digital_packet_sink.h

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/* -*- c++ -*- */
/*
 * Copyright 2005,2012 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_PACKET_SINK_H
#define INCLUDED_GR_PACKET_SINK_H

#include <digital_api.h>
#include <gr_sync_block.h>
#include <gr_msg_queue.h>

class digital_packet_sink;
typedef boost::shared_ptr<digital_packet_sink> digital_packet_sink_sptr;

DIGITAL_API digital_packet_sink_sptr
digital_make_packet_sink(const std::vector<unsigned char>& sync_vector,
                         gr_msg_queue_sptr target_queue,
                         int threshold = -1);                   // -1 -> use default

/*!
 * \brief process received  bits looking for packet sync, header, and process bits into packet
 * \ingroup packet_operators_blk
 *
 * \details
 * input: stream of symbols to be sliced.
 * 
 * output: none. Pushes assembled packet into target queue
 *
 * The packet sink takes in a stream of binary symbols that are sliced
 * around 0. The bits are then checked for the \p sync_vector to
 * determine find and decode the packet. It then expects a fixed
 * length header of 2 16-bit shorts containing the payload length,
 * followed by the payload. If the 2 16-bit shorts are not identical,
 * this packet is ignored. Better algs are welcome.
 *
 * This block is not very useful anymore as it only works with 2-level
 * modulations such as BPSK or GMSK. The block can generally be
 * replaced with a correlate access code and frame sink blocks.
 */
class DIGITAL_API digital_packet_sink : public gr_sync_block
{
  friend DIGITAL_API digital_packet_sink_sptr
    digital_make_packet_sink(const std::vector<unsigned char>& sync_vector,
                             gr_msg_queue_sptr target_queue,
                             int threshold);

 private:
  enum state_t {STATE_SYNC_SEARCH, STATE_HAVE_SYNC, STATE_HAVE_HEADER};

  static const int MAX_PKT_LEN    = 4096;
  static const int HEADERBITLEN   = 32;

  gr_msg_queue_sptr  d_target_queue;            // where to send the packet when received
  unsigned long long d_sync_vector;             // access code to locate start of packet
  unsigned int       d_threshold;               // how many bits may be wrong in sync vector

  state_t            d_state;

  unsigned long long d_shift_reg;               // used to look for sync_vector

  unsigned int       d_header;                  // header bits
  int                d_headerbitlen_cnt;        // how many so far

  unsigned char      d_packet[MAX_PKT_LEN];     // assembled payload
  unsigned char      d_packet_byte;             // byte being assembled
  int                d_packet_byte_index;       // which bit of d_packet_byte we're working on
  int                d_packetlen;               // length of packet
  int                d_packetlen_cnt;           // how many so far

 protected:
  /*!
   * Build a packet sink block.
   *
   * \param sync_vector The synchronization vector as a vector of 1's and 0's.
   * \param target_queue The message queue that packets are sent to.
   * \param threshold Number of bits that can be incorrect in the \p sync_vector.
   */
  digital_packet_sink(const std::vector<unsigned char>& sync_vector,
                      gr_msg_queue_sptr target_queue,
                      int threshold);

  void enter_search();
  void enter_have_sync();
  void enter_have_header(int payload_len);

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

  bool header_ok()
  {
    // confirm that two copies of header info are identical
    return ((d_header >> 16) ^ (d_header & 0xffff)) == 0;
  }

  int header_payload_len()
  {
    // header consists of two 16-bit shorts in network byte order
    int t = (d_header >> 16) & 0xffff;
    return t;
  }

 public:
  ~digital_packet_sink();

  int work(int noutput_items,
           gr_vector_const_void_star &input_items,
           gr_vector_void_star &output_items);


  //! return true if we detect carrier
  bool carrier_sensed() const
  {
    return d_state != STATE_SYNC_SEARCH;
  }

};

#endif /* INCLUDED_GR_PACKET_SINK_H */