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/*
 
 MinIMU-9-Arduino-AHRS
 Pololu MinIMU-9 + Arduino AHRS (Attitude and Heading Reference System)
 
 Copyright (c) 2011 Pololu Corporation.
 http://w...content-available-to-author-only...u.com/
 
 MinIMU-9-Arduino-AHRS is based on sf9domahrs by Doug Weibel and Jose Julio:
 http://code.google.com/p/sf9domahrs/
 
 sf9domahrs is based on ArduIMU v1.5 by Jordi Munoz and William Premerlani, Jose
 Julio and Doug Weibel:
 http://code.google.com/p/ardu-imu/
 
 MinIMU-9-Arduino-AHRS is free software: you can redistribute it and/or modify it
 under the terms of the GNU Lesser General Public License as published by the
 Free Software Foundation, either version 3 of the License, or (at your option)
 any later version.
 
 MinIMU-9-Arduino-AHRS is distributed in the hope that it will be useful, but
 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for
 more details.
 
 You should have received a copy of the GNU Lesser General Public License along
 with MinIMU-9-Arduino-AHRS. If not, see <http://w...content-available-to-author-only...u.org/licenses/>.
 
 */
void Calibrate(){
 
  while (digitalRead(CAL_FIN) == 0){
 
    compass.read();
 
    running_min.x = min(running_min.x, compass.m.x);
    running_min.y = min(running_min.y, compass.m.y);
    running_min.z = min(running_min.z, compass.m.z);
 
    running_max.x = max(running_max.x, compass.m.x);
    running_max.y = max(running_max.y, compass.m.y);
    running_max.z = max(running_max.z, compass.m.z);
    Serial.print("M min ");
    Serial.print("X: ");
    Serial.print((int)running_min.x);
    Serial.print(" Y: ");
    Serial.print((int)running_min.y);
    Serial.print(" Z: ");
    Serial.print((int)running_min.z);
    Serial.print(" M max ");  
    Serial.print("X: ");
    Serial.print((int)running_max.x);
    Serial.print(" Y: ");
    Serial.print((int)running_max.y);
    Serial.print(" Z: ");
    Serial.println((int)running_max.z);
 
    M_X_MIN = running_min.x;
    M_Y_MIN = running_min.y;
    M_Z_MIN = running_min.z;
    M_X_MAX = running_max.x;
    M_Y_MAX = running_max.y;
    M_Z_MAX = running_max.z;    
    delay(100);  
  }  
 
}
void Compass_Heading()
{
  float MAG_X;
  float MAG_Y;
  float cos_roll;
  float sin_roll;
  float cos_pitch;
  float sin_pitch;
 
  cos_roll = cos(roll);
  sin_roll = sin(roll);
  cos_pitch = cos(pitch);
  sin_pitch = sin(pitch);
 
  // adjust for LSM303 compass axis offsets/sensitivity differences by scaling to +/-0.5 range
  c_magnetom_x = (float)(magnetom_x - SENSOR_SIGN[6]*M_X_MIN) / (M_X_MAX - M_X_MIN) - SENSOR_SIGN[6]*0.5;
  c_magnetom_y = (float)(magnetom_y - SENSOR_SIGN[7]*M_Y_MIN) / (M_Y_MAX - M_Y_MIN) - SENSOR_SIGN[7]*0.5;
  c_magnetom_z = (float)(magnetom_z - SENSOR_SIGN[8]*M_Z_MIN) / (M_Z_MAX - M_Z_MIN) - SENSOR_SIGN[8]*0.5;
 
  // Tilt compensated Magnetic filed X:
  MAG_X = c_magnetom_x*cos_pitch+c_magnetom_y*sin_roll*sin_pitch+c_magnetom_z*cos_roll*sin_pitch;
  // Tilt compensated Magnetic filed Y:
  MAG_Y = c_magnetom_y*cos_roll-c_magnetom_z*sin_roll;
  // Magnetic Heading
  MAG_Heading = atan2(-MAG_Y,MAG_X);
}
 
void Normalize(void)
{
  float error=0;
  float temporary[3][3];
  float renorm=0;
 
  error= -Vector_Dot_Product(&DCM_Matrix[0][0],&DCM_Matrix[1][0])*.5; //eq.19
 
  Vector_Scale(&temporary[0][0], &DCM_Matrix[1][0], error); //eq.19
  Vector_Scale(&temporary[1][0], &DCM_Matrix[0][0], error); //eq.19
 
  Vector_Add(&temporary[0][0], &temporary[0][0], &DCM_Matrix[0][0]);//eq.19
  Vector_Add(&temporary[1][0], &temporary[1][0], &DCM_Matrix[1][0]);//eq.19
 
  Vector_Cross_Product(&temporary[2][0],&temporary[0][0],&temporary[1][0]); // c= a x b //eq.20
 
  renorm= .5 *(3 - Vector_Dot_Product(&temporary[0][0],&temporary[0][0])); //eq.21
  Vector_Scale(&DCM_Matrix[0][0], &temporary[0][0], renorm);
 
  renorm= .5 *(3 - Vector_Dot_Product(&temporary[1][0],&temporary[1][0])); //eq.21
  Vector_Scale(&DCM_Matrix[1][0], &temporary[1][0], renorm);
 
  renorm= .5 *(3 - Vector_Dot_Product(&temporary[2][0],&temporary[2][0])); //eq.21
  Vector_Scale(&DCM_Matrix[2][0], &temporary[2][0], renorm);
}
 
/**************************************************/
void Drift_correction(void)
{
  float mag_heading_x;
  float mag_heading_y;
  float errorCourse;
  //Compensation the Roll, Pitch and Yaw drift. 
  static float Scaled_Omega_P[3];
  static float Scaled_Omega_I[3];
  float Accel_magnitude;
  float Accel_weight;
 
 
  //*****Roll and Pitch***************
 
  // Calculate the magnitude of the accelerometer vector
  Accel_magnitude = sqrt(Accel_Vector[0]*Accel_Vector[0] + Accel_Vector[1]*Accel_Vector[1] + Accel_Vector[2]*Accel_Vector[2]);
  Accel_magnitude = Accel_magnitude / GRAVITY; // Scale to gravity.
  // Dynamic weighting of accelerometer info (reliability filter)
  // Weight for accelerometer info (<0.5G = 0.0, 1G = 1.0 , >1.5G = 0.0)
  Accel_weight = constrain(1 - 2*abs(1 - Accel_magnitude),0,1);  //  
 
  Vector_Cross_Product(&errorRollPitch[0],&Accel_Vector[0],&DCM_Matrix[2][0]); //adjust the ground of reference
  Vector_Scale(&Omega_P[0],&errorRollPitch[0],Kp_ROLLPITCH*Accel_weight);
 
  Vector_Scale(&Scaled_Omega_I[0],&errorRollPitch[0],Ki_ROLLPITCH*Accel_weight);
  Vector_Add(Omega_I,Omega_I,Scaled_Omega_I);     
 
  //*****YAW***************
  // We make the gyro YAW drift correction based on compass magnetic heading
 
  mag_heading_x = cos(MAG_Heading);
  mag_heading_y = sin(MAG_Heading);
  errorCourse=(DCM_Matrix[0][0]*mag_heading_y) - (DCM_Matrix[1][0]*mag_heading_x);  //Calculating YAW error
  Vector_Scale(errorYaw,&DCM_Matrix[2][0],errorCourse); //Applys the yaw correction to the XYZ rotation of the aircraft, depeding the position.
 
  Vector_Scale(&Scaled_Omega_P[0],&errorYaw[0],Kp_YAW);//.01proportional of YAW.
  Vector_Add(Omega_P,Omega_P,Scaled_Omega_P);//Adding  Proportional.
 
  Vector_Scale(&Scaled_Omega_I[0],&errorYaw[0],Ki_YAW);//.00001Integrator
  Vector_Add(Omega_I,Omega_I,Scaled_Omega_I);//adding integrator to the Omega_I
}
/**************************************************/
/*
void Accel_adjust(void)
 {
 Accel_Vector[1] += Accel_Scale(speed_3d*Omega[2]);  // Centrifugal force on Acc_y = GPS_speed*GyroZ
 Accel_Vector[2] -= Accel_Scale(speed_3d*Omega[1]);  // Centrifugal force on Acc_z = GPS_speed*GyroY 
 }
 */
/**************************************************/
 
void Matrix_update(void)
{
  Gyro_Vector[0]=Gyro_Scaled_X(gyro_x); //gyro x roll
  Gyro_Vector[1]=Gyro_Scaled_Y(gyro_y); //gyro y pitch
  Gyro_Vector[2]=Gyro_Scaled_Z(gyro_z); //gyro Z yaw
 
  Accel_Vector[0]=accel_x;
  Accel_Vector[1]=accel_y;
  Accel_Vector[2]=accel_z;
 
  Vector_Add(&Omega[0], &Gyro_Vector[0], &Omega_I[0]);  //adding proportional term
  Vector_Add(&Omega_Vector[0], &Omega[0], &Omega_P[0]); //adding Integrator term
  //Accel_adjust();    //Remove centrifugal acceleration.   We are not using this function in this version - we have no speed measuremet
#if OUTPUTMODE==1         
    Update_Matrix[0][0]=0;
  Update_Matrix[0][1]=-G_Dt*Omega_Vector[2];//-z
  Update_Matrix[0][2]=G_Dt*Omega_Vector[1];//y
  Update_Matrix[1][0]=G_Dt*Omega_Vector[2];//z
  Update_Matrix[1][1]=0;
  Update_Matrix[1][2]=-G_Dt*Omega_Vector[0];//-x
  Update_Matrix[2][0]=-G_Dt*Omega_Vector[1];//-y
  Update_Matrix[2][1]=G_Dt*Omega_Vector[0];//x
  Update_Matrix[2][2]=0;
#else                    // Uncorrected data (no drift correction)
  Update_Matrix[0][0]=0;
  Update_Matrix[0][1]=-G_Dt*Gyro_Vector[2];//-z
  Update_Matrix[0][2]=G_Dt*Gyro_Vector[1];//y
  Update_Matrix[1][0]=G_Dt*Gyro_Vector[2];//z
  Update_Matrix[1][1]=0;
  Update_Matrix[1][2]=-G_Dt*Gyro_Vector[0];
  Update_Matrix[2][0]=-G_Dt*Gyro_Vector[1];
  Update_Matrix[2][1]=G_Dt*Gyro_Vector[0];
  Update_Matrix[2][2]=0;
#endif
  Matrix_Multiply(DCM_Matrix,Update_Matrix,Temporary_Matrix); //a*b=c
  for(int x=0; x<3; x++) //Matrix Addition (update)
  {
    for(int y=0; y<3; y++)
    {
      DCM_Matrix[x][y]+=Temporary_Matrix[x][y];
    } 
  }
}
void Euler_angles(void)
{
  pitch = -asin(DCM_Matrix[2][0]);
  roll = atan2(DCM_Matrix[2][1],DCM_Matrix[2][2]);
  yaw = atan2(DCM_Matrix[1][0],DCM_Matrix[0][0]);
}
void I2C_Init()
{
  Wire.begin();
}
void Gyro_Init()
{
  gyro.writeReg(L3G4200D_CTRL_REG1, 0x0F); // normal power mode, all axes enabled, 100 Hz
  gyro.writeReg(L3G4200D_CTRL_REG4, 0x20); // 2000 dps full scale
}
void Read_Gyro()
{
  gyro.read();
  AN[0] = gyro.g.x;
  AN[1] = gyro.g.y;
  AN[2] = gyro.g.z;
  gyro_x = SENSOR_SIGN[0] * (AN[0] - AN_OFFSET[0]);
  gyro_y = SENSOR_SIGN[1] * (AN[1] - AN_OFFSET[1]);
  gyro_z = SENSOR_SIGN[2] * (AN[2] - AN_OFFSET[2]);
}
void Accel_Init()
{
  compass.writeAccReg(LSM303_CTRL_REG1_A, 0x27); // normal power mode, all axes enabled, 50 Hz
  compass.writeAccReg(LSM303_CTRL_REG4_A, 0x30); // 8 g full scale
}
// Reads x,y and z accelerometer registers
void Read_Accel()
{
  compass.readAcc();
  AN[3] = compass.a.x;
  AN[4] = compass.a.y;
  AN[5] = compass.a.z;
  accel_x = SENSOR_SIGN[3] * (AN[3] - AN_OFFSET[3]);
  accel_y = SENSOR_SIGN[4] * (AN[4] - AN_OFFSET[4]);
  accel_z = SENSOR_SIGN[5] * (AN[5] - AN_OFFSET[5]);
}
void Compass_Init()
{
  for(int j=5;j>0;j--){
    Serial.println(j);
    delay(1000);
  }
  compass.init();
  compass.enableDefault();
  compass.writeMagReg(LSM303_CRB_REG_M, MAG_GAIN);
  Serial.println("Wait for compass config");
  delay(5000);//neccessary to set the gain of the mag sensor
  //remove the above line and the IMU will not work
  compass.writeMagReg(LSM303_CRB_REG_M, MAG_GAIN);
  // 15 Hz default
}
void Read_Compass()
{
  compass.readMag();
  magnetom_x = SENSOR_SIGN[6] * compass.m.x;
  magnetom_y = SENSOR_SIGN[7] * compass.m.y;
  magnetom_z = SENSOR_SIGN[8] * compass.m.z;
}
float Vector_Dot_Product(float vector1[3],float vector2[3])
{
  float op=0;
 
  for(int c=0; c<3; c++)
  {
    op+=vector1[c]*vector2[c];
  }
 
  return op; 
}
//Computes the cross product of two vectors
void Vector_Cross_Product(float vectorOut[3], float v1[3],float v2[3])
{
  vectorOut[0]= (v1[1]*v2[2]) - (v1[2]*v2[1]);
  vectorOut[1]= (v1[2]*v2[0]) - (v1[0]*v2[2]);
  vectorOut[2]= (v1[0]*v2[1]) - (v1[1]*v2[0]);
}
//Multiply the vector by a scalar. 
void Vector_Scale(float vectorOut[3],float vectorIn[3], float scale2)
{
  for(int c=0; c<3; c++)
  {
    vectorOut[c]=vectorIn[c]*scale2; 
  }
}
 
void Vector_Add(float vectorOut[3],float vectorIn1[3], float vectorIn2[3])
{
  for(int c=0; c<3; c++)
  {
    vectorOut[c]=vectorIn1[c]+vectorIn2[c];
  }
}
void Matrix_Multiply(float a[3][3], float b[3][3],float mat[3][3])
{
  float op[3]; 
  for(int x=0; x<3; x++)
  {
    for(int y=0; y<3; y++)
    {
      for(int w=0; w<3; w++)
      {
        op[w]=a[x][w]*b[w][y];
      } 
      mat[x][y]=0;
      mat[x][y]=op[0]+op[1]+op[2];
 
      float test=mat[x][y];
    }
  }
}
 
long convert_to_dec(float x)
{
  return x*10000000;
}
 

prog.cpp: In function ‘void Calibrate()’:
prog.cpp:32: error: ‘CAL_FIN’ was not declared in this scope
prog.cpp:32: error: ‘digitalRead’ was not declared in this scope
prog.cpp:34: error: ‘compass’ was not declared in this scope
prog.cpp:36: error: ‘running_min’ was not declared in this scope
prog.cpp:36: error: ‘min’ was not declared in this scope
prog.cpp:40: error: ‘running_max’ was not declared in this scope
prog.cpp:40: error: ‘max’ was not declared in this scope
prog.cpp:43: error: ‘Serial’ was not declared in this scope
prog.cpp:58: error: ‘M_X_MIN’ was not declared in this scope
prog.cpp:59: error: ‘M_Y_MIN’ was not declared in this scope
prog.cpp:60: error: ‘M_Z_MIN’ was not declared in this scope
prog.cpp:61: error: ‘M_X_MAX’ was not declared in this scope
prog.cpp:62: error: ‘M_Y_MAX’ was not declared in this scope
prog.cpp:63: error: ‘M_Z_MAX’ was not declared in this scope
prog.cpp:64: error: ‘delay’ was not declared in this scope
prog.cpp: In function ‘void Compass_Heading()’:
prog.cpp:77: error: ‘roll’ was not declared in this scope
prog.cpp:77: error: ‘cos’ was not declared in this scope
prog.cpp:78: error: ‘sin’ was not declared in this scope
prog.cpp:79: error: ‘pitch’ was not declared in this scope
prog.cpp:83: error: ‘c_magnetom_x’ was not declared in this scope
prog.cpp:83: error: ‘magnetom_x’ was not declared in this scope
prog.cpp:83: error: ‘SENSOR_SIGN’ was not declared in this scope
prog.cpp:83: error: ‘M_X_MIN’ was not declared in this scope
prog.cpp:83: error: ‘M_X_MAX’ was not declared in this scope
prog.cpp:84: error: ‘c_magnetom_y’ was not declared in this scope
prog.cpp:84: error: ‘magnetom_y’ was not declared in this scope
prog.cpp:84: error: ‘M_Y_MIN’ was not declared in this scope
prog.cpp:84: error: ‘M_Y_MAX’ was not declared in this scope
prog.cpp:85: error: ‘c_magnetom_z’ was not declared in this scope
prog.cpp:85: error: ‘magnetom_z’ was not declared in this scope
prog.cpp:85: error: ‘M_Z_MIN’ was not declared in this scope
prog.cpp:85: error: ‘M_Z_MAX’ was not declared in this scope
prog.cpp:92: error: ‘MAG_Heading’ was not declared in this scope
prog.cpp:92: error: ‘atan2’ was not declared in this scope
prog.cpp: In function ‘void Normalize()’:
prog.cpp:101: error: ‘DCM_Matrix’ was not declared in this scope
prog.cpp:101: error: ‘Vector_Dot_Product’ was not declared in this scope
prog.cpp:103: error: ‘Vector_Scale’ was not declared in this scope
prog.cpp:106: error: ‘Vector_Add’ was not declared in this scope
prog.cpp:109: error: ‘Vector_Cross_Product’ was not declared in this scope
prog.cpp: In function ‘void Drift_correction()’:
prog.cpp:137: error: ‘Accel_Vector’ was not declared in this scope
prog.cpp:137: error: ‘sqrt’ was not declared in this scope
prog.cpp:138: error: ‘GRAVITY’ was not declared in this scope
prog.cpp:141: error: ‘abs’ was not declared in this scope
prog.cpp:141: error: ‘constrain’ was not declared in this scope
prog.cpp:143: error: ‘errorRollPitch’ was not declared in this scope
prog.cpp:143: error: ‘DCM_Matrix’ was not declared in this scope
prog.cpp:143: error: ‘Vector_Cross_Product’ was not declared in this scope
prog.cpp:144: error: ‘Omega_P’ was not declared in this scope
prog.cpp:144: error: ‘Kp_ROLLPITCH’ was not declared in this scope
prog.cpp:144: error: ‘Vector_Scale’ was not declared in this scope
prog.cpp:146: error: ‘Ki_ROLLPITCH’ was not declared in this scope
prog.cpp:147: error: ‘Omega_I’ was not declared in this scope
prog.cpp:147: error: ‘Vector_Add’ was not declared in this scope
prog.cpp:152: error: ‘MAG_Heading’ was not declared in this scope
prog.cpp:152: error: ‘cos’ was not declared in this scope
prog.cpp:153: error: ‘sin’ was not declared in this scope
prog.cpp:155: error: ‘errorYaw’ was not declared in this scope
prog.cpp:157: error: ‘Kp_YAW’ was not declared in this scope
prog.cpp:160: error: ‘Ki_YAW’ was not declared in this scope
prog.cpp: In function ‘void Matrix_update()’:
prog.cpp:175: error: ‘Gyro_Vector’ was not declared in this scope
prog.cpp:175: error: ‘gyro_x’ was not declared in this scope
prog.cpp:175: error: ‘Gyro_Scaled_X’ was not declared in this scope
prog.cpp:176: error: ‘gyro_y’ was not declared in this scope
prog.cpp:176: error: ‘Gyro_Scaled_Y’ was not declared in this scope
prog.cpp:177: error: ‘gyro_z’ was not declared in this scope
prog.cpp:177: error: ‘Gyro_Scaled_Z’ was not declared in this scope
prog.cpp:179: error: ‘Accel_Vector’ was not declared in this scope
prog.cpp:179: error: ‘accel_x’ was not declared in this scope
prog.cpp:180: error: ‘accel_y’ was not declared in this scope
prog.cpp:181: error: ‘accel_z’ was not declared in this scope
prog.cpp:183: error: ‘Omega’ was not declared in this scope
prog.cpp:183: error: ‘Omega_I’ was not declared in this scope
prog.cpp:183: error: ‘Vector_Add’ was not declared in this scope
prog.cpp:184: error: ‘Omega_Vector’ was not declared in this scope
prog.cpp:184: error: ‘Omega_P’ was not declared in this scope
prog.cpp:197: error: ‘Update_Matrix’ was not declared in this scope
prog.cpp:198: error: ‘G_Dt’ was not declared in this scope
prog.cpp:207: error: ‘DCM_Matrix’ was not declared in this scope
prog.cpp:207: error: ‘Temporary_Matrix’ was not declared in this scope
prog.cpp:207: error: ‘Matrix_Multiply’ was not declared in this scope
prog.cpp: In function ‘void Euler_angles()’:
prog.cpp:218: error: ‘pitch’ was not declared in this scope
prog.cpp:218: error: ‘DCM_Matrix’ was not declared in this scope
prog.cpp:218: error: ‘asin’ was not declared in this scope
prog.cpp:219: error: ‘roll’ was not declared in this scope
prog.cpp:219: error: ‘atan2’ was not declared in this scope
prog.cpp:220: error: ‘yaw’ was not declared in this scope
prog.cpp: In function ‘void I2C_Init()’:
prog.cpp:224: error: ‘Wire’ was not declared in this scope
prog.cpp: In function ‘void Gyro_Init()’:
prog.cpp:228: error: ‘gyro’ was not declared in this scope
prog.cpp:228: error: ‘L3G4200D_CTRL_REG1’ was not declared in this scope
prog.cpp:229: error: ‘L3G4200D_CTRL_REG4’ was not declared in this scope
prog.cpp: In function ‘void Read_Gyro()’:
prog.cpp:233: error: ‘gyro’ was not declared in this scope
prog.cpp:234: error: ‘AN’ was not declared in this scope
prog.cpp:237: error: ‘gyro_x’ was not declared in this scope
prog.cpp:237: error: ‘SENSOR_SIGN’ was not declared in this scope
prog.cpp:237: error: ‘AN_OFFSET’ was not declared in this scope
prog.cpp:238: error: ‘gyro_y’ was not declared in this scope
prog.cpp:239: error: ‘gyro_z’ was not declared in this scope
prog.cpp: In function ‘void Accel_Init()’:
prog.cpp:243: error: ‘compass’ was not declared in this scope
prog.cpp:243: error: ‘LSM303_CTRL_REG1_A’ was not declared in this scope
prog.cpp:244: error: ‘LSM303_CTRL_REG4_A’ was not declared in this scope
prog.cpp: In function ‘void Read_Accel()’:
prog.cpp:249: error: ‘compass’ was not declared in this scope
prog.cpp:250: error: ‘AN’ was not declared in this scope
prog.cpp:253: error: ‘accel_x’ was not declared in this scope
prog.cpp:253: error: ‘SENSOR_SIGN’ was not declared in this scope
prog.cpp:253: error: ‘AN_OFFSET’ was not declared in this scope
prog.cpp:254: error: ‘accel_y’ was not declared in this scope
prog.cpp:255: error: ‘accel_z’ was not declared in this scope
prog.cpp: In function ‘void Compass_Init()’:
prog.cpp:260: error: ‘Serial’ was not declared in this scope
prog.cpp:261: error: ‘delay’ was not declared in this scope
prog.cpp:263: error: ‘compass’ was not declared in this scope
prog.cpp:265: error: ‘LSM303_CRB_REG_M’ was not declared in this scope
prog.cpp:265: error: ‘MAG_GAIN’ was not declared in this scope
prog.cpp:266: error: ‘Serial’ was not declared in this scope
prog.cpp:267: error: ‘delay’ was not declared in this scope
prog.cpp: In function ‘void Read_Compass()’:
prog.cpp:274: error: ‘compass’ was not declared in this scope
prog.cpp:275: error: ‘magnetom_x’ was not declared in this scope
prog.cpp:275: error: ‘SENSOR_SIGN’ was not declared in this scope
prog.cpp:276: error: ‘magnetom_y’ was not declared in this scope
prog.cpp:277: error: ‘magnetom_z’ was not declared in this scope
prog.cpp: In function ‘void Matrix_Multiply(float (*)[3], float (*)[3], float (*)[3])’:
prog.cpp:327: warning: unused variable ‘test’

Standard output is empty