+/* -*- 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 <atsci_fs_correlator_naive.h>
+#include <atsci_sync_tag.h>
+#include <atsci_pnXXX.h>
+#include <iostream>
+#include <cstring>
+
+using std::cerr;
+using std::endl;
+
+static const int PN511_ERROR_LIMIT = 20; // max number of bits wrong
+static const int PN63_ERROR_LIMIT = 5;
+
+unsigned char atsci_fs_correlator_naive::s_511[LENGTH_511];
+unsigned char atsci_fs_correlator_naive::s_63[LENGTH_2ND_63];
+
+static void
+init_s_511 (unsigned char *p)
+{
+ *p++ = 1; // data segment sync pattern
+ *p++ = 0;
+ *p++ = 0;
+ *p++ = 1;
+
+ for (int i = 0; i < 511; i++){
+ p[i] = atsc_pn511[i];
+ }
+}
+
+static void
+init_s_63 (unsigned char *p)
+{
+ for (int i = 0; i < 63; i++){
+ p[i] = atsc_pn63[i];
+ }
+}
+
+atsci_fs_correlator_naive::atsci_fs_correlator_naive ()
+{
+ init_s_511 (s_511);
+ init_s_63 (s_63);
+ reset ();
+}
+
+atsci_fs_correlator_naive::~atsci_fs_correlator_naive ()
+{
+}
+
+void
+atsci_fs_correlator_naive::reset ()
+{
+ d_index = 0;
+ memset (d_sample_sr, 0, sizeof (d_sample_sr));
+ memset (d_bit_sr, 0, sizeof (d_bit_sr));
+}
+
+void
+atsci_fs_correlator_naive::filter (float input_sample,
+ float *output_sample, float *output_tag)
+{
+ // check for a hit on the PN 511 pattern
+ int errors = 0;
+ int start = wrap (d_index + OFFSET_511);
+
+ for (int i = 0; i < LENGTH_511 && errors < PN511_ERROR_LIMIT; i++)
+ errors += d_bit_sr[wrap (start + i)] ^ s_511[i];
+
+ if (errors >= PN511_ERROR_LIMIT)
+ *output_tag = atsc_sync_tag::NORMAL;
+
+ else { // 511 pattern is good. determine if this is field 1 or field 2
+ errors = 0;
+ start = wrap (d_index + OFFSET_2ND_63);
+ for (int i = 0; i < LENGTH_2ND_63; i++)
+ errors += d_bit_sr[wrap (start + i)] ^ s_63[i];
+
+ // we should have either field 1 (== PN63) or field 2 (== ~PN63)
+ if (errors <= PN63_ERROR_LIMIT)
+ *output_tag = atsc_sync_tag::START_FIELD_SYNC_1;
+
+ else if (errors >= (LENGTH_2ND_63 - PN63_ERROR_LIMIT))
+ *output_tag = atsc_sync_tag::START_FIELD_SYNC_2;
+
+ else {
+ // should be extremely rare.
+ cerr << "!!! atsci_fs_correlator_naive: PN63 error count = " << errors << endl;
+ *output_tag = atsc_sync_tag::NORMAL;
+ }
+ }
+
+ // return oldest sample
+ *output_sample = d_sample_sr[d_index];
+
+ // overwrite with newest sample;
+ d_sample_sr[d_index] = input_sample;
+ d_bit_sr[d_index] = input_sample < 0 ? 0 : 1;
+ d_index = incr (d_index);
+}
+
+int
+atsci_fs_correlator_naive::delay () const
+{
+ return SRSIZE;
+}