M17RX.cpp

/*
 *   Copyright (C) 2009-2018,2020,2021 by Jonathan Naylor G4KLX
 *   Copyright (C) 2016-2018 by Andy Uribe CA6JAU
 *
 *   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 2 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, write to the Free Software
 *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#include "Config.h"
#include "Globals.h"
#include "M17RX.h"
#include "Utils.h"

const uint8_t MAX_SYNC_BIT_START_ERRS = 0U;
const uint8_t MAX_SYNC_BIT_RUN_ERRS   = 2U;

const unsigned int MAX_SYNC_FRAMES = 3U + 1U;

const uint8_t BIT_MASK_TABLE[] = {0x80U, 0x40U, 0x20U, 0x10U, 0x08U, 0x04U, 0x02U, 0x01U};

#define WRITE_BIT1(p,i,b) p[(i)>>3] = (b) ? (p[(i)>>3] | BIT_MASK_TABLE[(i)&7]) : (p[(i)>>3] & ~BIT_MASK_TABLE[(i)&7])

CM17RX::CM17RX() :
m_state(M17RXS_NONE),
m_bitBuffer(0x00U),
m_outBuffer(),
m_buffer(NULL),
m_bufferPtr(0U),
m_lostCount(0U)
{
  m_buffer = m_outBuffer + 1U;
}

void CM17RX::reset()
{
  m_state     = M17RXS_NONE;
  m_bitBuffer = 0x00U;
  m_bufferPtr = 0U;
  m_lostCount = 0U;
}

void CM17RX::databit(bool bit)
{
  switch (m_state)  {
    case M17RXS_LINK_SETUP:
    case M17RXS_STREAM:
      processData(bit);
      break;
    default:
      processNone(bit);
      break;
  }
}

void CM17RX::processNone(bool bit)
{
  m_bitBuffer <<= 1;
  if (bit)
    m_bitBuffer |= 0x01U;

  // Exact matching of the link setup sync bit sequence
  if (countBits16(m_bitBuffer ^ M17_LINK_SETUP_SYNC_BITS) <= MAX_SYNC_BIT_START_ERRS) {
    DEBUG1("M17RX: link setup sync found in None");
    for (uint8_t i = 0U; i < M17_SYNC_BYTES_LENGTH; i++)
      m_buffer[i] = M17_LINK_SETUP_SYNC_BYTES[i];

    m_lostCount = MAX_SYNC_FRAMES;
    m_bufferPtr = M17_SYNC_LENGTH_BITS;
    m_state     = M17RXS_LINK_SETUP;

    io.setDecode(true);

    return;
  }

  // Exact matching of the stream sync bit sequence
  if (countBits16(m_bitBuffer ^ M17_STREAM_SYNC_BITS) <= MAX_SYNC_BIT_START_ERRS) {
    DEBUG1("M17RX: stream sync found in None");
    for (uint8_t i = 0U; i < M17_SYNC_BYTES_LENGTH; i++)
      m_buffer[i] = M17_STREAM_SYNC_BYTES[i];

    m_lostCount = MAX_SYNC_FRAMES;
    m_bufferPtr = M17_SYNC_LENGTH_BITS;
    m_state     = M17RXS_STREAM;

    io.setDecode(true);

    return;
  }
}

void CM17RX::processData(bool bit)
{
  m_bitBuffer <<= 1;
  if (bit)
    m_bitBuffer |= 0x01U;

  WRITE_BIT1(m_buffer, m_bufferPtr, bit);

  m_bufferPtr++;
  if (m_bufferPtr > M17_FRAME_LENGTH_BITS)
    reset();

  // Only search for the syncs in the right place +-1 bit
  if (m_bufferPtr >= (M17_SYNC_LENGTH_BITS - 1U) && m_bufferPtr <= (M17_SYNC_LENGTH_BITS + 1U)) {
    // Fuzzy matching of the link setup sync bit sequence
    if (countBits16(m_bitBuffer ^ M17_LINK_SETUP_SYNC_BITS) <= MAX_SYNC_BIT_RUN_ERRS) {
      DEBUG2("M17RX: found link setup sync, pos", m_bufferPtr - M17_SYNC_LENGTH_BITS);
      m_lostCount = MAX_SYNC_FRAMES;
      m_bufferPtr = M17_SYNC_LENGTH_BITS;
      m_state     = M17RXS_LINK_SETUP;
      return;
    }

    // Fuzzy matching of the stream sync bit sequence
    if (countBits16(m_bitBuffer ^ M17_STREAM_SYNC_BITS) <= MAX_SYNC_BIT_RUN_ERRS) {
      DEBUG2("M17RX: found stream sync, pos", m_bufferPtr - M17_SYNC_LENGTH_BITS);
      m_lostCount = MAX_SYNC_FRAMES;
      m_bufferPtr = M17_SYNC_LENGTH_BITS;
      m_state     = M17RXS_STREAM;
      return;
    }

    // Fuzzy matching of the EOT sync bit sequence
    if (countBits16(m_bitBuffer ^ M17_EOT_SYNC_BITS) <= MAX_SYNC_BIT_RUN_ERRS) {
      DEBUG2("M17RX: found eot sync, pos", m_bufferPtr - M17_SYNC_LENGTH_BITS);
      io.setDecode(false);
      serial.writeM17EOT();
      reset();
      return;
    }
  }

  // Send a frame to the host if the required number of bits have been received
  if (m_bufferPtr == M17_FRAME_LENGTH_BITS) {
    // We've not seen a sync for too long, signal RXLOST and change to RX_NONE
    m_lostCount--;
    if (m_lostCount == 0U) {
      DEBUG1("M17RX: sync timed out, lost lock");
      io.setDecode(false);
      serial.writeM17Lost();
      reset();
    } else {
      // Write data to host
      m_outBuffer[0U] = m_lostCount == (MAX_SYNC_FRAMES - 1U) ? 0x01U : 0x00U;

      switch (m_state) {
        case M17RXS_LINK_SETUP:
          writeRSSILinkSetup(m_outBuffer);
          break;
        case M17RXS_STREAM:
          writeRSSIStream(m_outBuffer);
          break;
        default:
          break;
      }

      // Start the next frame
      ::memset(m_outBuffer, 0x00U, M17_FRAME_LENGTH_BYTES + 3U);
      m_bufferPtr = 0U;
    }
  }
}

void CM17RX::writeRSSILinkSetup(uint8_t* data)
{
#if defined(SEND_RSSI_DATA)
  uint16_t rssi = io.readRSSI();

  data[49U] = (rssi >> 8) & 0xFFU;
  data[50U] = (rssi >> 0) & 0xFFU;

  serial.writeM17LinkSetup(data, M17_FRAME_LENGTH_BYTES + 3U);
#else
  serial.writeM17LinkSetup(data, M17_FRAME_LENGTH_BYTES + 1U);
#endif
}

void CM17RX::writeRSSIStream(uint8_t* data)
{
#if defined(SEND_RSSI_DATA)
  uint16_t rssi = io.readRSSI();

  data[49U] = (rssi >> 8) & 0xFFU;
  data[50U] = (rssi >> 0) & 0xFFU;

  serial.writeM17Stream(data, M17_FRAME_LENGTH_BYTES + 3U);
#else
  serial.writeM17Stream(data, M17_FRAME_LENGTH_BYTES + 1U);
#endif
}