GNU Radio 3.6.3 C++ API
digital_framer_sink_1.h
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1 /* -*- c++ -*- */
2 /*
3  * Copyright 2005,2006,2012 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_FRAMER_SINK_1_H
24 #define INCLUDED_GR_FRAMER_SINK_1_H
25 
26 #include <digital_api.h>
27 #include <gr_sync_block.h>
28 #include <gr_msg_queue.h>
29 
32 
35 
36 /*!
37  * \brief Given a stream of bits and access_code flags, assemble packets.
38  * \ingroup sink_blk
39  *
40  * input: stream of bytes from gr_correlate_access_code_bb
41  * output: none. Pushes assembled packet into target queue
42  *
43  * The framer expects a fixed length header of 2 16-bit shorts
44  * containing the payload length, followed by the payload. If the
45  * 2 16-bit shorts are not identical, this packet is ignored. Better
46  * algs are welcome.
47  *
48  * The input data consists of bytes that have two bits used.
49  * Bit 0, the LSB, contains the data bit.
50  * Bit 1 if set, indicates that the corresponding bit is the
51  * the first bit of the packet. That is, this bit is the first
52  * one after the access code.
53  */
55 {
58 
59  private:
60  enum state_t {STATE_SYNC_SEARCH, STATE_HAVE_SYNC, STATE_HAVE_HEADER};
61 
62  static const int MAX_PKT_LEN = 4096;
63  static const int HEADERBITLEN = 32;
64 
65  gr_msg_queue_sptr d_target_queue; // where to send the packet when received
66  state_t d_state;
67  unsigned int d_header; // header bits
68  int d_headerbitlen_cnt; // how many so far
69 
70  unsigned char d_packet[MAX_PKT_LEN]; // assembled payload
71  unsigned char d_packet_byte; // byte being assembled
72  int d_packet_byte_index; // which bit of d_packet_byte we're working on
73  int d_packetlen; // length of packet
74  int d_packet_whitener_offset; // offset into whitener string to use
75  int d_packetlen_cnt; // how many so far
76 
77  protected:
79 
80  void enter_search();
81  void enter_have_sync();
82  void enter_have_header(int payload_len, int whitener_offset);
83 
84  bool header_ok()
85  {
86  // confirm that two copies of header info are identical
87  return ((d_header >> 16) ^ (d_header & 0xffff)) == 0;
88  }
89 
90  void header_payload(int *len, int *offset)
91  {
92  // header consists of two 16-bit shorts in network byte order
93  // payload length is lower 12 bits
94  // whitener offset is upper 4 bits
95  *len = (d_header >> 16) & 0x0fff;
96  *offset = (d_header >> 28) & 0x000f;
97  }
98 
99  public:
101 
102  int work(int noutput_items,
103  gr_vector_const_void_star &input_items,
104  gr_vector_void_star &output_items);
105 };
106 
107 #endif /* INCLUDED_GR_FRAMER_SINK_1_H */