File content as of revision 21:c95c6b9e9377:

// Library for our MMA8452Q 3-axis accelerometer
// Based on the MMA8452Q Arduino Library by Jim Lindblom (SparkFun Electronics)

#include "mbed.h"
#include "MMA8452Q.h"

// Constructor
MMA8452Q::MMA8452Q(PinName sda, PinName scl, int addr) : m_i2c(sda, scl), m_addr(addr)
{
    // Initialize members
    scale = DEFAULT_FSR;    
}

// Destructor
MMA8452Q::~MMA8452Q()
{

}

// Initialization
bool MMA8452Q::init()
{
    // Check to make sure the chip's ID matches the factory ID
    uint8_t c = readRegister(REG_WHO_AM_I);
    if( c != FACTORY_ID ) {
        return false;
    }

    // Set default scale and data rate
    standby();
    setScale(DEFAULT_FSR);
    setODR(DEFAULT_ODR);
    active();

    return true;
}

// Set the full-scale range for x, y, and z data
void MMA8452Q::setScale(uint8_t fsr)
{
    uint8_t config = readRegister(REG_XYZ_DATA_CFG);
    scale = fsr;
    config &= 0xFC;                     // Mask out FSR bits
    fsr = fsr >> 2;                     // Trick to translate scale to FSR bits
    fsr &= 0x03;                        // Mask out acceptable FSRs
    config |= fsr;                      // Write FSR bits to config byte
    writeRegister(REG_XYZ_DATA_CFG, config);              // Write config back to register
}

// Set the Output Data Rate
void MMA8452Q::setODR(uint8_t odr)
{
    uint8_t ctrl = readRegister(REG_CTRL_REG1);
    ctrl &= 0xCF;                       // Mask out data rate bits
    odr &= 0x07;                        // Mask out acceptable ODRs
    ctrl |= (odr << 3);                 // Write ODR bits to control byte
    writeRegister(REG_CTRL_REG1, ctrl); // Write control back to register
}

// Set accelerometer into standby mode
void MMA8452Q::standby()
{
    uint8_t c = readRegister(REG_CTRL_REG1);
    c &= ~(0x01);                       // Clear bit 0 to go into standby
    writeRegister(REG_CTRL_REG1, c);    // Write back to CONTROL register
}

// Set accelerometer into active mode
void MMA8452Q::active()
{
    uint8_t c = readRegister(REG_CTRL_REG1);
    c |= 0x01;                          // Set bit 0 to go into active mode
    writeRegister(REG_CTRL_REG1, c);    // Write back to CONTROL register
}

// Read X registers
float MMA8452Q::readX()
{
    int16_t x = 0;
    float cx = 0;

    // Read MSB and LSB from X registers
    x = readRegister(OUT_X_MSB);
    x = x << 8;
    x |= readRegister(OUT_X_LSB);
    x = x >> 4;

    // Calculate human readable X
    cx = (float)x / (float)2048 * (float)(scale);

    return cx;
}

// Read Y registers
float MMA8452Q::readY()
{
    int16_t y = 0;
    float cy = 0;

    // Read MSB and LSB from Y registers
    y = readRegister(OUT_Y_MSB);
    y = y << 8;
    y |= readRegister(OUT_Y_LSB);
    y = y >> 4;

    // Calculate human readable Y
    cy = (float)y / (float)2048 * (float)(scale);

    return cy;
}

// Read Z registers
float MMA8452Q::readZ()
{
    int16_t z = 0;
    float cz = 0;

    // Read MSB and LSB from Z registers
    z = readRegister(OUT_Z_MSB);
    z = z << 8;
    z |= readRegister(OUT_Z_LSB);
    z = z >> 4;

    // Calculate human readable Z
    cz = (float)z / (float)2048 * (float)(scale);

    return cz;
}

// Raw read register over I2C
uint8_t MMA8452Q::readRegister(uint8_t reg)
{
    uint8_t dev_addr;
    uint8_t data;

    // I2C address are bits [6..1] in the transmitted byte, so we shift by 1
    dev_addr = m_addr << 1;

    // Write device address with a trailing 'write' bit
    m_i2c.start();
    m_i2c.write(dev_addr & 0xFE);

    // Write register address
    m_i2c.write(reg);

    // Write a start bit and device address with a trailing 'read' bit
    m_i2c.start();
    m_i2c.write(dev_addr | 0x01);

    // Read single byte from I2C device
    data = m_i2c.read(0);
    m_i2c.stop();

    return data;
}

// Raw write data to a register over I2C    
void MMA8452Q::writeRegister(uint8_t reg, uint8_t data)
{
    uint8_t dev_addr;

    // I2C address are bits [6..1] in the transmitted byte, so we shift by 1
    dev_addr = m_addr << 1;

    // Write device address with a trailing 'write' bit
    m_i2c.start();
    m_i2c.write(dev_addr & 0xFE);

    // Write register address
    m_i2c.write(reg);

    // Write the data to the register
    m_i2c.write(data);
    m_i2c.stop();
}