330 WIP - P25 C4FM decoder fully functional using DQPSK decoder and

new symbol timing error detector.  Each component now has a subclass
that supports instrumentation for use with the DemodulatorViewerFX
application.

src/main/java/io/github/dsheirer/dsp/psk/InterpolatingSampleBuffer.java

@@ -0,0 +1,167 @@
+/*******************************************************************************
+ * 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.psk;
+
+import io.github.dsheirer.dsp.filter.interpolator.RealInterpolator;
+import io.github.dsheirer.sample.complex.Complex;
+
+public class InterpolatingSampleBuffer
+{
+    private static final float MAXIMUM_DEVIATION_SAMPLES_PER_SYMBOL = 0.02f; // +/- 2% deviation
+
+    private Complex mPrecedingSample = new Complex(0,0);
+    private Complex mCurrentSample = new Complex(0,0);
+
+    private float[] mDelayLineInphase;
+    private float[] mDelayLineQuadrature;
+    private int mDelayLinePointer = 0;
+    private int mTwiceSamplesPerSymbol;
+
+    private float mSamplingPoint;
+    private float mSampleCounterGain = 0.05f;
+    private float mDetectedSamplesPerSymbol;
+    private float mDetectedSamplesPerSymbolGain = 0.1f * mSampleCounterGain * mSampleCounterGain;
+    private float mMaximumSamplesPerSymbol;
+    private float mMinimumSamplesPerSymbol;
+
+    private RealInterpolator mInterpolator = new RealInterpolator(1.0f);
+
+    /**
+     * Buffer to store complex sample data and produce interpolated samples.
+     * @param samplesPerSymbol
+     */
+    public InterpolatingSampleBuffer(float samplesPerSymbol)
+    {
+        mSamplingPoint = samplesPerSymbol;
+        mDetectedSamplesPerSymbol = samplesPerSymbol;
+        mMaximumSamplesPerSymbol = samplesPerSymbol * (1.0f + MAXIMUM_DEVIATION_SAMPLES_PER_SYMBOL);
+        mMinimumSamplesPerSymbol = samplesPerSymbol * (1.0f - MAXIMUM_DEVIATION_SAMPLES_PER_SYMBOL);
+        mTwiceSamplesPerSymbol = (int)Math.floor(2.0 * samplesPerSymbol);
+        mDelayLineInphase = new float[2 * mTwiceSamplesPerSymbol];
+        mDelayLineQuadrature = new float[2 * mTwiceSamplesPerSymbol];
+    }
+
+    /**
+     * Stores the sample in the buffer and updates pointers.
+     * @param sample
+     */
+    public void receive(Complex sample)
+    {
+        mSamplingPoint--;
+
+        //Fill up the delay line to use with the interpolator
+        mDelayLineInphase[mDelayLinePointer] = sample.inphase();
+        mDelayLineInphase[mDelayLinePointer + mTwiceSamplesPerSymbol] = sample.inphase();
+        mDelayLineQuadrature[mDelayLinePointer] = sample.quadrature();
+        mDelayLineQuadrature[mDelayLinePointer + mTwiceSamplesPerSymbol] = sample.quadrature();
+
+        //Increment pointer and keep pointer in bounds
+        mDelayLinePointer++;
+        mDelayLinePointer = mDelayLinePointer % mTwiceSamplesPerSymbol;
+    }
+
+    /**
+     * Updates the internal sample counter with additional samples to add to the symbol sample counter.
+     * @param samplesToAdd to the sample counter
+     */
+    public void increaseSampleCounter(float samplesToAdd)
+    {
+        mSamplingPoint += samplesToAdd;
+    }
+
+    /**
+     * 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)
+    {
+        //Adjust detected samples per symbol based on timing error
+        mDetectedSamplesPerSymbol = mDetectedSamplesPerSymbol + (symbolTimingError * mDetectedSamplesPerSymbolGain);
+
+        //Constrain detected samples per symbol to min/max values
+        if(mDetectedSamplesPerSymbol > mMaximumSamplesPerSymbol)
+        {
+            mDetectedSamplesPerSymbol = mMaximumSamplesPerSymbol;
+        }
+
+        if(mDetectedSamplesPerSymbol < mMinimumSamplesPerSymbol)
+        {
+            mDetectedSamplesPerSymbol = mMinimumSamplesPerSymbol;
+        }
+
+        //Add another symbol's worth of samples to the counter and adjust timing based on gardner error
+        increaseSampleCounter((mDetectedSamplesPerSymbol + (symbolTimingError * mSampleCounterGain)));
+    }
+
+    /**
+     * Current value of the detected samples per symbol
+     */
+    public float getSamplingPoint()
+    {
+        return mSamplingPoint;
+    }
+
+    /**
+     * Indicates if this buffer has accumulated a enough samples to represent a full symbol
+     */
+    public boolean hasSymbol()
+    {
+        return mSamplingPoint < 1.0f;
+    }
+
+    /**
+     * Un-interpolated sample that precedes the current interpolated sampling point.  The current sampling point falls
+     * somewhere between sample index 3 and index 4, therefore the preceding sample is located at index 3.
+     */
+    public Complex getPrecedingSample()
+    {
+        mPrecedingSample.setValues(mDelayLineInphase[mDelayLinePointer + 3], mDelayLineQuadrature[mDelayLinePointer + 3]);
+        return mPrecedingSample;
+    }
+
+    /**
+     * Interpolated middle sample for the symbol.  Note: this method should only be invoked after testing for a
+     * complete symbol with the hasSymbol() method.
+     */
+    public Complex getCurrentSample()
+    {
+        /* Calculate interpolated current sample */
+        mCurrentSample.setValues(getInphase(mSamplingPoint), getQuadrature(mSamplingPoint));
+        return mCurrentSample;
+    }
+
+    /**
+     * Returns the interpolated inphase value for the specified offset
+     * @param interpolation into the buffer to calculate the interpolated sample
+     * @return inphase value of the interpolated sample
+     */
+    public float getInphase(float interpolation)
+    {
+        return mInterpolator.filter(mDelayLineInphase, mDelayLinePointer, interpolation);
+    }
+
+    /**
+     * Returns the interpolated quadrature value for the specified offset
+     * @param interpolation into the buffer to calculate the interpolated sample
+     * @return quadrature value of the interpolated sample
+     */
+    public float getQuadrature(float interpolation)
+    {
+        return mInterpolator.filter(mDelayLineQuadrature, mDelayLinePointer, interpolation);
+    }
+}