165 lines
5.5 KiB
C++
165 lines
5.5 KiB
C++
/* -*- c++ -*- */
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/*
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* gr-satnogs: SatNOGS GNU Radio Out-Of-Tree Module
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*
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* Copyright (C) 2019, Libre Space Foundation <http://libre.space>
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef INCLUDED_SATNOGS_AX25_DECODER_H
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#define INCLUDED_SATNOGS_AX25_DECODER_H
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#include <satnogs/api.h>
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#include <satnogs/decoder.h>
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#include <gnuradio/digital/lfsr.h>
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#include <deque>
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namespace gr {
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namespace satnogs {
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/*!
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* \brief AX.25 decoder that supports the legacy hardware radios.
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*
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* This block takes as input a quadrature demodulated bit stream.
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* Each byte should contains only one bit of information at the LSB.
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*
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* The block will try to find an AX.25 frame. If the frame pass the
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* CRC check then a blob PMT message is produced at the message output
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* indicated with name 'out'. Otherwise if the frame did not pass the
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* CRC check or the size was invalid, a blob PMT message is generated at
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* the output port with the name 'fail'. This will help to recover at least
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* some bytes from a corrupted message.
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*
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* The block also supports destination callsign check. Only frames with
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* the right destination Callsign will be accepted. This feature can be
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* disabled using the promisc parameter.
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*
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* \ingroup satnogs
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*
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*/
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class SATNOGS_API ax25_decoder : public decoder {
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public:
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/**
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* The decoder take as input a quadrature demodulated bit stream.
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* Each byte should contains only one bit of information at the LSB.
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*
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* The decoder will try to find an AX.25 frame. If the frame pass the
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* CRC check then at the metadata the CRC_VALID option will be set to true,
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* otherwise to false. CRC invalid frames are meaningful because only one
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* bit of error can cause the entire frame to fail. This will help to recover
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* at least some bytes from a corrupted message.
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*
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* The decoder also supports destination callsign check. Only frames with
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* the right destination Callsign will be accepted. This feature can be
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* disabled using the promisc parameter.
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* @param addr the Callsign of the receiver
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* @param ssid the SSID of the receiver
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* @param promisc if set to yes, the Callsign check is disabled
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* @param descramble if set to yes, the data will be descrambled prior
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* decoding using the G3RUH self-synchronizing descrambler.
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* @param max_frame_len the maximum allowed frame length
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*
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* @return a shared pointer of the decoder instance
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*/
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static decoder::decoder_sptr
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make(const std::string &addr, uint8_t ssid, bool promisc = false,
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bool descramble = true, bool crc_check = true,
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size_t max_frame_len = 512);
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/**
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* The decoder take as input a quadrature demodulated bit stream.
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* Each byte should contains only one bit of information at the LSB.
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*
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* The decoder will try to find an AX.25 frame. If the frame pass the
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* CRC check then at the metadata the CRC_VALID option will be set to true,
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* otherwise to false. CRC invalid frames are meaningful because only one
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* bit of error can cause the entire frame to fail. This will help to recover
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* at least some bytes from a corrupted message.
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*
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* The decoder also supports destination callsign check. Only frames with
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* the right destination Callsign will be accepted. This feature can be
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* disabled using the promisc parameter.
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* @param addr the Callsign of the receiver
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* @param ssid the SSID of the receiver
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* @param promisc if set to yes, the Callsign check is disabled
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* @param descramble if set to yes, the data will be descrambled prior
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* decoding using the G3RUH self-synchronizing descrambler.
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* @param crc_check bypass the CRC check of the frame
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* @param max_frame_len the maximum allowed frame length
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*/
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ax25_decoder(const std::string &addr, uint8_t ssid, bool promisc = false,
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bool descramble = true, bool crc_check = true,
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size_t max_frame_len = 512);
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~ax25_decoder();
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decoder_status_t
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decode(const void *in, int len);
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void
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reset();
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private:
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typedef enum {
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NO_SYNC, IN_SYNC, DECODING
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} decoding_state_t;
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/**
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* If this flag is set, the decoder operates in promiscuous mode and
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* forwards all successfully decoded frames
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*/
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const bool d_promisc;
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const bool d_descramble;
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const bool d_crc_check;
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const size_t d_max_frame_len;
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decoding_state_t d_state;
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uint8_t d_shift_reg;
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uint8_t d_dec_b;
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uint8_t d_prev_bit_nrzi;
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size_t d_received_bytes;
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size_t d_decoded_bits;
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digital::lfsr d_lfsr;
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uint8_t *d_frame_buffer;
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std::deque<uint8_t> d_bitstream;
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size_t d_start_idx;
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uint64_t d_frame_start;
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uint64_t d_sample_cnt;
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void
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reset_state();
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void
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enter_sync_state();
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void
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enter_decoding_state();
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bool
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enter_frame_end(decoder_status_t &status);
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bool
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_decode(decoder_status_t &status);
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inline void
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decode_1b(uint8_t in);
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bool
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frame_check();
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};
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} // namespace satnogs
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} // namespace gr
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#endif /* INCLUDED_SATNOGS_AX25_DECODER_H */
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