header_format_crc.h

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/* -*- c++ -*- */
/* Copyright 2016 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_DIGITAL_HEADER_FORMAT_CRC_H
#define INCLUDED_DIGITAL_HEADER_FORMAT_CRC_H

#include <pmt/pmt.h>
#include <gnuradio/digital/api.h>
#include <gnuradio/digital/header_format_default.h>
#include <boost/crc.hpp>

namespace gr {
  namespace digital {

    /*!
     * \brief Header formatter that includes the payload length,
     * packet number, and a CRC check on the header.
     * \ingroup packet_operators_blk
     *
     * \details
     *
     * Child class of header_format_base. This version's header
     * format looks like:
     *
     * \li length (12 bits): length of the payload
     * \li number (12 bits): packet number
     * \li CRC8 (8 bits): A CRC8 check on the header contents
     *
     * Instead of duplicating the payload length, we only add it once
     * and use the CRC8 to make sure it's correctly received.
     *
     * \verbatim
         |  0 -- 11 | 12 -- 23 | 24 -- 31 |
         |    len   | pkt len  |   CRC8   |
       \endverbatim
     *
     * Reimplements packet_header_default in the style of the
     * header_format_base.
     */
    class DIGITAL_API header_format_crc
      : public header_format_base
    {
     public:
      header_format_crc(const std::string &len_key_name="packet_len",
                           const std::string &num_key_name="packet_num");
      virtual ~header_format_crc();

      void set_header_num(unsigned header_num) { d_header_number = header_num; };

      /*!
       * \brief Encodes the header information in the given tags into
       * bits and places them into \p out.
       *
       * \details
       * Uses the following header format:
       *  - Bits 0-11: The packet length (what was stored in the tag with key \p len_tag_key)
       *  - Bits 12-23: The header number (counts up everytime this function is called)
       *  - Bit 24-31: 8-Bit CRC
       */
      virtual bool format(int nbytes_in,
                          const unsigned char *input,
                          pmt::pmt_t &output,
                          pmt::pmt_t &info);

      virtual bool parse(int nbits_in,
                         const unsigned char *input,
                         std::vector<pmt::pmt_t> &info,
                         int &nbits_processed);

      /*!
       * Returns the length of the formatted header in bits.
       */
      virtual size_t header_nbits() const;

      /*!
       * Factory to create an async packet header formatter; returns
       * an sptr to the object.
       */
      static sptr make(const std::string &len_key_name="packet_len",
                       const std::string &num_key_name="packet_num");

    protected:
      uint16_t d_header_number;
      pmt::pmt_t d_len_key_name;
      pmt::pmt_t d_num_key_name;
      boost::crc_optimal<8, 0x07, 0xFF, 0x00, false, false>  d_crc_impl;

      //! Verify that the header is valid
      virtual bool header_ok();

      /*! Get info from the header; return payload length and package
       *  rest of data in d_info dictionary.
       */
      virtual int header_payload();
    };

  } // namespace digital
} // namespace gr

#endif /* INCLUDED_DIGITAL_HEADER_FORMAT_CRC_H */