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| 1 | +/**************************************************************************** |
| 2 | + * |
| 3 | + * Copyright (c) 2025 PX4 Development Team. All rights reserved. |
| 4 | + * |
| 5 | + * Redistribution and use in source and binary forms, with or without |
| 6 | + * modification, are permitted provided that the following conditions |
| 7 | + * are met: |
| 8 | + * |
| 9 | + * 1. Redistributions of source code must retain the above copyright |
| 10 | + * notice, this list of conditions and the following disclaimer. |
| 11 | + * 2. Redistributions in binary form must reproduce the above copyright |
| 12 | + * notice, this list of conditions and the following disclaimer in |
| 13 | + * the documentation and/or other materials provided with the |
| 14 | + * distribution. |
| 15 | + * 3. Neither the name PX4 nor the names of its contributors may be |
| 16 | + * used to endorse or promote products derived from this software |
| 17 | + * without specific prior written permission. |
| 18 | + * |
| 19 | + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
| 20 | + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
| 21 | + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS |
| 22 | + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE |
| 23 | + * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| 24 | + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, |
| 25 | + * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS |
| 26 | + * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED |
| 27 | + * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| 28 | + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN |
| 29 | + * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| 30 | + * POSSIBILITY OF SUCH DAMAGE. |
| 31 | + * |
| 32 | + ****************************************************************************/ |
| 33 | + |
| 34 | +/** |
| 35 | + * @file rtcm.cpp |
| 36 | + * |
| 37 | + * RTCM3 protocol parsing implementation. |
| 38 | + */ |
| 39 | + |
| 40 | +#include "rtcm.h" |
| 41 | +#include <cstring> |
| 42 | + |
| 43 | +namespace gnss |
| 44 | +{ |
| 45 | + |
| 46 | +uint32_t rtcm3_crc24q(const uint8_t *data, size_t len) |
| 47 | +{ |
| 48 | + uint32_t crc = 0; |
| 49 | + |
| 50 | + for (size_t i = 0; i < len; i++) { |
| 51 | + crc ^= static_cast<uint32_t>(data[i]) << 16; |
| 52 | + |
| 53 | + for (int j = 0; j < 8; j++) { |
| 54 | + crc <<= 1; |
| 55 | + |
| 56 | + if (crc & 0x1000000) { |
| 57 | + crc ^= RTCM3_CRC24Q_POLY; |
| 58 | + } |
| 59 | + } |
| 60 | + } |
| 61 | + |
| 62 | + return crc & 0xFFFFFF; |
| 63 | +} |
| 64 | + |
| 65 | +size_t Rtcm3Parser::addData(const uint8_t *data, size_t len) |
| 66 | +{ |
| 67 | + size_t space_available = BUFFER_SIZE - _buffer_len; |
| 68 | + size_t to_copy = (len < space_available) ? len : space_available; |
| 69 | + |
| 70 | + if (to_copy > 0) { |
| 71 | + memcpy(&_buffer[_buffer_len], data, to_copy); |
| 72 | + _buffer_len += to_copy; |
| 73 | + } |
| 74 | + |
| 75 | + return to_copy; |
| 76 | +} |
| 77 | + |
| 78 | +const uint8_t *Rtcm3Parser::getNextMessage(size_t *out_len) |
| 79 | +{ |
| 80 | + while (_buffer_len > 0) { |
| 81 | + int to_drop = 0; |
| 82 | + |
| 83 | + // Find preamble |
| 84 | + for (size_t i = 0; i < _buffer_len; i++) { |
| 85 | + if (_buffer[i] == RTCM3_PREAMBLE) { |
| 86 | + break; |
| 87 | + } |
| 88 | + |
| 89 | + to_drop++; |
| 90 | + } |
| 91 | + |
| 92 | + // Drop everything not being the preamble |
| 93 | + if (to_drop > 0) { |
| 94 | + _bytes_discarded += to_drop; |
| 95 | + discardBytes(to_drop); |
| 96 | + } |
| 97 | + |
| 98 | + // Need at least header to check length |
| 99 | + if (_buffer_len < RTCM3_HEADER_LEN) { |
| 100 | + return nullptr; |
| 101 | + } |
| 102 | + |
| 103 | + size_t payload_len = rtcm3_payload_length(_buffer); |
| 104 | + |
| 105 | + if (payload_len > RTCM3_MAX_PAYLOAD_LEN) { |
| 106 | + // Invalid length - not a valid frame, discard preamble |
| 107 | + _bytes_discarded++; |
| 108 | + discardBytes(1); |
| 109 | + continue; |
| 110 | + } |
| 111 | + |
| 112 | + size_t frame_len = RTCM3_HEADER_LEN + payload_len + RTCM3_CRC_LEN; |
| 113 | + |
| 114 | + // Check if we have the complete frame |
| 115 | + if (_buffer_len < frame_len) { |
| 116 | + return nullptr; |
| 117 | + } |
| 118 | + |
| 119 | + uint32_t calculated_crc = rtcm3_crc24q(_buffer, RTCM3_HEADER_LEN + payload_len); |
| 120 | + uint32_t received_crc = (static_cast<uint32_t>(_buffer[frame_len - 3]) << 16) | |
| 121 | + (static_cast<uint32_t>(_buffer[frame_len - 2]) << 8) | |
| 122 | + _buffer[frame_len - 1]; |
| 123 | + |
| 124 | + if (calculated_crc != received_crc) { |
| 125 | + _crc_errors++; |
| 126 | + discardBytes(1); |
| 127 | + continue; |
| 128 | + } |
| 129 | + |
| 130 | + *out_len = frame_len; |
| 131 | + return _buffer; |
| 132 | + } |
| 133 | + |
| 134 | + return nullptr; |
| 135 | +} |
| 136 | + |
| 137 | +void Rtcm3Parser::consumeMessage(size_t len) |
| 138 | +{ |
| 139 | + discardBytes(len); |
| 140 | + _messages_parsed++; |
| 141 | + _total_frame_bytes += len; |
| 142 | +} |
| 143 | + |
| 144 | +void Rtcm3Parser::discardBytes(size_t count) |
| 145 | +{ |
| 146 | + if (count >= _buffer_len) { |
| 147 | + _buffer_len = 0; |
| 148 | + |
| 149 | + } else { |
| 150 | + memmove(_buffer, &_buffer[count], _buffer_len - count); |
| 151 | + _buffer_len -= count; |
| 152 | + } |
| 153 | +} |
| 154 | + |
| 155 | +} // namespace gnss |
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