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MMDVM/M17RX.cpp

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/*
* Copyright (C) 2009-2017,2020,2021 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_M17)
#include "Globals.h"
#include "M17RX.h"
#include "Utils.h"
const q15_t SCALING_FACTOR = 18750; // Q15(0.55)
const uint8_t MAX_SYNC_BIT_START_ERRS = 0U;
const uint8_t MAX_SYNC_BIT_RUN_ERRS = 2U;
const uint8_t MAX_SYNC_SYMBOL_START_ERRS = 0U;
const uint8_t MAX_SYNC_SYMBOL_RUN_ERRS = 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])
const uint8_t NOAVEPTR = 99U;
const uint16_t NOENDPTR = 9999U;
const unsigned int MAX_SYNC_FRAMES = 3U + 1U;
CM17RX::CM17RX() :
m_state(M17RXS_NONE),
m_bitBuffer(),
m_buffer(),
m_bitPtr(0U),
m_dataPtr(0U),
m_startPtr(NOENDPTR),
m_endPtr(NOENDPTR),
m_syncPtr(NOENDPTR),
m_minSyncPtr(NOENDPTR),
m_maxSyncPtr(NOENDPTR),
m_maxCorr(0),
m_lostCount(0U),
m_countdown(0U),
m_nextState(M17RXS_NONE),
m_centre(),
m_centreVal(0),
m_threshold(),
m_thresholdVal(0),
m_averagePtr(NOAVEPTR),
m_rssiAccum(0U),
m_rssiCount(0U)
{
}
void CM17RX::reset()
{
m_state = M17RXS_NONE;
m_dataPtr = 0U;
m_bitPtr = 0U;
m_maxCorr = 0;
m_averagePtr = NOAVEPTR;
m_startPtr = NOENDPTR;
m_endPtr = NOENDPTR;
m_syncPtr = NOENDPTR;
m_minSyncPtr = NOENDPTR;
m_maxSyncPtr = NOENDPTR;
m_centreVal = 0;
m_thresholdVal = 0;
m_lostCount = 0U;
m_countdown = 0U;
m_nextState = M17RXS_NONE;
m_rssiAccum = 0U;
m_rssiCount = 0U;
}
void CM17RX::samples(const q15_t* samples, uint16_t* rssi, uint8_t length)
{
for (uint8_t i = 0U; i < length; i++) {
q15_t sample = samples[i];
m_rssiAccum += rssi[i];
m_rssiCount++;
m_bitBuffer[m_bitPtr] <<= 1;
if (sample < 0)
m_bitBuffer[m_bitPtr] |= 0x01U;
m_buffer[m_dataPtr] = sample;
switch (m_state) {
case M17RXS_LINK_SETUP:
case M17RXS_STREAM:
processData(sample);
break;
default:
processNone(sample);
break;
}
m_dataPtr++;
if (m_dataPtr >= M17_FRAME_LENGTH_SAMPLES)
m_dataPtr = 0U;
m_bitPtr++;
if (m_bitPtr >= M17_RADIO_SYMBOL_LENGTH)
m_bitPtr = 0U;
}
}
void CM17RX::processNone(q15_t sample)
{
bool ret1 = correlateSync(M17_LINK_SETUP_SYNC_SYMBOLS, M17_LINK_SETUP_SYNC_SYMBOLS_VALUES, M17_LINK_SETUP_SYNC_BYTES, MAX_SYNC_SYMBOL_START_ERRS, MAX_SYNC_BIT_START_ERRS);
bool ret2 = correlateSync(M17_STREAM_SYNC_SYMBOLS, M17_STREAM_SYNC_SYMBOLS_VALUES, M17_STREAM_SYNC_BYTES, MAX_SYNC_SYMBOL_START_ERRS, MAX_SYNC_BIT_START_ERRS);
if (ret1 || ret2) {
// On the first sync, start the countdown to the state change
if (m_countdown == 0U) {
m_rssiAccum = 0U;
m_rssiCount = 0U;
io.setDecode(true);
io.setADCDetection(true);
m_averagePtr = NOAVEPTR;
m_countdown = 5U;
if (ret1) m_nextState = M17RXS_LINK_SETUP;
if (ret2) m_nextState = M17RXS_STREAM;
}
}
if (m_countdown > 0U)
m_countdown--;
if (m_countdown == 1U) {
m_minSyncPtr = m_syncPtr + M17_FRAME_LENGTH_SAMPLES - 1U;
if (m_minSyncPtr >= M17_FRAME_LENGTH_SAMPLES)
m_minSyncPtr -= M17_FRAME_LENGTH_SAMPLES;
m_maxSyncPtr = m_syncPtr + 1U;
if (m_maxSyncPtr >= M17_FRAME_LENGTH_SAMPLES)
m_maxSyncPtr -= M17_FRAME_LENGTH_SAMPLES;
m_state = m_nextState;
m_countdown = 0U;
m_nextState = M17RXS_NONE;
}
}
void CM17RX::processData(q15_t sample)
{
bool eof = false;
if (m_minSyncPtr < m_maxSyncPtr) {
if (m_dataPtr >= m_minSyncPtr && m_dataPtr <= m_maxSyncPtr) {
bool ret = correlateSync(M17_STREAM_SYNC_SYMBOLS, M17_STREAM_SYNC_SYMBOLS_VALUES, M17_STREAM_SYNC_BYTES, MAX_SYNC_SYMBOL_RUN_ERRS, MAX_SYNC_BIT_RUN_ERRS);
eof = correlateSync(M17_EOF_SYNC_SYMBOLS, M17_EOF_SYNC_SYMBOLS_VALUES, M17_EOF_SYNC_BYTES, MAX_SYNC_SYMBOL_RUN_ERRS, MAX_SYNC_BIT_RUN_ERRS);
if (ret) m_state = M17RXS_STREAM;
}
} else {
if (m_dataPtr >= m_minSyncPtr || m_dataPtr <= m_maxSyncPtr) {
bool ret = correlateSync(M17_STREAM_SYNC_SYMBOLS, M17_STREAM_SYNC_SYMBOLS_VALUES, M17_STREAM_SYNC_BYTES, MAX_SYNC_SYMBOL_RUN_ERRS, MAX_SYNC_BIT_RUN_ERRS);
eof = correlateSync(M17_EOF_SYNC_SYMBOLS, M17_EOF_SYNC_SYMBOLS_VALUES, M17_EOF_SYNC_BYTES, MAX_SYNC_SYMBOL_RUN_ERRS, MAX_SYNC_BIT_RUN_ERRS);
if (ret) m_state = M17RXS_STREAM;
}
}
if (eof) {
DEBUG4("M17RX: eof sync found pos/centre/threshold", m_syncPtr, m_centreVal, m_thresholdVal);
io.setDecode(false);
io.setADCDetection(false);
serial.writeM17EOT();
m_state = M17RXS_NONE;
m_endPtr = NOENDPTR;
m_averagePtr = NOAVEPTR;
m_countdown = 0U;
m_nextState = M17RXS_NONE;
m_maxCorr = 0;
}
if (m_dataPtr == m_endPtr) {
// Only update the centre and threshold if they are from a good sync
if (m_lostCount == MAX_SYNC_FRAMES) {
m_minSyncPtr = m_syncPtr + M17_FRAME_LENGTH_SAMPLES - 1U;
if (m_minSyncPtr >= M17_FRAME_LENGTH_SAMPLES)
m_minSyncPtr -= M17_FRAME_LENGTH_SAMPLES;
m_maxSyncPtr = m_syncPtr + 1U;
if (m_maxSyncPtr >= M17_FRAME_LENGTH_SAMPLES)
m_maxSyncPtr -= M17_FRAME_LENGTH_SAMPLES;
}
calculateLevels(m_startPtr, M17_FRAME_LENGTH_SYMBOLS);
switch (m_state) {
case M17RXS_LINK_SETUP:
DEBUG4("M17RX: link setup sync found pos/centre/threshold", m_syncPtr, m_centreVal, m_thresholdVal);
break;
case M17RXS_STREAM:
DEBUG4("M17RX: stream sync found pos/centre/threshold", m_syncPtr, m_centreVal, m_thresholdVal);
break;
default:
break;
}
uint8_t frame[M17_FRAME_LENGTH_BYTES + 3U];
samplesToBits(m_startPtr, M17_FRAME_LENGTH_SYMBOLS, frame, 8U, m_centreVal, m_thresholdVal);
// We've not seen a stream 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);
io.setADCDetection(false);
serial.writeM17Lost();
m_state = M17RXS_NONE;
m_endPtr = NOENDPTR;
m_averagePtr = NOAVEPTR;
m_countdown = 0U;
m_nextState = M17RXS_NONE;
m_maxCorr = 0;
} else {
frame[0U] = m_lostCount == (MAX_SYNC_FRAMES - 1U) ? 0x01U : 0x00U;
switch (m_state) {
case M17RXS_LINK_SETUP:
writeRSSILinkSetup(frame);
break;
case M17RXS_STREAM:
writeRSSIStream(frame);
break;
default:
break;
}
m_maxCorr = 0;
m_nextState = M17RXS_NONE;
}
}
}
bool CM17RX::correlateSync(uint8_t syncSymbols, const int8_t* syncSymbolValues, const uint8_t* syncBytes, uint8_t maxSymbolErrs, uint8_t maxBitErrs)
{
if (countBits8(m_bitBuffer[m_bitPtr] ^ syncSymbols) <= maxSymbolErrs) {
uint16_t ptr = m_dataPtr + M17_FRAME_LENGTH_SAMPLES - M17_SYNC_LENGTH_SAMPLES + M17_RADIO_SYMBOL_LENGTH;
if (ptr >= M17_FRAME_LENGTH_SAMPLES)
ptr -= M17_FRAME_LENGTH_SAMPLES;
q31_t corr = 0;
q15_t min = 16000;
q15_t max = -16000;
for (uint8_t i = 0U; i < M17_SYNC_LENGTH_SYMBOLS; i++) {
q15_t val = m_buffer[ptr];
if (val > max)
max = val;
if (val < min)
min = val;
switch (syncSymbolValues[i]) {
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 += M17_RADIO_SYMBOL_LENGTH;
if (ptr >= M17_FRAME_LENGTH_SAMPLES)
ptr -= M17_FRAME_LENGTH_SAMPLES;
}
if (corr > m_maxCorr) {
if (m_averagePtr == NOAVEPTR) {
m_centreVal = (max + min) >> 1;
q31_t v1 = (max - m_centreVal) * SCALING_FACTOR;
m_thresholdVal = q15_t(v1 >> 15);
}
uint16_t startPtr = m_dataPtr + M17_FRAME_LENGTH_SAMPLES - M17_SYNC_LENGTH_SAMPLES + M17_RADIO_SYMBOL_LENGTH;
if (startPtr >= M17_FRAME_LENGTH_SAMPLES)
startPtr -= M17_FRAME_LENGTH_SAMPLES;
uint8_t sync[M17_SYNC_LENGTH_BYTES];
samplesToBits(startPtr, M17_SYNC_LENGTH_SYMBOLS, sync, 0U, m_centreVal, m_thresholdVal);
uint8_t errs = 0U;
for (uint8_t i = 0U; i < M17_SYNC_LENGTH_BYTES; i++)
errs += countBits8(sync[i] ^ syncBytes[i]);
if (errs <= maxBitErrs) {
m_maxCorr = corr;
m_lostCount = MAX_SYNC_FRAMES;
m_syncPtr = m_dataPtr;
m_startPtr = startPtr;
m_endPtr = m_dataPtr + M17_FRAME_LENGTH_SAMPLES - M17_SYNC_LENGTH_SAMPLES - 1U;
if (m_endPtr >= M17_FRAME_LENGTH_SAMPLES)
m_endPtr -= M17_FRAME_LENGTH_SAMPLES;
return true;
}
}
}
return false;
}
void CM17RX::calculateLevels(uint16_t start, uint16_t count)
{
q15_t maxPos = -16000;
q15_t minPos = 16000;
q15_t maxNeg = 16000;
q15_t minNeg = -16000;
for (uint16_t i = 0U; i < count; i++) {
q15_t sample = m_buffer[start];
if (sample > 0) {
if (sample > maxPos)
maxPos = sample;
if (sample < minPos)
minPos = sample;
} else {
if (sample < maxNeg)
maxNeg = sample;
if (sample > minNeg)
minNeg = sample;
}
start += M17_RADIO_SYMBOL_LENGTH;
if (start >= M17_FRAME_LENGTH_SAMPLES)
start -= M17_FRAME_LENGTH_SAMPLES;
}
q15_t posThresh = (maxPos + minPos) >> 1;
q15_t negThresh = (maxNeg + minNeg) >> 1;
q15_t centre = (posThresh + negThresh) >> 1;
q15_t threshold = posThresh - centre;
DEBUG5("M17RX: pos/neg/centre/threshold", posThresh, negThresh, centre, threshold);
if (m_averagePtr == NOAVEPTR) {
for (uint8_t i = 0U; i < 16U; i++) {
m_centre[i] = centre;
m_threshold[i] = threshold;
}
m_averagePtr = 0U;
} else {
m_centre[m_averagePtr] = centre;
m_threshold[m_averagePtr] = threshold;
m_averagePtr++;
if (m_averagePtr >= 16U)
m_averagePtr = 0U;
}
m_centreVal = 0;
m_thresholdVal = 0;
for (uint8_t i = 0U; i < 16U; i++) {
m_centreVal += m_centre[i];
m_thresholdVal += m_threshold[i];
}
m_centreVal >>= 4;
m_thresholdVal >>= 4;
}
void CM17RX::samplesToBits(uint16_t start, uint16_t count, uint8_t* buffer, uint16_t offset, q15_t centre, q15_t threshold)
{
for (uint16_t i = 0U; i < count; i++) {
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++;
}
start += M17_RADIO_SYMBOL_LENGTH;
if (start >= M17_FRAME_LENGTH_SAMPLES)
start -= M17_FRAME_LENGTH_SAMPLES;
}
}
void CM17RX::writeRSSILinkSetup(uint8_t* data)
{
#if defined(SEND_RSSI_DATA)
if (m_rssiCount > 0U) {
uint16_t rssi = m_rssiAccum / m_rssiCount;
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);
}
#else
serial.writeM17LinkSetup(data, M17_FRAME_LENGTH_BYTES + 1U);
#endif
m_rssiAccum = 0U;
m_rssiCount = 0U;
}
void CM17RX::writeRSSIStream(uint8_t* data)
{
#if defined(SEND_RSSI_DATA)
if (m_rssiCount > 0U) {
uint16_t rssi = m_rssiAccum / m_rssiCount;
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);
}
#else
serial.writeM17Stream(data, M17_FRAME_LENGTH_BYTES + 1U);
#endif
m_rssiAccum = 0U;
m_rssiCount = 0U;
}
#endif
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