File content as of revision 4:41bd7f360406:

#include "FXAS21000.h"

const uint16_t uint14_max = 0x3FFF;
void static inline normalize_14bits(int16_t &x)
{
    x = ((x) > (uint14_max/2)) ? (x - uint14_max) : (x);
}

static int16_t dummy_int16_t = 0;
static float dummy_float = 0.0f;

FXAS21000::FXAS21000(I2C &i2c, uint8_t addr)
{
    _i2c = &i2c;
    _addr = addr;
    // activate the peripheral
    uint8_t data[2];
    _i2c->frequency(400000);
    
    /*
     * | ZR_COND | RST | ST | DR[2:0] | Active | Ready |
     * |    0    |  0  | 0  |   010   |   0    |   0   |
     * ZR_COND - Offset compensation calibration
     * RST - Reset of the device
     * DR - Sampling rate 50Hz (010)
     * Active - Device is measuring
     * Ready - Device is ready to measure but not taking samples
     */
    data[0] = FXAS21000_CTRL_REG1;
    data[1] = 0x08; // 00001000
    writeRegs(data, 2);
    
    /*
     * CTRL_REG0 can be only modified in Standby or Read modes
     * | 0 | 0 | SPIW | SEL[1:0] | HPF_EN | FS[1:0] |
     * | 0 | 0 |  0   |    11    |   0    |    11   |
     * SPIW - SPI bus mode, zero for four wires
     * SEL - High pass filter frequency cut-off
     * HPF_EN - Enable high-pass filter
     * FS - Full scale ranges +-1600 dps when 00
     */
    data[0] = FXAS21000_CTRL_REG0;
    data[1] = 0x1B;
    writeRegs(data, 2);
    
    /*
     * Same a first write but Active bit gets enabled
     */
    data[0] = FXAS21000_CTRL_REG1;
    data[1] = 0x0A;
    writeRegs(data, 2);
}

FXAS21000::~FXAS21000()
{
    _i2c = 0;
    _addr = 0;
}

void FXAS21000::readRegs(uint8_t addr, uint8_t *data, uint32_t len) const
{
    uint8_t t[1] = {addr};
    _i2c->write(_addr, (char *)t, sizeof(t), true);
    _i2c->read(_addr, (char *)data, len);
}

uint8_t FXAS21000::whoAmI() const
{
    uint8_t who_am_i = 0;
    readRegs(FXAS21000_WHOAMI, &who_am_i, sizeof(who_am_i));
    return who_am_i;
}

void FXAS21000::writeRegs(uint8_t * data, uint32_t len) const
{
    _i2c->write(_addr, (char *)data, len);
}

int16_t FXAS21000::getSensorAxis(uint8_t addr) const
{
    uint8_t res[2];
    readRegs(addr, res, sizeof(res));
    return static_cast<int16_t>((res[0] << 8) | res[1]);
}

void FXAS21000::enable(void) const
{
    uint8_t data[2];
    readRegs(FXAS21000_CTRL_REG1, &data[1], 1);
    data[1] |= 0x0A; // 00000010 to turn on Active bit
    data[0] = FXAS21000_CTRL_REG1;
    writeRegs(data, sizeof(data));
}

void FXAS21000::disable(void) const
{
    uint8_t data[2];
    readRegs(FXAS21000_CTRL_REG1, &data[1], 1);
    data[1] &= 0xFD; // 11111101 to turn off Active bit
    data[0] = FXAS21000_CTRL_REG1;
    writeRegs(data, sizeof(data));
}

uint32_t FXAS21000::dataReady(void) const
{
    uint8_t stat = 0;
    readRegs(FXAS21000_STATUS, &stat, 1);
    stat &= 0x88; // 10001000 to zero out other bits
    if(stat == 0x88) { // If 7th and 4th bit are positive then return 1
        stat = 1;
    } else {
        stat = 0;    // Otherwise no data ready, return 0
    }
    return (uint32_t)stat;
}

// OK
uint32_t FXAS21000::sampleRate(uint32_t frequency) const
{
    return(50); // for now sample rate is fixed at 50Hz
}

int16_t FXAS21000Gyroscpe::getX(int16_t &x = dummy_int16_t) const
{
    x = getSensorAxis(FXAS21000_OUT_X_MSB) >> 2;
    normalize_14bits(x);
    return x;
}

int16_t FXAS21000Gyroscpe::getY(int16_t &y = dummy_int16_t) const
{
    y = getSensorAxis(FXAS21000_OUT_Y_MSB) >> 2;
    normalize_14bits(y);
    return y;
}

int16_t FXAS21000Gyroscpe::getZ(int16_t &z = dummy_int16_t) const
{
    z = getSensorAxis(FXAS21000_OUT_Z_MSB) >> 2;
    normalize_14bits(z);
    return z;
}

float FXAS21000Gyroscpe::getX(float &x = dummy_float) const
{
    int16_t val = getSensorAxis(FXAS21000_OUT_X_MSB) >> 2;
    normalize_14bits(val);
    x = val / 4096.0f;
    return x;
}

float FXAS21000Gyroscpe::getY(float &y = dummy_float) const
{
    int16_t val = getSensorAxis(FXAS21000_OUT_Y_MSB) >> 2;
    normalize_14bits(val);
    y = val / 4096.0f;
    return y;
}

float FXAS21000Gyroscpe::getZ(float &z = dummy_float) const
{
    int16_t val = getSensorAxis(FXAS21000_OUT_Z_MSB) >> 2;
    normalize_14bits(val);
    z = val / 4096.0f;
    return z;
}

void FXAS21000Gyroscpe::getAxis(motion_data_counts_t &xyz) const
{
    xyz.x = getSensorAxis(FXAS21000_OUT_X_MSB) >> 2;
    xyz.y = getSensorAxis(FXAS21000_OUT_Y_MSB) >> 2;
    xyz.z = getSensorAxis(FXAS21000_OUT_Z_MSB) >> 2;
    normalize_14bits(xyz.x);
    normalize_14bits(xyz.y);
    normalize_14bits(xyz.z);
}

void FXAS21000Gyroscpe::getAxis(motion_data_units_t &xyz) const
{
    motion_data_counts_t _xyz;
    FXAS21000Gyroscpe::getAxis(_xyz);
    xyz.x = _xyz.x / 4096.0f;
    xyz.y = _xyz.y / 4096.0f;
    xyz.z = _xyz.z / 4096.0f;
}