TMS320F28377S: ECAP TIME STAMP capture values are varying

Tool/software:

Hi 

I configured ECAP1 to measure period values of EPWM9, here in the modified version of example code that i made to work for my application.

void initEPWM()
{
//
// Disable sync(Freeze clock to PWM as well)
//
SysCtl_disablePeripheral(SYSCTL_PERIPH_CLK_TBCLKSYNC);

//
// Configure ePWM
// Counter runs in up-count mode.
// Action qualifier will toggle output on period match
//
EPWM_setTimeBaseCounterMode(EPWM9_BASE, EPWM_COUNTER_MODE_UP);
EPWM_setTimeBasePeriod(EPWM9_BASE, 1000);
EPWM_setPhaseShift(EPWM9_BASE, 0U);
/**
* Set up shadowing
*/
EPWM_setCounterCompareShadowLoadMode(EPWM9_BASE,
EPWM_COUNTER_COMPARE_A,
EPWM_COMP_LOAD_ON_CNTR_ZERO);
/**
* Set Compare values
*/
// 1.667us Clock pulse width
EPWM_setCounterCompareValue(EPWM9_BASE,
EPWM_COUNTER_COMPARE_A,
400);
EPWM_setActionQualifierAction(EPWM9_BASE,
EPWM_AQ_OUTPUT_A,
EPWM_AQ_OUTPUT_HIGH,
EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPA);
EPWM_setActionQualifierAction(EPWM9_BASE,
EPWM_AQ_OUTPUT_A,
EPWM_AQ_OUTPUT_LOW,
EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO );
EPWM_setClockPrescaler(EPWM9_BASE,
EPWM_CLOCK_DIVIDER_1,
EPWM_HSCLOCK_DIVIDER_1);

//epwm3TimerDirection = EPWM_TIMER_UP;

//
// Enable sync and clock to PWM
//
SysCtl_enablePeripheral(SYSCTL_PERIPH_CLK_TBCLKSYNC);
}

//
// initECAP - Configure eCAP
//
void initECAP()
{
//
// Disable ,clear all capture flags and interrupts
//
ECAP_disableInterrupt(ECAP1_BASE,
(ECAP_ISR_SOURCE_CAPTURE_EVENT_1 |
ECAP_ISR_SOURCE_CAPTURE_EVENT_2 |
ECAP_ISR_SOURCE_CAPTURE_EVENT_3 |
ECAP_ISR_SOURCE_CAPTURE_EVENT_4 |
ECAP_ISR_SOURCE_COUNTER_OVERFLOW |
ECAP_ISR_SOURCE_COUNTER_PERIOD |
ECAP_ISR_SOURCE_COUNTER_COMPARE));
ECAP_clearInterrupt(ECAP1_BASE,
(ECAP_ISR_SOURCE_CAPTURE_EVENT_1 |
ECAP_ISR_SOURCE_CAPTURE_EVENT_2 |
ECAP_ISR_SOURCE_CAPTURE_EVENT_3 |
ECAP_ISR_SOURCE_CAPTURE_EVENT_4 |
ECAP_ISR_SOURCE_COUNTER_OVERFLOW |
ECAP_ISR_SOURCE_COUNTER_PERIOD |
ECAP_ISR_SOURCE_COUNTER_COMPARE));

//
// Disable CAP1-CAP4 register loads
//
ECAP_disableTimeStampCapture(ECAP1_BASE);

//
// Configure eCAP
// Enable capture mode.
// One shot mode, stop capture at event 4.
// Set polarity of the events to rising, falling, rising, falling edge.
// Set capture in time difference mode.
// Select input from XBAR7.
// Enable eCAP module.
// Enable interrupt.
//
ECAP_stopCounter(ECAP1_BASE);
ECAP_enableCaptureMode(ECAP1_BASE);

ECAP_setCaptureMode(ECAP1_BASE, ECAP_CONTINUOUS_CAPTURE_MODE, ECAP_EVENT_4);

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

ECAP_enableCounterResetOnEvent(ECAP1_BASE, ECAP_EVENT_1);
ECAP_enableCounterResetOnEvent(ECAP1_BASE, ECAP_EVENT_2);
ECAP_enableCounterResetOnEvent(ECAP1_BASE, ECAP_EVENT_3);
ECAP_enableCounterResetOnEvent(ECAP1_BASE, ECAP_EVENT_4);

XBAR_setInputPin(XBAR_INPUT7, 74);

ECAP_enableLoadCounter(ECAP1_BASE);
ECAP_setSyncOutMode(ECAP1_BASE, ECAP_SYNC_OUT_SYNCI);
ECAP_startCounter(ECAP1_BASE);
ECAP_enableTimeStampCapture(ECAP1_BASE);
ECAP_reArm(ECAP1_BASE);

ECAP_enableInterrupt(ECAP1_BASE, ECAP_ISR_SOURCE_CAPTURE_EVENT_4);
}

//
// eCAP 1 ISR
//
__interrupt void ecap1ISR(void)
{
//
// Get the capture counts. Each capture should be 4x the ePWM count
// because of the ePWM clock dividers.
//
cap1Count = ECAP_getEventTimeStamp(ECAP1_BASE, ECAP_EVENT_1);
cap2Count = ECAP_getEventTimeStamp(ECAP1_BASE, ECAP_EVENT_2);
cap3Count = ECAP_getEventTimeStamp(ECAP1_BASE, ECAP_EVENT_3);
cap4Count = ECAP_getEventTimeStamp(ECAP1_BASE, ECAP_EVENT_4);

//
// Compare the period value with the captured count
//
epwm3PeriodCount = EPWM_getTimeBasePeriod(EPWM9_BASE);

if(cap2Count > ((epwm3PeriodCount * 4) + 4) ||
cap2Count < ((epwm3PeriodCount * 4) - 4))
{
error();
}

else if(cap3Count > ((epwm3PeriodCount * 4) + 4) ||
cap3Count < ((epwm3PeriodCount * 4) - 4))
{
error();
}

else if(cap4Count > ((epwm3PeriodCount * 4) + 4) ||
cap4Count < ((epwm3PeriodCount * 4) - 4))
{
error();
}
else
{
flag = 0;
}

ecap1IntCount++;

The timestamp capture values are reading fine.

I am getting an Issue when implementing, ECAP1 with my actual code, where there are other epwm configurations (epwm1, 2, 3) and 

I am using syncout sel mode to keep these in sync as they need to have some phase shift.

The time stamp  values are varying.

I want to know does syncout sel effect ecap TSCTR which is clocked from sysclk.

only when i disable the syncout sel configuration from epwm1 then only i get proper timestamp value.

i found this in Reference manual, my understanding is ecap synchronization is only for other ecap modules then why the syncout sel is effecting the ecap

Thanks & regards

Rupa