TMS320F28379d: PWM TBPRD reg changing on the fly

Serafin Bachman

Part Number: TMS320F28379D

Tool/software: Code Composer Studio

Hi,

I'm working on a basic stepper motor drive. I read all the topics on this forum (about this subject :) ). I 'm looking for a method on how to change register TBPRD of EPWM1 when... My EPWM1 is configured and synchronized with other EPWMs by ECAP with XBAR (it's working great) and driving the CLA task. EPWM1 configurations: up-down count mode, at zero PRD, generates an interrupt and starts the CLA task1. In this task, I'm going to give pulses and change EPWM frequency. My problem is how to change the frequency od PWM after for example 5 impulses.

I read that there are some shadow TBPRD registers, can I use it for that purpose? Also, I read that I can reload the TBPRD register when EPWM is disabled, change frequency and enable, what do you think?

Could you help me with how to do it? I'm concerned about finding the best possible method.

Best Regards,

Serafin

over 5 years ago

0 Nima Eskandari over 5 years ago

TI__Guru 52040 points

Absolutely. You can set the TBPRD register to operate in shadow mode and then on the 4th impulse, update the TBPRD value. The shadow register will automatically update the active on the 5th impulse.

Nima

0 Serafin Bachman over 5 years ago in reply to Nima Eskandari

Prodigy 60 points

Could you help me with settings?

I chose in TBCTL bit PRLD on Shadow mode, so if I will make EPwm1Regs.TBPRD = new_freq; it will update itself at the next impulse, am I right? There is a need for disabled the EPWM or any other action? It will be better to use it in the CLA task or the MCU task?

Best Regards,

Serafin

0 Nima Eskandari over 5 years ago in reply to Serafin Bachman

TI__Guru 52040 points

one PWM cycle before you want the update:

TBPRD=new_value;

0 Serafin Bachman over 5 years ago in reply to Nima Eskandari

Prodigy 60 points

Thank you for your suggestion.

Unfortunately, this solution doesn't work as I wish.

I change TBPRD reg by the line : EPwm1Regs.TBPRD = __mf32toui16r(CLAdiv( x.Speed,(1.0f + out) ));
Out is a output of some filter with range <0,1>, x.Speed is a f

This line of code is in the CLA task1 starter by interrupt EPWM1, done every interrupt.

This solution is making the algorithm crush. The counter value of the number of interrupts with/and without this line is different.

Do you have any suggestion, why it is happening?

0 Nima Eskandari over 5 years ago in reply to Serafin Bachman

TI__Guru 52040 points

you are changing the PWM period, what do you consider as "jitter"?

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TMS320F28379d: PWM TBPRD reg changing on the fly