GNU Radio 3.6.5 C++ API

gr_framer_sink_1.h

Go to the documentation of this file.
00001 /* -*- c++ -*- */
00002 /*
00003  * Copyright 2005,2006 Free Software Foundation, Inc.
00004  *
00005  * This file is part of GNU Radio
00006  *
00007  * GNU Radio is free software; you can redistribute it and/or modify
00008  * it under the terms of the GNU General Public License as published by
00009  * the Free Software Foundation; either version 3, or (at your option)
00010  * any later version.
00011  *
00012  * GNU Radio is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00015  * GNU General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU General Public License
00018  * along with GNU Radio; see the file COPYING.  If not, write to
00019  * the Free Software Foundation, Inc., 51 Franklin Street,
00020  * Boston, MA 02110-1301, USA.
00021  */
00022 
00023 #ifndef INCLUDED_GR_FRAMER_SINK_1_H
00024 #define INCLUDED_GR_FRAMER_SINK_1_H
00025 
00026 #include <gr_core_api.h>
00027 #include <gr_sync_block.h>
00028 #include <gr_msg_queue.h>
00029 
00030 class gr_framer_sink_1;
00031 typedef boost::shared_ptr<gr_framer_sink_1> gr_framer_sink_1_sptr;
00032 
00033 GR_CORE_API gr_framer_sink_1_sptr
00034 gr_make_framer_sink_1 (gr_msg_queue_sptr target_queue);
00035 
00036 /*!
00037  * \brief Given a stream of bits and access_code flags, assemble packets.
00038  *
00039  * input: stream of bytes from gr_correlate_access_code_bb
00040  * output: none.  Pushes assembled packet into target queue
00041  *
00042  * The framer expects a fixed length header of 2 16-bit shorts
00043  * containing the payload length, followed by the payload.  If the
00044  * 2 16-bit shorts are not identical, this packet is ignored.  Better
00045  * algs are welcome.
00046  *
00047  * The input data consists of bytes that have two bits used.
00048  * Bit 0, the LSB, contains the data bit.
00049  * Bit 1 if set, indicates that the corresponding bit is the
00050  * the first bit of the packet.  That is, this bit is the first
00051  * one after the access code.
00052  */
00053 class GR_CORE_API gr_framer_sink_1 : public gr_sync_block
00054 {
00055   friend GR_CORE_API gr_framer_sink_1_sptr
00056   gr_make_framer_sink_1 (gr_msg_queue_sptr target_queue);
00057 
00058  private:
00059   enum state_t {STATE_SYNC_SEARCH, STATE_HAVE_SYNC, STATE_HAVE_HEADER};
00060 
00061   static const int MAX_PKT_LEN    = 4096;
00062   static const int HEADERBITLEN   = 32;
00063 
00064   gr_msg_queue_sptr  d_target_queue;            // where to send the packet when received
00065   state_t            d_state;
00066   unsigned int       d_header;                  // header bits
00067   int                d_headerbitlen_cnt;        // how many so far
00068 
00069   unsigned char      d_packet[MAX_PKT_LEN];     // assembled payload
00070   unsigned char      d_packet_byte;             // byte being assembled
00071   int                d_packet_byte_index;       // which bit of d_packet_byte we're working on
00072   int                d_packetlen;               // length of packet
00073   int                d_packet_whitener_offset;  // offset into whitener string to use
00074   int                d_packetlen_cnt;           // how many so far
00075 
00076  protected:
00077   gr_framer_sink_1(gr_msg_queue_sptr target_queue);
00078 
00079   void enter_search();
00080   void enter_have_sync();
00081   void enter_have_header(int payload_len, int whitener_offset);
00082 
00083   bool header_ok()
00084   {
00085     // confirm that two copies of header info are identical
00086     return ((d_header >> 16) ^ (d_header & 0xffff)) == 0;
00087   }
00088 
00089   void header_payload(int *len, int *offset)
00090   {
00091     // header consists of two 16-bit shorts in network byte order
00092     // payload length is lower 12 bits
00093     // whitener offset is upper 4 bits
00094     *len = (d_header >> 16) & 0x0fff;
00095     *offset = (d_header >> 28) & 0x000f;
00096   }
00097 
00098  public:
00099   ~gr_framer_sink_1();
00100 
00101   int work(int noutput_items,
00102            gr_vector_const_void_star &input_items,
00103            gr_vector_void_star &output_items);
00104 };
00105 
00106 #endif /* INCLUDED_GR_FRAMER_SINK_1_H */