Add draft of M17Demodulator class

openrtx/include/protocols/M17/M17Demodulator.h

@@ -0,0 +1,98 @@
+/***************************************************************************
+ *   Copyright (C) 2021 by Federico Amedeo Izzo IU2NUO,                    *
+ *                         Niccolò Izzo IU2KIN                             *
+ *                         Wojciech Kaczmarski SP5WWP                      *
+ *                         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 M17_DEMODULATOR_H
+#define M17_DEMODULATOR_H
+
+#ifndef __cplusplus
+#error This header is C++ only!
+#endif
+
+namespace M17
+{
+
+class M17Demodulator
+{
+public:
+
+    /**
+     * Constructor.
+     */
+    M17Demodulator();
+
+    /**
+     * Destructor.
+     */
+    ~M17Demodulator();
+
+    /**
+     * Allocate buffers for baseband signal sampling and initialise demodulator.
+     */
+    void init();
+
+    /**
+     * Shutdown modulator and deallocate data buffers.
+     */
+    void terminate();
+
+    /**
+     * Starts the sampling of the baseband signal in a double buffer.
+     */
+    void startBasebandSampling();
+
+    /**
+     * Stops the sampling of the baseband signal in a double buffer.
+     */
+    void stopBasebandSampling();
+
+    /**
+     * Returns the next frame decoded from the baseband signal
+     */
+    const std::array<uint8_t, 48>& nextFrame();
+
+};
+
+private:
+
+    /**
+     * M17 syncword symbols after RRC sampled at 5 samples per symbol;
+     */
+    uint8_t syncword[] = { };
+
+    using dataBuffer_t = std::array< int16_t, M17_FRAME_SAMPLES >;
+    using dataFrame_t =  std::array< int8_t, M17_FRAME_SYMBOLS >;
+
+    int16_t      *baseband_buffer; ///< Buffer for baseband audio handling.
+    dataBuffer_t *activeBuffer;    ///< Half baseband buffer, in reception.
+    dataBuffer_t *idleBuffer;      ///< Half baseband buffer, to be processed.
+    dataFrame_t  *activeFrame;     ///< Half frame, in demodulation.
+    dataFrame_t  *idleFrame;       ///< Half frame, free to be processed.
+
+    /**
+     * Finds the index of the next syncword in the baseband stream.
+     *
+     * @param baseband: buffer containing the sampled baseband signal
+     * @param offset: offset of the buffer after which syncword are searched
+     * @return uint16_t index of the first syncword in the buffer after the offset
+     */ uint16_t nextSyncWord(int16_t *baseband);
+
+#endif /* M17_DEMODULATOR_H */