File content as of revision 2:39cdefe3c9f2:

/*
 * LSM303DLH Test program
 * @tosihisa
 */

#include "mbed.h"
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif

Serial debug(USBTX,USBRX);

I2C LSM303DLH(p28, p27);

const int addr_acc = 0x30;
const int addr_mag = 0x3c;

enum REG_ADDRS {
    /* --- Mag --- */
    CRA_REG_M   = 0x00,
    CRB_REG_M   = 0x01,
    MR_REG_M    = 0x02,
    OUT_X_M     = 0x03,
    OUT_Y_M     = 0x05,
    OUT_Z_M     = 0x07,
    /* --- Acc --- */
    CTRL_REG1_A = 0x20,
    CTRL_REG4_A = 0x23,
    OUT_X_A     = 0x28,
    OUT_Y_A     = 0x2A,
    OUT_Z_A     = 0x2C,
};

bool write_reg(int addr_i2c,int addr_reg, char v)
{
    char data[2] = {addr_reg, v}; 
    return LSM303DLH.write(addr_i2c, data, 2) == 0;
}

bool read_reg(int addr_i2c,int addr_reg, char *v)
{
    char data = addr_reg; 
    if ((LSM303DLH.write(addr_i2c, &data, 1) == 0) && (LSM303DLH.read(addr_i2c, &data, 1) == 0)){
        *v = data;
        return true;
    }
    return false;
}

bool read_reg_short(int addr_i2c,int addr_reg, short *v)
{
    char *pv = (char *)v;
    read_reg(addr_i2c,addr_reg+0,pv+1);
    return read_reg(addr_i2c,addr_reg+1,pv+0);
}

int main() {
    char reg_v;
    bool result;
    short a_x,a_y,a_z;
    short m_x,m_y,m_z;
    double m_deg;

    debug.format(8,Serial::None,1);
    debug.baud(115200);
    debug.printf("LSM303DLH Test\x0d\x0a");

    /* --- acc --- */
    reg_v = 0;
    result = read_reg(addr_acc,CTRL_REG1_A,&reg_v);
    debug.printf("(%s) CTRL_REG1_A=[0x%02X]\x0d\x0a",(result) ? "OK" : "NG",reg_v);

    reg_v = 0;
    result = read_reg(addr_mag,CRA_REG_M,&reg_v);
    debug.printf("(%s) CRA_REG_M=[0x%02X]\x0d\x0a",(result) ? "OK" : "NG",reg_v);

    reg_v = 0;
    reg_v |= 0x01 << 5;     /* Normal mode  */
    reg_v |= 0x07;          /* X/Y/Z axis enable. */
    result = write_reg(addr_acc,CTRL_REG1_A,reg_v);
    reg_v = 0;
    result = read_reg(addr_acc,CTRL_REG1_A,&reg_v);
    debug.printf("(%s) CTRL_REG1_A=[0x%02X]\x0d\x0a",(result) ? "OK" : "NG",reg_v);

    reg_v = 0;
    reg_v |= 0x01 << 6;     /* 1: data MSB @ lower address */
    reg_v |= 0x01 << 4;     /* +/- 4g */
    result = write_reg(addr_acc,CTRL_REG4_A,reg_v);

    /* -- mag --- */
    reg_v = 0;
    reg_v |= 0x04 << 2;     /* Minimum data output rate = 15Hz */
    result = write_reg(addr_mag,CRA_REG_M,reg_v);

    reg_v = 0;
    //reg_v |= 0x01 << 5;     /* +-1.3Gauss */
    reg_v |= 0x07 << 5;     /* +-8.1Gauss */
    result = write_reg(addr_mag,CRB_REG_M,reg_v);

    reg_v = 0;              /* Continuous-conversion mode */
    result = write_reg(addr_mag,MR_REG_M,reg_v);

    while(1) {
        read_reg_short(addr_acc,OUT_X_A,&a_x);
        read_reg_short(addr_acc,OUT_Y_A,&a_y);
        read_reg_short(addr_acc,OUT_Z_A,&a_z);
        read_reg_short(addr_mag,OUT_X_M,&m_x);
        read_reg_short(addr_mag,OUT_Y_M,&m_y);
        read_reg_short(addr_mag,OUT_Z_M,&m_z);
        m_deg = (atan2((double)(m_x),(double)(m_y)) * 180) / M_PI;
        if(m_deg < 0){
            m_deg = m_deg * -1.0;
        } else {
            m_deg = 360.0 - m_deg;
        }

        debug.printf("ACC:X=%-7d,Y=%-7d,Z=%-7d ",a_x,a_y,a_z);
        debug.printf("MAG:X=%-7d,Y=%-7d,Z=%-7d DEG=%f\x0d\x0a",m_x,m_y,m_z,m_deg);
        wait(0.1);
    }
}