TMS320F28379D: Help with ECAP not correctly capturing PWM input

Some further comment:

The Falling Edge captures seem to be correct.  The values there are ~50us, which matches.  It is the rising edge that is off.

If I switch which edges are rising and falling, the issue follows the rising edge:

ECAP_setEventPolarity(ecap_bases[i], ECAP_EVENT_1, ECAP_EVNT_RISING_EDGE);
ECAP_setEventPolarity(ecap_bases[i], ECAP_EVENT_2, ECAP_EVNT_FALLING_EDGE);
ECAP_setEventPolarity(ecap_bases[i], ECAP_EVENT_3, ECAP_EVNT_RISING_EDGE);
ECAP_setEventPolarity(ecap_bases[i], ECAP_EVENT_4, ECAP_EVNT_FALLING_EDGE);

If I set all edges to rising edge, I get 0x1C for all CAP registers.

So it seems the rising edge capture is the issue.

I have also tried all different settings for input qualification, with no change in behavior.

Hi Mark Feller,

First can you confirm if the example 2 of the eCAP works as expected? I am able to correctly run this example.

I also switched the example over to sample from pin 104. I see no issues.

//#############################################################################
//
// FILE:    ecap_capture_pwm.c
//
// TITLE:   Capture ePWM3.
//
//! \addtogroup driver_example_list
//! <h1>eCAP Capture PWM Example</h1>
//!
//! This example configures ePWM3A for:
//! - Up count mode
//! - Period starts at 500 and goes up to 8000
//! - Toggle output on PRD
//!
//! eCAP1 is configured to capture the time between rising
//! and falling edge of the ePWM3A output.
//!
//! \b External \b Connections \n
//! - eCAP1 is on GPIO16
//! - ePWM3A is on GPIO4
//! - Connect GPIO4 to GPIO16.
//!
//! \b Watch \b Variables \n
//! - \b ecap1PassCount - Successful captures.
//! - \b ecap1IntCount - Interrupt counts.
//
//#############################################################################
//
// 
// $Copyright:
// Copyright (C) 2013-2024 Texas Instruments Incorporated - http://www.ti.com/
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// Redistribution and use in source and binary forms, with or without 
// modification, are permitted provided that the following conditions 
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// 
//   Redistributions of source code must retain the above copyright 
//   notice, this list of conditions and the following disclaimer.
// 
//   Redistributions in binary form must reproduce the above copyright
//   notice, this list of conditions and the following disclaimer in the 
//   documentation and/or other materials provided with the   
//   distribution.
// 
//   Neither the name of Texas Instruments Incorporated nor the names of
//   its contributors may be used to endorse or promote products derived
//   from this software without specific prior written permission.
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// $
//#############################################################################

//
// Included Files
//
#include "driverlib.h"
#include "device.h"

//
// Defines
//
#define PWM3_TIMER_MIN     500U
#define PWM3_TIMER_MAX     8000U
#define EPWM_TIMER_UP      1U
#define EPWM_TIMER_DOWN    0U

//
// Globals
//
uint32_t ecap1IntCount;
uint32_t ecap1PassCount;
uint32_t epwm3TimerDirection;
volatile uint16_t cap2Count;
volatile uint16_t cap3Count;
volatile uint16_t cap4Count;
volatile uint16_t epwm3PeriodCount;

//
// Function Prototypes
//
void error(void);
void initECAP(void);
void initEPWM(void);
__interrupt void ecap1ISR(void);

//
// Main
//
void main(void)
{
    //
    // Initialize device clock and peripherals
    //
    Device_init();

    //
    // Disable pin locks and enable internal pullups.
    //
    Device_initGPIO();

    //
    // Initialize PIE and clear PIE registers. Disables CPU interrupts.
    //
    Interrupt_initModule();

    //
    // Initialize the PIE vector table with pointers to the shell Interrupt
    // Service Routines (ISR).
    //
    Interrupt_initVectorTable();

    //
    // Configure GPIO4/5 as ePWM3A/3B
    //
    GPIO_setPadConfig(4, GPIO_PIN_TYPE_STD);
    GPIO_setPinConfig(GPIO_4_EPWM3A);
    GPIO_setPadConfig(5, GPIO_PIN_TYPE_STD);
    GPIO_setPinConfig(GPIO_5_EPWM3B);

    //
    // Configure GPIO 16 as eCAP input
    //
    XBAR_setInputPin(XBAR_INPUT7, 104);
    GPIO_setPinConfig(GPIO_104_GPIO104);
    GPIO_setDirectionMode(16, GPIO_DIR_MODE_IN);
    GPIO_setQualificationMode(16, GPIO_QUAL_ASYNC);

    //
    // Interrupts that are used in this example are re-mapped to ISR functions
    // found within this file.
    //
    Interrupt_register(INT_ECAP1, &ecap1ISR);

    //
    // Configure ePWM and eCAP
    //
    initEPWM();
    initECAP();

    //
    // Initialize counters:
    //
    cap2Count = 0U;
    cap3Count = 0U;
    cap4Count = 0U;
    ecap1IntCount = 0U;
    ecap1PassCount = 0U;
    epwm3PeriodCount = 0U;

    //
    // Enable interrupts required for this example
    //
    Interrupt_enable(INT_ECAP1);

    //
    // Enable Global Interrupt (INTM) and Real time interrupt (DBGM)
    //
    EINT;
    ERTM;

    //
    // Loop forever. Suspend or place breakpoints to observe the buffers.
    //
    for(;;)
    {
       NOP;
    }
}

//
// initEPWM - Configure ePWM
//
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(EPWM3_BASE, EPWM_COUNTER_MODE_UP);
    EPWM_setTimeBasePeriod(EPWM3_BASE, PWM3_TIMER_MIN);
    EPWM_setPhaseShift(EPWM3_BASE, 0U);
    EPWM_setActionQualifierAction(EPWM3_BASE,
                                  EPWM_AQ_OUTPUT_A,
                                  EPWM_AQ_OUTPUT_TOGGLE,
                                  EPWM_AQ_OUTPUT_ON_TIMEBASE_PERIOD);
    EPWM_setClockPrescaler(EPWM3_BASE,
                           EPWM_CLOCK_DIVIDER_1,
                           EPWM_HSCLOCK_DIVIDER_2);

    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, 104);

    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.
    //
    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(EPWM3_BASE);

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

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

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

    ecap1IntCount++;

    //
    // Keep track of the ePWM direction and adjust period accordingly to
    // generate a variable frequency PWM.
    //
    if(epwm3TimerDirection == EPWM_TIMER_UP)
    {
        if(epwm3PeriodCount < PWM3_TIMER_MAX)
        {
           EPWM_setTimeBasePeriod(EPWM3_BASE, ++epwm3PeriodCount);
        }
        else
        {
           epwm3TimerDirection = EPWM_TIMER_DOWN;
           EPWM_setTimeBasePeriod(EPWM3_BASE, ++epwm3PeriodCount);
        }
    }
    else
    {
        if(epwm3PeriodCount > PWM3_TIMER_MIN)
        {
            EPWM_setTimeBasePeriod(EPWM3_BASE, --epwm3PeriodCount);
        }
        else
        {
           epwm3TimerDirection = EPWM_TIMER_UP;
           EPWM_setTimeBasePeriod(EPWM3_BASE, ++epwm3PeriodCount);
        }
    }

    //
    // Count correct captures
    //
    ecap1PassCount++;

    //
    // Clear interrupt flags for more interrupts.
    //
    ECAP_clearInterrupt(ECAP1_BASE,ECAP_ISR_SOURCE_CAPTURE_EVENT_4);
    ECAP_clearGlobalInterrupt(ECAP1_BASE);

    //
    // Start eCAP
    //
    ECAP_reArm(ECAP1_BASE);

    //
    // Acknowledge the group interrupt for more interrupts.
    //
    Interrupt_clearACKGroup(INTERRUPT_ACK_GROUP4);
}

//
// error - Error function
//
void error()
{
    ESTOP0;
}

Best,

Ryan Ma

Hi Ryan,

The example2  works.  I changed to pin 104, and also changed to EPWM1, and the example2  still works. 

I switched to one-shot mode in my project, in order to match the example, and there is still the issue with rising edge capture.  If I look at the register contents for ECAP1, these all look as expected.

I provided code snippet for your configuration for pin 104. I didn't see any issues with using epwm1.

Can you confirm?

Best,

Ryan Ma

Hi Mark, 

Got it, sync in was being set causing TSCTR to change.

Good catch!

Best regards,

Ryan Ma