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99 lines
2.6 KiB
99 lines
2.6 KiB
/*
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* Copyright (C) 2010,2012,2018 by Jonathan Naylor G4KLX
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* Copyright (C) 2021-2022 by Geoffrey Merck F4FXL / KC3FRA
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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 2 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, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <cstring>
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#include <cassert>
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#include <boost/algorithm/string.hpp>
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#include "GPSACollector.h"
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#include "StringUtils.h"
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#include "Log.h"
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const unsigned int APRS_CSUM_LENGTH = 4U;
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CGPSACollector::CGPSACollector() :
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CSentenceCollector(SLOW_DATA_TYPE_GPS, "$$CRC", '\x0D')
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{
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}
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bool CGPSACollector::isValidSentence(const std::string& sentence)
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{
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return isValidGPSA(sentence);
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}
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bool CGPSACollector::isValidGPSA(const std::string& gpsa)
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{
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if(gpsa.length() < 10U || !boost::starts_with(gpsa, "$$CRC"))
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return false;
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auto csum = calcCRC(gpsa);
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auto csumStr = CStringUtils::string_format("%04X", csum);
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auto expectedCsum = gpsa.substr(5U, APRS_CSUM_LENGTH);
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bool res = ::strcasecmp(csumStr.c_str(), expectedCsum.c_str()) == 0;
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return res;
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}
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unsigned int CGPSACollector::calcCRC(const std::string& gpsa)
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{
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unsigned int icomcrc = 0xFFFFU;
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auto length = gpsa.length();
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for (unsigned int j = 10U; j < length; j++) {
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unsigned char ch = (unsigned char)gpsa[j];
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for (unsigned int i = 0U; i < 8U; i++) {
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bool xorflag = (((icomcrc ^ ch) & 0x01U) == 0x01U);
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icomcrc >>= 1;
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if (xorflag)
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icomcrc ^= 0x8408U;
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ch >>= 1;
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}
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}
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return ~icomcrc & 0xFFFFU;
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}
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unsigned int CGPSACollector::getDataInt(unsigned char * data, unsigned int length)
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{
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if(data == nullptr || length == 0U || getSentence().empty())
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return 0U;
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auto aprsFrame = getSentence();
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if(aprsFrame.length() < 11U)
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return 0U;
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aprsFrame = aprsFrame.substr(10).append("\r\n");
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auto aprsFrameLen = aprsFrame.length();
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if(length < aprsFrameLen) {
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CLog::logDebug("Not enough space to copy GPS-A APRS frame");
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return 0U;
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}
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for(unsigned int i = 0U; i < aprsFrameLen; i++){
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data[i] = aprsFrame[i];
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}
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return aprsFrameLen;
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} |