TMS320F28335: eQEP module - high speed measurement update rate too slow

Hi Arne,

EQEP module can generally measure signals of quite high frequencies if Unit Timeout Measurement approach is used so ideally there should not be any issue in your case where signals are around 20kHZ.  Can you provide more details about your configuration of eQEP, are you using unit time out interrupt i.e. speed calculation occurs after every unit timeout (20 ms in your case) .

Thanks & Regards

Himanshu

Thank you Himanshu for your help so far.

I tried various things but it's always the same result with the wrong speed measurement for one time period.
Here is the simplest code example with the result from the diagram.

/*init interrupts*/
// Clear all interrupts and initialize PIE vector table:
// Disable CPU interrupts
   DINT;

// Initialize the PIE control registers to their default state.
// The default state is all PIE interrupts disabled and flags
// are cleared.
   InitPieCtrl();

// Disable CPU interrupts and clear all CPU interrupt flags:
   IER = 0x0000;
   IFR = 0x0000;

// Initialize the PIE vector table with pointers to the shell Interrupt
// Service Routines (ISR).
// This will populate the entire table, even if the interrupt
// is not used.  This is useful for debug purposes.
   InitPieVectTable();

// Interrupts that are used in this example are re-mapped to
// ISR functions found within this file.
   EALLOW;  
   PieVectTable.EQEP1_INT = EQEP1_isr;
   EDIS;    

// Enable CPU INTs
   IER |= M_INT5;      // for EQEP


// Enable INTn in the PIE:
   PieCtrlRegs.PIEIER5.bit.INTx1 = 1;       // enable EQEP1_INT


// Enable global Interrupts and higher priority real-time debug events:
   EINT;   // Enable Global interrupt INTM
   ERTM;   // Enable Global realtime interrupt DBGM

/*init function for the eQEP module, executed one time during boot*/

void InitEQep(void) {
  /* Quadrature Count Mode */
  EQep1Regs.QDECCTL.bit.QSRC = QEP_QUADRATURE_ENCODER_COUNT_MODE;
  /* Count both signal edges (rising & falling)  */
  EQep1Regs.QDECCTL.bit.XCR  = QEP_EXT_CLOCK_RATE_X2;
  /* swap direction */
  EQep1Regs.QDECCTL.bit.SWAP = QEP_SWAP_DIRECTION;
  /* Reset QEP-Counter automatically when reaching reference point */
  EQep1Regs.QEPCTL.bit.PCRM = QEP_RESET_ON_REFERENCE_POINT;
  /* Enable QEP-Counter */
  EQep1Regs.QEPCTL.bit.QPEN = QEP_QUAD_COUNTER_ENABLE;
  /* Enable QEP-Timer */
  EQep1Regs.QEPCTL.bit.UTE  = QEP_QUAD_TIMER_ENABLE;
  /* Use Software Index Marker; Latching Position value at Index */
  EQep1Regs.QEPCTL.bit.IEL = 3;
  /* Set Encoder maximum increments into count register */
  EQep1Regs.QPOSMAX = 0xFFFFFFFF;
  /* initialize Count with zero */
  EQep1Regs.QPOSCNT = 0;
  EQep1Regs.QEINT.bit.IEL = 1; //enable Index event latch interrupt
  EQep1Regs.QEINT.bit.UTO = 1;  //Unit time out interrupt
  EQep1Regs.QEPCTL.bit.UTE = 1; // enable Unit Timer
  EQep1Regs.QEPCTL.bit.QCLM = 1; // enable capture latch mode
  EQep1Regs.QUPRD = 3000000; //periode of timer


/*Interrupt function in main.c */
void EQEP1_isr(void) {
   pos_past = pos;                                
   pos = EQep1Regs.QPOSLAT;
   v = (pos-pos_past)*750/EQep1Regs.QUPRD;
   EQep1Regs.QCLR.all=0xFFE;
   PieCtrlRegs.PIEACK.all |= PIEACK_GROUP5;
}

With an nearly empty main function the interrupt function "EQEP1_isr" is executed every 20ms because of the unit time interrupt without a problem. But when I put a loop with a counter in the main function, the counter won't be interrupted by the unit time interrupt. The counter just counts for many seconds and the speed isn't calculated once during the loop. So I think there must be an error with my interrupt initialization. If this is the case, the interrupt function "EQEP1_isr" shouldn't be executed once or am I wrong?

Best regards
Arne