ePWM Synchronization for F28335

Prem,

You certainly can synchronize ePWM2, 3 & 5 together.  The only limitation is that you will only be able to synchronize ePWM4 with ePWM3 or use no synchronization on ePWM4.

It looks like you've got the SYNCOSEL bits for each respective PWM correct.  The following must also be configured (in addition to the SYNCOSEL bit) to get everything working:
- the PHSEN bit of TBCTL also needs to be set correctly on each PWM (disable for the master, enable for the slaves)
- Each PWMs' TBPHS should be configured correctly
- TBCLKSYNC needs to be called and clocks need to be enabled.  The order in which you configure register bits does matter some here.  The PWM user's guide for your device will go through the proper procedure.


Thank you,
Brett

Thanks Brett for your reply.

Does F28335 Hardware Allow ePWM4,5 to synchronize with ePWM2,3.... when ePWM2 is configured as master?

we are NOT considering ePWM1 as Master. Can you please look into of page no: 29 of datasheet at below Link.

http://www.ti.com/lit/ug/spru791f/spru791f.pdf

Regards,

Prem Prakash

Hi Brett,

One More concern.

Is it necessary Slave should be operating higher OR equal frequency compare to frequency of  Master PWM during synchronization.

for example: ePWM2_(Master), ePWM3_(Slave) during PWM synchronization, Frequency of ePWM3 >= Frequency of ePWM2. If Yes then why?

Best Regards,

Prem

Prem,

Synchronization occurs when an upstream PWM reaches its ZRO event (or maybe CMPB). 

Let's assume that you're synchronizing PWM2 and PWM3 together.  

Case 1: If PWM2 runs at 50kHz and PWM3 runs at 100kHz, PWM2 will generate a synchronization event every 50kHz.  PWM3 will finish 2 full periods before it gets the upstream synchronization event which forces it to a certain value.  Everything should work nicely.

Case 2: If you want PWM2 to run at 100kHz and PWM3 to run at 50kHz, PWM2 will generate a synchronization event every 100kHz.  However, PWM3 will never finish a full period before the upstream synch event occurs which will force it back to a certain value.  Because of this, PWM2 and PWM3 will effectively be 100kHz signals.  Note that this really isn't an issue as long as you expect it.

In most application cases, you'd want the frequency of PWM3 to be an integer multiple of PWM2.  (as long as you understand what the module is doing, other ideas are possible though)

Hopefully this answers your question.  Let me know if it doesn't.


Thank you,
Brett

Dear Zeng,

Case-1. starting Multiple PWM  at ABSOLUTELY same time, and they end them at absolutely same time:

              Do you have any constraint of Phase synchronization?

              If YES, then It is not at all possible.

              If NO, then Case-1 is 100% possible.

Case-2. different ePWM can have different frequency:

               Disable phase Synchronization  bit (SYNCOSEL) in TBCTL register for all the PWM -> configure frequency in individual register through TBPRD register->clear counter.

Hope this should work.

Best Regards,

Prem

Dear Prem

    Thank you for your reply!

Case-1

    The answer is NO. Please tell some details for starting Multiple PWM  at ABSOLUTELY same time, and then end them at absolutely same time.

    Thanks for your concern again!

    Best Regards!

   Zeng

Dear Prem,

Your answer have enlightened me, thank you!

I have achieve diffrent chanels of ePWM started at the same time, and they can have different frequency.When the required numbers of pulse obtained, I stop these chanels of ePWM at the same time.

My setting:

EPwm1Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN; // synchronize when external signal come in

EPwm2Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN;// follow Previous PWM

EPwm3Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN;

EPwm4Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN;

EPwm5Regs.TBCTL.bit.SYNCOSEL = TB_SYNC_IN;

EPwm6Regs.TBCTL.bit.SYNCOSEL  = TB_SYNC_IN;

//to start them

EALLOW;
SysCtrlRegs.PCLKCR0.bit.TBCLKSYNC = 1;
EDIS;

//to stop them

EALLOW;
SysCtrlRegs.PCLKCR0.bit.TBCLKSYNC = 0;
EDIS;

and they have different frequency. Since the phase  synchronization is not the focus, I just want diffrent ePWM start at the same time and stop at the same time, so I will never give a external singnal to force the phase synchronization. 

I have test my configuration on the hardware and use the oscilloscope watch the ePWMs, the result is acceptable(several numbers of PWM pulses error).

If you have any confusion due to my bad explaination, just tell me.

Best Regards,

ZENG

Hi, 

I have EPWM1 as master and other EPWMs are sychronized to it. EPWM1 is the reference and other EPWM channels are phase shifted from it.

I want to update the TBPHS register for the SYNC-IN EPWM channels from an interrupt routine.

The interrupt routine is called twice in a PWM cycle, at CTR_ZERO and at CTR_PRD using a UPDOWN_COUNTER. But the TBPHS register is getting updated only once at CTR_ZERO.

I need to update TBPHS twice in a cycle.

Can anybody help on this?

Thanks

Ritwik

Prem,

Have you looked at figure 9 in the ePWM Reference Guide? This describes the sync chain.

How have you configured PHSEN for all PWMs? This will determine how the syncpulses propagate through the system.

It should be possible to sync ePWM2/3/5 to ePWM1, but I don't think you could sync ePWM5 to ePWM2 directly.

Regards,

Cody

Hi Ramesh,

We'll continue discussion of your situation in your thread:
https://e2e.ti.com/support/microcontrollers/c2000/f/171/t/623241


Thank you,
Brett