DMRSlotRX.cpp

/*
 *   Copyright (C) 2009-2017,2020 by Jonathan Naylor G4KLX
 *
 *   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"

#if defined(MODE_DMR)

#include "Globals.h"
#include "DMRSlotRX.h"
#include "DMRSlotType.h"
#include "Utils.h"

const uint16_t SCAN_START = 400U;
const uint16_t SCAN_END   = 490U;

const q15_t SCALING_FACTOR = 19505;      // Q15(0.60)

const uint8_t MAX_SYNC_SYMBOLS_ERRS = 2U;
const uint8_t MAX_SYNC_BYTES_ERRS   = 3U;

const uint8_t MAX_SYNC_LOST_FRAMES  = 13U;

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])

const uint16_t NOENDPTR = 9999U;

const uint8_t CONTROL_NONE  = 0x00U;
const uint8_t CONTROL_VOICE = 0x20U;
const uint8_t CONTROL_DATA  = 0x40U;

CDMRSlotRX::CDMRSlotRX(bool slot) :
m_slot(slot),
m_bitBuffer(),
m_buffer(),
m_bitPtr(0U),
m_dataPtr(0U),
m_syncPtr(0U),
m_startPtr(0U),
m_endPtr(NOENDPTR),
m_delayPtr(0U),
m_maxCorr(0),
m_centre(),
m_threshold(),
m_averagePtr(0U),
m_control(CONTROL_NONE),
m_syncCount(0U),
m_colorCode(0U),
m_delay(0U),
m_state(DMRRXS_NONE),
m_n(0U),
m_type(0U),
m_rssi()
{
}

void CDMRSlotRX::start()
{
  m_dataPtr  = 0U;
  m_delayPtr = 0U;
  m_bitPtr   = 0U;
  m_maxCorr  = 0;
  m_control  = CONTROL_NONE;
}

void CDMRSlotRX::reset()
{
  m_syncPtr   = 0U;
  m_dataPtr   = 0U;
  m_delayPtr  = 0U;
  m_bitPtr    = 0U;
  m_maxCorr   = 0;
  m_control   = CONTROL_NONE;
  m_syncCount = 0U;
  m_state     = DMRRXS_NONE;
  m_startPtr  = 0U;
  m_endPtr    = NOENDPTR;
}

bool CDMRSlotRX::processSample(q15_t sample, uint16_t rssi)
{
  m_delayPtr++;
  if (m_delayPtr < m_delay)
    return m_state != DMRRXS_NONE;

  // Ensure that the buffer doesn't overflow
  if (m_dataPtr > m_endPtr || m_dataPtr >= 900U)
    return m_state != DMRRXS_NONE;

  m_buffer[m_dataPtr] = sample;
  m_rssi[m_dataPtr] = rssi;
  
  m_bitBuffer[m_bitPtr] <<= 1;
  if (sample < 0)
    m_bitBuffer[m_bitPtr] |= 0x01U;

  if (m_state == DMRRXS_NONE) {
    if (m_dataPtr >= SCAN_START && m_dataPtr <= SCAN_END)
      correlateSync(true);
  } else {

    uint16_t min = m_syncPtr - 1U;
    uint16_t max = m_syncPtr + 1U;
    if (m_dataPtr >= min && m_dataPtr <= max)
      correlateSync(false);
  }

  if (m_dataPtr == m_endPtr) {
    // Find the average centre and threshold values
    q15_t centre    = (m_centre[0U]    + m_centre[1U]    + m_centre[2U]    + m_centre[3U])    >> 2;
    q15_t threshold = (m_threshold[0U] + m_threshold[1U] + m_threshold[2U] + m_threshold[3U]) >> 2;

    uint8_t frame[DMR_FRAME_LENGTH_BYTES + 3U];
    frame[0U] = m_control;

    uint16_t ptr = m_endPtr - DMR_FRAME_LENGTH_SAMPLES + DMR_RADIO_SYMBOL_LENGTH + 1U;
    samplesToBits(ptr, DMR_FRAME_LENGTH_SYMBOLS, frame, 8U, centre, threshold);

    if (m_control == CONTROL_DATA) {
      // Data sync
      uint8_t colorCode;
      uint8_t dataType;
      CDMRSlotType slotType;
      slotType.decode(frame + 1U, colorCode, dataType);

      if (colorCode == m_colorCode) {
        m_syncCount = 0U;
        m_n         = 0U;

        frame[0U] |= dataType;

        switch (dataType) {
          case DT_DATA_HEADER:
            DEBUG5("DMRSlotRX: data header found slot/pos/centre/threshold", m_slot ? 2U : 1U, m_syncPtr, centre, threshold);
            writeRSSIData(frame);
            m_state = DMRRXS_DATA;
            m_type  = 0x00U;
            break;
          case DT_RATE_12_DATA:
          case DT_RATE_34_DATA:
          case DT_RATE_1_DATA:
            if (m_state == DMRRXS_DATA) {
              DEBUG5("DMRSlotRX: data payload found slot/pos/centre/threshold", m_slot ? 2U : 1U, m_syncPtr, centre, threshold);
              writeRSSIData(frame);
              m_type = dataType;
            }
            break;
          case DT_VOICE_LC_HEADER:
            DEBUG5("DMRSlotRX: voice header found slot/pos/centre/threshold", m_slot ? 2U : 1U, m_syncPtr, centre, threshold);
            writeRSSIData(frame);
            m_state = DMRRXS_VOICE;
            break;
          case DT_VOICE_PI_HEADER:
            if (m_state == DMRRXS_VOICE) {
              DEBUG5("DMRSlotRX: voice pi header found slot/pos/centre/threshold", m_slot ? 2U : 1U, m_syncPtr, centre, threshold);
              writeRSSIData(frame);
            }
            m_state = DMRRXS_VOICE;
            break;
          case DT_TERMINATOR_WITH_LC:
            if (m_state == DMRRXS_VOICE) {
              DEBUG5("DMRSlotRX: voice terminator found slot/pos/centre/threshold", m_slot ? 2U : 1U, m_syncPtr, centre, threshold);
              writeRSSIData(frame);
              m_state  = DMRRXS_NONE;
              m_endPtr = NOENDPTR;
            }
            break;
          default:    // DT_CSBK
            DEBUG5("DMRSlotRX: csbk found slot/pos/centre/threshold", m_slot ? 2U : 1U, m_syncPtr, centre, threshold);
            writeRSSIData(frame);
            m_state  = DMRRXS_NONE;
            m_endPtr = NOENDPTR;
            break;
        }
      }
    } else if (m_control == CONTROL_VOICE) {
      // Voice sync
      DEBUG5("DMRSlotRX: voice sync found slot/pos/centre/threshold", m_slot ? 2U : 1U, m_syncPtr, centre, threshold);
      writeRSSIData(frame);
      m_state     = DMRRXS_VOICE;
      m_syncCount = 0U;
      m_n         = 0U;
    } else {
      if (m_state != DMRRXS_NONE) {
        m_syncCount++;
        if (m_syncCount >= MAX_SYNC_LOST_FRAMES) {
          serial.writeDMRLost(m_slot);
          m_state  = DMRRXS_NONE;
          m_endPtr = NOENDPTR;
        }
      }

      if (m_state == DMRRXS_VOICE) {
        if (m_n >= 5U) {
          frame[0U] = CONTROL_VOICE;
          m_n = 0U;
        } else {
          frame[0U] = ++m_n;
        }

        serial.writeDMRData(m_slot, frame, DMR_FRAME_LENGTH_BYTES + 1U);
      } else if (m_state == DMRRXS_DATA) {
        if (m_type != 0x00U) {
          frame[0U] = CONTROL_DATA | m_type;
          writeRSSIData(frame);
        }
      }
    }
  }

  m_dataPtr++;

  m_bitPtr++;
  if (m_bitPtr >= DMR_RADIO_SYMBOL_LENGTH)
    m_bitPtr = 0U;

  return m_state != DMRRXS_NONE;
}

void CDMRSlotRX::correlateSync(bool first)
{
  uint8_t errs = countBits32((m_bitBuffer[m_bitPtr] & DMR_SYNC_SYMBOLS_MASK) ^ DMR_MS_DATA_SYNC_SYMBOLS);

  // The voice sync is the complement of the data sync
  bool data  = (errs <= MAX_SYNC_SYMBOLS_ERRS);
  bool voice = (errs >= (DMR_SYNC_LENGTH_SYMBOLS - MAX_SYNC_SYMBOLS_ERRS));

  if (data || voice) {
    uint16_t ptr = m_dataPtr - DMR_SYNC_LENGTH_SAMPLES + DMR_RADIO_SYMBOL_LENGTH;

    q31_t corr = 0;
    q15_t min =  16000;
    q15_t max = -16000;

    for (uint8_t i = 0U; i < DMR_SYNC_LENGTH_SYMBOLS; i++) {
      q15_t val = m_buffer[ptr];

      if (val > max)
        max = val;
      if (val < min)
        min = val;

      int8_t corrVal;
      if (data)
        corrVal = DMR_MS_DATA_SYNC_SYMBOLS_VALUES[i];
      else
        corrVal = DMR_MS_VOICE_SYNC_SYMBOLS_VALUES[i];

      switch (corrVal) {
      case +3:
        corr -= (val + val + val);
        break;
      case +1:
        corr -= val;
        break;
      case -1:
        corr += val;
        break;
      default:  // -3
        corr += (val + val + val);
        break;
      }

      ptr += DMR_RADIO_SYMBOL_LENGTH;
    }

    if (corr > m_maxCorr) {
      q15_t centre = (max + min) >> 1;

      q31_t v1 = (max - centre) * SCALING_FACTOR;
      q15_t threshold = q15_t(v1 >> 15);

      uint8_t sync[DMR_SYNC_BYTES_LENGTH];
      uint16_t ptr = m_dataPtr - DMR_SYNC_LENGTH_SAMPLES + DMR_RADIO_SYMBOL_LENGTH;
      samplesToBits(ptr, DMR_SYNC_LENGTH_SYMBOLS, sync, 4U, centre, threshold);

      if (data) {
        uint8_t errs = 0U;
        for (uint8_t i = 0U; i < DMR_SYNC_BYTES_LENGTH; i++)
          errs += countBits8((sync[i] & DMR_SYNC_BYTES_MASK[i]) ^ DMR_MS_DATA_SYNC_BYTES[i]);

        if (errs <= MAX_SYNC_BYTES_ERRS) {
          if (first) {
            m_threshold[0U] = m_threshold[1U] = m_threshold[2U] = m_threshold[3U] = threshold;
            m_centre[0U]    = m_centre[1U]    = m_centre[2U]    = m_centre[3U]    = centre;
            m_averagePtr    = 0U;
          } else {
            m_threshold[m_averagePtr] = threshold;
            m_centre[m_averagePtr]    = centre;

            m_averagePtr++;
            if (m_averagePtr >= 4U)
              m_averagePtr = 0U;
          }

          m_maxCorr  = corr;
          m_control  = CONTROL_DATA;
          m_syncPtr  = m_dataPtr;
          m_startPtr = m_dataPtr - DMR_SLOT_TYPE_LENGTH_SAMPLES / 2U - DMR_INFO_LENGTH_SAMPLES / 2U - DMR_SYNC_LENGTH_SAMPLES;
          m_endPtr   = m_dataPtr + DMR_SLOT_TYPE_LENGTH_SAMPLES / 2U + DMR_INFO_LENGTH_SAMPLES / 2U - 1U;
        }
      } else {  // if (voice)
        uint8_t errs = 0U;
        for (uint8_t i = 0U; i < DMR_SYNC_BYTES_LENGTH; i++)
          errs += countBits8((sync[i] & DMR_SYNC_BYTES_MASK[i]) ^ DMR_MS_VOICE_SYNC_BYTES[i]);

        if (errs <= MAX_SYNC_BYTES_ERRS) {
          if (first) {
            m_threshold[0U] = m_threshold[1U] = m_threshold[2U] = m_threshold[3U] = threshold;
            m_centre[0U]    = m_centre[1U]    = m_centre[2U]    = m_centre[3U]    = centre;
            m_averagePtr    = 0U;
          } else {
            m_threshold[m_averagePtr] = threshold;
            m_centre[m_averagePtr]    = centre;

            m_averagePtr++;
            if (m_averagePtr >= 4U)
              m_averagePtr = 0U;
          }

          m_maxCorr  = corr;
          m_control  = CONTROL_VOICE;
          m_syncPtr  = m_dataPtr;
          m_startPtr = m_dataPtr - DMR_SLOT_TYPE_LENGTH_SAMPLES / 2U - DMR_INFO_LENGTH_SAMPLES / 2U - DMR_SYNC_LENGTH_SAMPLES;
          m_endPtr   = m_dataPtr + DMR_SLOT_TYPE_LENGTH_SAMPLES / 2U + DMR_INFO_LENGTH_SAMPLES / 2U - 1U;
        }
      }
    }
  }
}

void CDMRSlotRX::samplesToBits(uint16_t start, uint8_t count, uint8_t* buffer, uint16_t offset, q15_t centre, q15_t threshold)
{
  for (uint8_t i = 0U; i < count; i++, start += DMR_RADIO_SYMBOL_LENGTH) {
    q15_t sample = m_buffer[start] - centre;

    if (sample < -threshold) {
      WRITE_BIT1(buffer, offset, false);
      offset++;
      WRITE_BIT1(buffer, offset, true);
      offset++;
    } else if (sample < 0) {
      WRITE_BIT1(buffer, offset, false);
      offset++;
      WRITE_BIT1(buffer, offset, false);
      offset++;
    } else if (sample < threshold) {
      WRITE_BIT1(buffer, offset, true);
      offset++;
      WRITE_BIT1(buffer, offset, false);
      offset++;
    } else {
      WRITE_BIT1(buffer, offset, true);
      offset++;
      WRITE_BIT1(buffer, offset, true);
      offset++;
    }
  }
}

void CDMRSlotRX::setColorCode(uint8_t colorCode)
{
  m_colorCode = colorCode;
}

void CDMRSlotRX::setDelay(uint8_t delay)
{
  m_delay = delay;
}

void CDMRSlotRX::writeRSSIData(uint8_t* frame)
{
#if defined(SEND_RSSI_DATA)
  // Calculate RSSI average over a burst period. We don't take into account 2.5 ms at the beginning and 2.5 ms at the end
  uint16_t start = m_startPtr + DMR_SYNC_LENGTH_SAMPLES / 2U;

  uint32_t accum = 0U;
  for (uint16_t i = 0U; i < (DMR_FRAME_LENGTH_SAMPLES - DMR_SYNC_LENGTH_SAMPLES); i++)
    accum += m_rssi[start++];

  uint16_t avg = accum / (DMR_FRAME_LENGTH_SAMPLES - DMR_SYNC_LENGTH_SAMPLES);
  frame[34U] = (avg >> 8) & 0xFFU;
  frame[35U] = (avg >> 0) & 0xFFU;

  serial.writeDMRData(m_slot, frame, DMR_FRAME_LENGTH_BYTES + 3U);
#else
  serial.writeDMRData(m_slot, frame, DMR_FRAME_LENGTH_BYTES + 1U);
#endif
}

#endif