GNU Radio 3.6.3 C++ API
gr_simple_correlator.h
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1 /* -*- c++ -*- */
2 /*
3  * Copyright 2004 Free Software Foundation, Inc.
4  *
5  * This file is part of GNU Radio
6  *
7  * GNU Radio is free software; you can redistribute it and/or modify
8  * it under the terms of the GNU General Public License as published by
9  * the Free Software Foundation; either version 3, or (at your option)
10  * any later version.
11  *
12  * GNU Radio is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15  * GNU General Public License for more details.
16  *
17  * You should have received a copy of the GNU General Public License
18  * along with GNU Radio; see the file COPYING. If not, write to
19  * the Free Software Foundation, Inc., 51 Franklin Street,
20  * Boston, MA 02110-1301, USA.
21  */
22 
23 #ifndef INCLUDED_GR_SIMPLE_CORRELATOR_H
24 #define INCLUDED_GR_SIMPLE_CORRELATOR_H
25 
26 #include <gr_core_api.h>
27 #include <gr_block.h>
28 #include <assert.h>
29 
30 //#define DEBUG_SIMPLE_CORRELATOR
31 
34 
36 
37 /*!
38  * \brief inverse of gr_simple_framer (more or less)
39  * \ingroup sync_blk
40  */
42 {
43  static const int OVERSAMPLE = 8;
44  enum state_t { ST_LOOKING, ST_UNDER_THRESHOLD, ST_LOCKED };
45 
46  int d_payload_bytesize;
47  state_t d_state;
48  unsigned int d_osi; // over sample index [0,OVERSAMPLE-1]
49  unsigned int d_transition_osi; // first index where Hamming dist < thresh
50  unsigned int d_center_osi; // center of bit
51  unsigned long long int d_shift_reg[OVERSAMPLE];
52  int d_bblen; // length of bitbuf
53  unsigned char *d_bitbuf; // demodulated bits
54  unsigned char *d_pktbuf; // temp packet buf
55  int d_bbi; // bitbuf index
56 
57  static const int AVG_PERIOD = 512; // must be power of 2 (for freq offset correction)
58  int d_avbi;
59  float d_avgbuf[AVG_PERIOD];
60  float d_avg;
61  float d_accum;
62 
63 #ifdef DEBUG_SIMPLE_CORRELATOR
64  FILE *d_debug_fp; // binary log file
65 #endif
66 
68  gr_simple_correlator (int payload_bytesize);
69 
70 
71  inline int slice (float x)
72  {
73  return x >= d_avg ? 1 : 0;
74  }
75 
76  void update_avg(float x);
77 
78  void enter_locked ();
79  void enter_under_threshold ();
80  void enter_looking ();
81 
82  static int add_index (int a, int b)
83  {
84  int t = a + b;
85  if (t >= OVERSAMPLE)
86  t -= OVERSAMPLE;
87  assert (t >= 0 && t < OVERSAMPLE);
88  return t;
89  }
90 
91  static int sub_index (int a, int b)
92  {
93  int t = a - b;
94  if (t < 0)
95  t += OVERSAMPLE;
96  assert (t >= 0 && t < OVERSAMPLE);
97  return t;
98  }
99 
100 
101  public:
103 
104  int general_work (int noutput_items,
105  gr_vector_int &ninput_items,
106  gr_vector_const_void_star &input_items,
107  gr_vector_void_star &output_items);
108 };
109 
110 
111 #endif /* INCLUDED_GR_SIMPLE_CORRELATOR_H */