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64 lines
2.3 KiB
64 lines
2.3 KiB
/*
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* Copyright (C) 2010 by Jonathan Naylor, G4KLX
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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; version 2 of the License.
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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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#ifndef SlowDataEncoder_H
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#define SlowDataEncoder_H
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#include "HeaderData.h"
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#include <string>
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/*
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* Encodes D-Star slow data into the 3-byte data field of each DV frame.
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*
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* Two independent payloads can be encoded:
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* Header — a copy of the radio header, split across 8 tagged 6-byte blocks
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* with a CCITT-16 checksum appended. Used by the repeater to
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* re-broadcast the header to late-joining receivers.
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* Text — a 20-character free-text message split across 4 tagged blocks.
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*
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* Each block is 6 bytes: 1-byte type/sequence tag followed by 5 payload bytes.
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* getHeaderData() and getTextData() each return 3 bytes (half a block) per
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* call, cycling back to the start after all blocks have been emitted.
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*
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* Before writing to the DV frame the 3 bytes are XOR-scrambled with the
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* repeating key SCRAMBLER_BYTE1/SCRAMBLER_BYTE2/SCRAMBLER_BYTE3. sync()
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* resets the read pointer to the beginning of the sequence so that the
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* encoder is aligned with the data-sync frame position in the stream.
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*/
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class CSlowDataEncoder {
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public:
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CSlowDataEncoder();
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~CSlowDataEncoder();
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void setHeaderData(const CHeaderData& header);
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void setTextData(const std::string& text);
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// Returns the next 3 scrambled bytes of the header slow-data sequence.
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void getHeaderData(unsigned char* data);
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// Returns the next 3 scrambled bytes of the text slow-data sequence.
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void getTextData(unsigned char* data);
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void reset();
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// Resets read pointers to the start of the sequence (call on each sync frame).
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void sync();
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private:
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unsigned char* m_headerData; // Pre-packed, unscrambled header slow-data bytes.
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unsigned char* m_textData; // Pre-packed, unscrambled text slow-data bytes.
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unsigned int m_headerPtr; // Current read offset into m_headerData.
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unsigned int m_textPtr; // Current read offset into m_textData.
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};
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#endif
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