Add Downsampling

FM.cpp

@@ -41,7 +41,8 @@ m_filterStage2(32768,      0,-32768, 32768, -50339, 19052),
 m_filterStage3(32768, -65536, 32768, 32768, -64075, 31460),
 m_blanking(),
 m_useCOS(true),
-m_rfAudioBoost(1U)
+m_rfAudioBoost(1U),
+m_downsampler(1024)//Size might need adjustement
 {
 }
 
@@ -101,6 +102,8 @@ void CFM::samples(bool cos, q15_t* samples, uint8_t length)
 
     currentSample = q15_t(m_filterStage3.filter(m_filterStage2.filter(m_filterStage1.filter(currentSample))));
 
+    m_downsampler.addSample(currentSample);
+
     currentSample += m_ctcssTX.getAudio();
 
     samples[i] = currentSample;

FM.h

@@ -28,6 +28,7 @@
 #include "FMKeyer.h"
 #include "FMTimer.h"
 #include "FMDirectForm1.h"
+#include "FMDownsampler.h"
 
 enum FM_STATE {
   FS_LISTENING,
@@ -78,6 +79,7 @@ private:
   CFMBlanking          m_blanking;
   bool                 m_useCOS;
   q15_t                m_rfAudioBoost;
+  CFMDownsampler       m_downsampler;
 
   void stateMachine(bool validSignal, uint8_t length);
   void listeningState(bool validSignal);

FMDownsampleRB.cpp

@@ -0,0 +1,101 @@
+/*
+ *   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.
+ */
+
+
+#include "FMDownsampleRB.h"
+
+CFMDownsampleRB::CFMDownsampleRB(uint16_t length) :
+m_length(length),
+m_head(0U),
+m_tail(0U),
+m_full(false),
+m_overflow(false)
+{
+  m_samples = new uint8_t[length];
+}
+
+uint16_t CFMDownsampleRB::getSpace() const
+{
+  uint16_t n = 0U;
+
+  if (m_tail == m_head)
+    n = m_full ? 0U : m_length;
+  else if (m_tail < m_head)
+    n = m_length - m_head + m_tail;
+  else
+    n = m_tail - m_head;
+
+  if (n > m_length)
+    n = 0U;
+
+  return n;
+}
+
+uint16_t CFMDownsampleRB::getData() const
+{
+  if (m_tail == m_head)
+    return m_full ? m_length : 0U;
+  else if (m_tail < m_head)
+    return m_head - m_tail;
+  else
+    return m_length - m_tail + m_head;
+}
+
+bool CFMDownsampleRB::put(uint8_t sample)
+{
+  if (m_full) {
+    m_overflow = true;
+    return false;
+  }
+
+  m_samples[m_head] = sample;
+
+  m_head++;
+  if (m_head >= m_length)
+    m_head = 0U;
+
+  if (m_head == m_tail)
+    m_full = true;
+
+  return true;
+}
+
+bool CFMDownsampleRB::get(uint8_t& sample)
+{
+  if (m_head == m_tail && !m_full)
+    return false;
+
+  sample = m_samples[m_tail];
+
+  m_full = false;
+
+  m_tail++;
+  if (m_tail >= m_length)
+    m_tail = 0U;
+
+  return true;
+}
+
+bool CFMDownsampleRB::hasOverflowed()
+{
+  bool overflow = m_overflow;
+
+  m_overflow = false;
+
+  return overflow;
+}

FMDownsampleRB.h

@@ -0,0 +1,68 @@
+/*
+ *   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(FMRB_H)
+#define  FMRB_H
+
+#if defined(STM32F4XX)
+#include "stm32f4xx.h"
+#elif defined(STM32F7XX)
+#include "stm32f7xx.h"
+#elif defined(STM32F105xC)
+#include "stm32f1xx.h"
+#include <cstddef>
+#else
+#include <Arduino.h>
+#endif
+
+#if defined(__SAM3X8E__) || defined(STM32F105xC)
+#define  ARM_MATH_CM3
+#elif defined(STM32F7XX)
+#define  ARM_MATH_CM7
+#elif defined(STM32F4XX) || defined(__MK20DX256__) || defined(__MK64FX512__) || defined(__MK66FX1M0__)
+#define  ARM_MATH_CM4
+#else
+#error "Unknown processor type"
+#endif
+
+#include <arm_math.h>
+
+class CFMDownsampleRB {
+public:
+  CFMDownsampleRB(uint16_t length);
+  
+  uint16_t getSpace() const;
+  
+  uint16_t getData() const;
+
+  bool put(uint8_t sample);
+
+  bool get(uint8_t& sample);
+
+  bool hasOverflowed();
+
+private:
+  uint16_t          m_length;
+  volatile uint8_t* m_samples;
+  volatile uint16_t m_head;
+  volatile uint16_t m_tail;
+  volatile bool     m_full;
+  bool              m_overflow;
+};
+
+#endif

FMDownsampler.cpp

@@ -0,0 +1,63 @@
+/*
+ *   Copyright (C) 2020 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2020 by 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 "Config.h"
+#include "FMDownsampler.h"
+
+
+CFMDownsampler::CFMDownsampler(uint16_t length) :
+m_ringBuffer(length),//length might need tweaking
+m_packIndex(0),
+m_downSampleIndex(0)
+{
+    m_samplePack = 0;
+}
+
+void CFMDownsampler::addSample(q15_t sample)
+{
+    //only take one of three samples
+    if(m_downSampleIndex == 0) {
+      switch(m_packIndex){
+        case 0:
+          m_samplePack = int32_t(sample) << 12;
+        break;
+        case 1:{
+            m_samplePack |= int32_t(sample);
+            
+            //we did not use MSB; skip it
+            m_ringBuffer.put(m_samplePackBytes[1]); 
+            m_ringBuffer.put(m_samplePackBytes[2]); 
+            m_ringBuffer.put(m_samplePackBytes[3]); 
+
+            m_samplePack = 0;
+        }
+        break;
+        default:
+            //should never happen
+        break;
+        }
+        m_packIndex++;
+        if(m_packIndex >= 2)
+            m_packIndex = 0;  
+    }
+
+    m_downSampleIndex++;
+    if(m_downSampleIndex >= 3)
+        m_downSampleIndex = 0;
+}

FMDownsampler.h

@@ -0,0 +1,43 @@
+/*
+ *   Copyright (C) 2020 by Jonathan Naylor G4KLX
+ *   Copyright (C) 2020 by 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.
+ */
+
+#if !defined(FMDOWNSAMPLER_H)
+#define FMDOWNSAMPLER_H
+
+#include "Config.h"
+#include "FMDownsampleRB.h"
+
+class CFMDownsampler {
+public:
+  CFMDownsampler(uint16_t length);
+  void addSample(q15_t sample);
+  inline bool getPackedData(uint8_t& data){ return m_ringBuffer.get(data); };
+  inline bool hasOverflowed() { return m_ringBuffer.hasOverflowed(); };
+
+private:
+  CFMDownsampleRB m_ringBuffer;
+  union {
+    int32_t m_samplePack;
+    int8_t  m_samplePackBytes[4];
+  };
+  uint8_t m_packIndex;
+  uint8_t m_downSampleIndex;
+};
+
+#endif