mirror of
https://github.com/SatDump/SatDump
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132 lines
4.9 KiB
C++
132 lines
4.9 KiB
C++
/* -*- c++ -*- */
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/*
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* Copyright 2013-2014 Free Software Foundation, Inc.
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*
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* This file is part of GNU Radio
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*
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* SPDX-License-Identifier: GPL-3.0-or-later
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*
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*/
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#pragma once
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#include "cc_common.h"
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#include "generic_decoder.h"
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#include <map>
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#include <string>
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namespace fec
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{
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namespace code
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{
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typedef void (*conv_kernel)(unsigned char *Y,
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unsigned char *X,
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unsigned char *syms,
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unsigned char *dec,
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unsigned int framebits,
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unsigned int excess,
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unsigned char *Branchtab);
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/*!
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* \brief Convolutional Code Decoding class.
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* \ingroup error_coding_blk
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*
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* \details
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* This class performs convolutional decoding via the Viterbi
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* algorithm. While it is set up to take variable values for K,
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* rate, and the polynomials, currently, the block is only
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* capable of handling the following settings:
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*
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* \li K = 7
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* \li rate = 1/2 (given as 2 to the constructor)
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* \li polynomials = [109, 79]
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*
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* This is the well-known convolutional part of the Voyager code
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* implemented in the CCSDS encoder.
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*
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* The intent of having this FECAPI code classes fully
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* parameterizable is to eventually allow it to take on generic
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* settings, much like the cc_encoder class where the CCSDS
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* settings would be a highly-optimized version of this.
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*
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* The decoder is set up with a number of bits per frame in the
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* constructor. When not being used in a tagged stream mode,
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* this encoder will only process frames of the length provided
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* here. If used in a tagged stream block, this setting becomes
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* the maximum allowable frame size that the block may process.
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*
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* The \p mode is a cc_mode_t that specifies how the convolutional
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* encoder will behave and under what conditions.
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*
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* \li 'CC_STREAMING': mode expects an uninterrupted flow of
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* samples into the encoder, and the output stream is
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* continually encoded. This mode is the only mode for this
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* decoder that has a history requirement because it requires
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* rate*(K-1) bits more to finish the decoding properly. This
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* mode does not work with any deployments that do not allow
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* history.
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*
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* \li 'CC_TERMINATED': is a mode designed for packet-based
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* systems. This mode adds rate*(k-1) bits to the output as a
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* way to help flush the decoder.
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*
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* \li 'CC_TAILBITING': is another packet-based method. Instead of
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* adding bits onto the end of the packet, this mode will
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* continue the code between the payloads of packets by
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* pre-initializing the state of the new packet based on the
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* state of the last packet for (k-1) bits.
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*
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* \li 'CC_TRUNCATED': a truncated code always resets the registers
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* to the \p start_state between frames.
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*
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* A common convolutional encoder uses K=7, Rate=1/2,
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* Polynomials=[109, 79]. This is the Voyager code from NASA:
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* \li 109: b(1101101) --> 1 + x + x^3 + x^4 + x^6
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* \li 79: b(1001111) --> 1 + x^3 + x^4 + x^5 + x^6
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*/
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class cc_decoder : virtual public generic_decoder
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{
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public:
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/*!
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* Build a convolutional code decoding FEC API object.
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*
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* \param frame_size Number of bits per frame. If using in the
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* tagged stream style, this is the maximum allowable
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* number of bits per frame.
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* \param k Constraint length (K) of the encoder.
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* \param rate Inverse of the coder's rate
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* (rate=2 means 2 output bits per 1 input).
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* \param polys Vector of polynomials as integers.
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* \param start_state Initialization state of the shift register.
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* \param end_state Ending state of the shift register.
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* \param mode cc_mode_t mode of the encoding.
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* \param padded true if the encoded frame is padded
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* to the nearest byte.
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*/
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static generic_decoder::sptr make(int frame_size,
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int k,
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int rate,
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std::vector<int> polys,
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int start_state = 0,
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int end_state = -1,
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cc_mode_t mode = CC_STREAMING,
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bool padded = false);
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/*!
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* Sets the uncoded frame size to \p frame_size. If \p
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* frame_size is greater than the value given to the
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* constructor, the frame size will be capped by that initial
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* value and this function will return false. Otherwise, it
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* returns true.
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*/
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bool set_frame_size(unsigned int frame_size) override = 0;
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/*!
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* Returns the coding rate of this encoder.
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*/
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double rate() override = 0;
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};
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} /* namespace code */
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} /* namespace fec */
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