add CTCSS decoder

CTCSSDecoder.cpp

@@ -0,0 +1,46 @@
+/*
+ *   Copyright (C) 2020 by Jonathan Naylor G4KLX / Geoffrey Merck F4FXL - KC3FRA
+ *
+ *   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.
+ */
+
+#include "CTCSSDecoder.h"
+
+CCTCSSDEcoder::CCTCSSDEcoder(const TCTCSSTone& tone, q15_t threshold) :
+m_thresholdSquared(threshold * threshold),
+m_hasCTCSS(false)
+{
+    m_goertzel = new CGoertzel(tone.toneLow, tone.tone, tone.toneHi, HANN_WINDOW, HANN_WINDOW_CORR, N_SAMPLES);
+}
+
+
+void CCTCSSDEcoder::samples(const q15_t* samples, uint8_t length)
+{
+    unsigned int f1MagSquared, f2MagSquared, f3MagSquared;
+    GOERTZEL_RESULT result = m_goertzel->samples(samples, length, &f1MagSquared, &f2MagSquared, &f3MagSquared);
+    
+    if(result == GR_READY) {
+        // Goertzel says it has something for us, so checkt it
+        // make sure the strongest tone is the wanted one and not the neighbouring tone
+        m_hasCTCSS  =   f2MagSquared >= m_thresholdSquared
+                        && f2MagSquared > f1MagSquared
+                        && f2MagSquared > f3MagSquared;
+    }
+}
+
+bool CCTCSSDEcoder::hasCTCSS()
+{
+    return m_hasCTCSS;
+}