diff options
| -rw-r--r-- | docs/doxygen/other/msg_passing.dox | 2 | ||||
| -rw-r--r-- | gr-blocks/include/gnuradio/blocks/repack_bits_bb.h | 38 |
2 files changed, 30 insertions, 10 deletions
diff --git a/docs/doxygen/other/msg_passing.dox b/docs/doxygen/other/msg_passing.dox index 882252bee2..47d6768ea0 100644 --- a/docs/doxygen/other/msg_passing.dox +++ b/docs/doxygen/other/msg_passing.dox @@ -239,7 +239,7 @@ shown below. \code void -tagged_stream_to_pdu_impl::send_meassage() +tagged_stream_to_pdu_impl::send_message() { if(pmt::length(d_pdu_vector) != d_pdu_length) { throw std::runtime_error("msg length not correct"); diff --git a/gr-blocks/include/gnuradio/blocks/repack_bits_bb.h b/gr-blocks/include/gnuradio/blocks/repack_bits_bb.h index c594966e6e..e094e6815a 100644 --- a/gr-blocks/include/gnuradio/blocks/repack_bits_bb.h +++ b/gr-blocks/include/gnuradio/blocks/repack_bits_bb.h @@ -30,7 +30,7 @@ namespace gr { namespace blocks { /*! - * \brief Pack \p k bits from the input stream onto \p l bits of the output stream. + * \brief Repack \p k bits from the input stream onto \p l bits of the output stream. * \ingroup byte_operators_blk * * \details @@ -38,11 +38,31 @@ namespace gr { * On every fresh input byte, it starts reading on the LSB, and starts copying * to the LSB as well. * - * If a packet length tag is given, this block assumes a tagged stream. - * In this case, the tag with the packet length is updated accordingly. - * Also, the number of input bits is padded with zeros if the number of input - * bits is not an integer multiple of \p l, or bits are truncated from the input - * if \p align_output is set to true. + * When supplying a tag name, this block operates on tagged streams. + * In this case, it can happen that the input data or the output data + * becomes unaligned when k * input length is not equal to l * output length. + * In this case, the \p align_output parameter is used to decide which + * data packet to align. + * + * Usually, \p align_output is false for unpacking (k=8, l < 8) and false for + * reversing that. + * + * \section gr_blocks_repack_example Example + * + * Say you're tx'ing 8-PSK and therefore set k=8, l=3 on the transmit side + * before the modulator. Now assume you're transmitting a single byte of data. + * Your incoming tagged stream has length 1, the outgoing has length 3. However, + * the third item is actually only carrying 2 bits of relevant data, the bits + * do not align with the boundaries. So you set \p align_output = false, + * because the output can be unaligned. + * + * Now say you're doing the inverse: packing those three items into full + * bytes. How do you interpret those three bytes? Without this flag, + * you'd have to assume there's 9 relevant bits in there, so you'd end up + * with 2 bytes of output data. But in the packing case, you want the + * \b output to be aligned; all output bits must be useful. By asserting this flag, + * the packing algorithm tries to do this and in this case assumes that + * since we have alignment after 8 bits, the 9th can be discarded. */ class BLOCKS_API repack_bits_bb : virtual public tagged_stream_block { @@ -52,11 +72,11 @@ namespace gr { /*! * \param k Number of relevant bits on the input stream * \param l Number of relevant bits on the output stream - * \param len_tag_key If not empty, this is the key for the length tag. - * \param align_output If len_tag_key is given, this controls if the input + * \param tsb_tag_key If not empty, this is the key for the length tag. + * \param align_output If tsb_tag_key is given, this controls if the input * or the output is aligned. */ - static sptr make(int k, int l=8, const std::string &len_tag_key="", bool align_output=false); + static sptr make(int k, int l=8, const std::string &tsb_tag_key="", bool align_output=false); }; } // namespace blocks |