GNU Radio Manual and C++ API Reference 3.8.5.0
The Free & Open Software Radio Ecosystem
 
Loading...
Searching...
No Matches
repack_bits_bb.h
Go to the documentation of this file.
1/* -*- c++ -*- */
2/*
3 * Copyright 2012 Free Software Foundation, Inc.
4 *
5 * This file is part of GNU Radio
6 *
7 * GNU Radio is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 3, or (at your option)
10 * any later version.
11 *
12 * GNU Radio is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with GNU Radio; see the file COPYING. If not, write to
19 * the Free Software Foundation, Inc., 51 Franklin Street,
20 * Boston, MA 02110-1301, USA.
21 */
22
23#ifndef INCLUDED_BLOCKS_REPACK_BITS_BB_H
24#define INCLUDED_BLOCKS_REPACK_BITS_BB_H
25
26#include <gnuradio/blocks/api.h>
27#include <gnuradio/endianness.h>
29
30namespace gr {
31namespace blocks {
32
33/*!
34 * \brief Repack \p k bits from the input stream onto \p l bits of the output stream.
35 * \ingroup byte_operators_blk
36 *
37 * \details
38 * No bits are lost here; any value for k and l (within [1, 8]) is allowed.
39 * On every fresh input byte, it starts reading on the LSB, and starts copying
40 * to the LSB as well.
41 *
42 * When supplying a tag name, this block operates on tagged streams.
43 * In this case, it can happen that the input data or the output data
44 * becomes unaligned when k * input length is not equal to l * output length.
45 * In this case, the \p align_output parameter is used to decide which
46 * data packet to align.
47 *
48 * Usually, \p align_output is false for unpacking (k=8, l < 8) and false for
49 * reversing that.
50 *
51 * \section gr_blocks_repack_example Example
52 *
53 * Say you're tx'ing 8-PSK and therefore set k=8, l=3 on the transmit side
54 * before the modulator. Now assume you're transmitting a single byte of data.
55 * Your incoming tagged stream has length 1, the outgoing has length 3. However,
56 * the third item is actually only carrying 2 bits of relevant data, the bits
57 * do not align with the boundaries. So you set \p align_output = false,
58 * because the output can be unaligned.
59 *
60 * Now say you're doing the inverse: packing those three items into full
61 * bytes. How do you interpret those three bytes? Without this flag,
62 * you'd have to assume there's 9 relevant bits in there, so you'd end up
63 * with 2 bytes of output data. But in the packing case, you want the
64 * \b output to be aligned; all output bits must be useful. By asserting this flag,
65 * the packing algorithm tries to do this and in this case assumes that
66 * since we have alignment after 8 bits, the 9th can be discarded.
67 */
69{
70public:
71 typedef boost::shared_ptr<repack_bits_bb> sptr;
72
73 /*!
74 * \param k Number of relevant bits on the input stream
75 * \param l Number of relevant bits on the output stream
76 * \param tsb_tag_key If not empty, this is the key for the length tag.
77 * \param align_output If tsb_tag_key is given, this controls if the input
78 * or the output is aligned.
79 * \param endianness The endianness of the output data stream (LSB or MSB).
80 */
81 static sptr make(int k,
82 int l = 8,
83 const std::string& tsb_tag_key = "",
84 bool align_output = false,
85 endianness_t endianness = GR_LSB_FIRST);
86 virtual void set_k_and_l(int k, int l) = 0; // callback function for bits per input
87 // byte k and bits per output byte l.
88};
89
90} // namespace blocks
91} // namespace gr
92
93#endif /* INCLUDED_BLOCKS_REPACK_BITS_BB_H */
Repack k bits from the input stream onto l bits of the output stream.
Definition repack_bits_bb.h:69
static sptr make(int k, int l=8, const std::string &tsb_tag_key="", bool align_output=false, endianness_t endianness=GR_LSB_FIRST)
virtual void set_k_and_l(int k, int l)=0
boost::shared_ptr< repack_bits_bb > sptr
Definition repack_bits_bb.h:71
Block that operates on PDUs in form of tagged streams.
Definition tagged_stream_block.h:38
#define BLOCKS_API
Definition gr-blocks/include/gnuradio/blocks/api.h:30
GNU Radio logging wrapper for log4cpp library (C++ port of log4j)
Definition basic_block.h:46
endianness_t
Definition endianness.h:28