gr_simple_correlator.h

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/* -*- c++ -*- */
/*
 * Copyright 2004 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.
 */

#ifndef INCLUDED_GR_SIMPLE_CORRELATOR_H
#define INCLUDED_GR_SIMPLE_CORRELATOR_H

#include <gr_block.h>
#include <assert.h>

//#define       DEBUG_SIMPLE_CORRELATOR

class gr_simple_correlator;
typedef boost::shared_ptr<gr_simple_correlator> gr_simple_correlator_sptr;

gr_simple_correlator_sptr gr_make_simple_correlator (int payload_bytesize);

/*!
 * \brief inverse of gr_simple_framer (more or less)
 * \ingroup sync_blk
 */
class gr_simple_correlator : public gr_block
{
  static const int OVERSAMPLE = 8;
  enum state_t { ST_LOOKING, ST_UNDER_THRESHOLD, ST_LOCKED };
  
  int            d_payload_bytesize;
  state_t        d_state;
  unsigned int   d_osi;                         // over sample index [0,OVERSAMPLE-1]
  unsigned int   d_transition_osi;              // first index where Hamming dist < thresh
  unsigned int   d_center_osi;                  // center of bit
  unsigned long long int d_shift_reg[OVERSAMPLE];
  int            d_bblen;                       // length of bitbuf
  unsigned char *d_bitbuf;                      // demodulated bits
  int            d_bbi;                         // bitbuf index

  static const int AVG_PERIOD = 512;            // must be power of 2 (for freq offset correction)
  int   d_avbi;
  float d_avgbuf[AVG_PERIOD];
  float d_avg;
  float d_accum;

#ifdef DEBUG_SIMPLE_CORRELATOR
  FILE          *d_debug_fp;                    // binary log file
#endif

  friend gr_simple_correlator_sptr gr_make_simple_correlator (int payload_bytesize);
  gr_simple_correlator (int payload_bytesize);


  inline int slice (float x)
  {
    return x >= d_avg ? 1 : 0;
  }

  void update_avg(float x);

  void enter_locked ();
  void enter_under_threshold ();
  void enter_looking ();
  
  static int add_index (int a, int b)
  {
    int t = a + b;
    if (t >= OVERSAMPLE)
      t -= OVERSAMPLE;
    assert (t >= 0 && t < OVERSAMPLE);
    return t;
  }

  static int sub_index (int a, int b)
  {
    int t = a - b;
    if (t < 0)
      t += OVERSAMPLE;
    assert (t >= 0 && t < OVERSAMPLE);
    return t;
  }

  
 public:
  ~gr_simple_correlator ();

  int general_work (int noutput_items,
                    gr_vector_int &ninput_items,
                    gr_vector_const_void_star &input_items,
                    gr_vector_void_star &output_items);
};


#endif /* INCLUDED_GR_SIMPLE_CORRELATOR_H */