soft_uart.h 63.5 KB
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/**
 ** soft_uart library
 ** Copyright (C) 2015-2020
 **
 **   Antonio C. Domínguez Brito <antonio.dominguez@ulpgc.es>
 **     División de Robótica y Oceanografía Computacional <www.roc.siani.es>
 **     and Departamento de Informática y Sistemas <www.dis.ulpgc.es>
 **     Universidad de Las Palmas de Gran  Canaria (ULPGC) <www.ulpgc.es>
 **  
 ** This file is part of the soft_uart library.
 ** The soft_uart library 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  any
 ** later version.
 ** 
 ** The  soft_uart 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  General
 ** Public License for more details.
 ** 
 ** You should have received a copy  (COPYING file) of  the  GNU  General  Public
 ** License along with the soft_uart library.
 ** If not, see: <http://www.gnu.org/licenses/>.
 **/
/*
 * File: soft_uart.h 
 * Description:  This  is  an  implementation  of  a  software	UART  (Universal
 * Asynchronous Receiver  Transmitter)	library  for  the  Arduino  Due's  Atmel
 * ATSAM3X8E micro-controller.
 * Date: June 22nd, 2015
 * Author: Antonio C. Dominguez-Brito <antonio.dominguez@ulpgc.es>
 * ROC-SIANI - Universidad de Las Palmas de Gran Canaria - Spain
 */

#ifndef SOFT_UART_H
  #define SOFT_UART_H

  #include <cstdint>
    
  #include "fifo.h"

  namespace soft_uart
  {

    enum bit_rates: uint32_t
    {
      MIN_BIT_RATE=75,
      MAX_BIT_RATE=115200,
      DEFAULT_BIT_RATE=9600
    };
    
    enum class return_codes: int32_t
    {
      EVERYTHING_OK=0,
      BAD_BIT_RATE_ERROR=-1,
      BAD_RX_PIN=-2,
      BAD_TX_PIN=-3,
      BAD_HALF_DUPLEX_PIN=-4
    };
    
    enum class data_bit_codes: uint32_t
    {
      FIVE_BITS=5,
      SIX_BITS=6,
      SEVEN_BITS=7,
      EIGHT_BITS=8,
      NINE_BITS=9,
    };
    
    enum class parity_codes: uint32_t
    {
      NO_PARITY=0,
      EVEN_PARITY=1,
      ODD_PARITY=2
    };
    
    enum class stop_bit_codes: uint32_t
    {
      ONE_STOP_BIT=1,
      TWO_STOP_BITS=2
    };
    
    enum class rx_status_codes: uint32_t
    {
      LISTENING,
      RECEIVING
    };
    
    enum rx_data_status_codes: uint32_t
    {
      NO_DATA_AVAILABLE=0,
      DATA_AVAILABLE=1,
      DATA_LOST=2,
      BAD_START_BIT=4,
      BAD_PARITY=8,
      BAD_STOP_BIT=16,
    };
    
    enum class tx_status_codes: uint32_t
    {
      IDLE,
      SENDING
    };

    enum class mode_codes: int32_t
    {
      INVALID_MODE=-1,
      FULL_DUPLEX=0,
      RX_MODE=1,
      TX_MODE=2
    };
      

  } // namespace soft_uart
    
  #ifndef CHIBIOS_PORT
  
    #include "Arduino.h"
    
    #include <type_traits>
    
    #define serial_tc_declaration(id,rx_length,tx_length) \
    void TC##id##_Handler(void) \
    { \
      uint32_t status=TC_GetStatus( \
        soft_uart::arduino_due::tc_timer_table[ \
          static_cast<uint32_t>( \
            soft_uart::arduino_due::timer_ids::TIMER_TC##id \
          ) \
        ].tc_p, \
        soft_uart::arduino_due::tc_timer_table[ \
          static_cast<uint32_t>( \
            soft_uart::arduino_due::timer_ids::TIMER_TC##id \
          ) \
        ].channel \
      ); \
      \
      soft_uart::arduino_due::uart< \
        soft_uart::arduino_due::timer_ids::TIMER_TC##id, \
        rx_length, \
        tx_length \
      >::tc_interrupt(status); \
    } \
    \
    typedef soft_uart::arduino_due::serial< \
      soft_uart::arduino_due::timer_ids::TIMER_TC##id, \
      rx_length, \
      tx_length \
    > serial_tc##id##_t; \
    \
    serial_tc##id##_t serial_tc##id;
    
    #define serial_tc0_declaration(rx_length,tx_length) \
    serial_tc_declaration(0,rx_length,tx_length)
    
    #define serial_tc1_declaration(rx_length,tx_length) \
    serial_tc_declaration(1,rx_length,tx_length)
    
    #define serial_tc2_declaration(rx_length,tx_length) \
    serial_tc_declaration(2,rx_length,tx_length)
    
    #define serial_tc3_declaration(rx_length,tx_length) \
    serial_tc_declaration(3,rx_length,tx_length)
    
    #define serial_tc4_declaration(rx_length,tx_length) \
    serial_tc_declaration(4,rx_length,tx_length)
    
    #define serial_tc5_declaration(rx_length,tx_length) \
    serial_tc_declaration(5,rx_length,tx_length)
    
    #define serial_tc6_declaration(rx_length,tx_length) \
    serial_tc_declaration(6,rx_length,tx_length)
    
    #define serial_tc7_declaration(rx_length,tx_length) \
    serial_tc_declaration(7,rx_length,tx_length)
    
    #define serial_tc8_declaration(rx_length,tx_length) \
    serial_tc_declaration(8,rx_length,tx_length)
    
    /** \brief  Get Enabled Interrupt
    
      This function reads the set-enable register in the NVIC and returns the enabled bit
      for the specified interrupt.
    
      \param [in]      IRQn  Number of the interrupt for get pending
      \return             0  Interrupt status is not enabled 
      \return             1  Interrupt status is enabled 
     */
    static __INLINE uint32_t NVIC_GetEnabledIRQ(IRQn_Type IRQn)
    {
      return((uint32_t) ((NVIC->ISER[(uint32_t)(IRQn) >> 5] & (1 << ((uint32_t)(IRQn) & 0x1F)))?1:0)); /* Return 1 if enabled else 0 */
    }

    namespace soft_uart
    {
    
      namespace arduino_due
      {
      
        enum class timer_ids: uint32_t
        {
          TIMER_TC0=0,
          TIMER_TC1=1,
          TIMER_TC2=2,
          TIMER_TC3=3,
          TIMER_TC4=4,
          TIMER_TC5=5,
          TIMER_TC6=6,
          TIMER_TC7=7,
          TIMER_TC8=8,
          TIMER_IDS
        };
      
        enum default_pins: uint32_t
        {
          DEFAULT_RX_PIN=2,
          DEFAULT_TX_PIN=3
        };
      
        struct tc_timer_data
        { 
          Tc* tc_p; 
          uint32_t channel;
          IRQn_Type irq;
        };
      
        class interrupt_guard
        {
          public:
      
            interrupt_guard() { __disable_irq(); }
            ~interrupt_guard() { __enable_irq(); }
        };
      
        extern tc_timer_data 
          tc_timer_table[static_cast<uint32_t>(timer_ids::TIMER_IDS)];
        
        template<
          timer_ids TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > class uart 
        {
          static_assert(TIMER<timer_ids::TIMER_IDS,"[ERROR] Bad TC id provided to instantiate template uart");
      
          public:
      
            uart() { _mode_=mode_codes::INVALID_MODE; }
      
            ~uart() { end(); }
        
            uart(const uart&) = delete;
            uart(uart&&) = delete;
            uart& operator=(const uart&) = delete;
            uart& operator=(uart&&) = delete;
      
            return_codes config(
              uint32_t rx_pin = default_pins::DEFAULT_RX_PIN,
              uint32_t tx_pin = default_pins::DEFAULT_TX_PIN,
              uint32_t bit_rate = bit_rates::DEFAULT_BIT_RATE,
              data_bit_codes the_data_bits = data_bit_codes::EIGHT_BITS,
              parity_codes the_parity = parity_codes::EVEN_PARITY,
              stop_bit_codes the_stop_bits = stop_bit_codes::ONE_STOP_BIT
            ) 
            {
              _mode_=mode_codes::INVALID_MODE;
              
              if(rx_pin>=NUM_DIGITAL_PINS)
                return return_codes::BAD_RX_PIN;
      
              if(tx_pin>=NUM_DIGITAL_PINS)
                return return_codes::BAD_TX_PIN;
      
              return_codes ret_code=
                _ctx_.config(
                  rx_pin,
                  tx_pin,
                  bit_rate,
                  the_data_bits,
                  the_parity,
                  the_stop_bits
                ); 
      
              if(ret_code!=return_codes::EVERYTHING_OK) return ret_code;
                      
              // cofigure tx pin
              pinMode(tx_pin,OUTPUT);
              digitalWrite(tx_pin,HIGH);
      
              // configure & attatch interrupt on rx pin
              pinMode(rx_pin,INPUT_PULLUP);
              attachInterrupt(rx_pin,uart::rx_interrupt,CHANGE);
      
              _mode_=mode_codes::FULL_DUPLEX;
      
              return return_codes::EVERYTHING_OK;
            }
      	
            return_codes half_duplex_config(
              uint32_t rx_tx_pin = default_pins::DEFAULT_RX_PIN,
              uint32_t bit_rate = bit_rates::DEFAULT_BIT_RATE,
              data_bit_codes the_data_bits = data_bit_codes::EIGHT_BITS,
              parity_codes the_parity = parity_codes::EVEN_PARITY,
              stop_bit_codes the_stop_bits = stop_bit_codes::ONE_STOP_BIT,
              bool in_rx_mode = true
            ) 
            {
              _mode_=mode_codes::INVALID_MODE;
      
              if(rx_tx_pin>=NUM_DIGITAL_PINS)
                return return_codes::BAD_HALF_DUPLEX_PIN;
      
              return_codes ret_code=
                _ctx_.config(
                  rx_tx_pin,
                  rx_tx_pin,
                  bit_rate,
                  the_data_bits,
                  the_parity,
                  the_stop_bits
                ); 
      
              if(ret_code!=return_codes::EVERYTHING_OK) return ret_code;
      
              if(in_rx_mode)
              {
                // configure & attatch interrupt on rx pin
                pinMode(rx_tx_pin,INPUT_PULLUP);
                attachInterrupt(rx_tx_pin,uart::rx_interrupt,CHANGE);
                _mode_=mode_codes::RX_MODE;
              }
              else
              {
                // cofigure tx pin
                pinMode(rx_tx_pin,OUTPUT);
                digitalWrite(rx_tx_pin,HIGH);
                _mode_=mode_codes::TX_MODE;
              }
      
              return return_codes::EVERYTHING_OK;
            }
      
            mode_codes get_mode() { return _mode_; }
      
            bool set_rx_mode()
            {
              if( 
                (_mode_==mode_codes::INVALID_MODE) ||
                (_mode_==mode_codes::FULL_DUPLEX)
              ) return false;
      
              if(_mode_==mode_codes::RX_MODE) return true; 
              flush();
      
              pinMode(_ctx_.rx_pin,INPUT_PULLUP);
              attachInterrupt(_ctx_.rx_pin,uart::rx_interrupt,CHANGE);
              
              _mode_=mode_codes::RX_MODE;
              return true;
            }
      
            bool set_tx_mode()
            {
              if( 
                (_mode_==mode_codes::INVALID_MODE) ||
                (_mode_==mode_codes::FULL_DUPLEX)
              ) return false;
      
              if(_mode_==mode_codes::TX_MODE) return true;
      
              // waiting to finish reception
              while(_ctx_.rx_status==rx_status_codes::RECEIVING) { /* do nothing */ } 
      
              detachInterrupt(_ctx_.rx_pin);
              pinMode(_ctx_.tx_pin,OUTPUT);
              digitalWrite(_ctx_.tx_pin,HIGH);
      
              _mode_=mode_codes::TX_MODE;
              return true;
            }
      
            void end() { _ctx_.end(); }
      
            int available() { return _ctx_.available(); }
      
            static void tc_interrupt(uint32_t the_status)
            { _ctx_.tc_interrupt(the_status); }
      
            static void rx_interrupt() { _ctx_.rx_interrupt(); }
      
            timer_ids get_timer() { return TIMER; }
      
            size_t get_rx_buffer_length() { return RX_BUFFER_LENGTH; }
            size_t get_tx_buffer_length() { return TX_BUFFER_LENGTH; }
        
            uint32_t get_bit_rate() { return _ctx_.bit_rate; }
            double get_bit_time() { return _ctx_.bit_time; }	
            double get_frame_time() { return _ctx_.frame_time; }	
      
            uint32_t get_rx_data(uint32_t& data) 
            { 
              return (
                (
                  (_mode_==mode_codes::FULL_DUPLEX) ||
                  (_mode_==mode_codes::RX_MODE)
                )? 
                  _ctx_.get_rx_data(data): 
                  static_cast<uint32_t>(
                    rx_data_status_codes::NO_DATA_AVAILABLE
                  )
              );
            }
      
            bool data_available(uint32_t status)
            { return _ctx_.data_available(status); }
      
            bool data_lost(uint32_t status)
            { return _ctx_.data_lost(status); }
      
            bool bad_status(uint32_t status) 
            { return _ctx_.bad_status(status); }
            
            bool bad_start_bit(uint32_t status) 
            { return _ctx_.bad_start_bit(status); }
            
            bool bad_parity(uint32_t status) 
            { return _ctx_.bad_parity(status); }
      
            bool bad_stop_bit(uint32_t status) 
            { return _ctx_.bad_stop_bit(status); }
      
            // is TX buffer full?
            bool is_tx_full() 
            { 
              return (
                (
                  (_mode_==mode_codes::FULL_DUPLEX) ||
                  (_mode_==mode_codes::TX_MODE)
                )? _ctx_.is_tx_full(): false
              ); 
            }
      
            // is TX buffer full?
            bool available_for_write() 
            { 
              return (
                (
                  (_mode_==mode_codes::FULL_DUPLEX) ||
                  (_mode_==mode_codes::TX_MODE)
                )? _ctx_.available_for_write(): 0 
              ); 
            }
      
            // NOTE: data is 5, 6, 7, 8 or 9 bits length
            bool set_tx_data(uint32_t data) 
            { 
              return (
                (
                  (_mode_==mode_codes::FULL_DUPLEX) ||
                  (_mode_==mode_codes::TX_MODE)
                )? _ctx_.set_tx_data(data): false
              ); 
            }
      
            tx_status_codes get_tx_status() { return _ctx_.get_tx_status(); }
      
            void flush() { _ctx_.flush(); }
      
            void flush_rx() { _ctx_.flush_rx(); }
      
          private:
      
            struct _uart_ctx_
            {
      
              return_codes config(
                uint32_t the_rx_pin,
                uint32_t the_tx_pin,
                uint32_t the_bit_rate,
                data_bit_codes the_data_bits,
                parity_codes the_parity,
                stop_bit_codes the_stop_bits
              );
      
              void end()
              {
                flush();
      
                disable_tc_interrupts(); disable_rx_interrupts();
      
                stop_tc_interrupts(); detachInterrupt(rx_pin);
      
                pmc_disable_periph_clk(uint32_t(timer_p->irq));
              }
      
              void tc_interrupt(uint32_t the_status);
              void rx_interrupt();
      
              uint32_t get_rx_data(uint32_t& data);
      
              int available()
              {
                interrupt_guard guard;
                return rx_buffer.items();
              }
      
              bool data_available(uint32_t status)
              { 
                return (
                  status&(
                    rx_data_status_codes::DATA_AVAILABLE|
                    rx_data_status_codes::DATA_LOST
                  )
                ); 
              }
      
              bool data_lost(uint32_t status)
              { return (status&rx_data_status_codes::DATA_LOST); }
      
              bool bad_status(uint32_t status)
              {
                return (
                  status&(
                    rx_data_status_codes::BAD_START_BIT|
                    rx_data_status_codes::BAD_PARITY|
                    rx_data_status_codes::BAD_STOP_BIT
                  )
                );
              }
      
              bool bad_start_bit(uint32_t status)
              { return (status&rx_data_status_codes::BAD_START_BIT); }
              
              bool bad_parity(uint32_t status)
              { return (status&rx_data_status_codes::BAD_PARITY); }
              
              bool bad_stop_bit(uint32_t status)
              { return (status&rx_data_status_codes::BAD_STOP_BIT); }
      
              // is TX buffer full?
              bool is_tx_full() 
              { 
                interrupt_guard guard;
                return tx_buffer.is_full();
              }
      
              int available_for_write() 
              { 
                interrupt_guard guard;
                return tx_buffer.available();
              }
      
              // NOTE: only the 5, 6, 7, 8  or 9 lowest significant bits
              // of data are send
              bool set_tx_data(uint32_t data);
      
              void flush()
              {
                // wait until sending everything
                while(tx_status!=tx_status_codes::IDLE) 
                { /*nothing */ }
              }
      
              void flush_rx()
              {
                interrupt_guard guard;
                rx_buffer.reset();
              }
      
              tx_status_codes get_tx_status() { return tx_status; }
      
              uint32_t get_even_parity(uint32_t data,uint32_t bits)
              {
                uint32_t odd_parity=data&1;
                for(uint32_t bit=1; bit<bits; bit++)
                  odd_parity=odd_parity^((data>>bit)&1);
                return odd_parity;
              }
      
              void config_rx_interrupt() 
              { NVIC_SetPriority(rx_irq,0); NVIC_EnableIRQ(timer_p->irq); }
      
              void enable_rx_interrupts() { rx_pio_p->PIO_IER=rx_mask; }
      
              void disable_rx_interrupts() { rx_pio_p->PIO_IDR=rx_mask; }
      
              bool is_rx_interrupts_enabled() { return bool{rx_pio_p->PIO_IMR & rx_mask}; }
      
              void config_tc_interrupt() { NVIC_SetPriority(timer_p->irq,0); }
      
              void enable_tc_interrupts() { NVIC_EnableIRQ(timer_p->irq); }
              
              void disable_tc_interrupts() { NVIC_DisableIRQ(timer_p->irq); }
      
              bool is_tc_interrupts_enabled()
              { return bool{NVIC_GetEnabledIRQ(timer_p->irq)}; }
      
              void start_tc_interrupts()
              {
                NVIC_ClearPendingIRQ(timer_p->irq);
                enable_tc_interrupts();
                TC_Start(timer_p->tc_p,timer_p->channel);
              }
      
              void stop_tc_interrupts()
              {
                disable_tc_interrupts();
                TC_Stop(timer_p->tc_p,timer_p->channel);
              }
      
              void enable_tc_ra_interrupt()
              {
                timer_p->tc_p->TC_CHANNEL[timer_p->channel].TC_IER=
                  TC_IER_CPAS;
              }
      
              bool is_enabled_ra_interrupt()
              {
                return (
                  timer_p->tc_p->TC_CHANNEL[timer_p->channel].TC_IMR &
                  TC_IMR_CPAS
                );
              }
      
              void disable_tc_ra_interrupt()
              {
                timer_p->tc_p->TC_CHANNEL[timer_p->channel].TC_IDR=
                  TC_IDR_CPAS;
              }
      
              void enable_tc_rc_interrupt()
              {
                timer_p->tc_p->TC_CHANNEL[timer_p->channel].TC_IER=
                  TC_IER_CPCS;
              }
      
              bool is_enabled_rc_interrupt()
              {
                return (
                  timer_p->tc_p->TC_CHANNEL[timer_p->channel].TC_IMR &
                  TC_IMR_CPCS
                );
              }
      
              void disable_tc_rc_interrupt()
              {
                timer_p->tc_p->TC_CHANNEL[timer_p->channel].TC_IDR=
                  TC_IDR_CPCS;
              }
      
              void get_incoming_bit()
              { rx_data |= (rx_bit<<rx_bit_counter); }
      
              void update_rx_data_buffer()
              {
                rx_data_status=(
                  (rx_buffer.push(static_cast<uint32_t>(rx_data)))?
                    rx_data_status_codes::DATA_AVAILABLE:
                    rx_data_status_codes::DATA_LOST
                );
              }
      
              void set_outgoing_bit()
              {
                if((tx_data>>tx_bit_counter) & 1) 
                  PIO_Set(tx_pio_p,tx_mask);
                else PIO_Clear(tx_pio_p,tx_mask);
              }
      
              tc_timer_data* timer_p;
              uint32_t rx_pin;
              Pio* rx_pio_p;
              uint32_t rx_mask;
              IRQn_Type rx_irq;
      
              uint32_t tx_pin;
              Pio* tx_pio_p;
              uint32_t tx_mask;
      
              double tc_tick;
              double bit_time;
              double frame_time;
              uint32_t bit_ticks;
              uint32_t bit_1st_half;
              uint32_t bit_1st_quarter;
      
              // serial protocol
              uint32_t bit_rate;
              data_bit_codes data_bits;
              parity_codes parity;
              stop_bit_codes stop_bits;
              uint32_t rx_frame_bits;
              uint32_t tx_frame_bits;
              uint32_t parity_bit_pos;
              uint32_t first_stop_bit_pos;
              uint32_t data_mask;
      
              // rx data
              circular_fifo<uint32_t,RX_BUFFER_LENGTH> rx_buffer;
              volatile uint32_t rx_data;
              volatile uint32_t rx_bit_counter;
              volatile uint32_t rx_bit;
              volatile rx_status_codes rx_status;
              volatile uint32_t rx_data_status;
              //volatile bool rx_at_end_quarter;
              volatile uint32_t rx_interrupt_counter;
      
              // tx data
              fifo<uint32_t,TX_BUFFER_LENGTH> tx_buffer;
              volatile uint32_t tx_data;
              volatile uint32_t tx_bit_counter;
              volatile tx_status_codes tx_status;
              volatile uint32_t tx_interrupt_counter;
            };
        
            static _uart_ctx_ _ctx_;
      
            mode_codes _mode_;
        };
      
        template<
          timer_ids TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > class serial: public HardwareSerial 
        {
          public:
      
            typedef uart<TIMER,RX_BUFFER_LENGTH,TX_BUFFER_LENGTH> raw_uart;
      
            serial() 
            { 
              _peek_data_valid_=false; 
              _last_data_status_=rx_data_status_codes::NO_DATA_AVAILABLE;
            }
      
            serial(const serial&) = delete;
            serial(serial&&) = delete;
            serial& operator=(const serial&) = delete;
            serial& operator=(serial&&) = delete;
            
            void begin(unsigned long baud_rate)
            {
              _tc_uart_.config(
                default_pins::DEFAULT_RX_PIN,
                default_pins::DEFAULT_TX_PIN,
                static_cast<uint32_t>(baud_rate),
                data_bit_codes::EIGHT_BITS,
                parity_codes::NO_PARITY,
                stop_bit_codes::ONE_STOP_BIT
              );
            }
      
            void begin(
              uint32_t rx_pin = default_pins::DEFAULT_RX_PIN,
              uint32_t tx_pin = default_pins::DEFAULT_TX_PIN,
              uint32_t bit_rate = bit_rates::DEFAULT_BIT_RATE,
              data_bit_codes the_data_bits = data_bit_codes::EIGHT_BITS,
              parity_codes the_parity = parity_codes::NO_PARITY,
              stop_bit_codes the_stop_bits = stop_bit_codes::ONE_STOP_BIT
            )
            {
              _tc_uart_.config(
                rx_pin,
                tx_pin,
                bit_rate,
                the_data_bits,
                the_parity,
                the_stop_bits
              );
            }
      
            // NOTE: on function half_duplex_begin() the last function 
            // argument specifies the operation mode: true (RX_MODE, 
            // reception mode, the default) or false (TX_MODE, trans-
            // mission mode)
            return_codes half_duplex_begin(
              uint32_t rx_tx_pin = default_pins::DEFAULT_RX_PIN,
              uint32_t bit_rate = bit_rates::DEFAULT_BIT_RATE,
              data_bit_codes the_data_bits = data_bit_codes::EIGHT_BITS,
              parity_codes the_parity = parity_codes::NO_PARITY,
              stop_bit_codes the_stop_bits = stop_bit_codes::ONE_STOP_BIT,
              bool in_rx_mode = true
            )
            {
              return _tc_uart_.half_duplex_config(
                rx_tx_pin,
                bit_rate,
                the_data_bits,
                the_parity,
                the_stop_bits,
                in_rx_mode
              );
            }
      
            void end() { _tc_uart_.end(); }
      
            int available(void) { return _tc_uart_.available(); }
      
            int availableForWrite(void)
            { return available_for_write(); }
      
            int available_for_write(void) 
            { return _tc_uart_.available_for_write(); }
      
            int peek(void) 
            {
              if(_peek_data_valid_) return _last_data_;
      
              _last_data_status_=_tc_uart_.get_rx_data(_last_data_);
      
              if(
                !_tc_uart_.data_available(_last_data_status_) ||
                _tc_uart_.bad_status(_last_data_status_)
              ) return -1;
      
              _peek_data_valid_=true;
      
              return _last_data_;
            }
      
            int read(void) 
            {
              if(_peek_data_valid_) 
              { _peek_data_valid_=false; return _last_data_; }
      
              _last_data_status_=_tc_uart_.get_rx_data(_last_data_);
      
              if(
                !_tc_uart_.data_available(_last_data_status_) ||
                _tc_uart_.bad_status(_last_data_status_)
              ) return -1;
      
              return _last_data_; 
            }
      
            bool data_available() { return _tc_uart_.data_available(_last_data_status_); }
      
            bool data_lost() { return _tc_uart_.data_lost(_last_data_status_); }
      
            bool bad_status() { return _tc_uart_.bad_status(_last_data_status_); }
            
            bool bad_start_bit() { return _tc_uart_.bad_start_bit(_last_data_status_); }
            
            bool bad_parity() { return _tc_uart_.bad_parity(_last_data_status_); }
            bool bad_stop_bit() { return _tc_uart_.bad_stop_bit(_last_data_status_); }
            
            void flush(void) { _tc_uart_.flush(); } 
            
            void flushRX(void) { _tc_uart_.flush_rx(); }
            
            size_t write(uint8_t data) 
            {
              while(!available_for_write()) { /* nothing */ }
      
              return (
                  (_tc_uart_.set_tx_data(static_cast<uint32_t>(data)))? 
                    1: 0 
              ); 
            } 
      
            size_t write(uint32_t data) 
            {
              while(!available_for_write()) { /* nothing */ }
      
              return (
                  (_tc_uart_.set_tx_data(data))? 
                    1: 0 
              ); 
            }
      
            mode_codes get_mode() { return _tc_uart_.get_mode(); }
      
            bool set_rx_mode() { return _tc_uart_.set_rx_mode(); }
            bool set_tx_mode() { return _tc_uart_.set_tx_mode(); }
      
            uint32_t get_last_data() { return _last_data_; }
            uint32_t get_last_data_status() { return _last_data_status_; }
            double get_bit_time() { return _tc_uart_.get_bit_time(); }
            double get_frame_time() { return _tc_uart_.get_frame_time(); }
            timer_ids get_timer() { return _tc_uart_.get_timer(); }
      
            using Print::write; // pull in write(str) and write(buf, size) from Print
            operator bool() { return true; } 
      
          private:
      
            //uart<TIMER,RX_BUFFER_LENGTH,TX_BUFFER_LENGTH> _tc_uart_;
            raw_uart _tc_uart_;
      
            uint32_t _last_data_;
            uint32_t _last_data_status_;
            bool _peek_data_valid_;
        };
      
        template<
          timer_ids TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > typename uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_ 
          uart<TIMER,RX_BUFFER_LENGTH,TX_BUFFER_LENGTH>::_ctx_;
      
        template<
          timer_ids TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > return_codes uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_::config(
          uint32_t the_rx_pin,
          uint32_t the_tx_pin,
          uint32_t the_bit_rate,
          data_bit_codes the_data_bits,
          parity_codes the_parity,
          stop_bit_codes the_stop_bits
        )
        {
          if(
            (the_bit_rate<bit_rates::MIN_BIT_RATE) || 
            (the_bit_rate>bit_rates::MAX_BIT_RATE)
          ) return return_codes::BAD_BIT_RATE_ERROR;
      
          timer_p=&(tc_timer_table[static_cast<uint32_t>(TIMER)]);
          bit_rate=the_bit_rate;
          
          // NOTE: we will be using the fastest clock for TC ticks
          // just using a prescaler of 2
          tc_tick=double(1)/double((VARIANT_MCK)>>1);
          bit_time=double(1)/double(bit_rate);
        
          bit_ticks=static_cast<uint32_t>(bit_time/tc_tick);
          bit_1st_half=(bit_ticks>>1);
          bit_1st_quarter=(bit_ticks>>2);
      
          data_bits=the_data_bits; parity=the_parity; stop_bits=the_stop_bits;
      
          // reception frame length in bits
          rx_frame_bits=1 + // the start bit
            static_cast<uint32_t>(data_bits) + // the data bits
            ((parity!=parity_codes::NO_PARITY)? 1: 0) + // the parity?
            1; // for reception we ONLY consider one stop bit
      
          // transmission frame length in bits
          tx_frame_bits=rx_frame_bits;
          if(stop_bits==stop_bit_codes::TWO_STOP_BITS) 
          {
            // for transmission we DO consider also the second stop bit
            tx_frame_bits++; 
          }
      
          frame_time=tx_frame_bits*bit_time;
      
          parity_bit_pos=1 + // the start bit
            static_cast<uint32_t>(data_bits); // the data bits
      
          first_stop_bit_pos=parity_bit_pos +
            ((parity!=parity_codes::NO_PARITY)? 1: 0); // the parity?
      
          data_mask=(1<<static_cast<uint32_t>(data_bits))-1;
      
          rx_pin=the_rx_pin;
          rx_pio_p=g_APinDescription[rx_pin].pPort;
          rx_mask=g_APinDescription[rx_pin].ulPin;
          rx_status=rx_status_codes::LISTENING;
          rx_data_status=rx_data_status_codes::NO_DATA_AVAILABLE;
          rx_buffer.reset();
          rx_interrupt_counter=0;
      
          rx_irq=(
            (rx_pio_p==PIOA)? 
              PIOA_IRQn:
              (
                (rx_pio_p==PIOB)? 
                  PIOB_IRQn: ((rx_pio_p==PIOC)? PIOC_IRQn: PIOD_IRQn)
              )
          );
      
          tx_pin=the_tx_pin;
          tx_pio_p=g_APinDescription[tx_pin].pPort;
          tx_mask=g_APinDescription[tx_pin].ulPin;
          tx_status=tx_status_codes::IDLE;
          tx_buffer.reset();
          tx_interrupt_counter=0;
      
          // PMC settings
          pmc_set_writeprotect(0);
          pmc_enable_periph_clk(uint32_t(timer_p->irq));
        
          // timing setings
          TC_Configure(
            timer_p->tc_p,
            timer_p->channel,
            TC_CMR_TCCLKS_TIMER_CLOCK1 |
            TC_CMR_WAVE |
            TC_CMR_WAVSEL_UP_RC
          );
          
          //TC_SetRA(timer_p->tc_p,timer_p->channel,bit_1st_half);
          //disable_tc_ra_interrupt();
      
          //TC_SetRC(timer_p->tc_p,timer_p->channel,bit_ticks);
          //TC_SetRC(timer_p->tc_p,timer_p->channel,bit_1st_half);
          TC_SetRC(timer_p->tc_p,timer_p->channel,bit_1st_quarter);
          //disable_tc_rc_interrupt();
          enable_tc_rc_interrupt();
      
          config_rx_interrupt();
          config_tc_interrupt();
          stop_tc_interrupts();
      
          return return_codes::EVERYTHING_OK;
        }
      
        template<
          timer_ids TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > void uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_::tc_interrupt(
          uint32_t the_status
        )
        {
          // RC compare interrupt
          if((the_status & TC_SR_CPCS) && is_enabled_rc_interrupt())
          {
            // rx code
            if(rx_status==rx_status_codes::RECEIVING)
            {
              if(rx_interrupt_counter==1)
              {
                get_incoming_bit(); 
                rx_bit_counter++;
                if(rx_bit_counter==rx_frame_bits)
                {
                  if(stop_bits==stop_bit_codes::TWO_STOP_BITS)
                    get_incoming_bit();
      
                  if(tx_status==tx_status_codes::IDLE) stop_tc_interrupts(); 
      
                  update_rx_data_buffer();
      
                  rx_status=rx_status_codes::LISTENING;
                }
              }
              rx_interrupt_counter=(rx_interrupt_counter+1)&0x3;
            }
      
            // tx code
            if(tx_status==tx_status_codes::SENDING)
            {
              if(tx_interrupt_counter==0)
              {
                if(tx_bit_counter>=tx_frame_bits)
                {
                  uint32_t data_to_send;
                  if(tx_buffer.pop(data_to_send)) 
                  { 
                    tx_data=data_to_send; tx_bit_counter=0; 
                    set_outgoing_bit(); tx_bit_counter++;
                  }
                  else
                  {
                    if(rx_status==rx_status_codes::LISTENING) 
                      stop_tc_interrupts(); 
      
                    tx_status=tx_status_codes::IDLE;
                  }
                }
                else { set_outgoing_bit(); tx_bit_counter++; }
              }
              tx_interrupt_counter=(tx_interrupt_counter+1)&0x3;
            }
          }
        }
        
        template<
          timer_ids TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > void uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_::rx_interrupt()
        {
          register uint32_t sampled_bit=
            PIO_Get(rx_pio_p,PIO_INPUT,rx_mask);
      
          switch(rx_status)
          {
            case rx_status_codes::LISTENING:
              if(!sampled_bit)
              {
                rx_status=rx_status_codes::RECEIVING;
                rx_data=rx_bit_counter=rx_bit=0;
                rx_interrupt_counter=0;
                
                if(tx_status==tx_status_codes::IDLE) 
                { start_tc_interrupts(); rx_interrupt_counter=1; }
              } 
              break;
              
            case rx_status_codes::RECEIVING:
              rx_bit=sampled_bit;
              break;
          }
        }
      
        template<
          timer_ids TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > uint32_t uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_::get_rx_data(
          uint32_t& data
        )
        {
          register uint32_t status;
          register bool not_empty;
          uint32_t data_received;
          
          {
            interrupt_guard guard;
            
            status=(not_empty=rx_buffer.pop(data_received))?
              rx_data_status_codes::DATA_AVAILABLE:
              rx_data_status_codes::NO_DATA_AVAILABLE;
          }
      
          if(!not_empty) return status;
          
          // checking start bit
          status=(data_received & 1)?
            status|rx_data_status_codes::BAD_START_BIT:
            status&(~rx_data_status_codes::BAD_START_BIT);
      
          // cheking parity
          if(parity!=parity_codes::NO_PARITY)
          {
            register uint32_t data_parity=get_even_parity(
              (data_received>>1),
              static_cast<uint32_t>(data_bits)
            );
      
            if(parity==parity_codes::ODD_PARITY) 
              data_parity=data_parity^1;
      
            register uint32_t received_parity=
              (data_received>>parity_bit_pos) & 1;
      
            // verifying parity bit
            status=(received_parity^data_parity)?
                status|rx_data_status_codes::BAD_PARITY:
                status&(~rx_data_status_codes::BAD_PARITY);
          }
      
          // checking stop bit
          // NOTE: we only verify the first stop bit
          status=((data_received>>first_stop_bit_pos) & 1)?
            status&(~rx_data_status_codes::BAD_STOP_BIT):
            status|rx_data_status_codes::BAD_STOP_BIT;
      
          // NOTE: in case of error, we put the received raw data
          // on the high 16 bits of status
          if(bad_status(status)) status=status|(data_received<<16);
      
          data=(data_received>>1)&data_mask;
      
          return status;
        }
      
        template<
          timer_ids TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > bool uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_::set_tx_data(
          uint32_t data
        )
        {
          // setting the data to send
          uint32_t data_to_send=data&data_mask;
         
          // setting the parity bit
          if(parity!=parity_codes::NO_PARITY)
          {
            register uint32_t data_parity=get_even_parity(
              data_to_send,
              static_cast<uint32_t>(data_bits)
            );
      
            if(parity==parity_codes::ODD_PARITY) 
              data_parity=data_parity^1;
      
            data_to_send=
              (data_to_send<<1)|(data_parity<<parity_bit_pos);
          }
          else data_to_send=(data_to_send<<1);
      
          // setting the stop bits
          if(stop_bits==stop_bit_codes::ONE_STOP_BIT)
            data_to_send=data_to_send|(1<<first_stop_bit_pos);
          else
            data_to_send=data_to_send|(0x3<<first_stop_bit_pos);
      
          interrupt_guard guard;
      
          if(!tx_buffer.push(data_to_send))  
            return false; // tx buffer full
      
          if(tx_status==tx_status_codes::IDLE)
          {
            tx_buffer.pop(data_to_send); 
            tx_data=data_to_send; tx_bit_counter=0; 
            tx_interrupt_counter=0;
          }
      
          if(
            (rx_status==rx_status_codes::LISTENING)
            && (tx_status==tx_status_codes::IDLE) 
          ) start_tc_interrupts();
      
          tx_status=tx_status_codes::SENDING;
      
          return true;
        }
      
      } // namespace arduino_due

    } // namespace soft_uart
  
  #else // #ifdef CHIBIOS_PORT

    #include "ch.h"
    #include "hal.h"

    namespace soft_uart 
    {

      namespace chibios
      {
        constexpr uint32_t NUM_DIGITAL_PINS=16;

        class interrupt_guard
        {
          public:
      
            interrupt_guard() { chSysLockFromISR(); }
            ~interrupt_guard() { chSysUnlockFromISR(); }
        };

        class system_guard
        {
          public:
      
            system_guard() { chSysLock(); }
            ~system_guard() { chSysUnlock(); }
        };

        template<
          GPTDriver* TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > class uart 
        {
          public:

            typedef decltype(GPIOA) gpio_port_t;
            //typedef stm32_gpio_t* gpio_port_t;
      
            uart() { _mode_=mode_codes::INVALID_MODE; }
      
            ~uart() { end(); }
        
            uart(const uart&) = delete;
            uart(uart&&) = delete;
            uart& operator=(const uart&) = delete;
            uart& operator=(uart&&) = delete;
      
            return_codes config(
              gpio_port_t rx_port, uint32_t rx_pin,
              gpio_port_t tx_port, uint32_t tx_pin,
              uint32_t bit_rate = bit_rates::DEFAULT_BIT_RATE,
              data_bit_codes the_data_bits = data_bit_codes::EIGHT_BITS,
              parity_codes the_parity = parity_codes::EVEN_PARITY,
              stop_bit_codes the_stop_bits = stop_bit_codes::ONE_STOP_BIT
            ) 
            {
              _mode_=mode_codes::INVALID_MODE;
              
              if(rx_pin>=NUM_DIGITAL_PINS)
                return return_codes::BAD_RX_PIN;
      
              if(tx_pin>=NUM_DIGITAL_PINS)
                return return_codes::BAD_TX_PIN;
      
              return_codes ret_code=
                _ctx_.config(
                  rx_port,rx_pin,
                  rx_port,tx_pin,
                  bit_rate,
                  the_data_bits,
                  the_parity,
                  the_stop_bits
                ); 
      
              if(ret_code!=return_codes::EVERYTHING_OK) return ret_code;
                      
              // cofigure tx pin
              palSetPadMode(
                tx_port,tx_pin,
                PAL_MODE_OUTPUT_PUSHPULL
              );
              palSetPad(tx_port,tx_pin);
      
              // configure & attatch interrupt on rx pin
              palSetPadMode(
                rx_port,rx_pin,
                PAL_MODE_INPUT_PULLUP
              );
              palSetPadCallback(
                rx_port,rx_pin,
                uart::_rx_callback_,
                reinterpret_cast<void*>(this)
              );
              palEnablePadEvent(
                rx_port,rx_pin,
                PAL_EVENT_MODE_BOTH_EDGES
              ); 
      
              _mode_=mode_codes::FULL_DUPLEX;
      
              return return_codes::EVERYTHING_OK;
            }
      	
            return_codes half_duplex_config(
              gpio_port_t rx_tx_port, uint32_t rx_tx_pin,
              uint32_t bit_rate = bit_rates::DEFAULT_BIT_RATE,
              data_bit_codes the_data_bits = data_bit_codes::EIGHT_BITS,
              parity_codes the_parity = parity_codes::EVEN_PARITY,
              stop_bit_codes the_stop_bits = stop_bit_codes::ONE_STOP_BIT,
              bool in_rx_mode = true
            ) 
            {
              _mode_=mode_codes::INVALID_MODE;
      
              if(rx_tx_pin>=NUM_DIGITAL_PINS)
                return return_codes::BAD_HALF_DUPLEX_PIN;
      
              return_codes ret_code=
                _ctx_.config(
                  rx_tx_port,rx_tx_pin,
                  rx_tx_port,rx_tx_pin,
                  bit_rate,
                  the_data_bits,
                  the_parity,
                  the_stop_bits
                ); 
      
              if(ret_code!=return_codes::EVERYTHING_OK) return ret_code;
      
              if(in_rx_mode)
              {
                // configure & attatch interrupt on rx pin
                palSetPadMode(
                  rx_tx_port,rx_tx_pin,
                  PAL_MODE_INPUT_PULLUP
                );
                palSetPadCallback(
                  rx_tx_port,rx_tx_pin,
                  uart::_rx_callback_,
                  reinterpret_cast<void*>(this)
                );
                palEnablePadEvent(
                  rx_tx_port,rx_tx_pin,
                  PAL_EVENT_MODE_BOTH_EDGES
                ); 

                _mode_=mode_codes::RX_MODE;
              }
              else
              {
                // cofigure tx pin
                palSetPadMode(
                  rx_tx_port,rx_tx_pin,
                  PAL_MODE_OUTPUT_PUSHPULL
                );
                palSetPad(rx_tx_port,rx_tx_pin);
                _mode_=mode_codes::TX_MODE;
              }
      
              return return_codes::EVERYTHING_OK;
            }
      
            mode_codes get_mode() { return _mode_; }
      
            bool set_rx_mode()
            {
              if( 
                (_mode_==mode_codes::INVALID_MODE) ||
                (_mode_==mode_codes::FULL_DUPLEX)
              ) return false;
      
              if(_mode_==mode_codes::RX_MODE) return true; 
              flush();
      
              // configure & attatch interrupt on rx pin
              palSetPadMode(
                _ctx_.rx_port,_ctx_.rx_pin,
                PAL_MODE_INPUT_PULLUP
              );
              palSetPadCallback(
                _ctx_.rx_port,_ctx_.rx_pin,
                uart::_rx_callback_,
                reinterpret_cast<void*>(this)
              );
              palEnablePadEvent(
                _ctx_.rx_port,_ctx_.rx_pin,
                PAL_EVENT_MODE_BOTH_EDGES
              ); 
              
              _mode_=mode_codes::RX_MODE;
              return true;
            }
      
            bool set_tx_mode()
            {
              if( 
                (_mode_==mode_codes::INVALID_MODE) ||
                (_mode_==mode_codes::FULL_DUPLEX)
              ) return false;
      
              if(_mode_==mode_codes::TX_MODE) return true;
      
              // waiting to finish reception
              while(_ctx_.rx_status==rx_status_codes::RECEIVING) { /* do nothing */ } 
      
              palDisablePadEvent(_ctx_.rx_port,_ctx_.rx_pin);
              // cofigure tx pin
              palSetPadMode(
                _ctx_.tx_port,_ctx_.tx_pin,
                PAL_MODE_OUTPUT_PUSHPULL
              );
              palSetPad(_ctx_.tx_port,_ctx_.tx_pin);

              _mode_=mode_codes::TX_MODE;
              return true;
            }
      
            void end() { _ctx_.end(); }
      
            int available() { return _ctx_.available(); }
      
            GPTDriver* get_timer() { return TIMER; }
      
            size_t get_rx_buffer_length() { return RX_BUFFER_LENGTH; }
            size_t get_tx_buffer_length() { return TX_BUFFER_LENGTH; }
        
            uint32_t get_bit_rate() { return _ctx_.bit_rate; }
            double get_bit_time() { return _ctx_.bit_time; }	
            double get_frame_time() { return _ctx_.frame_time; }	
      
            uint32_t get_rx_data(uint32_t& data) 
            { 
              return (
                (
                  (_mode_==mode_codes::FULL_DUPLEX) ||
                  (_mode_==mode_codes::RX_MODE)
                )? 
                  _ctx_.get_rx_data(data): 
                  static_cast<uint32_t>(
                    rx_data_status_codes::NO_DATA_AVAILABLE
                  )
              );
            }
      
            bool data_available(uint32_t status)
            { return _ctx_.data_available(status); }
      
            bool data_lost(uint32_t status)
            { return _ctx_.data_lost(status); }
      
            bool bad_status(uint32_t status) 
            { return _ctx_.bad_status(status); }
            
            bool bad_start_bit(uint32_t status) 
            { return _ctx_.bad_start_bit(status); }
            
            bool bad_parity(uint32_t status) 
            { return _ctx_.bad_parity(status); }
      
            bool bad_stop_bit(uint32_t status) 
            { return _ctx_.bad_stop_bit(status); }
      
            // is TX buffer full?
            bool is_tx_full() 
            { 
              return (
                (
                  (_mode_==mode_codes::FULL_DUPLEX) ||
                  (_mode_==mode_codes::TX_MODE)
                )? _ctx_.is_tx_full(): false
              ); 
            }
      
            // is TX buffer full?
            bool available_for_write() 
            { 
              return (
                (
                  (_mode_==mode_codes::FULL_DUPLEX) ||
                  (_mode_==mode_codes::TX_MODE)
                )? _ctx_.available_for_write(): 0 
              ); 
            }
      
            // NOTE: data is 5, 6, 7, 8 or 9 bits length
            bool set_tx_data(uint32_t data) 
            { 
              return (
                (
                  (_mode_==mode_codes::FULL_DUPLEX) ||
                  (_mode_==mode_codes::TX_MODE)
                )? _ctx_.set_tx_data(data): false
              ); 
            }
      
            tx_status_codes get_tx_status() { return _ctx_.get_tx_status(); }
      
            void flush() { _ctx_.flush(); }
      
            void flush_rx() { _ctx_.flush_rx(); }
      
          private:

            static void _gpt_callback_(GPTDriver* gptp)
            { _ctx_.tc_interrupt(); }

            static const GPTConfig _gpt_config_;

            static void _rx_callback_(void* obj) 
            { reinterpret_cast<uart*>(obj)->_ctx_.rx_interrupt(); }
      
            struct _uart_ctx_
            {
      
              return_codes config(
                gpio_port_t the_rx_port, uint32_t the_rx_pin,
                gpio_port_t the_tx_port, uint32_t the_tx_pin,
                uint32_t the_bit_rate,
                data_bit_codes the_data_bits,
                parity_codes the_parity,
                stop_bit_codes the_stop_bits
              );
      
              void end()
              {
                flush();

                // stopping timer
                gptStopTimer(TIMER); gptStop(TIMER);

                // disabling reception
                palDisablePadEvent(rx_port,rx_pin);
              }

              void tc_interrupt();
              void rx_interrupt();
      
              uint32_t get_rx_data(uint32_t& data);
      
              int available()
              {
                system_guard guard;
                return rx_buffer.items();
              }
      
              bool data_available(uint32_t status)
              { 
                return (
                  status&(
                    rx_data_status_codes::DATA_AVAILABLE|
                    rx_data_status_codes::DATA_LOST
                  )
                ); 
              }
      
              bool data_lost(uint32_t status)
              { return (status&rx_data_status_codes::DATA_LOST); }
      
              bool bad_status(uint32_t status)
              {
                return (
                  status&(
                    rx_data_status_codes::BAD_START_BIT|
                    rx_data_status_codes::BAD_PARITY|
                    rx_data_status_codes::BAD_STOP_BIT
                  )
                );
              }
      
              bool bad_start_bit(uint32_t status)
              { return (status&rx_data_status_codes::BAD_START_BIT); }
              
              bool bad_parity(uint32_t status)
              { return (status&rx_data_status_codes::BAD_PARITY); }
              
              bool bad_stop_bit(uint32_t status)
              { return (status&rx_data_status_codes::BAD_STOP_BIT); }
      
              // is TX buffer full?
              bool is_tx_full() 
              { 
                system_guard guard;
                return tx_buffer.is_full();
              }
      
              int available_for_write() 
              { 
                system_guard guard;
                return tx_buffer.available();
              }
      
              // NOTE: only the 5, 6, 7, 8  or 9 lowest significant bits
              // of data are send
              bool set_tx_data(uint32_t data);
      
              void flush()
              {
                // wait until sending everything
                while(tx_status!=tx_status_codes::IDLE) 
                { /*nothing */ }
              }
      
              void flush_rx()
              {
                system_guard guard;
                rx_buffer.reset();
              }
      
              tx_status_codes get_tx_status() { return tx_status; }
      
              uint32_t get_even_parity(uint32_t data,uint32_t bits)
              {
                uint32_t odd_parity=data&1;
                for(uint32_t bit=1; bit<bits; bit++)
                  odd_parity=odd_parity^((data>>bit)&1);
                return odd_parity;
              }
      
              void get_incoming_bit()
              { rx_data |= (rx_bit<<rx_bit_counter); }
      
              void update_rx_data_buffer()
              {
                rx_data_status=(
                  (rx_buffer.push(static_cast<uint32_t>(rx_data)))?
                    rx_data_status_codes::DATA_AVAILABLE:
                    rx_data_status_codes::DATA_LOST
                );
              }
      
              void set_outgoing_bit()
              {
                if((tx_data>>tx_bit_counter) & 1) 
                  palSetPad(tx_port,tx_pin);
                else palClearPad(tx_port,tx_pin);
              }
      
              gpio_port_t rx_port;
              uint32_t rx_pin;
      
              gpio_port_t tx_port;
              uint32_t tx_pin;
      
              double tc_tick;
              double bit_time;
              double frame_time;
              uint32_t bit_ticks;
              uint32_t bit_1st_half;
              uint32_t bit_1st_quarter;
      
              // serial protocol
              uint32_t bit_rate;
              data_bit_codes data_bits;
              parity_codes parity;
              stop_bit_codes stop_bits;
              uint32_t rx_frame_bits;
              uint32_t tx_frame_bits;
              uint32_t parity_bit_pos;
              uint32_t first_stop_bit_pos;
              uint32_t data_mask;
      
              // rx data
              circular_fifo<uint32_t,RX_BUFFER_LENGTH> rx_buffer;
              volatile uint32_t rx_data;
              volatile uint32_t rx_bit_counter;
              volatile uint32_t rx_bit;
              volatile rx_status_codes rx_status;
              volatile uint32_t rx_data_status;
              volatile uint32_t rx_interrupt_counter;
      
              // tx data
              fifo<uint32_t,TX_BUFFER_LENGTH> tx_buffer;
              volatile uint32_t tx_data;
              volatile uint32_t tx_bit_counter;
              volatile tx_status_codes tx_status;
              volatile uint32_t tx_interrupt_counter;
            };
        
            static _uart_ctx_ _ctx_;
      
            mode_codes _mode_;
        };

        template<
          GPTDriver* TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > const GPTConfig uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_gpt_config_=
        {
          10000000, /* timer clock (Hz).*/ 
          uart<
            TIMER,
            RX_BUFFER_LENGTH,
            TX_BUFFER_LENGTH
          >::_gpt_callback_,   /* Timer callback.*/ 
          0, 
          0
        };

        template<
          GPTDriver* TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > typename uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_ 
          uart<TIMER,RX_BUFFER_LENGTH,TX_BUFFER_LENGTH>::_ctx_;
      
        template<
          GPTDriver* TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > return_codes uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_::config(
          gpio_port_t the_rx_port, uint32_t the_rx_pin,
          gpio_port_t the_tx_port, uint32_t the_tx_pin,
          uint32_t the_bit_rate,
          data_bit_codes the_data_bits,
          parity_codes the_parity,
          stop_bit_codes the_stop_bits
        )
        {
          if(
            (the_bit_rate<bit_rates::MIN_BIT_RATE) || 
            (the_bit_rate>bit_rates::MAX_BIT_RATE)
          ) return return_codes::BAD_BIT_RATE_ERROR;
      
          bit_rate=the_bit_rate;
          
          tc_tick=double(1)/double(_gpt_config_.frequency);
          bit_time=double(1)/double(bit_rate);
        
          bit_1st_quarter=static_cast<uint32_t>(bit_time/(4*tc_tick));
          bit_1st_half=(bit_1st_quarter<<1);
          bit_ticks=(bit_1st_half<<1);
      
          data_bits=the_data_bits; parity=the_parity; stop_bits=the_stop_bits;
      
          // reception frame length in bits
          rx_frame_bits=1 + // the start bit
            static_cast<uint32_t>(data_bits) + // the data bits
            ((parity!=parity_codes::NO_PARITY)? 1: 0) + // the parity?
            1; // for reception we ONLY consider one stop bit
      
          // transmission frame length in bits
          tx_frame_bits=rx_frame_bits;
          if(stop_bits==stop_bit_codes::TWO_STOP_BITS) 
          {
            // for transmission we DO consider also the second stop bit
            tx_frame_bits++; 
          }
      
          frame_time=tx_frame_bits*bit_time;
      
          parity_bit_pos=1 + // the start bit
            static_cast<uint32_t>(data_bits); // the data bits
      
          first_stop_bit_pos=parity_bit_pos +
            ((parity!=parity_codes::NO_PARITY)? 1: 0); // the parity?
      
          data_mask=(1<<static_cast<uint32_t>(data_bits))-1;
      
          rx_port=the_rx_port; rx_pin=the_rx_pin;
          rx_status=rx_status_codes::LISTENING;
          rx_data_status=rx_data_status_codes::NO_DATA_AVAILABLE;
          rx_buffer.reset();
          rx_interrupt_counter=0;
      
          tx_port=the_tx_port; tx_pin=the_tx_pin;
          tx_status=tx_status_codes::IDLE;
          tx_buffer.reset();
          tx_interrupt_counter=0;

          gptStart(TIMER,&_gpt_config_);
      
          return return_codes::EVERYTHING_OK;
        }
      
        template<
          GPTDriver* TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > void uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_::tc_interrupt()
        {
          // rx code
          if(rx_status==rx_status_codes::RECEIVING)
          {
            if(rx_interrupt_counter==1)
            {
              get_incoming_bit(); 
              rx_bit_counter++;
              if(rx_bit_counter==rx_frame_bits)
              {
                if(stop_bits==stop_bit_codes::TWO_STOP_BITS)
                  get_incoming_bit();
      
                if(tx_status==tx_status_codes::IDLE) 
                { interrupt_guard guard; gptStopTimerI(TIMER); }
      
                update_rx_data_buffer();
      
                rx_status=rx_status_codes::LISTENING;
              }
            }
            rx_interrupt_counter=(rx_interrupt_counter+1)&0x3;
          }
      
          // tx code
          if(tx_status==tx_status_codes::SENDING)
          {
            if(tx_interrupt_counter==0)
            {
              if(tx_bit_counter>=tx_frame_bits)
              {
                uint32_t data_to_send;
                if(tx_buffer.pop(data_to_send)) 
                { 
                  tx_data=data_to_send; tx_bit_counter=0; 
                  set_outgoing_bit(); tx_bit_counter++;
                }
                else
                {
                  if(rx_status==rx_status_codes::LISTENING) 
                  { interrupt_guard guard; gptStopTimerI(TIMER); }
      
                  tx_status=tx_status_codes::IDLE;
                }
              }
              else { set_outgoing_bit(); tx_bit_counter++; }
            }
            tx_interrupt_counter=(tx_interrupt_counter+1)&0x3;
          }
        }
        
        template<
          GPTDriver* TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > void uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_::rx_interrupt()
        {
          register uint32_t sampled_bit= 
            (palReadPad(rx_port,rx_pin)==PAL_HIGH)? 1:0;
      
          switch(rx_status)
          {
            case rx_status_codes::LISTENING:
              if(!sampled_bit)
              {
                rx_status=rx_status_codes::RECEIVING;
                rx_data=rx_bit_counter=rx_bit=0;
                rx_interrupt_counter=0;
                
                if(tx_status==tx_status_codes::IDLE) 
                { 
                  {
                    interrupt_guard guard;
                    gptStartContinuousI(TIMER,bit_1st_quarter);
                  }
                  rx_interrupt_counter=1; }
              } 
              break;
              
            case rx_status_codes::RECEIVING:
              rx_bit=sampled_bit;
              break;
          }
        }
      
        template<
          GPTDriver* TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > uint32_t uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_::get_rx_data(
          uint32_t& data
        )
        {
          register uint32_t status;
          register bool not_empty;
          uint32_t data_received;
          
          {
            system_guard guard;
            
            status=(not_empty=rx_buffer.pop(data_received))?
              rx_data_status_codes::DATA_AVAILABLE:
              rx_data_status_codes::NO_DATA_AVAILABLE;
          }
      
          if(!not_empty) return status;
          
          // checking start bit
          status=(data_received & 1)?
            status|rx_data_status_codes::BAD_START_BIT:
            status&(~rx_data_status_codes::BAD_START_BIT);
      
          // cheking parity
          if(parity!=parity_codes::NO_PARITY)
          {
            register uint32_t data_parity=get_even_parity(
              (data_received>>1),
              static_cast<uint32_t>(data_bits)
            );
      
            if(parity==parity_codes::ODD_PARITY) 
              data_parity=data_parity^1;
      
            register uint32_t received_parity=
              (data_received>>parity_bit_pos) & 1;
      
            // verifying parity bit
            status=(received_parity^data_parity)?
                status|rx_data_status_codes::BAD_PARITY:
                status&(~rx_data_status_codes::BAD_PARITY);
          }
      
          // checking stop bit
          // NOTE: we only verify the first stop bit
          status=((data_received>>first_stop_bit_pos) & 1)?
            status&(~rx_data_status_codes::BAD_STOP_BIT):
            status|rx_data_status_codes::BAD_STOP_BIT;
      
          // NOTE: in case of error, we put the received raw data
          // on the high 16 bits of status
          if(bad_status(status)) status=status|(data_received<<16);
      
          data=(data_received>>1)&data_mask;
      
          return status;
        }
      
        template<
          GPTDriver* TIMER,
          size_t RX_BUFFER_LENGTH,
          size_t TX_BUFFER_LENGTH
        > bool uart<
          TIMER,
          RX_BUFFER_LENGTH,
          TX_BUFFER_LENGTH
        >::_uart_ctx_::set_tx_data(
          uint32_t data
        )
        {
          // setting the data to send
          uint32_t data_to_send=data&data_mask;
         
          // setting the parity bit
          if(parity!=parity_codes::NO_PARITY)
          {
            register uint32_t data_parity=get_even_parity(
              data_to_send,
              static_cast<uint32_t>(data_bits)
            );
      
            if(parity==parity_codes::ODD_PARITY) 
              data_parity=data_parity^1;
      
            data_to_send=
              (data_to_send<<1)|(data_parity<<parity_bit_pos);
          }
          else data_to_send=(data_to_send<<1);
      
          // setting the stop bits
          if(stop_bits==stop_bit_codes::ONE_STOP_BIT)
            data_to_send=data_to_send|(1<<first_stop_bit_pos);
          else
            data_to_send=data_to_send|(0x3<<first_stop_bit_pos);
      
	        rx_status_codes rx_status_tmp; 
	        tx_status_codes tx_status_tmp;
	        {
            system_guard guard;
            
            if(!tx_buffer.push(data_to_send))  
              return false; // tx buffer full
            
            if(tx_status==tx_status_codes::IDLE)
            {
              tx_buffer.pop(data_to_send); 
              tx_data=data_to_send; tx_bit_counter=0; 
              tx_interrupt_counter=0;
            }

	          rx_status_tmp=rx_status;
	          tx_status_tmp=tx_status;

            tx_status=tx_status_codes::SENDING;
	        }

          if(
            (rx_status_tmp==rx_status_codes::LISTENING)
            && (tx_status_tmp==tx_status_codes::IDLE) 
          ) gptStartContinuous(TIMER,bit_1st_quarter);
      
          return true;
        }

      } // namespace chibios
    } // namespace soft_uart
  
  #endif // CHIBIOS_PORT

#endif // SOFT_UART_H