topic Re: S32K116 PWM generation using FLEXIO - Cannot set duty cycle to 0 in S32 SDK

S32K116 PWM generation using FLEXIO - Cannot set duty cycle to 0

junxi_cai — Mon, 21 Mar 2022 23:24:33 GMT

Hello there,

I am currently working on a project using FLEXIO to emulate the PWM generation.

Here is the problem I am facing:

When I am trying to stop PWM generation for the duty cycle 0 case, I cannot do that. It outputs the clock fed to the FLEXIO instead of the voltage low.

As the application note AN12174 suggests 'flexio_pwm_stop() function disables the timer0 by setting TIMOD and disable generating the PWM.' I set TIMOD to 0 when the duty cycle is equal to 0.

Here is my code for reference:

if(duty > 0)
{
/*!
* FlexIO Timer Control:
* ============================
*/
FLEXIO->TIMCTL[0] |=
FLEXIO_TIMCTL_TIMOD(2) /* Dual 8-bit counters PWM high mode */
|FLEXIO_TIMCTL_PINSEL(0) /* Select FXIO_D0 */
|FLEXIO_TIMCTL_PINCFG(3); /* Timer pin output */

low = ( ( ( (4000000/20000) * (100-duty)) / 100) - 1) << 8;
high= ( ( (4000000/20000) * duty) / 100) - 1;

FLEXIO->TIMCMP[0] = high | low;
}
else
{
FLEXIO->TIMCTL[0] |=
FLEXIO_TIMCTL_TIMOD(0) /* Timer Disabled. */
|FLEXIO_TIMCTL_PINSEL(0 /* Select FXIO_D0 */
|FLEXIO_TIMCTL_PINCFG(3); /* Timer pin output */

}

Very appreciated for the help.

Thank you,

Junxi

Re: S32K116 PWM generation using FLEXIO - Cannot set duty cycle to 0

danielmartynek — Tue, 22 Mar 2022 12:49:13 GMT

Hello Junxi,

I'm not sure if I understand the question, but if you need an explanation why the duty cycle cannot be set to 0%, this is given by the operation of the 8bit PWM mode (54.3.1.21 Timer Compare N Register (TIMCMP0 - TIMCMP3)):

Regarding the AN12174 recommendation, do you have any problems with this approach?

Thanks,

BR, Daniel

Re: S32K116 PWM generation using FLEXIO - Cannot set duty cycle to 0

junxi_cai — Tue, 22 Mar 2022 13:47:12 GMT

Hello Daniel,

Thank you for the response. Sorry for the confusion. Let me clarify it.

What I want to achieve is when the duty cycle is 0, the PWM output should be at voltage level low always.

My PWM is using FLEXIO which fed by SIRCDIV2_CLK (4MHz), the frequency is 20kHz.

My first approach is as what you said, set FLEXIO->TIMCMP[0] = 0x0000 to configure the comparison counter to be 0.

So I set the duty cycle of the PWM to be 50% first to get a 20kHz, 50% duty cycle PWM. Then I set the duty cycle to be 0 by setting FLEXIO->TIMCMP[0] = 0x0000

However, when the TIMCMP[0] = 0, I measured a PWM with 2MHz and 50% duty cycle on my oscilloscope instead of a straight line at 0v.

Then my second approach is to disable the timer0 by setting TIMOD to 0.

So I repeat the sample step as above, after I set the duty cycle to 50%, I can see the TIMOD bit of TIMCTL0 set to be 2, and PWM generated correctly.

Then I tried set duty cycle to 0 by set TIMOD bit of TIMCTL0 to be 0 to stop the PWM.

However, it doesn't all me to configure the TIMOD again. It stays at 2.

And the PWM is still at 50% duty cycle instead of getting off.

Could you please let me know if I did something wrong?

Thank you,

Junxi

Re: S32K116 PWM generation using FLEXIO - Cannot set duty cycle to 0

danielmartynek — Thu, 24 Mar 2022 17:07:02 GMT

Hi @junxi_cai,

I have been testing it today.

It works with this configuration:

FLEXIO->SHIFTCTL[0] |= (1 << 7); // PINPOL = 1, Pin is active low

Can you test it on your side?

BR, Daniel

Re: S32K116 PWM generation using FLEXIO - Cannot set duty cycle to 0

junxi_cai — Mon, 04 Apr 2022 15:51:57 GMT

Hello Daniel,

Sorry for the late response. I also tried that, it is not get set to Low.

Instead, I use the clear register API to clear the TIMCTL register as below to solve the problem.

REG_BIT_CLEAR32(&FLEXIO->TIMCTL[ChannelNumber],0xFFFFFFFFu);

Thanks a lot.