Store FM output in a ring buffer.

FM.cpp

@@ -31,6 +31,8 @@ q15_t FILTER_COEFFS[] = {
 
 const uint16_t FILTER_COEFFS_LEN = 101U;
 
+const uint16_t OUTPUT_BUFFER_SIZE = 1000U;
+
 CFM::CFM() :
 m_filter(),
 m_filterState(),
@@ -48,7 +50,8 @@ m_holdoffTimer(),
 m_kerchunkTimer(),
 m_ackMinTimer(),
 m_ackDelayTimer(),
-m_hangTimer()
+m_hangTimer(),
+m_ringBuffer(OUTPUT_BUFFER_SIZE)
 {
   ::memset(m_filterState, 0x00U, 230U * sizeof(q15_t));
 
@@ -86,11 +89,28 @@ void CFM::samples(bool cos, q15_t* samples, uint8_t length)
 
   m_ctcssTX.getAudio(output, length);
 
-  io.write(STATE_FM, output, length);
+  for (uint8_t i = 0U; i < length; i++) {
+    bool ret = m_ringBuffer.put(output[i]);
+    if (!ret) {
+      DEBUG1("Overflow in the FM ring buffer");
+      break;
+    }
+  }
 }
 
 void CFM::process()
 {
+  uint16_t space = io.getSpace();
+  uint16_t data  = m_ringBuffer.getData();
+  if (data < space)
+    space = data;
+
+  for (uint16_t i = 0U; i < space; i++) {
+    q15_t sample;
+    m_ringBuffer.get(sample);
+
+    io.write(STATE_FM, &sample, 1U);
+  }
 }
 
 void CFM::reset()

FM.h

@@ -26,6 +26,7 @@
 #include "FMTimeout.h"
 #include "FMKeyer.h"
 #include "FMTimer.h"
+#include "FMRB.h"
 
 enum FM_STATE {
   FS_LISTENING,
@@ -69,6 +70,7 @@ private:
   CFMTimer             m_ackMinTimer;
   CFMTimer             m_ackDelayTimer;
   CFMTimer             m_hangTimer;
+  CFMRB                m_ringBuffer;
 
   void stateMachine(bool validSignal, uint8_t length);
   void listeningState(bool validSignal);

FMRB.cpp

@@ -0,0 +1,102 @@
+/*
+TX fifo control - Copyright (C) KI6ZUM 2015
+Copyright (C) 2015,2016,2020 by Jonathan Naylor G4KLX
+
+This library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Library General Public
+License as published by the Free Software Foundation; either
+version 2 of the License, or (at your option) any later version.
+
+This library 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
+Library General Public License for more details.
+
+You should have received a copy of the GNU Library General Public
+License along with this library; if not, write to the
+Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+Boston, MA  02110-1301, USA.
+*/
+
+#include "FMRB.h"
+
+CFMRB::CFMRB(uint16_t length) :
+m_length(length),
+m_head(0U),
+m_tail(0U),
+m_full(false),
+m_overflow(false)
+{
+  m_samples = new q15_t[length];
+}
+
+uint16_t CFMRB::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 CFMRB::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 CFMRB::put(q15_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 CFMRB::get(q15_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 CFMRB::hasOverflowed()
+{
+  bool overflow = m_overflow;
+
+  m_overflow = false;
+
+  return overflow;
+}

FMRB.h

@@ -0,0 +1,70 @@
+/*
+Serial fifo control - Copyright (C) KI6ZUM 2015
+Copyright (C) 2015,2016,2020 by Jonathan Naylor G4KLX
+
+This library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Library General Public
+License as published by the Free Software Foundation; either
+version 2 of the License, or (at your option) any later version.
+
+This library 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
+Library General Public License for more details.
+
+You should have received a copy of the GNU Library General Public
+License along with this library; if not, write to the
+Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+Boston, MA  02110-1301, 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 CFMRB {
+public:
+  CFMRB(uint16_t length);
+  
+  uint16_t getSpace() const;
+  
+  uint16_t getData() const;
+
+  bool put(q15_t sample);
+
+  bool get(q15_t& sample);
+
+  bool hasOverflowed();
+
+private:
+  uint16_t          m_length;
+  volatile q15_t*   m_samples;
+  volatile uint16_t m_head;
+  volatile uint16_t m_tail;
+  volatile bool     m_full;
+  bool              m_overflow;
+};
+
+#endif