[WIP] Creates a new AFSK-1200 correlation decoder and updates the

Fleetsync II decoder to use it.  Adds instrumented version of the decoder
and a new Fleetsync2 FX pane to the DemodulatorViewerFX tool.

Note: the remaining AFSK-1200 based decoders will all be ported to use
this new AFSK1200 decoder (MDC1200, Tait1200, LowJack1200).

src/main/java/io/github/dsheirer/dsp/afsk/AFSKSampleBuffer.java

@@ -0,0 +1,121 @@
+/*******************************************************************************
+ * sdr-trunk
+ * Copyright (C) 2014-2018 Dennis Sheirer
+ *
+ * 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 3 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, see <http://www.gnu.org/licenses/>
+ *
+ ******************************************************************************/
+package io.github.dsheirer.dsp.afsk;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class AFSKSampleBuffer
+{
+    private final static Logger mLog = LoggerFactory.getLogger(AFSKSampleBuffer.class);
+
+    private final static float SYMBOL_SAMPLE_THRESHOLD = 1.0f;
+    protected boolean[] mDelayLine;
+    protected int mDelayLinePointer = 0;
+
+    private int mHalfIntegerSamplesPerSymbol;
+    private int mPositiveSampleDecisionCount;
+    protected int mTwiceSamplesPerSymbol;
+    protected int mSymbolStart;
+    protected int mSymbolEnd;
+    protected int mSamplesPerSymbol;
+    protected float mSymbolSamplingPoint;
+    protected float mSymbolTimingGain;
+
+    /**
+     * Buffer to store complex sample data and produce interpolated samples.
+     * @param samplesPerSymbol
+     */
+    public AFSKSampleBuffer(int samplesPerSymbol, float symbolTimingGain)
+    {
+        mSamplesPerSymbol = samplesPerSymbol;
+        mSymbolTimingGain = symbolTimingGain;
+
+        mHalfIntegerSamplesPerSymbol = samplesPerSymbol / 2;
+        mSymbolSamplingPoint = samplesPerSymbol;
+        mTwiceSamplesPerSymbol = 2 * samplesPerSymbol;
+        mDelayLine = new boolean[2 * mTwiceSamplesPerSymbol];
+    }
+
+    /**
+     * Stores the sample in the sample buffer to support making symbol decisions.
+     *
+     * Note: use the hasSymbol() method to determine if sufficient samples have been collected to make a symbol
+     * determination.
+     *
+     * @param sample to store in the sample buffer
+     */
+    public void receive(boolean sample)
+    {
+        mSymbolSamplingPoint--;
+
+        mDelayLine[mDelayLinePointer] = sample;
+        mDelayLine[mDelayLinePointer + mTwiceSamplesPerSymbol] = sample;
+
+        //Increment pointer and keep pointer in bounds
+        mDelayLinePointer++;
+        mDelayLinePointer = mDelayLinePointer % mTwiceSamplesPerSymbol;
+    }
+
+    /**
+     * Adjusts samples per symbol and symbol timing counters and increments the sample counter to collect another
+     * symbol.
+     *
+     * @param symbolTimingError from a symbol timing error detector
+     */
+    public void resetAndAdjust(float symbolTimingError)
+    {
+        mSymbolSamplingPoint += (mSamplesPerSymbol + (symbolTimingError * mSymbolTimingGain));
+    }
+
+    public void setTimingGain(float gain)
+    {
+        mSymbolTimingGain = gain;
+    }
+
+    /**
+     * Indicates if this buffer has accumulated enough samples to represent a full symbol
+     */
+    public boolean hasSymbol()
+    {
+        return mSymbolSamplingPoint < SYMBOL_SAMPLE_THRESHOLD;
+    }
+
+    /**
+     * Calculates the symbol as a majority decision where the number of positive/true samples are greater than half
+     * of the samples per symbol.  Symbol decision is based on the samples collected over the preceeding 1.0 to 2.0
+     * symbol periods.
+     *
+     * @return a true symbol if the majority of the samples were true or positive, otherwise a false symbol.
+     */
+    public boolean getSymbol()
+    {
+        mPositiveSampleDecisionCount = 0;
+
+        mSymbolStart = mDelayLinePointer;
+        mSymbolEnd = mDelayLinePointer + mSamplesPerSymbol - 1;
+
+        for(int x = mSymbolStart; x <= mSymbolEnd; x++)
+        {
+            if(mDelayLine[x])
+            {
+                mPositiveSampleDecisionCount++;
+            }
+        }
+
+        return mPositiveSampleDecisionCount > mHalfIntegerSamplesPerSymbol;
+    }
+}