File content as of revision 2:79d0d565c3af:

/**
@file BMP180.cpp

@brief Member functions implementations

*/
#include "mbed.h"
#include "BMP180.h"

BMP180::BMP180(PinName sdaPin, PinName sclPin)
{
    i2c = new I2C(sdaPin,sclPin); // create new I2C instance and initialise
    i2c->frequency(400000);       // I2C Fast Mode - 400kHz
    leds = new BusOut(LED4,LED3,LED2,LED1);
}

Measurement BMP180::readValues()
{
    // algorithm for taking measurement is taken from datasheet
    int32_t UT = readUncompensatedTemperatureValue();
    int32_t UP = readUncompensatedPressureValue();
    // once you have the uncompensated T and P, you can calculate the true T and P
    // using the equations from the datasheet
    int32_t T = calcTrueTemperature(UT);
    int32_t P = calcTruePressure(UP);

    Measurement measurement;
    measurement.temperature = T*0.1;  // scaled by 0.1 C
    measurement.pressure = P*0.01;    // Put pressure in mb

    return measurement;
}

int32_t BMP180::readUncompensatedTemperatureValue()
{
    // from algorithm in datasheet - p15
    sendByteToRegister(0x2E,0xF4);
    wait_ms(5);  // 4.5 ms delay for OSS = 1
    char MSB = readByteFromRegister(0xF6);
    char LSB = readByteFromRegister(0xF7);
    // combine in 16-bit value
    int UT = (MSB << 8) | LSB;   
    //int32_t UT = 27898;  // test data from datasheet
    //printf("\n\nUT = %d\n",UT);
    return UT;
}

int32_t BMP180::readUncompensatedPressureValue()
{
    // from datasheet
    char byte = 0x34 + (oss << 6);
    sendByteToRegister(byte,0xF4);
    wait_ms(8);  // 7.5 ms delay for OSS = 1

    char MSB = readByteFromRegister(0xF6);
    char LSB = readByteFromRegister(0xF7);
    char XLSB = readByteFromRegister(0xF7);
    // just do 16-bit, not 19-bit
    //int UP = (MSB << 16 | LSB << 8 | XLSB) >> (8 - oss);
    int UP = (MSB << 16 | LSB << 8) >> (8 - oss);
    
    //int32_t UP = 23843;   // test data from datasheet
    //printf("UP = %d\n",UP);
    return UP;
}

int32_t BMP180::calcTrueTemperature(int32_t UT)
{
    // equations from data sheet
    X1 = ((UT - calibration.AC6)*calibration.AC5) >> 15;
    X2 = (calibration.MC << 11) / (X1 + calibration.MD);
    B5 = X1 + X2;
    int32_t T = (B5 + 8) >> 4;
    //printf("X1=%d\nX2=%d\nB5=%d\n*****\nT=%d\n******\n",X1,X2,B5,T);
    return T;
}

int32_t BMP180::calcTruePressure(int32_t UP)
{
    // equations from data sheet
    B6 = B5 - 4000;
    //printf("\n********\nB6=%d\n",B6);
    X1 = (calibration.B2 * ((B6*B6) >> 12))>>11;
    X2 = (calibration.AC2*B6)>>11;
    X3 = X1 + X2;
    B3 = (((calibration.AC1*4 + X3) << oss)+2)/4;
    //printf("X1=%d\nX2=%d\nX3=%d\nB3=%d\n",X1,X2,X3,B3);
    X1 = (calibration.AC3*B6)>>13;
    X2 = (calibration.B1*((B6*B6)>>12))>>16;
    X3 = ((X1+X2)+2)/4;
    B4 = (calibration.AC4*(uint32_t)(X3+32768))>>15;
    //printf("X1=%d\nX2=%d\nX3=%d\nB4=%u\n",X1,X2,X3,B4);
    B7 = ((uint32_t)UP - B3)*(50000>>oss);
    //printf("B7=%u\n",B7);
    int32_t P;
    if (B7 < 0x80000000)
        P = (B7*2)/B4;
    else
        P = (B7/B4)*2;
    //printf("P=%d\n",P);
    X1 = (P>>8)*(P>>8);
    //printf("X1=%d\n",X1);
    X1 = (X1*3038)>>16;
    //printf("X1=%d\n",X1);
    X2 = (-7357*P)>>16;
    //printf("X2=%d\n",X2);
    P = P + (X1+X2+3791)/16;
    //printf("P=%d\n",P);
    
    return P;

}

// configure the barometer
void BMP180::init()
{
    i2c->frequency(400000); // set Fast Mode I2C frequency

    char data = readByteFromRegister(ID_REG);  // Section 4 - datasheet
    if (data != 0x55) { // if correct ID not found, hang and flash error message
        error();
    }
    
    readCalibrationData();
    oss = 1;  // standard power oversampling setting
    //oss = 0;  // used when testing data sheet example

}

// Reads factory calibrated data
void BMP180::readCalibrationData()
{
    
    char eeprom[22];

    readBytesFromRegister(EEPROM_REG_ADD,22,eeprom);
    // store calibration data in structure
    calibration.AC1 = (int16_t) (eeprom[0] << 8) | eeprom[1];
    calibration.AC2 = (int16_t) (eeprom[2] << 8) | eeprom[3];
    calibration.AC3 = (int16_t) (eeprom[4] << 8) | eeprom[5];
    calibration.AC4 = (uint16_t) (eeprom[6] << 8) | eeprom[7];
    calibration.AC5 = (uint16_t) (eeprom[8] << 8) | eeprom[9];
    calibration.AC6 = (uint16_t) (eeprom[10] << 8) | eeprom[11];
    calibration.B1 = (int16_t) (eeprom[12] << 8) | eeprom[13];
    calibration.B2 = (int16_t) (eeprom[14] << 8) | eeprom[15];
    calibration.MB = (int16_t) (eeprom[16] << 8) | eeprom[17];
    calibration.MC = (int16_t) (eeprom[18] << 8) | eeprom[19];
    calibration.MD = (int16_t) (eeprom[20] << 8) | eeprom[21];
    
    // test data from data sheet
    //calibration.AC1 = 408;calibration.AC2 = -72;calibration.AC3 = -14383;calibration.AC4 = 32741;calibration.AC5 = 32757;
    //calibration.AC6 = 23153;calibration.B1 = 6190;calibration.B2 = 4;calibration.MB = -32768;calibration.MC = -8711;calibration.MD = 2868;
    //printf("AC1=%d\nAC2=%d\nAC3=%d\nAC4=%u\nAC5=%u\nAC6=%u\nB1=%d\nB2=%d\nMB=%d\nMC=%d\nMD=%d\n",
    // calibration.AC1,calibration.AC2,calibration.AC3,calibration.AC4,calibration.AC5,calibration.AC6,
    // calibration.B1,calibration.B2,calibration.MB,calibration.MC,calibration.MD);
}


// reads a byte from a specific register
char BMP180::readByteFromRegister(char reg)
{
    int nack = i2c->write(BMP180_W_ADDRESS,&reg,1,true);  // send the register address to the slave
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

    char rx;
    nack = i2c->read(BMP180_W_ADDRESS,&rx,1);  // read a byte from the register and store in buffer
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

    return rx;
}

// reads a series of bytes, starting from a specific register
void BMP180::readBytesFromRegister(char reg,int numberOfBytes,char bytes[])
{
    int nack = i2c->write(BMP180_W_ADDRESS,&reg,1,true);  // send the slave write address and the configuration register address

    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

    nack = i2c->read(BMP180_W_ADDRESS,bytes,numberOfBytes);  // read bytes
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

}

// sends a byte to a specific register
void BMP180::sendByteToRegister(char byte,char reg)
{
    char data[2];
    data[0] = reg;
    data[1] = byte;
    // send the register address, followed by the data
    int nack = i2c->write(BMP180_W_ADDRESS,data,2);
    if (nack)
        error();  // if we don't receive acknowledgement, flash error message

}

void BMP180::error()
{
    while(1) {
        leds->write(15);
        wait(0.1);
        leds->write(0);
        wait(0.1);
    }
}