mirror of
https://github.com/gnss-sdr/gnss-sdr
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111 lines
3.7 KiB
C
111 lines
3.7 KiB
C
/*!
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* \file cnav_msg.h
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* \brief Utilities for CNAV message manipulation of the libswiftnav library
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* \author Valeri Atamaniouk <valeri@swift-nav.com>
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*
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* -----------------------------------------------------------------------------
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* GNSS-SDR is a Global Navigation Satellite System software-defined receiver.
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* This file is part of GNSS-SDR.
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*
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* This file was originally borrowed from libswiftnav
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* <https://github.com/swift-nav/libswiftnav>,
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* a portable C library implementing GNSS related functions and algorithms,
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* and then modified by J. Arribas and C. Fernandez
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*
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* Copyright (C) 2016 Swift Navigation Inc.
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* Contact: Valeri Atamaniouk <valeri@swift-nav.com>
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*
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* SPDX-License-Identifier: LGPL-3.0-only
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*
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*/
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#ifndef GNSS_SDR_CNAV_MSG_H
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#define GNSS_SDR_CNAV_MSG_H
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#include "fec.h"
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#include "swift_common.h"
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#include <limits.h>
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#include <stdbool.h>
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#include <stdint.h>
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#include <stdlib.h>
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/** \addtogroup Telemetry_Decoder
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* \{ */
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/** \addtogroup Telemetry_Decoder_libswiftcnav
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* \{ */
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/** Size of the Viterbi decoder history. */
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#define GPS_L2_V27_HISTORY_LENGTH_BITS 64
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/** Bits to accumulate before decoding starts. */
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#define GPS_L2C_V27_INIT_BITS (32)
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/** Bits to decode at a time. */
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#define GPS_L2C_V27_DECODE_BITS (32)
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/** Bits in decoder tail. We ignore them. */
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#define GPS_L2C_V27_DELAY_BITS (32)
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/**
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* GPS CNAV message container.
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*
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* @sa cnav_msg_decoder_add_symbol
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*/
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typedef struct
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{
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uint8_t prn; /**< SV PRN. 0..31 */
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uint8_t msg_id; /**< Message id. 0..31 */
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uint32_t tow; /**< GPS ToW in 6-second units. Multiply to 6 to get seconds. */
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bool alert; /**< CNAV message alert flag */
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uint8_t raw_msg[GPS_L2C_V27_DECODE_BITS + GPS_L2C_V27_DELAY_BITS]; /**< RAW MSG for GNSS-SDR */
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} cnav_msg_t;
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/**
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* GPS CNAV decoder component.
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* This component controls symbol decoding string.
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*
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* @sa cnav_msg_decoder_t
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*/
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typedef struct
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{
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v27_t dec; /**< Viterbi block decoder object */
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v27_decision_t decisions[GPS_L2_V27_HISTORY_LENGTH_BITS];
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/**< Decision graph */
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unsigned char symbols[(GPS_L2C_V27_INIT_BITS + GPS_L2C_V27_DECODE_BITS) * 2];
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/**< Symbol buffer */
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size_t n_symbols; /**< Count of symbols in the symbol buffer */
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unsigned char decoded[GPS_L2C_V27_DECODE_BITS + GPS_L2C_V27_DELAY_BITS];
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/**< Decode buffer */
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size_t n_decoded; /**< Number of bits in the decode buffer */
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bool preamble_seen; /**< When true, the decode buffer is aligned on
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* preamble. */
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bool invert; /**< When true, indicates the bits are inverted */
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bool message_lock; /**< When true, indicates the message boundary
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* is found. */
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bool crc_ok; /**< Flag that the last message had good CRC */
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size_t n_crc_fail; /**< Counter for CRC failures */
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bool init; /**< Initial state flag. When true, initial bits
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* do not produce output. */
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} cnav_v27_part_t;
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/**
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* GPS CNAV message lock and decoder object.
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*
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* Decoder uses two Viterbi decoder objects to ensure the lock is acquired when
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* the input symbol phase is not known.
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*/
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typedef struct
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{
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cnav_v27_part_t part1; /**< Decoder for odd symbol pairs */
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cnav_v27_part_t part2; /**< Decoder for even symbol pairs */
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} cnav_msg_decoder_t;
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const v27_poly_t *cnav_msg_decoder_get_poly(void);
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void cnav_msg_decoder_init(cnav_msg_decoder_t *dec);
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bool cnav_msg_decoder_add_symbol(cnav_msg_decoder_t *dec,
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unsigned char symbol,
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cnav_msg_t *msg,
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uint32_t *delay);
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/** \} */
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/** \} */
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#endif /* GNSS_SDR_CNAV_MSG_H_ */
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