portapack-mayhem/firmware/common/tpms_packet.cpp

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/*
* Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
*
* This file is part of PortaPack.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2, or (at your option)
* any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#include "tpms_packet.hpp"
#include "crc.hpp"
namespace tpms {
Timestamp Packet::received_at() const {
return packet_.timestamp();
}
ManchesterFormatted Packet::symbols_formatted() const {
return format_manchester(decoder_);
}
Optional<Reading> Packet::reading(const SignalType signal_type) const {
if( signal_type == SignalType::FLM ) {
const auto length = crc_valid_length();
switch(length) {
case 64:
return Reading {
Reading::Type::FLM_64,
reader_.read(0, 32),
Pressure { static_cast<int>(reader_.read(32, 8)) * 4 / 3 },
Temperature { static_cast<int>(reader_.read(40, 8) & 0x7f) - 50 }
};
case 72:
return Reading {
Reading::Type::FLM_72,
reader_.read(0, 32),
Pressure { static_cast<int>(reader_.read(40, 8)) * 4 / 3 },
Temperature { static_cast<int>(reader_.read(48, 8)) - 50 }
};
case 80:
return Reading {
Reading::Type::FLM_80,
reader_.read(8, 32),
Pressure { static_cast<int>(reader_.read(48, 8)) * 4 / 3 },
Temperature { static_cast<int>(reader_.read(56, 8)) - 50 }
};
default:
return { };
}
}
if( signal_type == SignalType::Subaru ) {
return Reading {
Reading::Type::SUB_35,
reader_.read(3, 25),
Pressure { static_cast<int>(reader_.read(28, 8)) }
};
}
if( signal_type == SignalType::GMC ) {
return Reading {
Reading::Type::GMC_96,
reader_.read(20, 32),
Pressure { static_cast<int>(reader_.read(52, 8)) }
};
}
return { };
}
size_t Packet::crc_valid_length() const {
constexpr uint32_t checksum_bytes = 0b1111111;
constexpr uint32_t crc_72_bytes = 0b111111111;
constexpr uint32_t crc_80_bytes = 0b1111111110;
std::array<uint8_t, 10> bytes;
for(size_t i=0; i<bytes.size(); i++) {
bytes[i] = reader_.read(i * 8, 8);
}
uint32_t checksum = 0;
CRC<8> crc_72 { 0x01, 0x00 };
CRC<8> crc_80 { 0x01, 0x00 };
for(size_t i=0; i<bytes.size(); i++) {
const uint32_t byte_mask = 1 << i;
const auto byte = bytes[i];
if( checksum_bytes & byte_mask ) {
checksum += byte;
}
if( crc_72_bytes & byte_mask ) {
crc_72.process_byte(byte);
}
if( crc_80_bytes & byte_mask ) {
crc_80.process_byte(byte);
}
}
if( crc_80.checksum() == 0 ) {
return 80;
} else if( crc_72.checksum() == 0 ) {
return 72;
} else if( (checksum & 0xff) == bytes[7] ) {
return 64;
} else {
return 0;
}
}
} /* namespace tpms */