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/**

 * Marlin 3D Printer Firmware

 * Copyright (C) 2016 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]

 *

 * Based on Sprinter and grbl.

 * Copyright (C) 2011 Camiel Gubbels / Erik van der Zalm

 *

 * This program 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.

 *

 * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.

 *

 */

/**

 * MarlinSerial.cpp - Hardware serial library for Wiring

 * Copyright (c) 2006 Nicholas Zambetti.  All right reserved.

 *

 * Modified 23 November 2006 by David A. Mellis

 * Modified 28 September 2010 by Mark Sproul

 * Modified 14 February 2016 by Andreas Hardtung (added tx buffer)

 * Modified 01 October 2017 by Eduardo José Tagle (added XON/XOFF)

 * Modified 10 June 2018 by Eduardo José Tagle (See #10991)

 */

// Disable HardwareSerial.cpp to support chips without a UART (Attiny, etc.)

#include "MarlinConfig.h"

#if USE_MARLINSERIAL && (defined(UBRRH) || defined(UBRR0H) || defined(UBRR1H) || defined(UBRR2H) || defined(UBRR3H))

  #include "MarlinSerial.h"

  #include "Marlin.h"

  struct ring_buffer_r {

    unsigned char buffer[RX_BUFFER_SIZE];

    volatile ring_buffer_pos_t head, tail;

  };

  #if TX_BUFFER_SIZE > 0

    struct ring_buffer_t {

      unsigned char buffer[TX_BUFFER_SIZE];

      volatile uint8_t head, tail;

    };

  #endif

  #if UART_PRESENT(SERIAL_PORT)

    ring_buffer_r rx_buffer = { { 0 }, 0, 0 };

    #if TX_BUFFER_SIZE > 0

      ring_buffer_t tx_buffer = { { 0 }, 0, 0 };

    #endif

    static bool _written;

  #endif

  #if ENABLED(SERIAL_XON_XOFF)

    constexpr uint8_t XON_XOFF_CHAR_SENT = 0x80,  // XON / XOFF Character was sent

                      XON_XOFF_CHAR_MASK = 0x1F;  // XON / XOFF character to send

    // XON / XOFF character definitions

    constexpr uint8_t XON_CHAR  = 17, XOFF_CHAR = 19;

    uint8_t xon_xoff_state = XON_XOFF_CHAR_SENT | XON_CHAR;

  #endif

  #if ENABLED(SERIAL_STATS_DROPPED_RX)

    uint8_t rx_dropped_bytes = 0;

  #endif

  #if ENABLED(SERIAL_STATS_RX_BUFFER_OVERRUNS)

    uint8_t rx_buffer_overruns = 0;

  #endif

  #if ENABLED(SERIAL_STATS_RX_FRAMING_ERRORS)

    uint8_t rx_framing_errors = 0;

  #endif

  #if ENABLED(SERIAL_STATS_MAX_RX_QUEUED)

    ring_buffer_pos_t rx_max_enqueued = 0;

  #endif

  // A SW memory barrier, to ensure GCC does not overoptimize loops

  #define sw_barrier() asm volatile("": : :"memory");

  #if ENABLED(EMERGENCY_PARSER)

    #include "emergency_parser.h"

  #endif

  // "Atomically" read the RX head index value without disabling interrupts:

  // This MUST be called with RX interrupts enabled, and CAN'T be called

  // from the RX ISR itself!

  FORCE_INLINE ring_buffer_pos_t atomic_read_rx_head() {

    #if RX_BUFFER_SIZE > 256

      // Keep reading until 2 consecutive reads return the same value,

      // meaning there was no update in-between caused by an interrupt.

      // This works because serial RX interrupts happen at a slower rate

      // than successive reads of a variable, so 2 consecutive reads with

      // the same value means no interrupt updated it.

      ring_buffer_pos_t vold, vnew = rx_buffer.head;

      sw_barrier();

      do {

        vold = vnew;

        vnew = rx_buffer.head;

        sw_barrier();

      } while (vold != vnew);

      return vnew;

    #else

      // With an 8bit index, reads are always atomic. No need for special handling

      return rx_buffer.head;

    #endif

  }

  #if RX_BUFFER_SIZE > 256

    static volatile bool rx_tail_value_not_stable = false;

    static volatile uint16_t rx_tail_value_backup = 0;

  #endif

  // Set RX tail index, taking into account the RX ISR could interrupt

  //  the write to this variable in the middle - So a backup strategy

  //  is used to ensure reads of the correct values.

  //    -Must NOT be called from the RX ISR -

  FORCE_INLINE void atomic_set_rx_tail(ring_buffer_pos_t value) {

    #if RX_BUFFER_SIZE > 256

      // Store the new value in the backup

      rx_tail_value_backup = value;

      sw_barrier();

      // Flag we are about to change the true value

      rx_tail_value_not_stable = true;

      sw_barrier();

      // Store the new value

      rx_buffer.tail = value;

      sw_barrier();

      // Signal the new value is completely stored into the value

      rx_tail_value_not_stable = false;

      sw_barrier();

    #else

      rx_buffer.tail = value;

    #endif

  }

  // Get the RX tail index, taking into account the read could be

  //  interrupting in the middle of the update of that index value

  //    -Called from the RX ISR -

  FORCE_INLINE ring_buffer_pos_t atomic_read_rx_tail() {

    #if RX_BUFFER_SIZE > 256

      // If the true index is being modified, return the backup value

      if (rx_tail_value_not_stable) return rx_tail_value_backup;

    #endif

    // The true index is stable, return it

    return rx_buffer.tail;

  }

  // (called with RX interrupts disabled)

  FORCE_INLINE void store_rxd_char() {

    // Get the tail - Nothing can alter its value while this ISR is executing, but there's

    // a chance that this ISR interrupted the main process while it was updating the index.

    // The backup mechanism ensures the correct value is always returned.

    const ring_buffer_pos_t t = atomic_read_rx_tail();

    // Get the head pointer - This ISR is the only one that modifies its value, so it's safe to read here

    ring_buffer_pos_t h = rx_buffer.head;

    // Get the next element

    ring_buffer_pos_t i = (ring_buffer_pos_t)(h + 1) & (ring_buffer_pos_t)(RX_BUFFER_SIZE - 1);

    // This must read the M_UCSRxA register before reading the received byte to detect error causes

    #if ENABLED(SERIAL_STATS_DROPPED_RX)

      if (TEST(M_UCSRxA, M_DORx) && !++rx_dropped_bytes) --rx_dropped_bytes;

    #endif

    #if ENABLED(SERIAL_STATS_RX_BUFFER_OVERRUNS)

      if (TEST(M_UCSRxA, M_DORx) && !++rx_buffer_overruns) --rx_buffer_overruns;

    #endif

    #if ENABLED(SERIAL_STATS_RX_FRAMING_ERRORS)

      if (TEST(M_UCSRxA, M_FEx) && !++rx_framing_errors) --rx_framing_errors;

    #endif

    // Read the character from the USART

    uint8_t c = M_UDRx;

    #if ENABLED(EMERGENCY_PARSER)

      emergency_parser.update(c);

    #endif

    // If the character is to be stored at the index just before the tail

    // (such that the head would advance to the current tail), the RX FIFO is

    // full, so don't write the character or advance the head.

    if (i != t) {

      rx_buffer.buffer[h] = c;

      h = i;

    }

    #if ENABLED(SERIAL_STATS_DROPPED_RX)

      else if (!++rx_dropped_bytes) --rx_dropped_bytes;

    #endif

    #if ENABLED(SERIAL_STATS_MAX_RX_QUEUED)

      // Calculate count of bytes stored into the RX buffer

      const ring_buffer_pos_t rx_count = (ring_buffer_pos_t)(h - t) & (ring_buffer_pos_t)(RX_BUFFER_SIZE - 1);

      // Keep track of the maximum count of enqueued bytes

      NOLESS(rx_max_enqueued, rx_count);

    #endif

    #if ENABLED(SERIAL_XON_XOFF)

      // If the last char that was sent was an XON

      if ((xon_xoff_state & XON_XOFF_CHAR_MASK) == XON_CHAR) {

        // Bytes stored into the RX buffer

        const ring_buffer_pos_t rx_count = (ring_buffer_pos_t)(h - t) & (ring_buffer_pos_t)(RX_BUFFER_SIZE - 1);

        // If over 12.5% of RX buffer capacity, send XOFF before running out of

        // RX buffer space .. 325 bytes @ 250kbits/s needed to let the host react

        // and stop sending bytes. This translates to 13mS propagation time.

        if (rx_count >= (RX_BUFFER_SIZE) / 8) {

          // At this point, definitely no TX interrupt was executing, since the TX ISR can't be preempted.

          // Don't enable the TX interrupt here as a means to trigger the XOFF char, because if it happens

          // to be in the middle of trying to disable the RX interrupt in the main program, eventually the

          // enabling of the TX interrupt could be undone. The ONLY reliable thing this can do to ensure

          // the sending of the XOFF char is to send it HERE AND NOW.

          // About to send the XOFF char

          xon_xoff_state = XOFF_CHAR | XON_XOFF_CHAR_SENT;

          // Wait until the TX register becomes empty and send it - Here there could be a problem

          // - While waiting for the TX register to empty, the RX register could receive a new

          //   character. This must also handle that situation!

          while (!TEST(M_UCSRxA, M_UDREx)) {

            if (TEST(M_UCSRxA,M_RXCx)) {

              // A char arrived while waiting for the TX buffer to be empty - Receive and process it!

              i = (ring_buffer_pos_t)(h + 1) & (ring_buffer_pos_t)(RX_BUFFER_SIZE - 1);

              // Read the character from the USART

              c = M_UDRx;

              #if ENABLED(EMERGENCY_PARSER)

                emergency_parser.update(c);

              #endif

              // If the character is to be stored at the index just before the tail

              // (such that the head would advance to the current tail), the FIFO is

              // full, so don't write the character or advance the head.

              if (i != t) {

                rx_buffer.buffer[h] = c;

                h = i;

              }

              #if ENABLED(SERIAL_STATS_DROPPED_RX)

                else if (!++rx_dropped_bytes) --rx_dropped_bytes;

              #endif

            }

            sw_barrier();

          }

          M_UDRx = XOFF_CHAR;

          // Clear the TXC bit -- "can be cleared by writing a one to its bit

          // location". This makes sure flush() won't return until the bytes

          // actually got written

          SBI(M_UCSRxA, M_TXCx);

          // At this point there could be a race condition between the write() function

          // and this sending of the XOFF char. This interrupt could happen between the

          // wait to be empty TX buffer loop and the actual write of the character. Since

          // the TX buffer is full because it's sending the XOFF char, the only way to be

          // sure the write() function will succeed is to wait for the XOFF char to be

          // completely sent. Since an extra character could be received during the wait

          // it must also be handled!

          while (!TEST(M_UCSRxA, M_UDREx)) {

            if (TEST(M_UCSRxA,M_RXCx)) {

              // A char arrived while waiting for the TX buffer to be empty - Receive and process it!

              i = (ring_buffer_pos_t)(h + 1) & (ring_buffer_pos_t)(RX_BUFFER_SIZE - 1);

              // Read the character from the USART

              c = M_UDRx;

              #if ENABLED(EMERGENCY_PARSER)

                emergency_parser.update(c);

              #endif

              // If the character is to be stored at the index just before the tail

              // (such that the head would advance to the current tail), the FIFO is

              // full, so don't write the character or advance the head.

              if (i != t) {

                rx_buffer.buffer[h] = c;

                h = i;

              }

              #if ENABLED(SERIAL_STATS_DROPPED_RX)

                else if (!++rx_dropped_bytes) --rx_dropped_bytes;

              #endif

            }

            sw_barrier();

          }

          // At this point everything is ready. The write() function won't

          // have any issues writing to the UART TX register if it needs to!

        }

      }

    #endif // SERIAL_XON_XOFF

    // Store the new head value - The main loop will retry until the value is stable

    rx_buffer.head = h;

  }

  #if TX_BUFFER_SIZE > 0

    // (called with TX irqs disabled)

    FORCE_INLINE void _tx_udr_empty_irq(void) {

      // Read positions

      uint8_t t = tx_buffer.tail;

      const uint8_t h = tx_buffer.head;

      #if ENABLED(SERIAL_XON_XOFF)

        // If an XON char is pending to be sent, do it now

        if (xon_xoff_state == XON_CHAR) {

          // Send the character

          M_UDRx = XON_CHAR;

          // clear the TXC bit -- "can be cleared by writing a one to its bit

          // location". This makes sure flush() won't return until the bytes

          // actually got written

          SBI(M_UCSRxA, M_TXCx);

          // Remember we sent it.

          xon_xoff_state = XON_CHAR | XON_XOFF_CHAR_SENT;

          // If nothing else to transmit, just disable TX interrupts.

          if (h == t) CBI(M_UCSRxB, M_UDRIEx); // (Non-atomic, could be reenabled by the main program, but eventually this will succeed)

          return;

        }

      #endif

      // If nothing to transmit, just disable TX interrupts. This could

      // happen as the result of the non atomicity of the disabling of RX

      // interrupts that could end reenabling TX interrupts as a side effect.

      if (h == t) {

        CBI(M_UCSRxB, M_UDRIEx); // (Non-atomic, could be reenabled by the main program, but eventually this will succeed)

        return;

      }

      // There is something to TX, Send the next byte

      const uint8_t c = tx_buffer.buffer[t];

      t = (t + 1) & (TX_BUFFER_SIZE - 1);

      M_UDRx = c;

      tx_buffer.tail = t;

      // Clear the TXC bit (by writing a one to its bit location).

      // Ensures flush() won't return until the bytes are actually written/

      SBI(M_UCSRxA, M_TXCx);

      // Disable interrupts if there is nothing to transmit following this byte

      if (h == t) CBI(M_UCSRxB, M_UDRIEx); // (Non-atomic, could be reenabled by the main program, but eventually this will succeed)

    }

    #ifdef M_USARTx_UDRE_vect

      ISR(M_USARTx_UDRE_vect) { _tx_udr_empty_irq(); }

    #endif

  #endif // TX_BUFFER_SIZE

  #ifdef M_USARTx_RX_vect

    ISR(M_USARTx_RX_vect) { store_rxd_char(); }

  #endif

  // Public Methods

  void MarlinSerial::begin(const long baud) {

    uint16_t baud_setting;

    bool useU2X = true;

    #if F_CPU == 16000000UL && SERIAL_PORT == 0

      // Hard-coded 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) useU2X = false;

    #endif

    if (useU2X) {

      M_UCSRxA = _BV(M_U2Xx);

      baud_setting = (F_CPU / 4 / baud - 1) / 2;

    }

    else {

      M_UCSRxA = 0;

      baud_setting = (F_CPU / 8 / baud - 1) / 2;

    }

    // assign the baud_setting, a.k.a. ubbr (USART Baud Rate Register)

    M_UBRRxH = baud_setting >> 8;

    M_UBRRxL = baud_setting;

    SBI(M_UCSRxB, M_RXENx);

    SBI(M_UCSRxB, M_TXENx);

    SBI(M_UCSRxB, M_RXCIEx);

    #if TX_BUFFER_SIZE > 0

      CBI(M_UCSRxB, M_UDRIEx);

    #endif

    _written = false;

  }

  void MarlinSerial::end() {

    CBI(M_UCSRxB, M_RXENx);

    CBI(M_UCSRxB, M_TXENx);

    CBI(M_UCSRxB, M_RXCIEx);

    CBI(M_UCSRxB, M_UDRIEx);

  }

  int MarlinSerial::peek(void) {

    const ring_buffer_pos_t h = atomic_read_rx_head(), t = rx_buffer.tail;

    return h == t ? -1 : rx_buffer.buffer[t];

  }

  int MarlinSerial::read(void) {

    const ring_buffer_pos_t h = atomic_read_rx_head();

    // Read the tail. Main thread owns it, so it is safe to directly read it

    ring_buffer_pos_t t = rx_buffer.tail;

    // If nothing to read, return now

    if (h == t) return -1;

    // Get the next char

    const int v = rx_buffer.buffer[t];

    t = (ring_buffer_pos_t)(t + 1) & (RX_BUFFER_SIZE - 1);

    // Advance tail - Making sure the RX ISR will always get an stable value, even

    // if it interrupts the writing of the value of that variable in the middle.

    atomic_set_rx_tail(t);

    #if ENABLED(SERIAL_XON_XOFF)

      // If the XOFF char was sent, or about to be sent...

      if ((xon_xoff_state & XON_XOFF_CHAR_MASK) == XOFF_CHAR) {

        // Get count of bytes in the RX buffer

        const ring_buffer_pos_t rx_count = (ring_buffer_pos_t)(h - t) & (ring_buffer_pos_t)(RX_BUFFER_SIZE - 1);

        if (rx_count < (RX_BUFFER_SIZE) / 10) {

          #if TX_BUFFER_SIZE > 0

            // Signal we want an XON character to be sent.

            xon_xoff_state = XON_CHAR;

            // Enable TX ISR. Non atomic, but it will eventually enable them

            SBI(M_UCSRxB, M_UDRIEx);

          #else

            // If not using TX interrupts, we must send the XON char now

            xon_xoff_state = XON_CHAR | XON_XOFF_CHAR_SENT;

            while (!TEST(M_UCSRxA, M_UDREx)) sw_barrier();

            M_UDRx = XON_CHAR;

          #endif

        }

      }

    #endif

    return v;

  }

  ring_buffer_pos_t MarlinSerial::available(void) {

    const ring_buffer_pos_t h = atomic_read_rx_head(), t = rx_buffer.tail;

    return (ring_buffer_pos_t)(RX_BUFFER_SIZE + h - t) & (RX_BUFFER_SIZE - 1);

  }

  void MarlinSerial::flush(void) {

    // Set the tail to the head:

    //  - Read the RX head index in a safe way. (See atomic_read_rx_head.)

    //  - Set the tail, making sure the RX ISR will always get a stable value, even

    //    if it interrupts the writing of the value of that variable in the middle.

    atomic_set_rx_tail(atomic_read_rx_head());

    #if ENABLED(SERIAL_XON_XOFF)

      // If the XOFF char was sent, or about to be sent...

      if ((xon_xoff_state & XON_XOFF_CHAR_MASK) == XOFF_CHAR) {

        #if TX_BUFFER_SIZE > 0

          // Signal we want an XON character to be sent.

          xon_xoff_state = XON_CHAR;

          // Enable TX ISR. Non atomic, but it will eventually enable it.

          SBI(M_UCSRxB, M_UDRIEx);

        #else

          // If not using TX interrupts, we must send the XON char now

          xon_xoff_state = XON_CHAR | XON_XOFF_CHAR_SENT;

          while (!TEST(M_UCSRxA, M_UDREx)) sw_barrier();

          M_UDRx = XON_CHAR;

        #endif

      }

    #endif

  }

  #if TX_BUFFER_SIZE > 0

    void MarlinSerial::write(const uint8_t c) {

      _written = true;

      // If the TX interrupts are disabled and the data register

      // is empty, just write the byte to the data register and

      // be done. This shortcut helps significantly improve the

      // effective datarate at high (>500kbit/s) bitrates, where

      // interrupt overhead becomes a slowdown.

      // Yes, there is a race condition between the sending of the

      // XOFF char at the RX ISR, but it is properly handled there

      if (!TEST(M_UCSRxB, M_UDRIEx) && TEST(M_UCSRxA, M_UDREx)) {

        M_UDRx = c;

        // clear the TXC bit -- "can be cleared by writing a one to its bit

        // location". This makes sure flush() won't return until the bytes

        // actually got written

        SBI(M_UCSRxA, M_TXCx);

        return;

      }

      const uint8_t i = (tx_buffer.head + 1) & (TX_BUFFER_SIZE - 1);

      // If global interrupts are disabled (as the result of being called from an ISR)...

      if (!ISRS_ENABLED()) {

        // Make room by polling if it is possible to transmit, and do so!

        while (i == tx_buffer.tail) {

          // If we can transmit another byte, do it.

          if (TEST(M_UCSRxA, M_UDREx)) _tx_udr_empty_irq();

          // Make sure compiler rereads tx_buffer.tail

          sw_barrier();

        }

      }

      else {

        // Interrupts are enabled, just wait until there is space

        while (i == tx_buffer.tail) { sw_barrier(); }

      }

      // Store new char. head is always safe to move

      tx_buffer.buffer[tx_buffer.head] = c;

      tx_buffer.head = i;

      // Enable TX ISR - Non atomic, but it will eventually enable TX ISR

      SBI(M_UCSRxB, M_UDRIEx);

    }

    void MarlinSerial::flushTX(void) {

      // No bytes written, no need to flush. This special case is needed since there's

      // no way to force the TXC (transmit complete) bit to 1 during initialization.

      if (!_written) return;

      // If global interrupts are disabled (as the result of being called from an ISR)...

      if (!ISRS_ENABLED()) {

        // Wait until everything was transmitted - We must do polling, as interrupts are disabled

        while (tx_buffer.head != tx_buffer.tail || !TEST(M_UCSRxA, M_TXCx)) {

          // If there is more space, send an extra character

          if (TEST(M_UCSRxA, M_UDREx))

            _tx_udr_empty_irq();

          sw_barrier();

        }

      }

      else {

        // Wait until everything was transmitted

        while (tx_buffer.head != tx_buffer.tail || !TEST(M_UCSRxA, M_TXCx)) sw_barrier();

      }

      // At this point nothing is queued anymore (DRIE is disabled) and

      // the hardware finished transmission (TXC is set).

    }

  #else // TX_BUFFER_SIZE == 0

    void MarlinSerial::write(const uint8_t c) {

      _written = true;

      while (!TEST(M_UCSRxA, M_UDREx)) sw_barrier();

      M_UDRx = c;

    }

    void MarlinSerial::flushTX(void) {

      // No bytes written, no need to flush. This special case is needed since there's

      // no way to force the TXC (transmit complete) bit to 1 during initialization.

      if (!_written) return;

      // Wait until everything was transmitted

      while (!TEST(M_UCSRxA, M_TXCx)) sw_barrier();

      // At this point nothing is queued anymore (DRIE is disabled) and

      // the hardware finished transmission (TXC is set).

    }

  #endif // TX_BUFFER_SIZE == 0

  /**

   * Imports from print.h

   */

  void MarlinSerial::print(char c, int base) {

    print((long)c, base);

  }

  void MarlinSerial::print(unsigned char b, int base) {

    print((unsigned long)b, base);

  }

  void MarlinSerial::print(int n, int base) {

    print((long)n, base);

  }

  void MarlinSerial::print(unsigned int n, int base) {

    print((unsigned long)n, base);

  }

  void MarlinSerial::print(long n, int base) {

    if (base == 0) write(n);

    else if (base == 10) {

      if (n < 0) { print('-'); n = -n; }

      printNumber(n, 10);

    }

    else

      printNumber(n, base);

  }

  void MarlinSerial::print(unsigned long n, int base) {

    if (base == 0) write(n);

    else printNumber(n, base);

  }

  void MarlinSerial::print(double n, int digits) {

    printFloat(n, digits);

  }

  void MarlinSerial::println(void) {

    print('\r');

    print('\n');

  }

  void MarlinSerial::println(const String& s) {

    print(s);

    println();

  }

  void MarlinSerial::println(const char c[]) {

    print(c);

    println();

  }

  void MarlinSerial::println(char c, int base) {

    print(c, base);

    println();

  }

  void MarlinSerial::println(unsigned char b, int base) {

    print(b, base);

    println();

  }

  void MarlinSerial::println(int n, int base) {

    print(n, base);

    println();

  }

  void MarlinSerial::println(unsigned int n, int base) {

    print(n, base);

    println();

  }

  void MarlinSerial::println(long n, int base) {

    print(n, base);

    println();

  }

  void MarlinSerial::println(unsigned long n, int base) {

    print(n, base);

    println();

  }

  void MarlinSerial::println(double n, int digits) {

    print(n, digits);

    println();

  }

  // Private Methods

  void MarlinSerial::printNumber(unsigned long n, uint8_t base) {

    if (n) {

      unsigned char buf[8 * sizeof(long)]; // Enough space for base 2

      int8_t i = 0;

      while (n) {

        buf[i++] = n % base;

        n /= base;

      }

      while (i--)

        print((char)(buf[i] + (buf[i] < 10 ? '0' : 'A' - 10)));

    }

    else

      print('0');

  }

  void MarlinSerial::printFloat(double number, uint8_t digits) {

    // Handle negative numbers

    if (number < 0.0) {

      print('-');

      number = -number;

    }

    // Round correctly so that print(1.999, 2) prints as "2.00"

    double rounding = 0.5;

    for (uint8_t i = 0; i < digits; ++i)

      rounding *= 0.1;

    number += rounding;

    // Extract the integer part of the number and print it

    unsigned long int_part = (unsigned long)number;

    double remainder = number - (double)int_part;

    print(int_part);

    // Print the decimal point, but only if there are digits beyond

    if (digits) {

      print('.');

      // Extract digits from the remainder one at a time

      while (digits--) {

        remainder *= 10.0;

        int toPrint = int(remainder);

        print(toPrint);

        remainder -= toPrint;

      }

    }

  }

  // Preinstantiate

  MarlinSerial customizedSerial;

#endif // USE_MARLINSERIAL && (UBRRH || UBRR0H || UBRR1H || UBRR2H || UBRR3H)

// For AT90USB targets use the UART for BT interfacing

#if !USE_MARLINSERIAL && ENABLED(BLUETOOTH)

  HardwareSerial bluetoothSerial;

#endif