File content as of revision 2:1052b1b97cc2:

#include "mbed.h"
#include <math.h>
#include "LSM303.h"

#define ACCELE_SCALE 2  // accelerometer full-scale, should be 2

I2C i2c(P0_5, P0_4);

int LSM303::setup()
{
#if 1 //set to 0 when calibrating
    m_max.x = 462;
    m_max.y = 416;
    m_max.z = 439;
    m_min.x = -645;
    m_min.y = -647;
    m_min.z = -589;
#else 
    m_max.x = 1;
    m_max.y = 1;
    m_max.z = 1;
    m_min.x = 0;
    m_min.y = 0;
    m_min.z = 0;
#endif
    LSM303_write(0x00, CTRL_REG4_A);
    LSM303_write(MAG_SCALE_1_3, CRB_REG_M); //magnetic scale = +/-1.3Gauss
    LSM303_write(0x00, MR_REG_M);  // 0x00 = continouous conversion mode

    return 1; //success
}
int LSM303::testAcc()
{
    if (i2c.write(LSM303_ACC, NULL, 0) ==0) return LSM303_ACC;
    return 255;
}

int LSM303::testMag()
{
    if (i2c.write(LSM303_MAG, NULL, 0) ==0)
        if (LSM303_read(LSM303_WHO_AM_I_M)==0x3C) {
            return LSM303_WHO_AM_I_M;
        } else {
            return LSM303_MAG;
        }

    return 255;
}

float LSM303::getTiltHeading()
{
    //shift and scale
    a.x = a.x / 32768 * ACCELE_SCALE;
    a.y = a.y / 32768 * ACCELE_SCALE;
    a.z = a.z + 950;
    a.z = a.z / 32768 * ACCELE_SCALE;

    m.x = (m.x - m_min.x) / (m_max.x - m_min.x) * 2 - 1.0;
    m.y = (m.y - m_min.y) / (m_max.y - m_min.y) * 2 - 1.0;
    m.z = (m.z - m_min.z) / (m_max.z - m_min.z) * 2 - 1.0;

    vector_normalize(&a);
    vector_normalize(&m);
    //see appendix A in app note AN3192
    pitch = asin(-a.x);
    roll = asin(a.y/cos(pitch));
    float heading = 0;
    float xh = m.x * cos(pitch) + m.z * sin(pitch);
    float yh = m.x * sin(roll) * sin(pitch) + m.y * cos(roll) - m.z * sin(roll) * cos(pitch);
    //float zh = -m.x * cos(roll) * sin(pitch) + m.y * sin(roll) + m.z * cos(roll) * cos(pitch);
    heading = 180 * atan2(yh, xh)/PI;
    if (heading < 0) heading += 360;
    return heading;
}

void LSM303::vector_cross( const Plane *a,const Plane *b, Plane *out )
{
    out->x = a->y*b->z - a->z*b->y;
    out->y = a->z*b->x - a->x*b->z;
    out->z = a->x*b->y - a->y*b->x;
}

float LSM303::vector_dot( const Plane *a,const Plane *b )
{
    return a->x*b->x+a->y*b->y+a->z*b->z;
}

void LSM303::vector_normalize( Plane *a )
{
    float mag = sqrt(vector_dot(a,a));
    a->x /= mag;
    a->y /= mag;
    a->z /= mag;
}

int LSM303::getLSM303_accel()
{
    char data[1] = { OUT_X_L_A | (1<<7)};
    char out[6] = {0,0,0,0,0,0};
    i2c.write( LSM303_ACC, data,1);
    i2c.read( LSM303_ACC, out, 6);

    a.x = short( (((short)out[1]) << 8) | out[0] );
    a.y = short( (((short)out[3]) << 8) | out[2] );
    a.z = short( (((short)out[5]) << 8) | out[4] );
    return  0;
}

void LSM303::getLSM303_mag()
{
    char data[1] = { OUT_X_H_M };
    char out[6];

    i2c.write( LSM303_MAG, data, 1 );
    i2c.read( LSM303_MAG, out, 6 );
    // DLM, DLHC: register address for Z comes before Y
    m.x = short( out[0] << 8 | out[1] );
    m.y = short( out[4] << 8 | out[5] );
    m.z= short( out[2] << 8 | out[3] );
}

int LSM303::LSM303_read(int address)
{
    if (address >= 0x20) {
        _i2c_address = LSM303_ACC;
    } else {
        _i2c_address = LSM303_MAG;
    }

    char value[1];

    char data[1] = { address };
    i2c.write( _i2c_address, data, 1 );
    i2c.read( _i2c_address, value, 1 );
    return value[0];
}

int LSM303::LSM303_write(int data, int address)
{
    if (address >= 0x20) {
        _i2c_address = LSM303_ACC;
    } else {
        _i2c_address = LSM303_MAG;
    }

    char out[2] = { address, data };
    i2c.write( _i2c_address, out, 2 );
    return 0;
}