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TMS320F280049: Sync Pulse mechanism for HRPWM

Gökhan Bayraktar
Prodigy 120 points

Part Number: TMS320F280049
Other Parts Discussed in Thread: C2000WARE, SYSCONFIG

Tool/software:

Hello all,

I have configured 4 HRPWM module for high-res frequency and phase shift control.

I have selected the EPWM1 as the master and rest are the slaves.

In general I managed to obtained desired frequency and phase shift however I have a question for sync mechanism.

I am calculating the period and phase shift values in every 80 us control period.

Then I want to update the phase shift value for each slave PWM when the PWM1 time base counter = 0.

So far there is no problem I can do this. But I would like to disable the sync mechanism after the sync pulse is fired so that jittering problem due to using HRPWM would have less affect.

Here the problem starts. Here are my tries:

1- PWM Interrupt method

  • I have configured the PWM1 Interrupt which is triggered when the PWM1 Time Base CTR = 0.  
  • At the end of my PWM_update function I call this line for activating sync mechanism EPWM_setSyncOutPulseMode(myEPWM1_BASE, EPWM_SYNC_OUT_PULSE_ON_COUNTER_ZERO);
  • Then I enable the PWM1 INT by HRPWM_enableInterrupt(myEPWM1_BASE);
  • In the PWM ISR, I disable the sync mechanism and also PWM interrupt to be enabled again at the next PWM_update function
    •  HRPWM_setSyncOutPulseMode(myEPWM1_BASE, EPWM_SYNC_OUT_PULSE_DISABLED);
    •  EPwm1Regs.ETSEL.bit.INTEN=0;  //disable ePWM1interrupt
  • This method works fine generally but randomly creates problem such that:
    • Sometimes the sync pulse is not fired although I could see that SW entered the PWM1 INT (according to logic PWM int should be entered after the sync pulse fired, at least I hoped )
    • Sometimes EPWM1 interrupts affects ADC INT. ADC INT is triggered by a dummy PWM which is not HR mode and totally independent from the 4 HRPWM modules
  • I guess the these problem arise due to interrupt handling and lack of nesting logic but I am not sure may be they are about using the same event ( PWM1 TBCTR = 0 ) for the sync pulse firing and PWM interrupt triggering

2- My second theriacal method is using the sync pulse as a trigger for PWM interrupt ( I guess as TZ event interrupt with the digital compare submodule) . With this method I would be sure that PWM interrupt ISR will be entered sync pulse. Then I would safely disable the sync pulse mechanism.

  • So far I could not manage to enabled the PWM ISR with this method

3- My third method is using the already configured ADC interrupt

  • In this method after the EPWM_setSyncOutPulseMode(myEPWM1_BASE, EPWM_SYNC_OUT_PULSE_ON_COUNTER_ZERO); line in the PWM_update function, I make a flag variable 1.
  • Then ın the ADC interrupt (ADC INT fperiod is 5us) I increment a counter up to a threshold which corresponds 10us. This threshold time is sufficient for the all frequency range that my PWM can have.
    • I mean at min frequency I am guaranteed that at least one sync pulse is fired before I disable the sync mechanism. 
  • However, as you can understand easily when my switching frequency for HRPWM increases more than one sync pulses are fired before I disable the sync mechanism. 
    • This increases the jittering problem affect upon the  PWMs. I can see on the scope screen PWM signals are not exactly stable.

To sum up I am looking a way to fire sync pulse for the slave HRPWM when the Master HRPWM TBCTR = 0 since this makes all the transition smoother. 

I can try any other advice.

Best regards,

Gökhan

  • 0
    Prodigy 120 points

    Actually, a mechanism that sends a one-shot sync pulse when CTR = 0 and then disables itself would be quite useful.

  • 0 in reply to Gökhan Bayraktar
    TI__Mastermind 27736 points

    Hi Gokhan,

    Have you look at our ePWM ex 14 in our C2000WARE SDK? This does a one shot load, using CTR=ZRO event to sync other PWMs. Then it only loads once the global one shot latch is set.

    Best,

    Ryan Ma

  • 0 in reply to Ryan Ma
    Prodigy 120 points

    Hi Ryan,

    I run that ex but it is sending sync pulse at every period as I cans see on the scope screen.
    Also, in  the code I could not see the one shot load using CTR=0. In the sysconfig the "Sync out pulse" is set to " Sync pulse is generated when time base counter equals zero". This means sync pulse is fired at every cycle. In the main I did not see a code that disables that.

    For my case I am looking for a solution that sends sync pulse when CTR = 0 and disables the sync mechanism immediately so the sync pulse will not be sent until the next control cycle.

  • 0 in reply to Gökhan Bayraktar
    TI__Mastermind 27736 points

    Hi Gokhan,

    Understood, I think what you want is this feature. This is the one shot latch feature for your SYNCOUT signal. Unfortunatley we do not have an exact example, however there should not be much configuration involved. Simply configure the OSHTSYNCMODE and write to the OSHTSYNC bit.

    Best,

    Ryan Ma

  • 0 in reply to Ryan Ma
    Prodigy 120 points

    Hi Ryan,

    Again thank you.

    I have a question then. 

    İ guess one shot load and and one shot Sync load is different. So the note for one-shot load, which states when high resolution is enabled, no one shot load, is not valid for one-shot sync

  • 0 in reply to Ryan Ma
    Prodigy 120 points

    Hi again Ryan,

    I have tried this one-shot sync  mechanism with HRPWM enabled. It worked great so far.

    Thank you.

    So the answer of my previous question is "One-shot sync can be used with HRPWM" right?

    I have a las question about this matter:

    Considering usage of HRPWM, which one is better for sync out pulse generation if I want to send sync pulse at CTR=0?

    1. EPWM_setSyncOutPulseMode(myEPWM1_BASE, EPWM_SYNC_OUT_PULSE_ON_COUNTER_ZERO);
    2. EPWM_setSyncOutPulseMode(myEPWM1_BASE, EPWM_SYNC_OUT_PULSE_ON_COUNTER_COMPARE_C); with CMPC value is 0.

    I asked this because the note from TRM

    I know with one-shot sync mode I prevent the jittering apart from the moment where sync pulse is need to be sent. But This note makes me wonder?

  • +1 in reply to Gökhan Bayraktar
    TI__Mastermind 27736 points

    Hi Gokhan,

    Gökhan Bayraktar said:
    So the answer of my previous question is "One-shot sync can be used with HRPWM" right?

    That's correct, you'll experience the +/- 1-2 cycle jitter as mentioned in our note when the sync occurs.

    Gökhan Bayraktar said:

    Considering usage of HRPWM, which one is better for sync out pulse generation if I want to send sync pulse at CTR=0?

    Either one of those configurations can work. I would suggest using the feature meant to sent a syncout on ZRO and using the one shot sync load.

    Best,

    Ryan Ma