RS485SoftwareSerial.cpp

/*

RS485SoftwareSerial.cpp - Implementation of a sofware 9bit RS485 based on 
the 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 <RS485SoftwareSerial.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
RS485SoftwareSerial *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};

RS485SoftwareSerial::RS485SoftwareSerial()
{
  m_rxValid = m_txValid = m_txEnableValid = false;
  m_buffer = NULL;
  m_overflow = false;
  m_rxEnabled = false;
}

RS485SoftwareSerial::~RS485SoftwareSerial()
{
  enableRx(false);
  if (m_rxValid)
    ObjList[m_rxPin] = NULL;
  if (m_buffer)
    free(m_buffer);
}

bool RS485SoftwareSerial::isValidGPIOpin(int pin)
{
  return (pin >= 0 && pin <= 5) || (pin >= 12 && pin <= MAX_PIN);
}

void RS485SoftwareSerial::setup(int receivePin, int transmitPin, bool inverse_logic, unsigned int buffSize)
{
  m_invert = inverse_logic;
  if (isValidGPIOpin(receivePin))
  {
    m_rxPin = receivePin;
    m_buffSize = buffSize;
    m_buffer = (uint16_t *)malloc(m_buffSize*2);
    if (m_buffer != NULL)
    {
      m_rxValid = true;
      m_inPos = m_outPos = 0;
      pinMode(m_rxPin, INPUT);
      ObjList[m_rxPin] = this;
      enableRx(true);
    }
  }
  if (isValidGPIOpin(transmitPin))
  {
    m_txValid = true;
    m_txPin = transmitPin;
    pinMode(m_txPin, OUTPUT);
    digitalWrite(m_txPin, !m_invert);
  }
}

void RS485SoftwareSerial::begin(long speed, byte dataBits)
{
  // Use getCycleCount() loop to get as exact timing as possible
  m_bitTime = ESP.getCpuFreqMHz() * 1000000 / speed;
  m_dataBits = dataBits;
  m_mask = 1 << (m_dataBits-1);
  if (!m_rxEnabled)
    enableRx(true);
}

long RS485SoftwareSerial::baudRate()
{
  return ESP.getCpuFreqMHz() * 1000000 / m_bitTime;
}

void RS485SoftwareSerial::setTransmitEnablePin(int transmitEnablePin, bool reverse)
{
  if (isValidGPIOpin(transmitEnablePin))
  {
    m_txEnableReverse = reverse;
    m_txEnableValid = true;
    m_txEnablePin = transmitEnablePin;
    pinMode(m_txEnablePin, OUTPUT);
    digitalWrite(m_txEnablePin, m_txEnableReverse ? HIGH : LOW);
  }
  else
  {
    m_txEnableValid = false;
  }
}

void RS485SoftwareSerial::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 RS485SoftwareSerial::read()
{
  if (!m_rxValid || (m_inPos == m_outPos))
    return -1;
  uint16_t ch = m_buffer[m_outPos];
  m_outPos = (m_outPos + 1) % m_buffSize;
  return ch;
}

int RS485SoftwareSerial::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) \
      ;                                        \
    wait += m_bitTime;                         \
  }

size_t RS485SoftwareSerial::write(uint16_t b)
{
  if (!m_txValid)
    return 0;

  if (m_invert)
    b = ~b;
  // Disable interrupts in order to get a clean transmit
  cli();
  if (m_txEnableValid)
    digitalWrite(m_txEnablePin, m_txEnableReverse ? LOW : 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 < m_dataBits; i++)
  {
    digitalWrite(m_txPin, (b & 1) ? HIGH : LOW);
    WAIT;
    b >>= 1;
  }
  // Stop bit
  digitalWrite(m_txPin, HIGH);
  WAIT;
  if (m_txEnableValid)
    digitalWrite(m_txEnablePin, m_txEnableReverse ? HIGH : LOW);
  sei();
  return 1;
}

void RS485SoftwareSerial::flush()
{
  m_inPos = m_outPos = 0;
}

bool RS485SoftwareSerial::overflow()
{
  bool res = m_overflow;
  m_overflow = false;
  return res;
}

int RS485SoftwareSerial::peek()
{
  if (!m_rxValid || (m_inPos == m_outPos))
    return -1;
  return m_buffer[m_outPos];
}

void ICACHE_RAM_ATTR RS485SoftwareSerial::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();
  uint16_t rec = 0;
  for (int i = 0; i < m_dataBits; i++)
  {
    rec >>= 1;
    WAIT;
    if (digitalRead(m_rxPin))
      rec |= m_mask;
  }
  if (m_invert)
    rec = ~rec;
  // 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);
}