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AP_Baro: update MS5837-30BA compensation #29132

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Feb 3, 2025
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AP_Baro: update MS5837-30BA compensation #29132

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34 changes: 21 additions & 13 deletions libraries/AP_Baro/AP_Baro_MS5611.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -486,29 +486,37 @@ void AP_Baro_MS56XX::_calculate_5637()
// Calculate Temperature and compensated Pressure in real units (Celsius degrees*100, mbar*100).
void AP_Baro_MS56XX::_calculate_5837()
{
int32_t dT, TEMP;
int64_t OFF, SENS;
int32_t dT, TEMP, T2;
int64_t OFF, OFF2, SENS, SENS2;
int32_t raw_pressure = _D1;
int32_t raw_temperature = _D2;

// note that MS5837 has no compensation for temperatures below -15C in the datasheet

dT = raw_temperature - (((uint32_t)_cal_reg.c5) << 8);
dT = raw_temperature - ((uint32_t)_cal_reg.c5 << 8);
TEMP = 2000 + ((int64_t)dT * (int64_t)_cal_reg.c6) / 8388608;
OFF = (int64_t)_cal_reg.c2 * (int64_t)65536 + ((int64_t)_cal_reg.c4 * (int64_t)dT) / (int64_t)128;
SENS = (int64_t)_cal_reg.c1 * (int64_t)32768 + ((int64_t)_cal_reg.c3 * (int64_t)dT) / (int64_t)256;

int64_t aux = sq(TEMP - 2000);
if (TEMP < 2000) {
// second order temperature compensation when under 20 degrees C
int32_t T2 = ((int64_t)3 * ((int64_t)dT * (int64_t)dT) / (int64_t)8589934592);
int64_t aux = (TEMP - 2000) * (TEMP - 2000);
int64_t OFF2 = 3 * aux / 2;
int64_t SENS2 = 5 * aux / 8;
// second order "low temperature" compensation when under 20 degrees C
T2 = (int64_t)3 * sq((int64_t)dT) / (int64_t)8589934592;
OFF2 = 3 * aux / 2;
SENS2 = 5 * aux / 8;

TEMP = TEMP - T2;
OFF = OFF - OFF2;
SENS = SENS - SENS2;
if (TEMP < -1500) {
// "very low temperature" compensation, when under -15 degrees C
OFF2 += 7 * sq(TEMP+1500);
SENS2 += 4 * sq(TEMP+1500);
}
} else {
// "high temperature" compensation, when at or over 20 degrees C
T2 = (int64_t)2 * sq((int64_t)dT) / (int64_t)137438953472;
OFF2 = aux / 16;
SENS2 = 0;
}
TEMP = TEMP - T2;
OFF = OFF - OFF2;
SENS = SENS - SENS2;

int32_t pressure = ((int64_t)raw_pressure * SENS / (int64_t)2097152 - OFF) / (int64_t)8192;
pressure = pressure * 10; // MS5837 only reports to 0.1 mbar
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