TMS320F28069M: How to use ENC +QEP to get the speed and position information?

I am using Launchpad 28069M + EVM DRV8305 to control a  outer-rotor PMSM with InstaSPIN FOC. Now I add a 3600P/R incremental encoder to read the speed  and position information  based on the example of lab11a. The documents of  enc.c,  enc.h,  qep.c and qep.h are got from lab 12b without  any  modification.

To read the speed, I follow the previous answers.

https://e2e.ti.com/support/microcontrollers/c2000-microcontrollers-group/c2000/f/c2000-microcontrollers-forum/501438/how-to-use-enc-qep-modules-to-measure-motor-speed-by-an-incremental-encoder/2054164?tisearch=e2e-sitesearch&keymatch=QEP%2525252520module#2054164

In main void, the ENC is initialized and setted up;

 // initialize the ENC module
  encHandle = ENC_init(&enc, sizeof(enc));

  // setup the ENC module
  ENC_setup(encHandle, USER_ENC_SAMPLE_PERIOD, USER_MOTOR_NUM_POLE_PAIRS, USER_MOTOR_ENCODER_LINES, 0, USER_IQ_FULL_SCALE_FREQ_Hz, USER_ISR_FREQ_Hz, 8000.0);

In hal.h,  two functions are added.

//! \brief      Return the index info from the QEP module
//! \param[in] encHandle                        Handle to the ENC object
//! \return     The flag that indicate the index of encoder (true or false)
static inline uint16_t HAL_getQepIndex(HAL_Handle handle)
{
    HAL_Obj *obj = (HAL_Obj *)handle;

    return (uint16_t)((QEP_QEPSTS_FIMF & QEP_read_status(obj->qepHandle[0]))>>1);
}

//! \brief      Return the direction info from the QEP module
//! \param[in] encHandle                        Handle to the ENC object
//! \return     The flag that indicate the direction of rotation (true for negative direction or false for positive direction)
static inline uint16_t HAL_getQepDirection(HAL_Handle handle)
{
    HAL_Obj *obj = (HAL_Obj *)handle;

    return (uint16_t)((QEP_QEPSTS_QDF&QEP_read_status(obj->qepHandle[0]))>>5);
}

The result from ENC_getSpeedRPM has  a same  number with the FAST speed  feedback, but it is always positive. Hence,  I add these in MainISR

 // run the ENC module
  ENC_run(encHandle, HAL_getQepPosnCounts(halHandle), HAL_getQepIndex(halHandle), HAL_getQepDirection(halHandle), true);


//get speed from ENC
dirFlag = HAL_getQepDirection(halHandle);
if(dirFlag==1) ENCSPEEDRPM = - ENC_getSpeedRPM(encHandle);
if(dirFlag==0) ENCSPEEDRPM = ENC_getSpeedRPM(encHandle);

Is it correct way to solve the problem?

Second, I also want to get the position.  Therefore, in MainISR,  I  read the  Position Counter (QPOSCNT) Register and try to find how many resolutions have been done.

//write at the beginning of proj_lab11a.c
 _iq MechPosCount;
float MechanicalPos = 0;




//in MainISR 
 uint16_t dirFlag;
  _iq PosCount_delta = 0;

  _iq MechPosCount_z1 = 0;
 
 MechPosCount = HAL_getQepPosnCounts(halHandle);

  //calculate position in revolution
  MechanicalPos= MechPosCount/(USER_MOTOR_ENCODER_LINES*4);
  PosCount_delta =  MechPosCount - MechPosCount_z1;

      if ((dirFlag == 0) && (PosCount_delta < 0))
      {
          MechanicalPos = MechanicalPos + 1;
      }
      else if ((dirFlag == 1) && (PosCount_delta > 0))
      {
          MechanicalPos = MechanicalPos - 1;
      }
      MechPosCount_z1 = MechPosCount;

But the value of MechanicalPos is random.  Even the motor  speed reference  is set to 0, that is,  the motor doesn't  rotate, the  value  of   MechanicalPos  is still changing randomly.

What is wrong with  my  method?