JeeLabs Café

//>>> The latest version of this code can be found at https://github.com/jcw/ !!

// Port library interface to BMP085 sensors connected via I2C

// 2009-02-17 <jcw@equi4.com> http://opensource.org/licenses/mit-license.php

// $Id$

// computation and algorithm taken from the Bosch Sensortec BMP085 data sheet

// (IIRC, I had to cast to an int32_t for the b3 calculation to work above 25C)

#include <Ports.h>

#include "PortsBMP085.h"

#include <WProgram.h>

uint8_t BMP085::startMeas(uint8_t type) const {

    send();

    write(0xF4);

    write(type == TEMP ? 0x2E : 0x34 | (oss << 6));

    stop();

    return oss == 0 ? 5 : oss == 1 ? 8 : oss == 2 ? 14 : 26;

}

int32_t BMP085::getResult(uint8_t type) {

    readFromReg(0xF6);

    if (type == TEMP)

        meas[TEMP] = readWord(1);

    else {

        meas[PRES] = readWord(0);

        meas[PRES] <<= oss;

        meas[PRES] |= read(1) >> (8-oss);

    }

    return meas[type];

}

void BMP085::getCalibData() {

    readFromReg(0xAA);

    ac1 = readWord(0);

    ac2 = readWord(0);

    ac3 = readWord(0);

    ac4 = readWord(0);

    ac5 = readWord(0);

    ac6 = readWord(0);

    b1 = readWord(0);

    b2 = readWord(0);

    mb = readWord(0);

    mc = readWord(0);

    md = readWord(1);

}

void BMP085::calculate(int16_t& tval, int32_t& pval) const {

    int32_t ut = meas[TEMP], up = meas[PRES];

    int32_t x1, x2, x3, b3, b5, b6, p;

    uint32_t b4, b7;

    x1 = (ut - ac6) * ac5 >> 15;

    x2 = ((int32_t) mc << 11) / (x1 + md);

    b5 = x1 + x2;

    tval = (b5 + 8) >> 4;

    b6 = b5 - 4000;

    x1 = (b2 * (b6 * b6 >> 12)) >> 11;

    x2 = ac2 * b6 >> 11;

    x3 = x1 + x2;

    b3 = ((((int32_t) ac1 * 4 + x3) << oss) + 2) >> 2;

    x1 = ac3 * b6 >> 13;

    x2 = (b1 * (b6 * b6 >> 12)) >> 16;

    x3 = ((x1 + x2) + 2) >> 2;

    b4 = (ac4 * (uint32_t) (x3 + 32768)) >> 15;

    b7 = ((uint32_t) up - b3) * (50000 >> oss);

    p = b7 < 0x80000000 ? (b7 * 2) / b4 : (b7 / b4) * 2;

    x1 = (p >> 8) * (p >> 8);

    x1 = (x1 * 3038) >> 16;

    x2 = (-7357 * p) >> 16;

    pval = p + ((x1 + x2 + 3791) >> 4);

}