gr_tagged_stream_block.h

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/* -*- c++ -*- */
/*
 * Copyright 2013 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_TAGGED_STREAM_BLOCK_H
#define INCLUDED_GR_TAGGED_STREAM_BLOCK_H

#include <gr_core_api.h>
#include <gr_block.h>

/*!
 * \brief Block that operates on PDUs in form of tagged streams
 * \ingroup base_blk
 *
 * Override work to provide the signal processing implementation.
 */
class GR_CORE_API gr_tagged_stream_block : public gr_block
{
 private:
  pmt::pmt_t d_length_tag_key; //!< This is the key for the tag that stores the PDU length
  gr_vector_int d_n_input_items_reqd; //!< How many input items do I need to process the next PDU?

 protected:
  std::string d_length_tag_key_str;
  gr_tagged_stream_block (void){} //allows pure virtual interface sub-classes
  gr_tagged_stream_block (const std::string &name,
                 gr_io_signature_sptr input_signature,
                 gr_io_signature_sptr output_signature,
                 const std::string &length_tag_key);

  /*!
   * \brief Parse all tags on the first sample of a PDU, return the number of items per input
   *        and prune the length tags.
   *
   * In most cases, you don't need to override this, unless the number of items read
   * is not directly coded in one single tag.
   *
   * Default behaviour:
   * - Go through all input ports
   * - On every input port, search for the tag with the key specified in \p length_tag_key
   * - Copy that value as an int to the corresponding position in \p n_input_items_reqd
   * - Remove the length tag.
   *
   * \param[in] tags All the tags found on the first item of every input port.
   * \param[out] n_input_items_reqd Number of items which will be read from every input
   */
  virtual void parse_length_tags(
      const std::vector<std::vector<gr_tag_t> > &tags,
      gr_vector_int &n_input_items_reqd
  );

  /*!
   * \brief Calculate the number of output items.
   *
   * This is basically the inverse function to forecast(): Given a number of input
   * items, it returns the maximum number of output items.
   *
   * You most likely need to override this function, unless your block is a sync
   * block or integer interpolator/decimator.
   *
   */
  virtual int calculate_output_stream_length(const gr_vector_int &ninput_items);

  /*!
   * \brief Set the new length tags on the output stream
   *
   * Default behaviour: Set a tag with key \p length_tag_key and
   * the number of produced items on every output port.
   *
   * For anything else, override this.
   *
   * \param n_produced Length of the new PDU
   * \param n_ports Number of output ports
   */
  virtual void update_length_tags(int n_produced, int n_ports);

 public:

  /*! \brief Don't override this.
   */
  void /* final */ forecast (int noutput_items, gr_vector_int &ninput_items_required);

  /*!
   * - Reads the number of input items from the tags using parse_length_tags()
   * - Checks there's enough data on the input and output buffers
   * - If not, inform the scheduler and do nothing
   * - Calls work() with the exact number of items per PDU
   * - Updates the tags using update_length_tags()
   */
  int general_work (int noutput_items,
                     gr_vector_int &ninput_items,
                     gr_vector_const_void_star &input_items,
                     gr_vector_void_star &output_items);

  /*!
   * \brief Just like gr_block::general_work, but makes sure the input is valid
   *
   * The user must override work to define the signal processing code.
   * Check the documentation for general_work() to see what happens here.
   *
   * Like gr_sync_block, this calls consume() for you (it consumes ninput_items[i]
   * items from the i-th port).
   *
   * A note on tag propagation: The PDU length tags are handled by other functions,
   * but all other tags are handled just as in any other \p gr_block. So, most likely,
   * you either set the tag propagation policy to TPP_DONT and handle the tag
   * propagation manually, or you propagate tags through the scheduler and don't
   * do anything here.
   *
   * \param noutput_items The size of the writable output buffer
   * \param ninput_items The exact size of the items on every input for this particular PDU.
   *                     These will be consumed if a length tag key is provided!
   * \param input_items See gr_block
   * \param output_items See gr_block
   */
  virtual int work (int noutput_items,
                    gr_vector_int &ninput_items,
                    gr_vector_const_void_star &input_items,
                    gr_vector_void_star &output_items) = 0;

};

#endif /* INCLUDED_GR_TAGGED_STREAM_BLOCK_H */