M17: add clock recovery module

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

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