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63 lines
1.9 KiB
63 lines
1.9 KiB
/*
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* Copyright (C) 2009,2010,2013,2014 by Jonathan Naylor, G4KLX
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; version 2 of the License.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*/
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#ifndef DStarGMSKDemodulator_H
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#define DStarGMSKDemodulator_H
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#include "DStarDefines.h"
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#include "FIRFilter.h"
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#include "Utils.h"
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/*
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* GMSK demodulator for D-Star 4800 bps received audio.
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*
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* Processes audio samples one at a time via decode(). Internally maintains a
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* software PLL to track symbol timing, and a FIR low-pass filter to remove
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* out-of-band noise before bit decisions are made.
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*
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* Returns TRISTATE:
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* STATE_TRUE — a '1' bit was clocked out at this sample
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* STATE_FALSE — a '0' bit was clocked out at this sample
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* STATE_UNKNOWN — mid-symbol; no bit decision yet
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*
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* lock() can be used to freeze PLL adaptation once a stable signal is detected,
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* preventing the PLL from wandering during long runs of the same bit value.
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*/
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class CDStarGMSKDemodulator {
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public:
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CDStarGMSKDemodulator();
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~CDStarGMSKDemodulator();
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TRISTATE decode(float val);
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void setInvert(bool set);
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void reset();
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// Freezes (on=true) or enables (on=false) PLL frequency adaptation.
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void lock(bool on);
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private:
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CFIRFilter m_filter;
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bool m_invert;
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unsigned int m_pll; // Current PLL phase accumulator.
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bool m_prev; // Previous bit value, used for GMSK differential decoding.
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unsigned int m_inc; // PLL phase increment per sample.
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bool m_locked;
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float m_offset;
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float m_accum;
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unsigned int m_count;
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};
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#endif
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