packet_header_default.h

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/* -*- c++ -*- */
/* Copyright 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_DIGITAL_PACKET_HEADER_DEFAULT_H
#define INCLUDED_DIGITAL_PACKET_HEADER_DEFAULT_H

#include <gnuradio/digital/api.h>
#include <gnuradio/tags.h>
#include <boost/crc.hpp>
#include <boost/enable_shared_from_this.hpp>

namespace gr {
namespace digital {

/*!
 * \brief Default header formatter for digital packet transmission.
 * \ingroup packet_operators_blk
 *
 * \details
 * For bursty/packetized digital transmission, packets are usually prepended
 * with a packet header, containing the number of bytes etc.
 * This class is not a block, but a tool to create these packet header.
 *
 * This is a default packet header (see header_formatter()) for a description
 * on the header format). To create other header, derive packet header creator
 * classes from this function.
 *
 * gr::digital::packet_headergenerator_bb uses header generators derived from
 * this class to create packet headers from data streams.
 */
class DIGITAL_API packet_header_default
    : public boost::enable_shared_from_this<gr::digital::packet_header_default>
{
public:
    typedef boost::shared_ptr<packet_header_default> sptr;

    packet_header_default(long header_len,
                          const std::string& len_tag_key = "packet_len",
                          const std::string& num_tag_key = "packet_num",
                          int bits_per_byte = 1);
    virtual ~packet_header_default();

    sptr base() { return shared_from_this(); };
    sptr formatter() { return shared_from_this(); };

    void set_header_num(unsigned header_num) { d_header_number = header_num; };
    long header_len() { return d_header_len; };
    pmt::pmt_t len_tag_key() { return d_len_tag_key; };

    /*!
     * \brief Encodes the header information in the given tags into bits and places them
     * into \p out
     *
     * 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
     * All other bits: Are set to zero
     *
     * If the header length is smaller than 32, bits are simply left out. For this
     * reason, they always start with the LSB.
     *
     * However, it is recommended to stay above 32 Bits, in order to have a working
     * CRC.
     */
    virtual bool header_formatter(long packet_len,
                                  unsigned char* out,
                                  const std::vector<tag_t>& tags = std::vector<tag_t>());

    /*!
     * \brief Inverse function to header_formatter().
     *
     * Reads the bit stream in \p header and writes a corresponding tag into \p tags.
     */
    virtual bool header_parser(const unsigned char* header, std::vector<tag_t>& tags);

    static sptr make(long header_len,
                     const std::string& len_tag_key = "packet_len",
                     const std::string& num_tag_key = "packet_num",
                     int bits_per_byte = 1);

protected:
    long d_header_len;
    pmt::pmt_t d_len_tag_key;
    pmt::pmt_t d_num_tag_key;
    int d_bits_per_byte;
    unsigned d_header_number;
    unsigned d_mask;
    boost::crc_optimal<8, 0x07, 0xFF, 0x00, false, false> d_crc_impl;
};

} // namespace digital
} // namespace gr

#endif /* INCLUDED_DIGITAL_PACKET_HEADER_DEFAULT_H */