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LAUNCHXL-F28379D: PWM glitches when using multiple PWM modules

Matthew Touma
Prodigy 120 points
Part Number: LAUNCHXL-F28379D


Hi all,

I am using EPWM4A, EPWM5A, and EPWM6A to generate independent PWM signals at various frequencies and duty cycles. For some reason, when I modify the PWM duty cycle of one module the other modules flicker and jitter. For example, if I change the duty cycle of EPWM4A, I notice little glitches on EPWM6A. Similarly, when adjusting the duty cycle of EPWM6A, I notice glitches and flickers on EPWM4A.

Any thoughts on why this would be happening? I need the PWMs to be stable! I tried experimenting with different sync sources, but I didn't find any solutions.

I hope somebody can help me.

Thanks,

- Matthew

  • 0
    TI__Mastermind 25780 points

    Hi Matthew, 

    Are you linking the compare values of the different EPWM modules? Could you please share your initialization of EPWM4A, 5A, and 6A? 

    Best Regards,

    Marlyn

  • 0 in reply to Marlyn Rosales Castaneda20
    Prodigy 120 points 

    void EPWM_init(){
    EPWM_setClockPrescaler(myEPWM4_BASE, EPWM_CLOCK_DIVIDER_1, EPWM_HSCLOCK_DIVIDER_2);
    EPWM_setTimeBasePeriod(myEPWM4_BASE, 0);
    EPWM_setTimeBaseCounter(myEPWM4_BASE, 0);
    EPWM_setTimeBaseCounterMode(myEPWM4_BASE, EPWM_COUNTER_MODE_STOP_FREEZE);
    EPWM_disablePhaseShiftLoad(myEPWM4_BASE);
    EPWM_setPhaseShift(myEPWM4_BASE, 0);
    EPWM_setCounterCompareValue(myEPWM4_BASE, EPWM_COUNTER_COMPARE_A, 0);
    EPWM_setCounterCompareShadowLoadMode(myEPWM4_BASE, EPWM_COUNTER_COMPARE_A, EPWM_COMP_LOAD_ON_CNTR_ZERO);
    EPWM_setCounterCompareValue(myEPWM4_BASE, EPWM_COUNTER_COMPARE_B, 0);
    EPWM_setCounterCompareShadowLoadMode(myEPWM4_BASE, EPWM_COUNTER_COMPARE_B, EPWM_COMP_LOAD_ON_CNTR_ZERO);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_PERIOD);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPA);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPB);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPB);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_PERIOD);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPA);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPB);
    EPWM_setActionQualifierAction(myEPWM4_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPB);

    EPWM_setClockPrescaler(myEPWM5_BASE, EPWM_CLOCK_DIVIDER_1, EPWM_HSCLOCK_DIVIDER_2);
    EPWM_setTimeBasePeriod(myEPWM5_BASE, 0);
    EPWM_setTimeBaseCounter(myEPWM5_BASE, 0);
    EPWM_setTimeBaseCounterMode(myEPWM5_BASE, EPWM_COUNTER_MODE_STOP_FREEZE);
    EPWM_disablePhaseShiftLoad(myEPWM5_BASE);
    EPWM_setPhaseShift(myEPWM5_BASE, 0);
    EPWM_setCounterCompareValue(myEPWM5_BASE, EPWM_COUNTER_COMPARE_A, 0);
    EPWM_setCounterCompareShadowLoadMode(myEPWM5_BASE, EPWM_COUNTER_COMPARE_A, EPWM_COMP_LOAD_ON_CNTR_ZERO);
    EPWM_setCounterCompareValue(myEPWM5_BASE, EPWM_COUNTER_COMPARE_B, 0);
    EPWM_setCounterCompareShadowLoadMode(myEPWM5_BASE, EPWM_COUNTER_COMPARE_B, EPWM_COMP_LOAD_ON_CNTR_ZERO);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_PERIOD);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPA);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPB);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPB);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_PERIOD);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPA);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPB);
    EPWM_setActionQualifierAction(myEPWM5_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPB);

    EPWM_setClockPrescaler(myEPWM6_BASE, EPWM_CLOCK_DIVIDER_1, EPWM_HSCLOCK_DIVIDER_2);
    EPWM_setTimeBasePeriod(myEPWM6_BASE, 0);
    EPWM_setTimeBaseCounter(myEPWM6_BASE, 0);
    EPWM_setTimeBaseCounterMode(myEPWM6_BASE, EPWM_COUNTER_MODE_STOP_FREEZE);
    EPWM_disablePhaseShiftLoad(myEPWM6_BASE);
    EPWM_setPhaseShift(myEPWM6_BASE, 0);
    EPWM_setCounterCompareValue(myEPWM6_BASE, EPWM_COUNTER_COMPARE_A, 0);
    EPWM_setCounterCompareShadowLoadMode(myEPWM6_BASE, EPWM_COUNTER_COMPARE_A, EPWM_COMP_LOAD_ON_CNTR_ZERO);
    EPWM_setCounterCompareValue(myEPWM6_BASE, EPWM_COUNTER_COMPARE_B, 0);
    EPWM_setCounterCompareShadowLoadMode(myEPWM6_BASE, EPWM_COUNTER_COMPARE_B, EPWM_COMP_LOAD_ON_CNTR_ZERO);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_PERIOD);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPA);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPB);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_A, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPB);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_ZERO);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_PERIOD);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPA);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPA);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_UP_CMPB);
    EPWM_setActionQualifierAction(myEPWM6_BASE, EPWM_AQ_OUTPUT_B, EPWM_AQ_OUTPUT_NO_CHANGE, EPWM_AQ_OUTPUT_ON_TIMEBASE_DOWN_CMPB);
}

  • 0 in reply to Marlyn Rosales Castaneda20
    Prodigy 120 points 

    void SYNC_init(){
	SysCtl_setSyncOutputConfig(SYSCTL_SYNC_OUT_SRC_EPWM1SYNCOUT);
	// For EPWM1, the sync input is: SYSCTL_SYNC_IN_SRC_EXTSYNCIN1
	SysCtl_setSyncInputConfig(SYSCTL_SYNC_IN_EPWM4, SYSCTL_SYNC_IN_SRC_EPWM1SYNCOUT);
	SysCtl_setSyncInputConfig(SYSCTL_SYNC_IN_EPWM7, SYSCTL_SYNC_IN_SRC_EPWM1SYNCOUT);
	SysCtl_setSyncInputConfig(SYSCTL_SYNC_IN_EPWM10, SYSCTL_SYNC_IN_SRC_EPWM1SYNCOUT);
	SysCtl_setSyncInputConfig(SYSCTL_SYNC_IN_ECAP1, SYSCTL_SYNC_IN_SRC_EPWM1SYNCOUT);
	SysCtl_setSyncInputConfig(SYSCTL_SYNC_IN_ECAP4, SYSCTL_SYNC_IN_SRC_EPWM1SYNCOUT);
	// SOCA
	SysCtl_enableExtADCSOCSource(0);
	// SOCB
	SysCtl_enableExtADCSOCSource(0);
}

  • 0 in reply to Marlyn Rosales Castaneda20
    Prodigy 120 points

    And here's how I adjust the duty cycle.

    // Set PWM (EPWM4A) duty cycle
// Arguments: the desired duty cycle as a decimal (0-1)
// Outputs: none, but the PWM output will be affected.
void apply_PWM4A(float duty){

    pwm4Signal.dutyValA = duty;

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

    //
    // Configuring ePWM module for desired frequency and duty
    //
    EPWM_configureSignal(myEPWM4_BASE, &pwm4Signal);
//    EPWM_configureSignal(myEPWM2_BASE, &pwmSignal);
//    EPWM_configureSignal(myEPWM3_BASE, &pwmSignal);

    //
    // ePWM4 SYNCO is generated on CTR=0
    //
    EPWM_setSyncOutPulseMode(myEPWM4_BASE, EPWM_SYNC_OUT_PULSE_ON_COUNTER_ZERO);

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

  • +1 in reply to Matthew Touma
    TI__Mastermind 25780 points

    Hi Matthew,

    Thank you for sharing your configuration. Where in your application do you call the 'apply_PWM4A' function? In general I do not recommend disabling the TBCLKSYNC, calling the configureSignal function, and then re-enabling the TBCLKSYNC. What you are doing is freezing the time base counter mid-operation and then resetting the epwm based on the values passed in through configureSignal which changes more than just the duty. Since you already have shadow loading enabled I recommend you just update your compare values in the 'apply_PWM4A' function, something like the below:

        EPWM_setCounterCompareValue(myEPWM4_BASE, EPWM_COUNTER_COMPARE_A, 50);
    EPWM_setCounterCompareValue(myEPWM4_BASE, EPWM_COUNTER_COMPARE_B, 100);

    The new compare values will take effect the next time the time-base counter is equal to zero.

    The following line of code can also be called during the initialization:

        EPWM_setSyncOutPulseMode(myEPWM4_BASE, EPWM_SYNC_OUT_PULSE_ON_COUNTER_ZERO);

    Best Regards,

    Marlyn

  • 0 in reply to Marlyn Rosales Castaneda20
    Prodigy 120 points

    Thanks for the reply. That makes sense, but how should I calculate the compare values based on my desired duty cycle?

    - Matthew

  • 0 in reply to Matthew Touma
    TI__Mastermind 25780 points

    Hi Matthew,

    Matthew Touma said:
    how should I calculate the compare values based on my desired duty cycle?

    This is explained in the following video (https://training.ti.com/c2000-enhanced-pulse-width-modulator-epwm-time-base-submodule) and within this application report (C2000 ePWM Developer's Guide)

    Best Regards,

    Marlyn