Add an experimental noise squelch.

FMNoiseSquelch.h

@@ -0,0 +1,52 @@
+/*
+ *   Copyright (C) 2020 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.
+ */
+
+#if !defined(FMNOISESQUELCH_H)
+#define  FMNOISESQUELCH_H
+
+#include "Config.h"
+
+const uint8_t NS_NONE  = 0U;
+const uint8_t NS_READY = 1U;
+const uint8_t NS_VALID = 2U;
+
+#define NSQ_READY(a) ((a & NS_READY) != 0)
+#define NSQ_NOT_READY(a) ((a & NS_READY) == 0)
+#define NSQ_VALID(a) ((a & NS_VALID) != 0)
+#define NSQ_NOT_VALID(a) ((a & NS_VALID) == 0)
+
+class CFMNoiseSquelch {
+public:
+  CFMNoiseSquelch();
+
+  void setParams(uint8_t highThreshold, uint8_t lowThreshold);
+  
+  uint8_t process(q15_t sample);
+
+  void reset();
+
+private:
+  q31_t    m_highThreshold;
+  q31_t    m_lowThreshold;
+  uint16_t m_count;
+  q31_t    m_q0;
+  q31_t    m_q1;
+  uint8_t  m_result;
+};
+
+#endif