M17: LinkSetupFrame: use new Callsign class

Replaced the old callsign handling based on std::strings with the new
Callsign class. This change freed 1808 byte of flash.

Signed-off-by: Silvano Seva <silseva@fastwebnet.it>

.clang-format

@@ -8,8 +8,11 @@
 #  - AlignTrailingComments:
 #      Kind: Always
 #      OverEmptyLines: 1
+#  - BraceWrapping:
+#      AfterClass: true
 #  - Standard: c++14
 #  - BreakBeforeBinaryOperators: NonAssignment
+#  - PenaltyBreakAssignment: 30
 # Original header below
 ##########################################################################
 # SPDX-License-Identifier: GPL-2.0
@@ -46,7 +49,7 @@ AlwaysBreakTemplateDeclarations: false
 BinPackArguments: true
 BinPackParameters: true
 BraceWrapping:
-  AfterClass: false
+  AfterClass: true
   AfterControlStatement: false
   AfterEnum: false
   AfterFunction: true
@@ -103,9 +106,10 @@ ObjCBinPackProtocolList: Auto
 ObjCBlockIndentWidth: 4
 ObjCSpaceAfterProperty: true
 ObjCSpaceBeforeProtocolList: true
+PackConstructorInitializers: NextLine
 
 # Taken from git's rules
-PenaltyBreakAssignment: 10
+PenaltyBreakAssignment: 30
 PenaltyBreakBeforeFirstCallParameter: 30
 PenaltyBreakComment: 10
 PenaltyBreakFirstLessLess: 0

.github/workflows/main.yml

@@ -121,6 +121,8 @@ jobs:
         run: meson test -C build "M17 Golay Unit Test"
       - name: M17 RRC Test
         run: meson test -C build "M17 RRC Test"
+      - name: M17 Callsign Unit Test
+        run: meson test -C build "M17 Callsign Unit Test"
       - name: Codeplug Test
         run: meson test -C build "Codeplug Test"
       - name: minmea Conversion Test

CMakeLists.txt

@@ -105,6 +105,7 @@ target_sources(app
     openrtx/src/protocols/M17/M17DSP.cpp
     openrtx/src/protocols/M17/M17Golay.cpp
     openrtx/src/protocols/M17/M17Callsign.cpp
+    openrtx/src/protocols/M17/Callsign.cpp
     openrtx/src/protocols/M17/M17Modulator.cpp
     openrtx/src/protocols/M17/M17Demodulator.cpp
     openrtx/src/protocols/M17/M17FrameEncoder.cpp

meson.build

@@ -62,6 +62,7 @@ openrtx_src = ['openrtx/src/core/state.c',
                'openrtx/src/protocols/M17/M17DSP.cpp',
                'openrtx/src/protocols/M17/M17Golay.cpp',
                'openrtx/src/protocols/M17/M17Callsign.cpp',
+               'openrtx/src/protocols/M17/Callsign.cpp',
                'openrtx/src/protocols/M17/M17Modulator.cpp',
                'openrtx/src/protocols/M17/M17Demodulator.cpp',
                'openrtx/src/protocols/M17/M17FrameEncoder.cpp',
@@ -1057,6 +1058,10 @@ m17_viterbi_test = executable('m17_viterbi_test',
                                sources : unit_test_src + ['tests/unit/M17_viterbi.cpp'],
                                kwargs  : unit_test_opts)
 
+m17_callsign_test = executable('m17_callsign_test',
+                      sources : unit_test_src + ['tests/unit/M17_callsign.cpp'],
+                      kwargs  : unit_test_opts)
+                 
 m17_demodulator_test = executable('m17_demodulator_test',
                             sources: unit_test_src + ['tests/unit/M17_demodulator.cpp'],
                             kwargs: unit_test_opts)
@@ -1089,6 +1094,7 @@ test('M17 Golay Unit Test',   m17_golay_test)
 test('M17 Viterbi Unit Test', m17_viterbi_test)
 ## test('M17 Demodulator Test',  m17_demodulator_test) # Skipped for now as this test no longer works after an M17 refactor
 test('M17 RRC Test',          m17_rrc_test)
+test('M17 Callsign Unit Test',          m17_callsign_test)
 test('Codeplug Test',         cps_test)
 ## test('Linux InputStream Test', linux_inputStream_test)
 ## test('Sine Test',             sine_test)

openrtx/include/protocols/M17/Callsign.hpp

@@ -0,0 +1,125 @@
+/***************************************************************************
+ *   Copyright (C) 2025 by Federico Amedeo Izzo IU2NUO,                    *
+ *                         Niccolò Izzo IU2KIN                             *
+ *                         Frederik Saraci IU2NRO                          *
+ *                         Silvano Seva IU2KWO                             *
+ *                                                                         *
+ *   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 3 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, see <http://www.gnu.org/licenses/>   *
+ ***************************************************************************/
+
+#ifndef CALLSIGN_H
+#define CALLSIGN_H
+
+#ifndef __cplusplus
+#error This header is C++ only!
+#endif
+
+#include <string>
+#include "M17Datatypes.hpp"
+
+namespace M17
+{
+
+/**
+ * Class representing an M17 callsign object.
+ */
+class Callsign
+{
+public:
+    /**
+     * Default constructor.
+     * By default, an uninitialized callsign is set to invalid.
+     */
+    Callsign();
+
+    /**
+     * Construct a callsign object from an std::string
+     * The callsign can have up to 9 characters
+     *
+     * @param callsign: callsign string
+     */
+    Callsign(const std::string callsign);
+
+    /**
+     * Construct a callsign object from a NULL-terminated string
+     * The callsign can have up to 9 characters
+     *
+     * @param callsign: callsign string
+     */
+    Callsign(const char *callsign);
+
+    /**
+     * Construct a callsign object from a base-40 encoded callsign
+     *
+     * @param encodedCall: encoded callsign value
+     */
+    Callsign(const call_t &encodedCall);
+
+    /**
+     * Test if callsign is empty.
+     * A callsign is considered empty when its first character is NULL.
+     *
+     * @return true if the callsign is empty
+     */
+    inline bool isEmpty() const
+    {
+        return call[0] == '\0';
+    }
+
+    /**
+     * Test if callsign is a special one.
+     *
+     * @return true if the callsign is either ALL, INFO or ECHO
+     */
+    bool isSpecial() const;
+
+    /**
+     * Type-conversion operator to retrieve the callsign in encoded format
+     *
+     * @return the base-40 encoded version of the callsign
+     */
+    operator call_t() const;
+
+    /**
+     * Type-conversion operator to retrieve the callsign as a std::string
+     *
+     * @return a std::string containing the callsign
+     */
+    operator std::string() const;
+
+    /**
+     * Type-conversion operator to retrieve the callsign as a NULL-terminated
+     * string
+     *
+     * @return the callsign as a NULL-terminated string
+     */
+    operator const char *() const;
+
+    /**
+     * Comparison operator.
+     *
+     * @param other the incoming callsign to compare against
+     * @return true if callsigns are equivalent
+     */
+    bool operator==(const Callsign &other) const;
+
+private:
+    static constexpr size_t MAX_CALLSIGN_CHARS = 9;
+    static constexpr size_t MAX_CALLSIGN_LEN = MAX_CALLSIGN_CHARS + 1;
+    char call[MAX_CALLSIGN_LEN];
+};
+
+} // namespace M17
+
+#endif // CALLSIGN_H

openrtx/include/protocols/M17/ClockRecovery.hpp

@@ -0,0 +1,136 @@
+/***************************************************************************
+ *   Copyright (C) 2025 by Federico Amedeo Izzo IU2NUO,                    *
+ *                         Niccolò Izzo IU2KIN                             *
+ *                         Frederik Saraci IU2NRO                          *
+ *                         Silvano Seva IU2KWO                             *
+ *                                                                         *
+ *   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 3 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, see <http://www.gnu.org/licenses/>   *
+ ***************************************************************************/
+
+#ifndef CLOCK_RECOVERY_H
+#define CLOCK_RECOVERY_H
+
+#include <cstdint>
+#include <cstdio>
+#include <array>
+
+/**
+ * Class to construct clock recovery objects.
+ * The clock recovery algorithm estimates the best sampling point by finding,
+ * within a symbol, the point with maximum energy. The algorithm will work
+ * properly only if correctly synchronized with the baseband stream.
+ */
+template <size_t SAMPLES_PER_SYMBOL>
+class ClockRecovery
+{
+public:
+    /**
+     * Constructor
+     */
+    ClockRecovery()
+    {
+        reset();
+    }
+
+    /**
+     * Destructor
+     */
+    ~ClockRecovery()
+    {
+    }
+
+    /**
+     * Reset the internal state.
+     */
+    void reset()
+    {
+        curIdx = 0;
+        prevSample = 0;
+        numSamples = 0;
+        updateReq = false;
+        energy.fill(0);
+    }
+
+    /**
+     * Process a new sample.
+     *
+     * @param sample: baseband sample.
+     */
+    void sample(int16_t &sample)
+    {
+        int32_t delta = static_cast<int32_t>(sample)
+                      - static_cast<int32_t>(prevSample);
+
+        if ((sample + prevSample) < 0)
+            delta = -delta;
+
+        energy[curIdx] += delta;
+        prevSample = sample;
+        curIdx = (curIdx + 1) % SAMPLES_PER_SYMBOL;
+        numSamples += 1;
+    }
+
+    /**
+     * Update the best sampling point estimate.
+     */
+    void update()
+    {
+        if (numSamples == 0)
+            return;
+
+        uint8_t index = 0;
+        bool is_positive = false;
+
+        for (size_t i = 0; i < SAMPLES_PER_SYMBOL; i++) {
+            int32_t phase = energy[i];
+
+            if (!is_positive && phase > 0) {
+                is_positive = true;
+            } else if (is_positive && phase < 0) {
+                index = i;
+                break;
+            }
+        }
+
+        if (index == 0)
+            sp = SAMPLES_PER_SYMBOL - 1;
+        else
+            sp = index - 1;
+
+        energy.fill(0);
+        numSamples = 0;
+    }
+
+    /**
+     * Get the best sampling point estimate.
+     * The returned value is within the space of a simbol, that is in the
+     * range [0 SAMPLES_PER_SYMBOL - 1].
+     *
+     * @return sampling point.
+     */
+    uint8_t samplingPoint()
+    {
+        return sp;
+    }
+
+private:
+    std::array<int32_t, SAMPLES_PER_SYMBOL> energy;
+    size_t curIdx;
+    size_t numSamples;
+    int16_t prevSample;
+    uint8_t sp;
+    bool updateReq;
+};
+
+#endif

openrtx/include/protocols/M17/DevEstimator.hpp

@@ -0,0 +1,139 @@
+/***************************************************************************
+ *   Copyright (C) 2025 by Federico Amedeo Izzo IU2NUO,                    *
+ *                         Niccolò Izzo IU2KIN                             *
+ *                         Frederik Saraci IU2NRO                          *
+ *                         Silvano Seva IU2KWO                             *
+ *                                                                         *
+ *   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 3 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, see <http://www.gnu.org/licenses/>   *
+ ***************************************************************************/
+
+#ifndef DEV_ESTIMATOR_H
+#define DEV_ESTIMATOR_H
+
+#include <cstdint>
+
+/**
+ * Symbol deviation estimator.
+ * This module allows to estimate the outer symbol deviation of a baseband
+ * stream. The baseband samples used for the estimation should be takend at the
+ * ideal sampling point. To work properly, the estimator needs to be initialized
+ * with a reference outer symbol deviation.
+ */
+class DevEstimator
+{
+public:
+    /**
+     * Constructor
+     */
+    DevEstimator() : outerDev({0, 0}), offset(0), posAccum(0), negAccum(0),
+                     posCnt(0), negCnt(0)
+    {
+    }
+
+    /**
+     * Destructor
+     */
+    ~DevEstimator()
+    {
+    }
+
+    /**
+     * Initialize the estimator state.
+     * Calling this function clears the internal state.
+     *
+     * @param outerDev: initial value for outer symbol deviation
+     */
+    void init(const std::pair<int32_t, int32_t> &outerDev)
+    {
+        this->outerDev = outerDev;
+        offset = 0;
+        posAccum = 0;
+        negAccum = 0;
+        posCnt = 0;
+        negCnt = 0;
+    }
+
+    /**
+     * Process a new sample.
+     *
+     * @param sample: baseband sample.
+     */
+    void sample(int16_t value)
+    {
+        int32_t posThresh = (2 * outerDev.first) / 3;
+        int32_t negThresh = (2 * outerDev.second) / 3;
+
+        if (value > posThresh) {
+            posAccum += value;
+            posCnt += 1;
+        }
+
+        if (value < negThresh) {
+            posAccum += value;
+            posCnt += 1;
+        }
+    }
+
+    /**
+     * Update the estimation of outer symbol deviation and zero-offset and
+     * start a new acquisition cycle.
+     */
+    void update()
+    {
+        if ((posCnt == 0) || (negCnt == 0))
+            return;
+
+        int32_t max = posAccum / posCnt;
+        int32_t min = negAccum / negCnt;
+        offset = (max + min) / 2;
+        outerDev.first = max - offset;
+        outerDev.second = min - offset;
+        posAccum = 0;
+        negAccum = 0;
+        posCnt = 0;
+        negCnt = 0;
+    }
+
+    /**
+     * Get the estimated outer symbol deviation from the last update.
+     * The function returns a std::pair where the first element is the positive
+     * deviation and the second the negative one.
+     *
+     * @return outer deviation.
+     */
+    std::pair<int32_t, int32_t> outerDeviation()
+    {
+        return outerDev;
+    }
+
+    /**
+     * Get the estimated zero-offset from the last update.
+     *
+     * @return zero-offset.
+     */
+    int32_t zeroOffset()
+    {
+        return offset;
+    }
+
+private:
+    std::pair<int32_t, int32_t> outerDev;
+    int32_t offset;
+    int32_t posAccum;
+    int32_t negAccum;
+    uint32_t posCnt;
+    uint32_t negCnt;
+};
+
+#endif

openrtx/include/protocols/M17/M17Demodulator.hpp

@@ -40,6 +40,8 @@
 #include "protocols/M17/M17Constants.hpp"
 #include "protocols/M17/Correlator.hpp"
 #include "protocols/M17/Synchronizer.hpp"
+#include "protocols/M17/DevEstimator.hpp"
+#include "protocols/M17/ClockRecovery.hpp"
 
 namespace M17
 {
@@ -136,10 +138,8 @@ private:
 
     /**
      * State handler function for DemodState::SYNC_UPDATE
-     *
-     * @param sample: current baseband sample
      */
-    void syncUpdateState(int16_t sample);
+    void syncUpdateState();
 
     /**
      * M17 baseband signal sampled at 24kHz, half of an M17 frame is processed
@@ -160,7 +160,7 @@ private:
         UNLOCKED,   ///< Not locked
         SYNCED,     ///< Synchronized, validate syncword
         LOCKED,     ///< Locked
-        SYNC_UPDATE ///< Updating the sampling point
+        SYNC_UPDATE ///< Updating the synchronization state
     };
 
     /**
@@ -176,20 +176,22 @@ private:
     std::unique_ptr<frame_t >      demodFrame;      ///< Frame being demodulated.
     std::unique_ptr<frame_t >      readyFrame;      ///< Fully demodulated frame to be returned.
     bool                           newFrame;        ///< A new frame has been fully decoded.
+    bool                           resetClockRec;   ///< Clock recovery reset request.
+    bool                           updateSampPoint; ///< Sampling point update pending.
     uint16_t                       frameIndex;      ///< Index for filling the raw frame.
     uint32_t                       sampleIndex;     ///< Sample index, from 0 to (SAMPLES_PER_SYMBOL - 1)
     uint32_t                       samplingPoint;   ///< Symbol sampling point
     uint32_t                       sampleCount;     ///< Free-running sample counter
     uint8_t                        missedSyncs;     ///< Counter of missed synchronizations
     uint32_t                       initCount;       ///< Downcounter for initialization
-    uint32_t                       syncCount;       ///< Downcounter for resynchronization
-    std::pair < int32_t, int32_t > outerDeviation;  ///< Deviation of outer symbols
     float                          corrThreshold;   ///< Correlation threshold
     struct dcBlock                 dcBlock;         ///< State of the DC removal filter
 
     Correlator   < M17_SYNCWORD_SYMBOLS, SAMPLES_PER_SYMBOL > correlator;
     Synchronizer < M17_SYNCWORD_SYMBOLS, SAMPLES_PER_SYMBOL > streamSync{{ -3, -3, -3, -3, +3, +3, -3, +3 }};
     Iir          < 3 >                                        sampleFilter{sfNum, sfDen};
+    DevEstimator                                              devEstimator;
+    ClockRecovery< SAMPLES_PER_SYMBOL >                       clockRec;
 };
 
 } /* M17 */

openrtx/include/protocols/M17/M17FrameDecoder.hpp

@@ -35,8 +35,7 @@
 namespace M17
 {
 
-enum class M17FrameType : uint8_t
-{
+enum class M17FrameType : uint8_t {
     PREAMBLE = 0,   ///< Frame contains a preamble.
     LINK_SETUP = 1, ///< Frame is a Link Setup Frame.
     STREAM = 2,     ///< Frame is a stream data frame.
@@ -50,7 +49,6 @@ enum class M17FrameType : uint8_t
 class M17FrameDecoder
 {
 public:
-
     /**
      * Constructor.
      */
@@ -97,7 +95,6 @@ public:
     }
 
 private:
-
     /**
      * Determine frame type by searching which syncword among the standard M17
      * ones has the minumum hamming distance from the given one. If the hamming
@@ -135,7 +132,6 @@ private:
      */
     bool decodeLich(std::array<uint8_t, 6> &segment, const lich_t &lich);
 
-
     uint8_t lsfSegmentMap;         ///< Bitmap for LSF reassembly from LICH
     M17LinkSetupFrame lsf;         ///< Latest LSF received.
     M17LinkSetupFrame lsfFromLich; ///< LSF assembled from LICH segments.
@@ -144,6 +140,9 @@ private:
 
     ///< Maximum allowed hamming distance when determining the frame type.
     static constexpr uint8_t MAX_SYNC_HAMM_DISTANCE = 4;
+
+    ///< Maximum number of corrected bit errors allowed in a stream frame.
+    static constexpr uint16_t MAX_VITERBI_ERRORS = 15;
 };
 
 } // namespace M17

openrtx/include/protocols/M17/M17LinkSetupFrame.hpp

@@ -28,6 +28,7 @@
 #include <string>
 #include <array>
 #include "M17Datatypes.hpp"
+#include "Callsign.hpp"
 
 namespace M17
 {
@@ -64,28 +65,28 @@ public:
      *
      * @param callsign: string containing the source callsign.
      */
-    void setSource(const std::string& callsign);
+    void setSource(const Callsign& callsign);
 
     /**
      * Get source callsign.
      *
      * @return: string containing the source callsign.
      */
-    std::string getSource();
+    Callsign getSource();
 
     /**
      * Set destination callsign.
      *
      * @param callsign: string containing the destination callsign.
      */
-    void setDestination(const std::string& callsign);
+    void setDestination(const Callsign& callsign);
 
     /**
      * Get destination callsign.
      *
      * @return: string containing the destination callsign.
      */
-    std::string getDestination();
+    Callsign getDestination();
 
     /**
      * Get stream type field.

openrtx/src/protocols/M17/Callsign.cpp

@@ -0,0 +1,153 @@
+/***************************************************************************
+ *   Copyright (C) 2025 by Federico Amedeo Izzo IU2NUO,                    *
+ *                         Niccolò Izzo IU2KIN                             *
+ *                         Frederik Saraci IU2NRO                          *
+ *                         Silvano Seva IU2KWO                             *
+ *                                                                         *
+ *   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 3 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, see <http://www.gnu.org/licenses/>   *
+ ***************************************************************************/
+
+#include <cstring>
+#include "protocols/M17/Callsign.hpp"
+
+using namespace M17;
+
+static const char BROADCAST_CALL[] = "ALL";
+static const char INVALID_CALL[] = "INVALID";
+static const char charMap[] = " ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-/.";
+
+Callsign::Callsign() : Callsign(INVALID_CALL)
+{
+}
+
+Callsign::Callsign(const std::string callsign) : Callsign(callsign.c_str())
+{
+}
+
+Callsign::Callsign(const char *callsign)
+{
+    std::memset(call, 0, sizeof(call));
+    std::strncpy(call, callsign, MAX_CALLSIGN_CHARS);
+}
+
+Callsign::Callsign(const call_t &encodedCall)
+{
+    bool isBroadcast = true;
+    bool isInvalid = true;
+
+    for (auto &elem : encodedCall) {
+        if (elem != 0xFF)
+            isBroadcast = false;
+
+        if (elem != 0x00)
+            isInvalid = false;
+    }
+
+    std::memset(call, 0, sizeof(call));
+
+    if (isBroadcast) {
+        std::strncpy(call, BROADCAST_CALL, sizeof(call));
+        return;
+    }
+
+    if (isInvalid) {
+        std::strncpy(call, INVALID_CALL, sizeof(call));
+        return;
+    }
+
+    // Convert to little endian format
+    uint64_t encoded = 0;
+    auto p = reinterpret_cast<uint8_t *>(&encoded);
+    std::copy(encodedCall.rbegin(), encodedCall.rend(), p);
+
+    size_t pos = 0;
+    while (encoded != 0 && pos < MAX_CALLSIGN_CHARS) {
+        call[pos++] = charMap[encoded % 40];
+        encoded /= 40;
+    }
+}
+
+bool Callsign::isSpecial() const
+{
+    if ((std::strcmp(call, "INFO") == 0) || (std::strcmp(call, "ECHO") == 0)
+        || (std::strcmp(call, "ALL") == 0))
+        return true;
+
+    return false;
+}
+
+Callsign::operator std::string() const
+{
+    return std::string(call);
+}
+
+Callsign::operator const char *() const
+{
+    return call;
+}
+
+Callsign::operator call_t() const
+{
+    call_t encoded;
+    uint64_t tmp = 0;
+
+    if (strcmp(call, BROADCAST_CALL) == 0) {
+        encoded.fill(0xFF);
+        return encoded;
+    }
+
+    if (strcmp(call, INVALID_CALL) == 0) {
+        encoded.fill(0x00);
+        return encoded;
+    }
+
+    for (int i = strlen(call) - 1; i >= 0; i--) {
+        tmp *= 40;
+
+        if (call[i] >= 'A' && call[i] <= 'Z') {
+            tmp += (call[i] - 'A') + 1;
+        } else if (call[i] >= '0' && call[i] <= '9') {
+            tmp += (call[i] - '0') + 27;
+        } else if (call[i] == '-') {
+            tmp += 37;
+        } else if (call[i] == '/') {
+            tmp += 38;
+        } else if (call[i] == '.') {
+            tmp += 39;
+        }
+    }
+
+    // Return encoded callsign in big endian format
+    auto *ptr = reinterpret_cast<uint8_t *>(&tmp);
+    std::copy(ptr, ptr + 6, encoded.rbegin());
+
+    return encoded;
+}
+
+bool Callsign::operator==(const Callsign &other) const
+{
+    // find slash and possibly truncate if slash is within first 3 chars
+    const char *truncatedLocal = call;
+    const char *truncatedIncoming = other.call;
+
+    const char *slash = std::strchr(call, '/');
+    if (slash && (slash - call) <= 2)
+        truncatedLocal = slash + 1;
+
+    slash = std::strchr(other.call, '/');
+    if (slash && (slash - other.call) <= 2)
+        truncatedIncoming = slash + 1;
+
+    return std::strcmp(truncatedLocal, truncatedIncoming) == 0;
+}

openrtx/src/protocols/M17/M17Demodulator.cpp

@@ -249,7 +249,23 @@ bool M17Demodulator::update(const bool invertPhase)
         if(invertPhase) elem   = 0.0f - elem;
         sample = static_cast< int16_t >(M17::rrc_24k(elem));
 
-        // Update correlator and sample filter for correlation thresholds
+        // Clock recovery reset MUST come before sampling
+        if((sampleIndex == 0) && resetClockRec) {
+            clockRec.reset();
+            resetClockRec = false;
+            updateSampPoint = false;
+        }
+
+        // Update sample point only when "far enough" from the last sampling,
+        // to avoid sampling issues when SP rolls over.
+        int diff = samplingPoint - sampleIndex;
+        if(updateSampPoint && (std::abs(diff) == SAMPLES_PER_SYMBOL/2)) {
+            clockRec.update();
+            samplingPoint = clockRec.samplingPoint();
+            updateSampPoint = false;
+        }
+
+        clockRec.sample(sample);
         correlator.sample(sample);
         corrThreshold = sampleFilter(std::abs(sample));
 
@@ -277,7 +293,7 @@ bool M17Demodulator::update(const bool invertPhase)
                 break;
 
             case DemodState::SYNC_UPDATE:
-                syncUpdateState(sample);
+                syncUpdateState();
                 break;
         }
 
@@ -290,6 +306,7 @@ bool M17Demodulator::update(const bool invertPhase)
 
 void M17Demodulator::quantize(stream_sample_t sample)
 {
+    auto outerDeviation = devEstimator.outerDeviation();
     int8_t symbol;
 
     if(sample > (2 * outerDeviation.first)/3)
@@ -311,13 +328,6 @@ void M17Demodulator::quantize(stream_sample_t sample)
 
     setSymbol(*demodFrame, frameIndex, symbol);
     frameIndex += 1;
-
-    if(frameIndex >= M17_FRAME_SYMBOLS)
-    {
-        std::swap(readyFrame, demodFrame);
-        frameIndex = 0;
-        newFrame   = true;
-    }
 }
 
 void M17Demodulator::reset()
@@ -345,8 +355,9 @@ void M17Demodulator::syncedState()
 {
     // Set sampling point and deviation, zero frame symbol count
     samplingPoint  = streamSync.samplingIndex();
-    outerDeviation = correlator.maxDeviation(samplingPoint);
+    auto deviation = correlator.maxDeviation(samplingPoint);
     frameIndex     = 0;
+    devEstimator.init(deviation);
 
     // Quantize the syncword taking data from the correlator
     // memory.
@@ -373,56 +384,38 @@ void M17Demodulator::lockedState(int16_t sample)
     if(sampleIndex != samplingPoint)
         return;
 
-    // Quantize and update frame at each sampling point
     quantize(sample);
+    devEstimator.sample(sample);
 
-    // When we have reached almost the end of a frame, switch
-    // to syncpoint update.
-    if(frameIndex == (M17_FRAME_SYMBOLS - M17_SYNCWORD_SYMBOLS/2)) {
+    if(frameIndex == M17_FRAME_SYMBOLS) {
+        devEstimator.update();
+        std::swap(readyFrame, demodFrame);
+
+        frameIndex = 0;
+        newFrame = true;
+        updateSampPoint = true;
         demodState = DemodState::SYNC_UPDATE;
-        syncCount  = SYNCWORD_SAMPLES * 2;
     }
 }
 
-void M17Demodulator::syncUpdateState(int16_t sample)
+void M17Demodulator::syncUpdateState()
 {
-    // Keep filling the ongoing frame!
-    if(sampleIndex == samplingPoint)
-        quantize(sample);
-
-    // Find the new correlation peak
-    int32_t syncThresh = static_cast< int32_t >(corrThreshold * 33.0f);
-    int8_t  syncStatus = streamSync.update(correlator, syncThresh, -syncThresh);
-
-    // Correlation has to coincide with a syncword!
-    if((syncStatus != 0) && (frameIndex == M17_SYNCWORD_SYMBOLS)) {
-        uint8_t hd = hammingDistance((*demodFrame)[0], STREAM_SYNC_WORD[0])
+    uint8_t streamHd = hammingDistance((*demodFrame)[0], STREAM_SYNC_WORD[0])
                      + hammingDistance((*demodFrame)[1], STREAM_SYNC_WORD[1]);
 
-        // Valid sync found: update deviation and sample
-        // point, then go back to locked state
-        if(hd <= 1) {
-            outerDeviation = correlator.maxDeviation(samplingPoint);
-            samplingPoint = streamSync.samplingIndex();
-            missedSyncs = 0;
-            demodState = DemodState::LOCKED;
-            return;
-        }
-    }
+    uint8_t eotHd = hammingDistance((*demodFrame)[0], EOT_SYNC_WORD[0])
+                  + hammingDistance((*demodFrame)[1], EOT_SYNC_WORD[1]);
 
-    // No syncword found within the window, increase the count
-    // of missed syncs and choose where to go. The lock is lost
-    // after four consecutive sync misses.
-    if(syncCount == 0) {
-        if(missedSyncs >= 4)
+    if(streamHd <= 1)
+        missedSyncs = 0;
+    else
+        missedSyncs += 1;
+
+    // The lock is lost after four consecutive sync misses or an EOT frame.
+    if((missedSyncs > 4) || (eotHd <= 1))
         demodState = DemodState::UNLOCKED;
     else
         demodState = DemodState::LOCKED;
-
-        missedSyncs += 1;
-    }
-
-    syncCount -= 1;
 }
 
 constexpr std::array < float, 3 > M17Demodulator::sfNum;

openrtx/src/protocols/M17/M17FrameDecoder.cpp

@@ -29,9 +29,13 @@
 
 using namespace M17;
 
-M17FrameDecoder::M17FrameDecoder() { }
+M17FrameDecoder::M17FrameDecoder()
+{
+}
 
-M17FrameDecoder::~M17FrameDecoder() { }
+M17FrameDecoder::~M17FrameDecoder()
+{
+}
 
 void M17FrameDecoder::reset()
 {
@@ -55,8 +59,7 @@ M17FrameType M17FrameDecoder::decodeFrame(const frame_t& frame)
 
     auto type = getFrameType(syncWord);
 
-    switch(type)
-    {
+    switch (type) {
         case M17FrameType::LINK_SETUP:
             decodeLSF(data);
             break;
@@ -72,7 +75,8 @@ M17FrameType M17FrameDecoder::decodeFrame(const frame_t& frame)
     return type;
 }
 
-M17FrameType M17FrameDecoder::getFrameType(const std::array< uint8_t, 2 >& syncWord)
+M17FrameType
+M17FrameDecoder::getFrameType(const std::array<uint8_t, 2> &syncWord)
 {
     // Preamble
     M17FrameType type = M17FrameType::PREAMBLE;
@@ -82,8 +86,8 @@ M17FrameType M17FrameDecoder::getFrameType(const std::array< uint8_t, 2 >& syncW
     // Link setup frame
     uint8_t hammDistance = hammingDistance(syncWord[0], LSF_SYNC_WORD[0])
                          + hammingDistance(syncWord[1], LSF_SYNC_WORD[1]);
-    if(hammDistance < minDistance)
-    {
+
+    if (hammDistance < minDistance) {
         type = M17FrameType::LINK_SETUP;
         minDistance = hammDistance;
     }
@@ -91,16 +95,15 @@ M17FrameType M17FrameDecoder::getFrameType(const std::array< uint8_t, 2 >& syncW
     // Stream frame
     hammDistance = hammingDistance(syncWord[0], STREAM_SYNC_WORD[0])
                  + hammingDistance(syncWord[1], STREAM_SYNC_WORD[1]);
-    if(hammDistance < minDistance)
-    {
+
+    if (hammDistance < minDistance) {
         type = M17FrameType::STREAM;
         minDistance = hammDistance;
     }
 
     // Check value of minimum hamming distance found, if exceeds the allowed
     // limit consider the frame as of unknown type.
-    if(minDistance > MAX_SYNC_HAMM_DISTANCE)
-    {
+    if (minDistance > MAX_SYNC_HAMM_DISTANCE) {
         type = M17FrameType::UNKNOWN;
     }
 
@@ -124,8 +127,7 @@ void M17FrameDecoder::decodeStream(const std::array< uint8_t, 46 >& data)
     std::copy_n(data.begin(), lich.size(), lich.begin());
     bool decodeOk = decodeLich(lsfSegment, lich);
 
-    if(decodeOk)
-    {
+    if (decodeOk) {
         // Append LICH segment
         uint8_t segmentNum = lsfSegment[5];
         uint8_t segmentSize = lsfSegment.size() - 1;
@@ -137,9 +139,9 @@ void M17FrameDecoder::decodeStream(const std::array< uint8_t, 46 >& data)
         lsfSegmentMap |= 1 << segmentNum;
 
         // Check if we have received all the six LICH segments
-        if(lsfSegmentMap == 0x3F)
-        {
-            if(lsfFromLich.valid()) lsf = lsfFromLich;
+        if (lsfSegmentMap == 0x3F) {
+            if (lsfFromLich.valid())
+                lsf = lsfFromLich;
             lsfSegmentMap = 0;
             lsfFromLich.clear();
         }
@@ -153,7 +155,9 @@ void M17FrameDecoder::decodeStream(const std::array< uint8_t, 46 >& data)
     begin += lich.size();
     std::copy(begin, data.end(), punctured.begin());
 
-    viterbi.decodePunctured(punctured, tmp, DATA_PUNCTURE);
+    // Skip payload copy if BER is too high to avoid audio artifacts
+    uint16_t bitErrs = viterbi.decodePunctured(punctured, tmp, DATA_PUNCTURE);
+    if (bitErrs < MAX_VITERBI_ERRORS)
         memcpy(&streamFrame.data, tmp.data(), tmp.size());
 }
 
@@ -176,26 +180,21 @@ bool M17FrameDecoder::decodeLich(std::array < uint8_t, 6 >& segment,
     size_t index = 0;
     uint32_t block = 0;
 
-    for(size_t i = 0; i < 4; i++)
-    {
+    for (size_t i = 0; i < 4; i++) {
         memcpy(&block, lich.data() + 3 * i, 3);
         block = __builtin_bswap32(block) >> 8;
         uint16_t decoded = golay24_decode(block);
 
         // Unrecoverable error, abort decoding
-        if(decoded == 0xFFFF)
-        {
+        if (decoded == 0xFFFF) {
             segment.fill(0x00);
             return false;
         }
 
-        if(i & 1)
-        {
+        if (i & 1) {
             segment[index++] |= (decoded >> 8);     // upper 4 bits
             segment[index++] = (decoded & 0xFF);    // lower 8 bits
-        }
-        else
-        {
+        } else {
             segment[index++] |= (decoded >> 4);     // upper 8 bits
             segment[index] = (decoded & 0x0F) << 4; // lower 4 bits
         }

openrtx/src/protocols/M17/M17LinkSetupFrame.cpp

@@ -41,24 +41,24 @@ void M17LinkSetupFrame::clear()
     data.dst.fill(0xFF);
 }
 
-void M17LinkSetupFrame::setSource(const std::string& callsign)
+void M17LinkSetupFrame::setSource(const Callsign& callsign)
 {
-    encode_callsign(callsign, data.src);
+    data.src = callsign;
 }
 
-std::string M17LinkSetupFrame::getSource()
+Callsign M17LinkSetupFrame::getSource()
 {
-    return decode_callsign(data.src);
+    return Callsign(data.src);
 }
 
-void M17LinkSetupFrame::setDestination(const std::string& callsign)
+void M17LinkSetupFrame::setDestination(const Callsign& callsign)
 {
-    encode_callsign(callsign, data.dst);
+    data.dst = callsign;
 }
 
-std::string M17LinkSetupFrame::getDestination()
+Callsign M17LinkSetupFrame::getDestination()
 {
-    return decode_callsign(data.dst);
+    return Callsign(data.dst);
 }
 
 streamType_t M17LinkSetupFrame::getType()

openrtx/src/rtx/OpMode_M17.cpp

@@ -206,8 +206,9 @@ void OpMode_M17::rxState(rtxStatus_t *const status)
                 dataValid = true;
 
                 // Retrieve stream source and destination data
-                std::string dst = lsf.getDestination();
-                std::string src = lsf.getSource();
+                Callsign dst = lsf.getDestination();
+                Callsign src = lsf.getSource();
+                strncpy(status->M17_dst, dst, 10);
 
                 // Retrieve extended callsign data
                 streamType_t streamType = lsf.getType();
@@ -218,8 +219,8 @@ void OpMode_M17::rxState(rtxStatus_t *const status)
                     extendedCall = true;
 
                     meta_t& meta = lsf.metadata();
-                    std::string exCall1 = decode_callsign(meta.extended_call_sign.call1);
-                    std::string exCall2 = decode_callsign(meta.extended_call_sign.call2);
+                    Callsign exCall1(meta.extended_call_sign.call1);
+                    Callsign exCall2(meta.extended_call_sign.call2);
 
                     //
                     // The source callsign only contains the last link when
@@ -227,21 +228,16 @@ void OpMode_M17::rxState(rtxStatus_t *const status)
                     // the true source of a transmission, we need to store the first
                     // extended callsign in M17_src.
                     //
-                    strncpy(status->M17_src,  exCall1.c_str(), 10);
-                    strncpy(status->M17_refl, exCall2.c_str(), 10);
-
-                    extendedCall = true;
+                    strncpy(status->M17_src,  exCall1, 10);
+                    strncpy(status->M17_refl, exCall2, 10);
+                    strncpy(status->M17_link, src, 10);
+                } else {
+                    strncpy(status->M17_src, src, 10);
                 }
 
                 // Set source and destination fields.
                 // If we have received an extended callsign the src will be the RF link address
                 // The M17_src will already be stored from the extended callsign
-                strncpy(status->M17_dst, dst.c_str(), 10);
-
-                if(extendedCall)
-                    strncpy(status->M17_link, src.c_str(), 10);
-                else
-                    strncpy(status->M17_src, src.c_str(), 10);
 
                 // Check CAN on RX, if enabled.
                 // If check is disabled, force match to true.
@@ -250,7 +246,8 @@ void OpMode_M17::rxState(rtxStatus_t *const status)
 
                 // Check if the destination callsign of the incoming transmission
                 // matches with ours
-                bool callMatch = compareCallsigns(std::string(status->source_address), dst);
+                bool callMatch = (Callsign(status->source_address) == dst)
+                               || dst.isSpecial();
 
                 // Open audio path only if CAN and callsign match
                 uint8_t pthSts = audioPath_getStatus(rxAudioPath);
@@ -306,13 +303,14 @@ void OpMode_M17::txState(rtxStatus_t *const status)
     {
         startTx = false;
 
-        std::string src(status->source_address);
-        std::string dst(status->destination_address);
         M17LinkSetupFrame lsf;
 
         lsf.clear();
-        lsf.setSource(src);
-        if(!dst.empty()) lsf.setDestination(dst);
+        lsf.setSource(status->source_address);
+
+        Callsign dst(status->destination_address);
+        if(!dst.isEmpty())
+            lsf.setDestination(dst);
 
         streamType_t type;
         type.fields.dataMode = M17_DATAMODE_STREAM;     // Stream

scripts/clang_format.sh

@@ -69,8 +69,12 @@ openrtx/include/interfaces/radio.h
 openrtx/include/peripherals/gps.h
 openrtx/include/peripherals/rng.h
 openrtx/include/peripherals/rtc.h
+openrtx/include/protocols/M17/Callsign.hpp
+openrtx/include/protocols/M17/M17FrameDecoder.hpp
 openrtx/src/core/dsp.cpp
 openrtx/src/core/memory_profiling.cpp
+openrtx/src/protocols/M17/Callsign.cpp
+openrtx/src/protocols/M17/M17FrameDecoder.cpp
 platform/drivers/ADC/ADC0_GDx.h
 platform/drivers/audio/MAX9814.h
 platform/drivers/baseband/MCP4551.h
@@ -88,6 +92,7 @@ platform/targets/linux/emulator/sdl_engine.h
 platform/targets/ttwrplus/pmu.h
 tests/platform/mic_test.c
 tests/platform/codec2_encode_test.c
+tests/unit/M17_callsign.cpp
 EOF
 )
 

tests/unit/M17_callsign.cpp

@@ -0,0 +1,90 @@
+/***************************************************************************
+ *   Copyright (C) 2021 - 2025 by Federico Amedeo Izzo IU2NUO,             *
+ *                                Niccolò Izzo IU2KIN                      *
+ *                                Frederik Saraci IU2NRO                   *
+ *                                Silvano Seva IU2KWO                      *
+ *                                                                         *
+ *                                                                         *
+ *   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 3 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, see <http://www.gnu.org/licenses/>   *
+ ***************************************************************************/
+
+#include <cstdio>
+#include <cstdint>
+#include <cstring>
+#include <array>
+#include <algorithm>
+#include <iostream>
+#include "protocols/M17/Callsign.hpp"
+#include "protocols/M17/M17Datatypes.hpp"
+
+using namespace std;
+
+int test_encode_ab1cd()
+{
+    const char callsign[] = "AB1CD";
+    M17::call_t expected = { 0x00, 0x00, 0x00, 0x9f, 0xdd, 0x51 };
+
+    M17::Callsign test = M17::Callsign(callsign);
+    M17::call_t actual = test;
+    if (equal(begin(actual), end(actual), begin(expected), end(expected))) {
+        return 0;
+    } else {
+        return -1;
+    }
+}
+
+int test_encode_empty()
+{
+    const char callsign[] = "";
+    M17::call_t expected = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 };
+
+    M17::Callsign test = M17::Callsign(callsign);
+    M17::call_t actual = test;
+    if (equal(begin(actual), end(actual), begin(expected), end(expected))) {
+        return 0;
+    } else {
+        return -1;
+    }
+}
+
+int test_decode_ab1cd()
+{
+    M17::call_t callsign = { 0x00, 0x00, 0x00, 0x9f, 0xdd, 0x51 };
+
+    M17::Callsign test = M17::Callsign(callsign);
+    const char expected[] = "AB1CD";
+    const char *actual = test;
+    if (strcmp(expected, actual) == 0) {
+        return 0;
+    } else {
+        return -1;
+    }
+}
+
+int main()
+{
+    if (test_encode_ab1cd()) {
+        printf("Error in encoding callsign ab1cd!\n");
+        return -1;
+    }
+    if (test_encode_empty()) {
+        printf("Error in encoding empty callsign !\n");
+        return -1;
+    }
+    if (test_decode_ab1cd()) {
+        printf("Error in decoding callsign ab1cd!\n");
+        return -1;
+    }
+    return 0;
+}