TMS320F28388D: PWM SyncTo question

Dorion,

Could you please explain your setting in terms of which ePWM is sending sync out and its associated channel who is taking that as sync in?

Regards,

Sumit

Hi Sumit, 

  I think this is what you are looking for. 

  We setup ePWM8 (we call BISS_PWM_POS_BASE) Below:

// FclConfigPWMCommon: Configures a single PWM channel to drive a three phase motor
// Includes configureation that is common to all channels and should be run for each PWM
void FocConfigPWM(uint32_t pwmBase, float32_t periodCount)
{    
     EPWM_setPeriodLoadMode(pwmBase, EPWM_PERIOD_DIRECT_LOAD);

     // Need to subtract 1 since we are in count up mode.
     EPWM_setTimeBasePeriod(BISS_PWM_POS_BASE, (MICROSECONDS_TO_SYSCLK_CYCLES(periodCount) -1));    

     EPWM_setPhaseShift(pwmBase, 0);
     EPWM_setTimeBaseCounter(pwmBase, 0U);

     // example shows enabling this but I am syncing similar to Maglev which disables it
     EPWM_disablePhaseShiftLoad(pwmBase);

     // Initialize PWMs to Freeze until told to Go.
     EPWM_setTimeBaseCounterMode(pwmBase, EPWM_COUNTER_MODE_STOP_FREEZE);

     // after sync count up.
     EPWM_setCountModeAfterSync(pwmBase, EPWM_COUNT_MODE_UP_AFTER_SYNC);

     // Counting up trigger on zero
     EPWM_setTimeBaseCounterMode(pwmBase, EPWM_COUNTER_MODE_UP);

     EPWM_setClockPrescaler(pwmBase, EPWM_CLOCK_DIVIDER_1, EPWM_HSCLOCK_DIVIDER_1);

     // Enable sync out pulse on zero.
     EPWM_enableSyncOutPulseSource(pwmBase, EPWM_SYNC_OUT_PULSE_ON_CNTR_ZERO);
}

We then setup ePWM1 which we cal U_PWM_BASE as follows:
    // PWM Deadband Count
    uint32_t dbPWMCount = MICROSECONDS_TO_SYSCLK_CYCLES(FCL_PWM_DB_USEC);
    
    EPWM_setPeriodLoadMode(pwmBase, EPWM_PERIOD_DIRECT_LOAD);
    EPWM_setTimeBasePeriod(pwmBase, *(pHwConfig->pPwmHalfPeriodCount));
    EPWM_setPhaseShift(pwmBase, 0);
    EPWM_setTimeBaseCounter(pwmBase, 0U);
    // example shows enabling this but I am syncing similar to Maglev which disables it
    EPWM_disablePhaseShiftLoad(pwmBase);
    // Initialize PWMs to Freeze until told to Go.
    EPWM_setTimeBaseCounterMode(pwmBase, EPWM_COUNTER_MODE_STOP_FREEZE);
    // after sync count up. 
    EPWM_setCountModeAfterSync(pwmBase, EPWM_COUNT_MODE_UP_AFTER_SYNC);
   
    // Counting up and down to center all PWM togeter
    EPWM_setTimeBaseCounterMode(pwmBase, EPWM_COUNTER_MODE_UP_DOWN);

    EPWM_setClockPrescaler(pwmBase, EPWM_CLOCK_DIVIDER_1,
                           EPWM_HSCLOCK_DIVIDER_1);
    
    // Counter Compare Submodule Registers
    // set duty 0% initially
    // Will load new shadow value on counter = 0
    EPWM_setCounterCompareValue(pwmBase, EPWM_COUNTER_COMPARE_A, 0);
    EPWM_setCounterCompareShadowLoadMode(pwmBase, EPWM_COUNTER_COMPARE_A, EPWM_COMP_LOAD_ON_CNTR_ZERO);
    
    // Action Qualifier SubModule Registers
    // Go low when cmpa counting up and high when compa counting down.
    EPWM_setActionQualifierActionComplete(pwmBase, EPWM_AQ_OUTPUT_A,
                                          (EPWM_ActionQualifierEventAction)(EPWM_AQ_OUTPUT_LOW_DOWN_CMPA |
                                                                            EPWM_AQ_OUTPUT_HIGH_UP_CMPA));         

    // set deadband clock to run at TBCK rate
    EPWM_setDeadBandCounterClock(pwmBase, EPWM_DB_COUNTER_CLOCK_FULL_CYCLE);
    
    // Both A and B outputs get input from A (IN_MODE, DEDB_MODE)
    EPWM_setRisingEdgeDeadBandDelayInput(pwmBase,EPWM_DB_INPUT_EPWMA);
    EPWM_setFallingEdgeDeadBandDelayInput(pwmBase,EPWM_DB_INPUT_EPWMA);
    
    // B falling edge output delay is inverted, A rising edge delay is not(POLSEL)
    EPWM_setDeadBandDelayPolarity(pwmBase, EPWM_DB_RED, EPWM_DB_POLARITY_ACTIVE_HIGH);
    EPWM_setDeadBandDelayPolarity(pwmBase, EPWM_DB_FED, EPWM_DB_POLARITY_ACTIVE_LOW);

    // A and B are fed from dead band modules (OUT_MODE)
    EPWM_setDeadBandDelayMode(pwmBase, EPWM_DB_RED, true);
    EPWM_setDeadBandDelayMode(pwmBase, EPWM_DB_FED, true);
    
    // No swapping, A gets A and B gets B (OUTSWAP)
    EPWM_setDeadBandOutputSwapMode(pwmBase,EPWM_DB_OUTPUT_A, false);
    EPWM_setDeadBandOutputSwapMode(pwmBase,EPWM_DB_OUTPUT_B, false);

    // For now assign fixed deadband 
    EPWM_setRisingEdgeDelayCount (pwmBase, dbPWMCount);
    EPWM_setFallingEdgeDelayCount(pwmBase,dbPWMCount);

==================================================================================

We then sync them this way: 
        PwmSyncTo(U1_PWM_BASE, BISS_PWM_POS_BASE);

Then if you set the BISS_PWM_POS_BASE period count like this: 

        SysCtl_disablePeripheral(SYSCTL_PERIPH_CLK_TBCLKSYNC);
        EPWM_setTimeBasePeriod(BISS_PWM_POS_BASE, (MICROSECONDS_TO_SYSCLK_CYCLES(periodCount) -1));

        The above line setTimeBasePeriod will change the U1_PWM_BASE TBCR count to the same periodCount as show above. 

Easy to reproduce. We just want to know if this is normal behavior? Is there something that we configure that makes it do this?

Dorion 

Forgot to include the pwmSyncTo function
void PwmSyncTo(uint32_t base, uint32_t syncBase)
{
    EPWM_enablePhaseShiftLoad(base);
    EPWM_setupEPWMLinks(base, GetLink(syncBase), EPWM_LINK_TBPRD);
    EPWM_setSyncInPulseSource(base, GetPulseSource(syncBase));
    EPWM_enableSyncOutPulseSource(syncBase, EPWM_SYNC_OUT_PULSE_ON_CNTR_ZERO);
}

Dorion,

Are you using sysconfig to configure this. I would suggest to refer to the example synchronization in ePMW in C2000Ware to verify your settings.

Regards,

Sumit

Sumit, 

  We have used sysconfig in the past to help set things up. I can try to do this again but I need an answer to my original question. Doing a sysconfig config will not give me the answer that I am looking for and take time. 

  My original question is If you have a PWM (A) sunk to another PWM (B) and you change the timeBaseCounter for PWM B does it directly change the TBPRD register for PWM A?

  We have worked around this by configuring PWM B first then PWM A, since the pwm clock is disable this won't hurt anything but we want to make sure we are not fighting something else. 

  There seems to be no documentation on this behavior. 

Dorion 

Synchronization does not change the TBPRD it only loads value from TBPHS to TBCTR when sync event occurs.

Regards,

Sumit