How to change pwm period on runtime in ncs?

RE: How to change pwm period on runtime in ncs?

ilockit_CFR — Thu, 05 Jun 2025 08:07:19 GMT

Thank you very much. Finally, after several months, there is a solution to the problem.

RE: How to change pwm period on runtime in ncs?

Sigurd — Mon, 26 May 2025 07:36:36 GMT

The Zephyr PWM API is a bit limited. I suggest using nrfx driver directly https://github.com/zephyrproject-rtos/hal_nordic/blob/master/nrfx/samples/src/nrfx_pwm/common_mode/main.c

RE: How to change pwm period on runtime in ncs?

ilockit_CFR — Thu, 10 Apr 2025 11:33:50 GMT

Is there anything else I can test? Can you provide an example where you change the frequency of two PWM channels?

RE: How to change pwm period on runtime in ncs?

ilockit_CFR — Thu, 13 Mar 2025 14:02:13 GMT

It's defined like this:

pwmpiezo0 {
		compatible = "pwm-leds";
		status = "okay";
	
		piezo_pwm_pos: piezo_pwm_pos {
				status = "okay";
				pwms = <&pwm1 0 PWM_HZ(7500) PWM_POLARITY_NORMAL>;
				label = "Piezo positive";
		};
	
		piezo_pwm_neg: piezo_pwm_neg {
				status = "okay";
				pwms = <&pwm1 1 PWM_HZ(7500) PWM_POLARITY_INVERTED>;
				label = "Piezo negative";
		};
	};

One of the pins is already inverted. I then call

ret = pwm_set_dt(&piezo_pwm_pos, PWM_HZ(m_piezo_params.frequency),
					PWM_HZ(m_piezo_params.frequency) / 2);

ret = pwm_set_dt(&piezo_pwm_neg, PWM_HZ(m_piezo_params.frequency),
				   PWM_HZ(m_piezo_params.frequency) / 2);

within a timeout handler every x ms. If m_piezo_params.frequency stays the same, the function calls return 0. But if I change the frequency it breaks after the first timeout.

RE: How to change pwm period on runtime in ncs?

Sigurd — Thu, 13 Mar 2025 11:32:47 GMT

Ah, right!

How do you define these channels?

If you do it like this in the dts:

https://github.com/nrfconnect/sdk-zephyr/blob/v3.7.99-ncs2/boards/nordic/nrf52dk/nrf52dk_nrf52832.dts#L48-L53

you can have e.g. pwm_led_0 with PWM_POLARITY_INVERTED,

and define a pwm_led_1 with PWM_POLARITY_NORMAL

RE: How to change pwm period on runtime in ncs?

ilockit_CFR — Wed, 12 Mar 2025 14:18:10 GMT

Hi,

you already suggested this, but it also results in "Incompatible period." and the functions return -EINVAL after the first time. Is it a problem, that I call these functions from a timeout handler?

In the nrf5 SDK there was NRF_DRV_PWM_EVT_FINISHED. In this event handler I could change the frequency of the pwm and it results in a nice alarm sound. Why is this not possible with the nrf connect SDK.

RE: How to change pwm period on runtime in ncs?

Sigurd — Wed, 12 Mar 2025 13:40:50 GMT

Try using the pwm_set_cycles() function. And use PWM_POLARITY_NORMAL on one channel, and

PWM_POLARITY_INVERTED on the other. Snippet:

ret = pwm_set_cycles(pwm_led0->dev, pwm_led0->channel, period_cycles, period_cycles / 2,
	PWM_POLARITY_INVERTED);

ret = pwm_set_cycles(pwm_led1->dev, pwm_led1->channel, period_cycles, period_cycles / 2,
		PWM_POLARITY_NORMAL);

RE: How to change pwm period on runtime in ncs?

ilockit_CFR — Wed, 12 Mar 2025 12:28:05 GMT

Hi,

in your case you just changed the period of one pin. If I do it also for only one channel everything works. I want to set two pins exactly inverted with changing frequency over time as seen in the image below.

But I only can change the frequency for one channel or set it once for two channels. It's not possible to change the frequency while the pwm is active. I could change the frequency if I disable the pwm for both channels before setting the new frequency, but this results in an interrupted output sound on the piezo.

How can I invert channel 1 in relation to channel 0?

Best regards,

Christian

RE: How to change pwm period on runtime in ncs?

Sigurd — Wed, 04 Dec 2024 11:29:30 GMT

Hi!

I tried repdicing the issues, but it works fine here.

Here is the project I used for testing:

devzone.nordicsemi.com/.../pwm_5F00_test.zip

Tested with NCS 2.8.0 and nRF52832DK(build target nrf52dk/nrf52832)

RE: How to change pwm period on runtime in ncs?

ilockit_CFR — Mon, 02 Dec 2024 07:06:13 GMT

Hi,

unfortunatelly this doesn't work either. If I set the period with this function I will just get some "clicking" sounds on the piezo. Is there a similar function like in the nrf5 SDK where I can start the PWM for n repeats and then it will automatically stop?

Best regards,

Christian

RE: How to change pwm period on runtime in ncs?

Sigurd — Tue, 26 Nov 2024 23:21:49 GMT

Try using pwm_set_cycles()

https://docs.nordicsemi.com/bundle/zephyr-apis-latest/page/group_pwm_interface.html#gaff280789f7b45fdefc354b3f841fe3ef

RE: How to change pwm period on runtime in ncs?

ilockit_CFR — Mon, 25 Nov 2024 07:19:39 GMT

Hi,

at the moment I'm using SDK5 and can easily change the frequency within an event handler, which is called when the PWM is finished. How is this possible in Nordic Connect SDK?

Best regards,

Christian

RE: How to change pwm period on runtime in ncs?

Sigurd — Thu, 21 Nov 2024 22:42:19 GMT

Hi!

I see you are getting this in the log: "Incompatible period". Looking at the source code where this is printed, https://github.com/nrfconnect/sdk-zephyr/blob/v3.7.99-ncs1/drivers/pwm/pwm_nrfx.c#L94, there is a comment that explains this error:

/* If any other channel is driven by the PWM peripheral, the period
* that is currently set cannot be changed, as this would influence
* the output for that channel.
*/