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ms5837.cpp
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ms5837.cpp
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#ifndef MS5837_CPP
#define MS5837_CPP
#include "ms5837.h"
#include "api/Common.h"
#include "logger.h"
#include "samd21/include/component/tc.h"
#define MS5837_ADDR 0x76
#define MS5837_RESET 0x1E
#define MS5837_ADC_READ 0x00
#define MS5837_PROM_READ 0xA0
#define MS5837_CONVERT_D1_8192 0x4A
#define MS5837_CONVERT_D1_4096 0x48
#define MS5837_CONVERT_D2_8192 0x5A
#define MS5837_CONVERT_D2_4096 0x58
bool MS5837Atomic::init() {
int32_t TEMP = 0;
int32_t P = 0;
ready = false;
delay(10);
// Reset the MS5837, per datasheet
Wire.beginTransmission(MS5837_ADDR);
Wire.write(MS5837_RESET);
Wire.endTransmission();
// Wait for reset to complete
delay(30);
// Read calibration values and CRC
for (uint8_t i = 0; i < 7; i++) {
Wire.beginTransmission(MS5837_ADDR);
Wire.write(MS5837_PROM_READ + i * 2);
Wire.endTransmission();
Wire.requestFrom(MS5837_ADDR, 2);
C[i] = (Wire.read() << 8) | Wire.read();
}
// Verify that data is correct with CRC
uint8_t crcRead = C[0] >> 12;
uint8_t crcCalculated = crc4(C);
if (crcCalculated == crcRead) {
delay(30);
state = requestD1;
return true; // Initialization success
}
return false; // CRC fail
}
void MS5837Atomic::loop() {
switch (state) {
case requestD1:
// Request D1
Wire.beginTransmission(MS5837_ADDR);
Wire.write(MS5837_CONVERT_D1_4096);
Wire.endTransmission();
state = waitD1;
time = micros();
break;
case requestD2:
// Request D2
Wire.beginTransmission(MS5837_ADDR);
Wire.write(MS5837_CONVERT_D2_4096);
Wire.endTransmission();
state = waitD2;
time = micros();
break;
case waitD1:
if (micros() - time < 20000ull) {
break;
}
state = acquireD1;
break;
case waitD2:
if (micros() - time < 20000ull) {
break;
}
state = acquireD2;
break;
case acquireD1:
Wire.beginTransmission(MS5837_ADDR);
Wire.write(MS5837_ADC_READ);
Wire.endTransmission();
Wire.requestFrom(MS5837_ADDR, 3);
D1 = 0;
D1 = Wire.read();
D1 = (D1 << 8) | Wire.read();
D1 = (D1 << 8) | Wire.read();
state = requestD2;
break;
case acquireD2:
Wire.beginTransmission(MS5837_ADDR);
Wire.write(MS5837_ADC_READ);
Wire.endTransmission();
Wire.requestFrom(MS5837_ADDR, 3);
D2 = 0;
D2 = Wire.read();
D2 = (D2 << 8) | Wire.read();
D2 = (D2 << 8) | Wire.read();
state = convertDD;
break;
case convertDD:
// Terms called
dT = D2 - uint32_t(C[5]) * 256l;
SENS = int64_t(C[1]) * 32768l + (int64_t(C[3]) * dT) / 256l;
OFF = int64_t(C[2]) * 65536l + (int64_t(C[4]) * dT) / 128l;
P = (D1 * SENS / (2097152l) - OFF) / (8192l);
// Temp conversion
TEMP = 2000l + int64_t(dT) * C[6] / 8388608LL;
// Second order compensation
if ((TEMP / 100) < 20) { // Low temp
Ti = (3 * int64_t(dT) * int64_t(dT)) / (8589934592LL);
OFFi = (3 * (TEMP - 2000) * (TEMP - 2000)) / 2;
SENSi = (5 * (TEMP - 2000) * (TEMP - 2000)) / 8;
if ((TEMP / 100) < -15) { // Very low temp
OFFi = OFFi + 7 * (TEMP + 1500l) * (TEMP + 1500l);
SENSi = SENSi + 4 * (TEMP + 1500l) * (TEMP + 1500l);
}
} else if ((TEMP / 100) >= 20) { // High temp
Ti = 2 * (dT * dT) / (137438953472LL);
OFFi = (1 * (TEMP - 2000) * (TEMP - 2000)) / 16;
SENSi = 0;
}
OFF2 = OFF - OFFi; // Calculate pressure and temp second order
SENS2 = SENS - SENSi;
TEMP = (TEMP - Ti);
P = (((D1 * SENS2) / 2097152l - OFF2) / 8192l);
state = requestD1;
ready = true;
}
}
uint8_t MS5837Atomic::crc4(uint16_t n_prom[]) {
uint16_t n_rem = 0;
n_prom[0] = ((n_prom[0]) & 0x0FFF);
n_prom[7] = 0;
for (uint8_t i = 0; i < 16; i++) {
if (i % 2 == 1) {
n_rem ^= (uint16_t)((n_prom[i >> 1]) & 0x00FF);
} else {
n_rem ^= (uint16_t)(n_prom[i >> 1] >> 8);
}
for (uint8_t n_bit = 8; n_bit > 0; n_bit--) {
if (n_rem & 0x8000) {
n_rem = (n_rem << 1) ^ 0x3000;
} else {
n_rem = (n_rem << 1);
}
}
}
n_rem = ((n_rem >> 12) & 0x000F);
return n_rem ^ 0x00;
}
#endif