--- /dev/null
+/* -*- c++ -*- */
+/*
+ * Copyright 2002 Free Software Foundation, Inc.
+ *
+ * This file is part of GNU Radio
+ *
+ * GNU Radio 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, or (at your option)
+ * any later version.
+ *
+ * GNU Radio 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 GNU Radio; see the file COPYING. If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#include <cmath>
+#include <GrAtscBitTimingLoop.h>
+#include "fpll_btloop_coupling.h"
+#include <algorithm>
+#include <atsc_consts.h>
+#include <stdio.h>
+#include <assert.h>
+
+using std::abs;
+
+static const int DEC = 2; // nominal decimation factor
+
+/*
+ * I strongly suggest that you not mess with these...
+ */
+static const double DEFAULT_TIMING_RATE = 2.19e-4 / FPLL_BTLOOP_COUPLING_CONST;
+static const double DEFAULT_LOOP_TAP = 0.05;
+
+
+GrAtscBitTimingLoop::GrAtscBitTimingLoop ()
+ : VrDecimatingSigProc<float,float> (1, DEC),
+ next_input(0), w (1.0), mu (0.5), last_right(0),
+ debug_no_update (false)
+{
+ d_timing_rate = DEFAULT_TIMING_RATE;
+ loop.set_taps (DEFAULT_LOOP_TAP);
+
+ history = 1500; // spare input samples in case we need them.
+
+#ifdef _BT_DIAG_OUTPUT_
+ fp_loop = fopen ("loop.out", "w");
+ if (fp_loop == 0){
+ perror ("loop.out");
+ exit (1);
+ }
+
+ fp_ps = fopen ("ps.out", "w");
+ if (fp_ps == 0){
+ perror ("ps.out");
+ exit (1);
+ }
+#endif
+}
+
+//
+// We are nominally a 2x decimator, but our actual rate varies slightly
+// depending on the difference between the transmitter and receiver
+// sampling clocks. Hence, we need to compute our input ranges
+// explictly.
+
+int
+GrAtscBitTimingLoop::forecast(VrSampleRange output,
+ VrSampleRange inputs[]) {
+ /* dec:1 ratio with history */
+ for(unsigned int i=0;i<numberInputs;i++) {
+ inputs[i].index=next_input;
+ inputs[i].size=output.size*decimation + history-1;
+ }
+ return 0;
+}
+
+inline double
+GrAtscBitTimingLoop::filter_error (double e)
+{
+ static const double limit = 50 * FPLL_BTLOOP_COUPLING_CONST;
+
+ // first limit
+
+ if (e > limit)
+ e = limit;
+ else if (e < -limit)
+ e = -limit;
+
+ return loop.filter (e);
+}
+
+int
+GrAtscBitTimingLoop::work (VrSampleRange output, void *ao[],
+ VrSampleRange inputs[], void *ai[])
+{
+ iType *in = ((iType **)ai)[0];
+ oType *out = ((oType **)ao)[0];
+
+ // Force in-order computation of output stream.
+ // This is required because of our slightly variable decimation factor
+ sync (output.index);
+
+
+ // We are tasked with producing output.size output samples.
+ // We will consume approximately 2 * output.size input samples.
+
+
+ unsigned int ii = 0; // input index
+ unsigned int k; // output index
+
+ // We look at a window of 3 samples that we call left (oldest),
+ // middle, right (newest). Each time through the loop, the previous
+ // right becomes the new left, and the new samples are middle and
+ // right.
+ //
+ // The basic game plan is to drive the average difference between
+ // right and left to zero. Given that all transitions are
+ // equiprobable (the data is white) and that the composite matched
+ // filter is symmetric (raised cosine) it turns out that in the
+ // average, if we drive that difference to zero, (implying that the
+ // average slope at the middle point is zero), we'll be sampling
+ // middle at the maximum or minimum point in the pulse.
+
+ iType left;
+ iType middle;
+ iType right = last_right;
+
+ for (k = 0; k < output.size; k++){
+
+ left = right;
+ middle = produce_sample (in, ii);
+ right = produce_sample (in, ii);
+
+ // assert (ii < inputs[0].size);
+ if (!(ii < inputs[0].size)){
+ fprintf (stderr, "ii < inputs[0].size\n");
+ fprintf (stderr, "ii = %d, inputs[0].size = %lu, k = %d, output.size = %lu\n",
+ ii, inputs[0].size, k, output.size);
+ assert (0);
+ }
+
+
+ out[k] = middle; // produce our output
+
+ double timing_error = -middle * ((double) right - left);
+
+ // update_timing_control_word
+
+ double filtered_timing_error = filter_error (timing_error);
+
+ if (!debug_no_update){
+ mu += filtered_timing_error * d_timing_rate;
+ }
+
+#ifdef _BT_DIAG_OUTPUT_
+ float iodata[8];
+ iodata[0] = left;
+ iodata[1] = middle;
+ iodata[2] = right;
+ iodata[3] = timing_error;
+ iodata[4] = filtered_timing_error;
+ iodata[5] = mu;
+ iodata[6] = w;
+ iodata[7] = 0;
+ if (fwrite (iodata, sizeof (iodata), 1, fp_loop) != 1){
+ perror ("fwrite: loop");
+ exit (1);
+ }
+#endif
+
+ }
+
+ last_right = right;
+ next_input += ii; // update next_input so forecast can get us what we need
+ return output.size;
+}
+
+/*!
+ * Produce samples equally spaced in time that are referenced
+ * to the transmitter's sample clock, not ours.
+ *
+ * See pp 523-527 of "Digital Communication Receivers", Meyr,
+ * Moeneclaey and Fechtel, Wiley, 1998.
+ */
+
+GrAtscBitTimingLoop::iType
+GrAtscBitTimingLoop::produce_sample (const iType *in, unsigned int &index)
+{
+ // update mu and index as function of control word, w
+
+ double sum = mu + w;
+ double f = floor (sum);
+ int incr = (int) f; // mostly 1, rarely 0 or 2
+ mu = sum - f;
+
+ assert (0 <= incr && incr <= 2);
+ assert (0.0 <= mu && mu <= 1.0);
+
+ index += incr;
+
+ iType n = intr.interpolate (&in[index], mu);
+
+#if defined(_BT_DIAG_OUTPUT_) && 0
+ float iodata[4];
+ iodata[0] = incr;
+ iodata[1] = mu;
+ iodata[2] = w;
+ iodata[3] = 0;
+ if (fwrite (iodata, sizeof (iodata), 1, fp_ps) != 1){
+ perror ("fwrite: ps");
+ exit (1);
+ }
+#endif
+
+ return n;
+}
projects / debian / gnuradio / blobdiff