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100 lines
3.8 KiB
C++
100 lines
3.8 KiB
C++
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///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2024 Jon Beniston, M7RCE <jon@beniston.com> //
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// Copyright (C) 2018 Eric Reuter //
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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 as 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 V3 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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#include "endoftrainpacket.h"
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#include "util/crc.h"
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// Reverse order of bits
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static quint32 reverse(quint32 x)
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{
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x = (((x & 0xaaaaaaaa) >> 1) | ((x & 0x55555555) << 1));
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x = (((x & 0xcccccccc) >> 2) | ((x & 0x33333333) << 2));
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x = (((x & 0xf0f0f0f0) >> 4) | ((x & 0x0f0f0f0f) << 4));
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x = (((x & 0xff00ff00) >> 8) | ((x & 0x00ff00ff) << 8));
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return((x >> 16) | (x << 16));
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}
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// Reverse order of bits, for specified number of bits
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static quint32 reverseBits(quint32 x, int bits)
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{
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return reverse(x) >> (32-bits);
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}
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// Decode end-of-train packet
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// Defined in:
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// AAR MSRP (Manual of Standards and Recommended Practices) - Section K Part II Locomotive Electronics and Train Consist System Architecture - S-9152 End of Train Communication
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// but not readily available, so see:
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// https://patents.google.com/patent/US5374015A/en
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// https://rdso.indianrailways.gov.in/uploads/files/TC0156_15_02_2022.pdf
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bool EndOfTrainPacket::decode(const QByteArray& packet)
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{
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//qDebug() << packet.toHex();
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if (packet.size() != 8) {
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return false;
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}
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m_chainingBits = packet[0] & 0x3;
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m_batteryCondition = (packet[0] >> 2) & 0x3;
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m_type = (packet[0] >> 4) & 0x7;
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m_address = ((packet[2] & 0xff) << 9) | ((packet[1] & 0xff) << 1) | ((packet[0] >> 7) & 0x1);
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m_pressure = packet[3] & 0x7f;
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m_discretionary = (packet[3] >> 7) & 1;
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m_batteryCharge = packet[4] & 0x7f;
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m_valveCircuitStatus = (packet[4] >> 7) & 1;
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m_confirmation = packet[5] & 1;
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m_turbine = (packet[5] >> 1) & 1;
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m_motion = (packet[5] >> 2) & 1;
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m_markerLightBatteryCondition = (packet[5] >> 3) & 1;
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m_markerLightStatus = (packet[5] >> 4) & 1;
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// Calculate and compare CRC
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crc crc18(18, 0x39A0F, true, 0, 0x2b770);
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// 45-bits are protected
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crc18.calculate(packet[5] & 0x1f, 5);
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crc18.calculate(packet[4] & 0xff, 8);
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crc18.calculate(packet[3] & 0xff, 8);
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crc18.calculate(packet[2] & 0xff, 8);
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crc18.calculate(packet[1] & 0xff, 8);
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crc18.calculate(packet[0] & 0xff, 8);
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m_crc = ((packet[7] & 0xff) << 11) | ((packet[6] & 0xff) << 3) | ((packet[5] >> 5) & 0x7);
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m_crcCalculated = reverseBits(crc18.get(), 18);
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m_crcValid = m_crc == m_crcCalculated;
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if (crc18.get() != m_crc) {
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qDebug() << "CRC Mismatch: " << QString::number(crc18.get(), 16) << QString::number(m_crc, 16);
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}
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m_dataHex = QString(packet.toHex());
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return m_crcValid;
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}
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