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Update MeterW1therm.cpp to catch erroneous temperature values #610

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Update MeterW1therm.cpp to catch erroneous temperature values #610

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7c33d0f
Update MeterW1therm.cpp
h-eff Nov 8, 2023
160df13
MeterW1therm: move quirks checking code into check_quirks()
r00t- Jan 5, 2024
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44 changes: 43 additions & 1 deletion src/protocols/MeterW1therm.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -83,8 +83,50 @@ bool MeterW1therm::W1sysHWif::readTemp(const std::string &device, double &value)
print(log_debug, "CRC not ok from %s (%s)", "w1t", dev.c_str(), buffer);
} else {
// crc ok
// now parse t=<value>
// now check for other errors:
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this comment is misplaced...
the result of fgets() is not only for error-checking, it's also what the reading is parsed from.

if (fgets(buffer, 100, fp)) { // e.g. 07 01 55 00 7f ff 0c 10 18 t=16437

///// Start of new code: Catch DS18B20-specific errors. /////
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maybe put this into a function to isolate it, instead of surrounding with comments?
private check_quirks(device,buffer){...
if (!check_quirks(device,buffer)) return false;

/// For reference: https://github.com/cpetrich/counterfeit_DS18B20
/// Check byte 6 of scratchpad to recognize error readings.
/// Genuine DS18B20 compute byte 6 as the difference from
/// 00001111 & <byte 0> to 00010000; most clones always use 0x0c.
/// Genuine DS18B20 are still in the 00000xxxxxxx address range
/// as of 2023; clones are not.

// Check for sensor family DS18B20 via device == "28*":
if (device[0]=='2' && device[1]=='8') {
if (!strncmp(buffer,"00 00 00 00 00 00 00 00 00",26)) {
// According to DS18B20 datasheet, this scratchpad-reading MUST be wrong.
print(log_debug, "only zeroes from %s (%s), "
"the 1wire-bus is probably unstable", "w1t", dev.c_str(), buffer);
return false;
}
// if (buffer == "?? ?? ?? ?? ?? ?? 0c*"), maybe an error has happened:
if (buffer[18]=='0' && buffer[19]=='c') {
// only do this handling for genuine DS18B20, e.g. device="28-0000*":
if (device[3]=='0' && buffer[4]=='0' && buffer[5]=='0' && buffer[6]=='0') {
// if (buffer == "50 05*"), 0x0550/16 = 85 degrees Celsius
if (!strncmp(buffer,"50 05",5)) {
// Sensor returned default boot-up value; did not complete temperature conversion.
print(log_debug, "85 degree error from %s (%s), "
"the 1wire-bus is probably unstable", "w1t", dev.c_str(), buffer);
return false;
}
// (if buffer == "ff 07*"), 0x07ff/16 = 127.9375 degrees Celsius
if (!strncmp(buffer,"ff 07",5)) {
// Sensor returned code for insufficient power during temperature conversion.
// This can happen in parasitic 2-wire circuits with floating Vcc pins.
print(log_debug, "insufficient power error from %s (%s), "
"maybe Vcc was left floating", "w1t", dev.c_str(), buffer);
return false;
}
}
}
}
///// End of new code. /////

// now parse t=<value>
char *pos = strstr(buffer, "t=");
if (pos) {
pos += 2;
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