File content as of revision 6:40ac13ef7290:

#include "GurvIMU.h"
#include "MPU6050.h"
#include "mbed.h"

#define  M_PI 3.1415926535897932384626433832795

#define twoKpDef    (2.0f * 2.0f)   // 2 * proportional gain
#define twoKiDef    (2.0f * 0.5f)   // 2 * integral gain


GurvIMU::GurvIMU()
{
    //MPU
    mpu = MPU6050(0x69); //0x69 = MPU6050 I2C ADDRESS

    // Variable definitions
    q0 = 1.0f, q1 = 0.0f, q2 = 0.0f, q3 = 0.0f;  // quaternion of sensor frame relative to auxiliary frame
    twoKp = twoKpDef;                                            // 2 * proportional gain (Kp)
    twoKi = twoKiDef;                                            // 2 * integral gain (Ki)
    integralFBx = 0.0f,  integralFBy = 0.0f, integralFBz = 0.0f; // integral error terms scaled by Ki
    cycle_nb = 0;
    timer_us.start();    
}

//Function definitions

void GurvIMU::getValues(float * values)
{
    int16_t accgyroval[6];
    mpu.getMotion6(&accgyroval[0], &accgyroval[1], &accgyroval[2], &accgyroval[3], &accgyroval[4], &accgyroval[5]);
    for(int i = 0; i<3; i++) values[i] = (float) accgyroval[i];
    for(int i = 3; i<6; i++) values[i] = (accgyroval[i]-offset[i]) * (M_PI / 180) / 16.4f;
}

void GurvIMU::getVerticalAcceleration(float av)
{
    float values[6];
    float q[4]; // quaternion
    float g_x, g_y, g_z; // estimated gravity direction
    getQ(q);
  
    g_x = 2 * (q[1]*q[3] - q[0]*q[2]);
    g_y = 2 * (q[0]*q[1] + q[2]*q[3]);
    g_z = q[0]*q[0] - q[1]*q[1] - q[2]*q[2] + q[3]*q[3];   
    
    getValues(values);
    av = g_x*values[0]+g_y*values[1]+g_z*values[2]-offset[2];
}
     

void GurvIMU::getOffset(void)
{
    int sample_nb = 50;
    float values[6];
    for(int i=0; i<6 ; i++) offset[i] = 0;
    for(int i=0; i<sample_nb; i++) {
        getValues(values);
        for(int j=0; j<6; j++) offset[j]+=values[j];        
    }     
    for(int j=0; j<6; j++) offset[j]/=sample_nb;
}


void GurvIMU::AHRS_update(float gx, float gy, float gz, float ax, float ay, float az)
{
    float recipNorm;
    float halfvx, halfvy, halfvz;
    float halfex, halfey, halfez;
    float qa, qb, qc;
    
    dt_us=timer_us.read_us();
    sample_freq = 1.0 / ((dt_us) / 1000000.0);
    timer_us.reset();
    
    // Compute feedback only if accelerometer measurement valid (avoids NaN in accelerometer normalisation)
    if(!((ax == 0.0f) && (ay == 0.0f) && (az == 0.0f))) {

        // Normalise accelerometer measurement
        recipNorm = invSqrt(ax * ax + ay * ay + az * az);
        ax *= recipNorm;
        ay *= recipNorm;
        az *= recipNorm;        

        // Estimated direction of gravity
        halfvx = q1 * q3 - q0 * q2;
        halfvy = q0 * q1 + q2 * q3;
        halfvz = q0 * q0 - 0.5f + q3 * q3;
    
        // Error is sum of cross product between estimated and measured direction of gravity
        halfex = (ay * halfvz - az * halfvy);
        halfey = (az * halfvx - ax * halfvz);
        halfez = (ax * halfvy - ay * halfvx);

        // Compute and apply integral feedback if enabled
        if(twoKi > 0.0f) {
            integralFBx += twoKi * halfex * (1.0f / sample_freq);    // integral error scaled by Ki
            integralFBy += twoKi * halfey * (1.0f / sample_freq);
            integralFBz += twoKi * halfez * (1.0f / sample_freq);
            gx += integralFBx;  // apply integral feedback
            gy += integralFBy;
            gz += integralFBz;
        }
        else {
            integralFBx = 0.0f; // prevent integral windup
            integralFBy = 0.0f;
            integralFBz = 0.0f;
        }

        // Apply proportional feedback
        gx += twoKp * halfex;
        gy += twoKp * halfey;
        gz += twoKp * halfez;
    }
    
    // Integrate rate of change of quaternion
    gx *= (0.5f * (1.0f / sample_freq));     // pre-multiply common factors
    gy *= (0.5f * (1.0f / sample_freq));
    gz *= (0.5f * (1.0f / sample_freq));
    qa = q0;
    qb = q1;
    qc = q2;
    q0 += (-qb * gx - qc * gy - q3 * gz);
    q1 += (qa * gx + qc * gz - q3 * gy);
    q2 += (qa * gy - qb * gz + q3 * gx);
    q3 += (qa * gz + qb * gy - qc * gx); 
    
    // Normalise quaternion
    recipNorm = invSqrt(q0 * q0 + q1 * q1 + q2 * q2 + q3 * q3);
    q0 *= recipNorm;
    q1 *= recipNorm;
    q2 *= recipNorm;
    q3 *= recipNorm;
}

void GurvIMU::getQ(float * q) {
  float val[6];
  getValues(val);
  //while(cycle_nb < 1000){
    AHRS_update(val[3], val[4], val[5], val[0], val[1], val[2]);
  //cycle_nb++;}

  q[0] = q0;
  q[1] = q1;
  q[2] = q2;
  q[3] = q3;
  
}

void GurvIMU::getYawPitchRollRad(float * ypr) {
  float q[4]; // quaternion
  float g_x, g_y, g_z; // estimated gravity direction
  getQ(q);
  
  g_x = 2 * (q[1]*q[3] - q[0]*q[2]);
  g_y = 2 * (q[0]*q[1] + q[2]*q[3]);
  g_z = q[0]*q[0] - q[1]*q[1] - q[2]*q[2] + q[3]*q[3];
  
  ypr[0] = atan2(2 * q[1] * q[2] - 2 * q[0] * q[3], 2 * q[0]*q[0] + 2 * q[1] * q[1] - 1);
  ypr[1] = atan(g_x * invSqrt(g_y*g_y + g_z*g_z));
  ypr[2] = atan(g_y * invSqrt(g_x*g_x + g_z*g_z));
}

void GurvIMU::init()
{
    mpu.initialize();
    mpu.setI2CMasterModeEnabled(0);
    mpu.setI2CBypassEnabled(1);
    mpu.setFullScaleGyroRange(MPU6050_GYRO_FS_2000);
    getOffset();
    wait(0.005);
}


float invSqrt(float number)
{
    volatile long i;
    volatile float x, y;
    volatile const float f = 1.5F;

    x = number * 0.5F;
    y = number;
    i = * ( long * ) &y;
    i = 0x5f375a86 - ( i >> 1 );
    y = * ( float * ) &i;
    y = y * ( f - ( x * y * y ) );
    return y;
}