text: /*
  
  SoftwareSerial8E1.cpp - Implementation of the Arduino software serial for ESP8266.
  Copyright (c) 2015-2016 Peter Lerup. All rights 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
  
  */
  
  #include <Arduino.h>
  
  // The Arduino standard GPIO routines are not enough,
  // must use some from the Espressif SDK as well
  extern "C" {
  #include "gpio.h"
  }
  
  #include "SoftwareSerial8E1.h"
  
  #define MAX_PIN 15
  
  // As the Arduino attachInterrupt has no parameter, lists of objects
  // and callbacks corresponding to each possible GPIO pins have to be defined
  SoftwareSerial8E1 *ObjList[MAX_PIN+1];
  
  void ICACHE_RAM_ATTR sws_isr_0() { ObjList[0]->rxRead(); };
  void ICACHE_RAM_ATTR sws_isr_1() { ObjList[1]->rxRead(); };
  void ICACHE_RAM_ATTR sws_isr_2() { ObjList[2]->rxRead(); };
  void ICACHE_RAM_ATTR sws_isr_3() { ObjList[3]->rxRead(); };
  void ICACHE_RAM_ATTR sws_isr_4() { ObjList[4]->rxRead(); };
  void ICACHE_RAM_ATTR sws_isr_5() { ObjList[5]->rxRead(); };
  // Pin 6 to 11 can not be used
  void ICACHE_RAM_ATTR sws_isr_12() { ObjList[12]->rxRead(); };
  void ICACHE_RAM_ATTR sws_isr_13() { ObjList[13]->rxRead(); };
  void ICACHE_RAM_ATTR sws_isr_14() { ObjList[14]->rxRead(); };
  void ICACHE_RAM_ATTR sws_isr_15() { ObjList[15]->rxRead(); };
  
  static void (*ISRList[MAX_PIN+1])() = {
        sws_isr_0,
        sws_isr_1,
        sws_isr_2,
        sws_isr_3,
        sws_isr_4,
        sws_isr_5,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        NULL,
        sws_isr_12,
        sws_isr_13,
        sws_isr_14,
        sws_isr_15
  };
  
  SoftwareSerial8E1::SoftwareSerial8E1(int receivePin, int transmitPin, bool inverse_logic, unsigned int buffSize, uint8_t parity) {
    m_oneWire = (receivePin == transmitPin);
    m_rxValid = m_txValid = m_txEnableValid = false;
    m_buffer = NULL;
    m_invert = inverse_logic;
    m_overflow = false;
    m_rxEnabled = false;
    m_parity = parity;
    if (isValidGPIOpin(receivePin)) {
      m_rxPin = receivePin;
      m_buffSize = buffSize;
      m_buffer = (uint8_t*)malloc(m_buffSize);
      if (m_buffer != NULL) {
        m_rxValid = true;
        m_inPos = m_outPos = 0;
        pinMode(m_rxPin, INPUT);
        ObjList[m_rxPin] = this;
      }
    }
    if (isValidGPIOpin(transmitPin) || (!m_oneWire && (transmitPin == 16))) {
      m_txValid = true;
      m_txPin = transmitPin;
      if (!m_oneWire) {
        pinMode(m_txPin, OUTPUT);
        digitalWrite(m_txPin, !m_invert);
      }
    }
  
  }
  
  SoftwareSerial8E1::~SoftwareSerial8E1() {
    enableRx(false);
    if (m_rxValid)
      ObjList[m_rxPin] = NULL;
    if (m_buffer)
      free(m_buffer);
  }
  
  bool SoftwareSerial8E1::isValidGPIOpin(int pin) {
    return (pin >= 0 && pin <= 5) || (pin >= 12 && pin <= MAX_PIN);
  }
  
  void SoftwareSerial8E1::begin(long speed) {
    // Use getCycleCount() loop to get as exact timing as possible
    m_bitTime = F_CPU/speed;
    // By default enable interrupt during tx only for low speed
    m_intTxEnabled = speed < 9600;
  
    if (!m_rxEnabled)
      enableRx(true);
  }
  
  long SoftwareSerial8E1::baudRate() {
    return F_CPU/m_bitTime;
  }
  
  void SoftwareSerial8E1::setTransmitEnablePin(int transmitEnablePin) {
    if (isValidGPIOpin(transmitEnablePin)) {
      m_txEnableValid = true;
      m_txEnablePin = transmitEnablePin;
      pinMode(m_txEnablePin, OUTPUT);
      digitalWrite(m_txEnablePin, LOW);
    } else {
      m_txEnableValid = false;
    }
  }
  
  void SoftwareSerial8E1::enableIntTx(bool on) {
    m_intTxEnabled = on;
  }
  
  void SoftwareSerial8E1::enableTx(bool on) {
    if (m_oneWire && m_txValid) {
      if (on) {
        enableRx(false);
        digitalWrite(m_txPin, !m_invert);
        pinMode(m_rxPin, OUTPUT);
      } else {
        digitalWrite(m_txPin, !m_invert);
        pinMode(m_rxPin, INPUT);
        enableRx(true);
      }
      delay(1); // it's important to have a delay after switching
    }
  }
  
  void SoftwareSerial8E1::enableRx(bool on) {
    if (m_rxValid) {
      if (on)
        attachInterrupt(m_rxPin, ISRList[m_rxPin], m_invert ? RISING : FALLING);
      else
        detachInterrupt(m_rxPin);
      m_rxEnabled = on;
    }
  }
  
  int SoftwareSerial8E1::read() {
    if (!m_rxValid || (m_inPos == m_outPos)) return -1;
    uint8_t ch = m_buffer[m_outPos];
    m_outPos = (m_outPos+1) % m_buffSize;
    return ch;
  }
  
  int SoftwareSerial8E1::available() {
    if (!m_rxValid) return 0;
    int avail = m_inPos - m_outPos;
    if (avail < 0) avail += m_buffSize;
    return avail;
  }
  
  #define WAIT { while (ESP.getCycleCount()-start < wait) if (m_intTxEnabled) optimistic_yield(1); wait += m_bitTime; }
  
  size_t SoftwareSerial8E1::write(uint8_t b) {
    boolean l_even=true;
    if (!m_txValid) return 0;
  
    if (m_invert) b = ~b;
    if (!m_intTxEnabled)
      // Disable interrupts in order to get a clean transmit
      cli();
    if (m_txEnableValid) digitalWrite(m_txEnablePin, HIGH);
    unsigned long wait = m_bitTime;
    digitalWrite(m_txPin, HIGH);
    unsigned long start = ESP.getCycleCount();
    // Start bit;
    digitalWrite(m_txPin, LOW);
    WAIT;
    for (int i = 0; i < 8; i++) {
      l_even=(b & 1)?!l_even:l_even;
  	digitalWrite(m_txPin, (b & 1) ? HIGH : LOW);
      WAIT;
      b >>= 1;
    }
    // Parity
    if(m_parity==EVEN){
  	digitalWrite(m_txPin, l_even?LOW:HIGH);
  	WAIT;
    }
    if(m_parity==ODD){
  	digitalWrite(m_txPin, l_even?HIGH:LOW);
  	WAIT;
    }
    // Stop bit
    digitalWrite(m_txPin, HIGH);
    WAIT;
    if (m_txEnableValid) digitalWrite(m_txEnablePin, LOW);
    if (!m_intTxEnabled)
      sei();
    return 1;
  }
  
  void SoftwareSerial8E1::flush() {
    m_inPos = m_outPos = 0;
  }
  
  bool SoftwareSerial8E1::overflow() {
    bool res = m_overflow;
    m_overflow = false;
    return res;
  }
  
  int SoftwareSerial8E1::peek() {
    if (!m_rxValid || (m_inPos == m_outPos)) return -1;
    return m_buffer[m_outPos];
  }
  
  void ICACHE_RAM_ATTR SoftwareSerial8E1::rxRead() {
    // Advance the starting point for the samples but compensate for the
    // initial delay which occurs before the interrupt is delivered
    unsigned long wait = m_bitTime + m_bitTime/3 - 500;
    unsigned long start = ESP.getCycleCount();
    uint8_t rec = 0;
    boolean l_even = true;
    for (int i = 0; i < 8; i++) {
      WAIT;
      rec >>= 1;
      if (digitalRead(m_rxPin)){
        rec |= 0x80;
        l_even = !l_even;
  	 }
    }
    if (m_invert) rec = ~rec;
    // Parity
    if(m_parity != NONE){
  	  WAIT;
  	  digitalRead(m_rxPin);
    }
    
    // Stop bit
    WAIT;
    // Store the received value in the buffer unless we have an overflow
    int next = (m_inPos+1) % m_buffSize;
    if (next != m_outPos) {
      m_buffer[m_inPos] = rec;
      m_inPos = next;
    } else {
      m_overflow = true;
    }
    // Must clear this bit in the interrupt register,
    // it gets set even when interrupts are disabled
    GPIO_REG_WRITE(GPIO_STATUS_W1TC_ADDRESS, 1 << m_rxPin);
  }
  