LAUNCHXL-F2800137: Time delay measurement using eCAP issue

Tool/software:

Hello,

I would like to use the eCAP module to measure the time delay between the falling edge of a PWM signal generated by the MCU and an external signal connected to a pin.

The way I approached this was by configuring the eCAP module to take its input on the pin via the Input Xbar, and to reset its counter on ePWM module CNT = CMPB event.

The issue that I am facing is that the eCAP get triggered almost instantly (11 sysclk ticks = 91ns) after the sync event, but the actual signal on the pin happens somewhere around 10us after. I do not understand what is the cause for this behaviour.

If I do not sync the eCAP module with the ePWM module, and measure the period and duty of the external signals, I get accurate capture results. Based on this I conclude that there is no glitch which would falsly trigger the eCAP modules.

I also tried enabling all four capture registers to see what they capture and to my suprise they all get loaded with 11 systicks. I dont understand how can this happen since only one register should get loaded per event.

I am wondering if the issue could be in the fact that I am using CNT = CMPB signal as the ePWM syncout signal to reset the eCAP counter, but i have the ePWM module in up-down counting mode and hence, CNT = CMPB happens twice in one period.

Here is my eCAP initialization sequence:

// Variables ===========================================================================================================

#define eCAP1_Pin                5               // GPIO5 uporabim kot input za eCAP1 modul.
#define eCAP1_PinConfig          GPIO_5_GPIO5    // pin 5 funkcionalnost je GPIO.

#define eCAP1_XBAR_INPUT_LINE    XBAR_INPUT1    // Izbere Input Xbar linijo preko katere povežem pin in eCAP1 modul.
#define eCAP1_InputMuxIndex

#define eCAP1_PRESCALER         0U              // Ne prescalam vhoda.


// Function definitions ===============================================================================================


void MyECAP1_init(void)
{

    // Konfiguriram izbran GPIO pin za eCAP1 vhod

    GPIO_setPinConfig(eCAP1_PinConfig);
    GPIO_setDirectionMode(eCAP1_Pin, GPIO_DIR_MODE_IN);
    GPIO_setPadConfig(eCAP1_Pin, GPIO_PIN_TYPE_STD);
    GPIO_setQualificationMode(eCAP1_Pin, GPIO_QUAL_6SAMPLE);


    // Povežem izbran pin na input xBar.

    XBAR_setInputPin(INPUTXBAR_BASE, eCAP1_XBAR_INPUT_LINE, eCAP1_Pin);


    // Izberem ustrezeno input xBar linijo v eCAP1 input muxu.

    ECAP_selectECAPInput(ECAP1_BASE, ECAP_INPUT_INPUTXBAR1);


    // Konfiguriram polariteto in event qualifier

    ECAP_setEventPrescaler(ECAP1_BASE, eCAP1_PRESCALER);    // Nastavim prescaler.

    ECAP_setEmulationMode(ECAP1_BASE, ECAP_EMULATION_FREE_RUN );    // Omogocim neprekinjeno delovanje tudi ob SW breakpointih.

    ECAP_setEventPolarity(ECAP1_BASE, ECAP_EVENT_1, ECAP_EVNT_FALLING_EDGE);
    ECAP_setEventPolarity(ECAP1_BASE, ECAP_EVENT_2, ECAP_EVNT_FALLING_EDGE);
    ECAP_setEventPolarity(ECAP1_BASE, ECAP_EVENT_3, ECAP_EVNT_FALLING_EDGE);
    ECAP_setEventPolarity(ECAP1_BASE, ECAP_EVENT_4, ECAP_EVNT_FALLING_EDGE);

    ECAP_enableCounterResetOnEvent(ECAP1_BASE, ECAP_EVENT_1);   // Prvi event resetira števec.
    ECAP_enableCounterResetOnEvent(ECAP1_BASE, ECAP_EVENT_2);   // Prvi event resetira števec.
    ECAP_enableCounterResetOnEvent(ECAP1_BASE, ECAP_EVENT_3);   // Prvi event resetira števec.
    ECAP_enableCounterResetOnEvent(ECAP1_BASE, ECAP_EVENT_4);   // Prvi event resetira števec.

    ECAP_enableTimeStampCapture(ECAP1_BASE);    // Omogočim, da se zajame vrednost števca ob nastanku eventa.

    ECAP_enableCaptureMode(ECAP1_BASE);     // Omogočim delovanje v capture in ne APWM režimu.

    ECAP_setCaptureMode(ECAP1_BASE, ECAP_CONTINUOUS_CAPTURE_MODE, ECAP_EVENT_4);

    ECAP_setSyncInPulseSource(ECAP1_BASE, ECAP_SYNC_IN_PULSE_SRC_SYNCOUT_EPWM2);    // Nastavim vir SyncIn pulza.

    ECAP_enableLoadCounter(ECAP1_BASE); // Omogocim nalaganje vrednosti v stevec ob syncin pulzu.

    ECAP_setPhaseShiftCount(ECAP1_BASE, 0U); // Nastavim vrednost s katere zacne stevec ob SyncIn pulzu.

    EPWM_enableSyncOutPulseSource(EPWM2_BASE, EPWM_SYNC_OUT_PULSE_ON_CNTR_ZERO);   // Nastavim vir epwm syncout pulza.

    ECAP_resetCounters(ECAP1_BASE);     // Ponastavim vse stevce v eCAP1 modulu in pripravim na zagon.

    ECAP_startCounter(ECAP1_BASE);      // Pozenem stevec eCAP1 modula.


    return;
}

I have also attached a .zip file of the entire project folder if that helps.

240614 TI e2e eCAP SupportTicket.zip

I am really looking forward to any suggestions.

Regards,

Samo