busy = true;
-  sei(); // Re enable interrupts (normally disabled while inside an interrupt handler)
-
   // If there is no current block, attempt to pop one from the buffer
   if (current_block == NULL) {
     // Anything in the buffer?
@@ -304,7 +282,7 @@ ISR(TIMER1_COMPA_vect)
 //      #endif
     } 
     else {
-//      DISABLE_STEPPER_DRIVER_INTERRUPT();
+        OCR1A=2000; // 1kHz.
     }    
   } 
 
@@ -404,8 +382,8 @@ ISR(TIMER1_COMPA_vect)
         count_direction[E_AXIS]=-1;
       }
     #endif //!ADVANCE
-
     for(int8_t i=0; i < step_loops; i++) { // Take multiple steps per interrupt (For high speed moves) 
+    MSerial.checkRx();
     /*
       counter_e += current_block->steps_e;
       if (counter_e > 0) {
@@ -470,6 +448,7 @@ ISR(TIMER1_COMPA_vect)
     unsigned short timer;
     unsigned short step_rate;
     if (step_events_completed <= current_block->accelerate_until) {
+      
       MultiU24X24toH16(acc_step_rate, acceleration_time, current_block->acceleration_rate);
       acc_step_rate += current_block->initial_rate;
       
@@ -519,8 +498,6 @@ ISR(TIMER1_COMPA_vect)
       plan_discard_current_block();
     }   
   } 
-  cli(); // disable interrupts
-  busy=false;
 }
 
 #ifdef ADVANCE