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TPMS: Validate checksum for the OOK 8k4 Schrader variant.

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This commit is contained in:
Jared Boone 2016-06-02 22:22:22 -07:00
parent 4734790518
commit 9628815da7
1 changed files with 33 additions and 5 deletions
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38
firmware/common/tpms_packet.cpp
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@ -80,11 +80,39 @@ Optional<Reading> Packet::reading_ook_8k192_schrader() const {
}
Optional<Reading> Packet::reading_ook_8k4_schrader() const {
return Reading {
Reading::Type::GMC_96,
reader_.read(20, 32),
Pressure { static_cast<int>(reader_.read(52, 8)) }
};
/*
* Preamble: 01*40
* System ID: 01100101, ??*20 (not really sure what this data is)
* ID: 32 Manchester symbols
* Value: 8 Manchester symbols (temperature?)
* Value: 8 Manchester symbols (pressure?)
* Checksum: 8 Manchester symbols (uint8_t sum of bytes starting with system ID)
*/
/* NOTE: First four bits of packet are consumed in preamble detection.
* Those bits assumed to be 0b0100", which may not be entirely true...
*/
constexpr uint8_t first_nibble = 0x4;
const auto system_id = (first_nibble << 20) | reader_.read(0, 20);
const auto id = reader_.read(20, 32);
const auto value_0 = reader_.read(52, 8);
const auto value_1 = reader_.read(60, 8);
const auto checksum = reader_.read(68, 8);
uint8_t checksum_calculated = (first_nibble << 4) | reader_.read(0, 4);
for(size_t i=4; i<68; i+=8) {
checksum_calculated += reader_.read(i, 8);
}
if( checksum_calculated == checksum ) {
return Reading {
Reading::Type::GMC_96,
id,
Pressure { static_cast<int>(value_1) * 4 / 3 },
Temperature { static_cast<int>(value_0) - 50 }
};
} else {
return { };
}
}
Optional<Reading> Packet::reading() const {