IMU.cpp

#include "Arduino.h"
#include "config.h"
#include "def.h"
#include "types.h"
#include "MultiWii.h"
#include "IMU.h"
#include "Sensors.h"

void getEstimatedAttitude();

void computeIMU () {
  uint8_t axis;
  static int16_t gyroADCprevious[3] = {0,0,0};
  static int16_t gyroADCinter[3];

  //we separate the 2 situations because reading gyro values with a gyro only setup can be acchieved at a higher rate
  //gyro+nunchuk: we must wait for a quite high delay betwwen 2 reads to get both WM+ and Nunchuk data. It works with 3ms
  //gyro only: the delay to read 2 consecutive values can be reduced to only 0.65ms
  #if defined(NUNCHUCK)
    static uint32_t timeInterleave = 0;
    annexCode();
    while((uint16_t)(micros()-timeInterleave)<INTERLEAVING_DELAY) ; //interleaving delay between 2 consecutive reads
    timeInterleave=micros();
    ACC_getADC();
    getEstimatedAttitude(); // computation time must last less than one interleaving delay
    while((uint16_t)(micros()-timeInterleave)<INTERLEAVING_DELAY) ; //interleaving delay between 2 consecutive reads
    timeInterleave=micros();
    f.NUNCHUKDATA = 1;
    while(f.NUNCHUKDATA) ACC_getADC(); // For this interleaving reading, we must have a gyro update at this point (less delay)

    for (axis = 0; axis < 3; axis++) {
      // empirical, we take a weighted value of the current and the previous values
      // /4 is to average 4 values, note: overflow is not possible for WMP gyro here
      imu.gyroData[axis] = (imu.gyroADC[axis]*3+gyroADCprevious[axis])>>2;
      gyroADCprevious[axis] = imu.gyroADC[axis];
    }
  #else
    uint16_t timeInterleave = 0;
    #if ACC
      ACC_getADC();
      getEstimatedAttitude();
    #endif
    #if GYRO
      Gyro_getADC();
    #endif
    for (axis = 0; axis < 3; axis++)
      gyroADCinter[axis] =  imu.gyroADC[axis];
    timeInterleave=micros();
    annexCode();
    uint8_t t=0;
    while((int16_t)(micros()-timeInterleave)<650) t=1; //empirical, interleaving delay between 2 consecutive reads
    if (!t) annex650_overrun_count++;
    #if GYRO
      Gyro_getADC();
    #endif
    for (axis = 0; axis < 3; axis++) {
      gyroADCinter[axis] =  imu.gyroADC[axis]+gyroADCinter[axis];
      // empirical, we take a weighted value of the current and the previous values
      imu.gyroData[axis] = (gyroADCinter[axis]+gyroADCprevious[axis])/3;
      gyroADCprevious[axis] = gyroADCinter[axis]>>1;
      if (!ACC) imu.accADC[axis]=0;
    }
  #endif
  #if defined(GYRO_SMOOTHING)
    static int16_t gyroSmooth[3] = {0,0,0};
    for (axis = 0; axis < 3; axis++) {
      imu.gyroData[axis] = (int16_t) ( ( (int32_t)((int32_t)gyroSmooth[axis] * (conf.Smoothing[axis]-1) )+imu.gyroData[axis]+1 ) / conf.Smoothing[axis]);
      gyroSmooth[axis] = imu.gyroData[axis];
    }
  #elif defined(TRI)
    static int16_t gyroYawSmooth = 0;
    imu.gyroData[YAW] = (gyroYawSmooth*2+imu.gyroData[YAW])/3;
    gyroYawSmooth = imu.gyroData[YAW];
  #endif
}

// **************************************************
// Simplified IMU based on "Complementary Filter"
// Inspired by http://starlino.com/imu_guide.html
//
// adapted by ziss_dm : http://www.multiwii.com/forum/viewtopic.php?f=8&t=198
//
// The following ideas was used in this project:
// 1) Rotation matrix: http://en.wikipedia.org/wiki/Rotation_matrix
// 2) Small-angle approximation: http://en.wikipedia.org/wiki/Small-angle_approximation
// 3) C. Hastings approximation for atan2()
// 4) Optimization tricks: http://www.hackersdelight.org/
//
// Currently Magnetometer uses separate CF which is used only
// for heading approximation.
//
// **************************************************

//******  advanced users settings *******************
/* Set the Low Pass Filter factor for ACC
   Increasing this value would reduce ACC noise (visible in GUI), but would increase ACC lag time
   Comment this if  you do not want filter at all.
   unit = n power of 2 */
// this one is also used for ALT HOLD calculation, should not be changed
#ifndef ACC_LPF_FACTOR
  #define ACC_LPF_FACTOR 4 // that means a LPF of 16
#endif

/* Set the Gyro Weight for Gyro/Acc complementary filter
   Increasing this value would reduce and delay Acc influence on the output of the filter*/
#ifndef GYR_CMPF_FACTOR
  #define GYR_CMPF_FACTOR 10 //  that means a CMP_FACTOR of 1024 (2^10)
#endif

/* Set the Gyro Weight for Gyro/Magnetometer complementary filter
   Increasing this value would reduce and delay Magnetometer influence on the output of the filter*/
#define GYR_CMPFM_FACTOR 8 // that means a CMP_FACTOR of 256 (2^8)


typedef struct  {
  int32_t X,Y,Z;
} t_int32_t_vector_def;

typedef struct  {
  uint16_t XL; int16_t X;
  uint16_t YL; int16_t Y;
  uint16_t ZL; int16_t Z;
} t_int16_t_vector_def;

// note: we use implicit first 16 MSB bits 32 -> 16 cast. ie V32.X>>16 = V16.X
typedef union {
  int32_t A32[3];
  t_int32_t_vector_def V32;
  int16_t A16[6];
  t_int16_t_vector_def V16;
} t_int32_t_vector;

//return angle , unit: 1/10 degree
int16_t _atan2(int32_t y, int32_t x){
  float z = y;
  int16_t a;
  uint8_t c;
  c = abs(y) < abs(x);
  if ( c ) {z = z / x;} else {z = x / z;}
  a = 2046.43 * (z / (3.5714 +  z * z));
  if ( c ){
   if (x<0) {
     if (y<0) a -= 1800;
     else a += 1800;
   }
  } else {
    a = 900 - a;
    if (y<0) a -= 1800;
  }
  return a;
}

float InvSqrt (float x){ 
  union{  
    int32_t i;  
    float   f; 
  } conv; 
  conv.f = x; 
  conv.i = 0x5f3759df - (conv.i >> 1); 
  return 0.5f * (conv.f * (3.0f - x * conv.f * conv.f));
}

// signed16 * signed16
// 22 cycles
// http://mekonik.wordpress.com/2009/03/18/arduino-avr-gcc-multiplication/
#define MultiS16X16to32(longRes, intIn1, intIn2) \
asm volatile ( \
"clr r26 \n\t" \
"mul %A1, %A2 \n\t" \
"movw %A0, r0 \n\t" \
"muls %B1, %B2 \n\t" \
"movw %C0, r0 \n\t" \
"mulsu %B2, %A1 \n\t" \
"sbc %D0, r26 \n\t" \
"add %B0, r0 \n\t" \
"adc %C0, r1 \n\t" \
"adc %D0, r26 \n\t" \
"mulsu %B1, %A2 \n\t" \
"sbc %D0, r26 \n\t" \
"add %B0, r0 \n\t" \
"adc %C0, r1 \n\t" \
"adc %D0, r26 \n\t" \
"clr r1 \n\t" \
: \
"=&r" (longRes) \
: \
"a" (intIn1), \
"a" (intIn2) \
: \
"r26" \
)

int32_t  __attribute__ ((noinline)) mul(int16_t a, int16_t b) {
  int32_t r;
  MultiS16X16to32(r, a, b);
  //r = (int32_t)a*b; without asm requirement
  return r;
}

// Rotate Estimated vector(s) with small angle approximation, according to the gyro data
void rotateV32( t_int32_t_vector *v,int16_t* delta) {
  int16_t X = v->V16.X;
  int16_t Y = v->V16.Y;
  int16_t Z = v->V16.Z;

  v->V32.Z -=  mul(delta[ROLL]  ,  X)  + mul(delta[PITCH] , Y);
  v->V32.X +=  mul(delta[ROLL]  ,  Z)  - mul(delta[YAW]   , Y);
  v->V32.Y +=  mul(delta[PITCH] ,  Z)  + mul(delta[YAW]   , X);
}

static int16_t accZ=0;

void getEstimatedAttitude(){
  uint8_t axis;
  int32_t accMag = 0;
  float scale;
  int16_t deltaGyroAngle16[3];
  static t_int32_t_vector EstG,EstM;
  static uint32_t LPFAcc[3];
  float invG; // 1/|G|
  static int16_t accZoffset = 0;
  int32_t accZ_tmp=0;
  static uint16_t previousT;
  uint16_t currentT = micros();

  // unit: radian per bit, scaled by 2^16 for further multiplication
  // with a delta time of 3000 us, and GYRO scale of most gyros, scale = a little bit less than 1
  scale = (currentT - previousT) * (GYRO_SCALE * 65536);
  previousT = currentT;

  // Initialization
  for (axis = 0; axis < 3; axis++) {
    // valid as long as LPF_FACTOR is less than 15
    imu.accSmooth[axis]  = LPFAcc[axis]>>ACC_LPF_FACTOR;
    LPFAcc[axis]      += imu.accADC[axis] - imu.accSmooth[axis];
    // used to calculate later the magnitude of acc vector
    accMag   += mul(imu.accSmooth[axis] , imu.accSmooth[axis]);
    // unit: radian scaled by 2^16
    // imu.gyroADC[axis] is 14 bit long, the scale factor ensure deltaGyroAngle16[axis] is still 14 bit long
    deltaGyroAngle16[axis] = imu.gyroADC[axis]  * scale;
  }

  // we rotate the intermediate 32 bit vector with the radian vector (deltaGyroAngle16), scaled by 2^16
  // however, only the first 16 MSB of the 32 bit vector is used to compute the result
  // it is ok to use this approximation as the 16 LSB are used only for the complementary filter part
  rotateV32(&EstG,deltaGyroAngle16);
  #if MAG
    rotateV32(&EstM,deltaGyroAngle16);
  #endif

  // Apply complimentary filter (Gyro drift correction)
  // If accel magnitude >1.15G or <0.85G and ACC vector outside of the limit range => we neutralize the effect of accelerometers in the angle estimation.
  // To do that, we just skip filter, as EstV already rotated by Gyro
  for (axis = 0; axis < 3; axis++) {
    if ( (int16_t)(0.85*ACC_1G*ACC_1G/256) < (int16_t)(accMag>>8) && (int16_t)(accMag>>8) < (int16_t)(1.15*ACC_1G*ACC_1G/256) )
      EstG.A32[axis] += (int32_t)(imu.accSmooth[axis] - EstG.A16[2*axis+1])<<(16-GYR_CMPF_FACTOR);
    accZ_tmp += mul(imu.accSmooth[axis] , EstG.A16[2*axis+1]);
    #if MAG
      EstM.A32[axis]  += (int32_t)(imu.magADC[axis] - EstM.A16[2*axis+1])<<(16-GYR_CMPFM_FACTOR);
    #endif
  }
  
  if (EstG.V16.Z > ACCZ_25deg)
    f.SMALL_ANGLES_25 = 1;
  else
    f.SMALL_ANGLES_25 = 0;

  // Attitude of the estimated vector
  int32_t sqGX_sqGZ = mul(EstG.V16.X,EstG.V16.X) + mul(EstG.V16.Z,EstG.V16.Z);
  invG = InvSqrt(sqGX_sqGZ + mul(EstG.V16.Y,EstG.V16.Y));
  att.angle[ROLL]  = _atan2(EstG.V16.X , EstG.V16.Z);
  att.angle[PITCH] = _atan2(EstG.V16.Y , InvSqrt(sqGX_sqGZ)*sqGX_sqGZ);

  #if MAG
    //note on the second term: mathematically there is a risk of overflow (16*16*16=48 bits). assumed to be null with real values
    att.heading = _atan2(
      mul(EstM.V16.Z , EstG.V16.X) - mul(EstM.V16.X , EstG.V16.Z),
      (EstM.V16.Y * sqGX_sqGZ  - (mul(EstM.V16.X , EstG.V16.X) + mul(EstM.V16.Z , EstG.V16.Z)) * EstG.V16.Y)*invG );
    att.heading += conf.mag_declination; // Set from GUI
    att.heading /= 10;
  #endif

  #if defined(THROTTLE_ANGLE_CORRECTION)
    cosZ = mul(EstG.V16.Z , 100) / ACC_1G ;                                                   // cos(angleZ) * 100 
    throttleAngleCorrection = THROTTLE_ANGLE_CORRECTION * constrain(100 - cosZ, 0, 100) >>3;  // 16 bit ok: 200*150 = 30000  
  #endif

  // projection of ACC vector to global Z, with 1G subtructed
  // Math: accZ = A * G / |G| - 1G
  accZ = accZ_tmp *  invG;
  if (!f.ARMED) {
    accZoffset -= accZoffset>>3;
    accZoffset += accZ;
  }  
  accZ -= accZoffset>>3;
}

#define UPDATE_INTERVAL 25000    // 40hz update rate (20hz LPF on acc)
#define BARO_TAB_SIZE   21

#define ACC_Z_DEADBAND (ACC_1G>>5) // was 40 instead of 32 now


#define applyDeadband(value, deadband)  \
  if(abs(value) < deadband) {           \
    value = 0;                          \
  } else if(value > 0){                 \
    value -= deadband;                  \
  } else if(value < 0){                 \
    value += deadband;                  \
  }

#if BARO
uint8_t getEstimatedAltitude(){
  int32_t  BaroAlt;
  static float baroGroundTemperatureScale,logBaroGroundPressureSum;
  static float vel = 0.0f;
  static uint16_t previousT;
  uint16_t currentT = micros();
  uint16_t dTime;

  dTime = currentT - previousT;
  if (dTime < UPDATE_INTERVAL) return 0;
  previousT = currentT;

  if(calibratingB > 0) {
    logBaroGroundPressureSum = log(baroPressureSum);
    baroGroundTemperatureScale = ((int32_t)baroTemperature + 27315) * (2 * 29.271267f); // 2 *  is included here => no need for * 2  on BaroAlt in additional LPF
    calibratingB--;
  }

  // baroGroundPressureSum is not supposed to be 0 here
  // see: https://code.google.com/p/ardupilot-mega/source/browse/libraries/AP_Baro/AP_Baro.cpp
  BaroAlt = ( logBaroGroundPressureSum - log(baroPressureSum) ) * baroGroundTemperatureScale;

  alt.EstAlt = (alt.EstAlt * 6 + BaroAlt ) >> 3; // additional LPF to reduce baro noise (faster by 30 µs)
  #if (defined(VARIOMETER) && (VARIOMETER != 2)) || !defined(SUPPRESS_BARO_ALTHOLD)
    //P
    int16_t error16 = constrain(AltHold - alt.EstAlt, -300, 300);
    applyDeadband(error16, 10); //remove small P parametr to reduce noise near zero position
    BaroPID = constrain((conf.pid[PIDALT].P8 * error16 >>7), -150, +150);

    //I
    errorAltitudeI += conf.pid[PIDALT].I8 * error16 >>6;
    errorAltitudeI = constrain(errorAltitudeI,-30000,30000);
    BaroPID += errorAltitudeI>>9; //I in range +/-60
 
    applyDeadband(accZ, ACC_Z_DEADBAND);

    static int32_t lastBaroAlt;
    // could only overflow with a difference of 320m, which is highly improbable here
    int16_t baroVel = mul((alt.EstAlt - lastBaroAlt) , (1000000 / UPDATE_INTERVAL));

    lastBaroAlt = alt.EstAlt;

    baroVel = constrain(baroVel, -300, 300); // constrain baro velocity +/- 300cm/s
    applyDeadband(baroVel, 10); // to reduce noise near zero

    // Integrator - velocity, cm/sec
    vel += accZ * ACC_VelScale * dTime;

    // apply Complimentary Filter to keep the calculated velocity based on baro velocity (i.e. near real velocity). 
    // By using CF it's possible to correct the drift of integrated accZ (velocity) without loosing the phase, i.e without delay
    vel = vel * 0.985f + baroVel * 0.015f;

    //D
    alt.vario = vel;
    applyDeadband(alt.vario, 5);
    BaroPID -= constrain(conf.pid[PIDALT].D8 * alt.vario >>4, -150, 150);
  #endif
  return 1;
}
#endif //BARO