Hi, I'm trying to play some sounds on a piezo with the help of the pwm. I tried to set the period with pwm_set_dt but only the first call is successful and every subsequent call raised an error. Here is my test code: for(uint16_t i = 400; i < 800; i++) { int ret = pwm_set_dt(&piezo_pwm_pos, PWM_HZ(i), PWM_HZ(i) / 2); LOG_DBG("pwm_set_dt = %d", ret); ret = pwm_set_dt(&piezo_pwm_neg, PWM_HZ(i), PWM_HZ(i) / 2); LOG_DBG("pwm_set_dt = %d", ret); k_msleep(10); } The results looked like this: 00> D: pwm_set_dt = 0 00> D: pwm_set_dt = 0 00> E: Incompatible period. 00> D: pwm_set_dt = -22 00> E: Incompatible period. 00> D: pwm_set_dt = -22 00> E: Incompatible period. 00> D: pwm_set_dt = -22 00> E: Incompatible period. 00> D: pwm_set_dt = -22 00> E: Incompatible period. 00> D: pwm_set_dt = -22 I didn't find anything in the documentation of pwm_set for the error 22. How can I change period and pulse while the pwm is running? Best regards, Christian

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

How to change pwm period on runtime in ncs?

ilockit_CFR 8 months ago

Hi,

I'm trying to play some sounds on a piezo with the help of the pwm. I tried to set the period with pwm_set_dt but only the first call is successful and every subsequent call raised an error.

Here is my test code:

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    for(uint16_t i = 400; i < 800; i++)
    {
        int ret = pwm_set_dt(&piezo_pwm_pos, PWM_HZ(i),
                           PWM_HZ(i) / 2);
        LOG_DBG("pwm_set_dt = %d", ret);
        ret = pwm_set_dt(&piezo_pwm_neg, PWM_HZ(i),
                           PWM_HZ(i) / 2);
        LOG_DBG("pwm_set_dt = %d", ret);
        k_msleep(10);
    }
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    for(uint16_t i = 400; i < 800; i++)
    {
        int ret = pwm_set_dt(&piezo_pwm_pos, PWM_HZ(i),
						   PWM_HZ(i) / 2);
        LOG_DBG("pwm_set_dt = %d", ret);

        ret = pwm_set_dt(&piezo_pwm_neg, PWM_HZ(i),
						   PWM_HZ(i) / 2);
        LOG_DBG("pwm_set_dt = %d", ret);
        k_msleep(10);
    }

The results looked like this:

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00> D: pwm_set_dt = 0
00> D: pwm_set_dt = 0
00> E: Incompatible period.
00> D: pwm_set_dt = -22
00> E: Incompatible period.
00> D: pwm_set_dt = -22
00> E: Incompatible period.
00> D: pwm_set_dt = -22
00> E: Incompatible period.
00> D: pwm_set_dt = -22
00> E: Incompatible period.
00> D: pwm_set_dt = -22
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

00> D: pwm_set_dt = 0
00> D: pwm_set_dt = 0
00> E: Incompatible period.
00> D: pwm_set_dt = -22
00> E: Incompatible period.
00> D: pwm_set_dt = -22
00> E: Incompatible period.
00> D: pwm_set_dt = -22
00> E: Incompatible period.
00> D: pwm_set_dt = -22
00> E: Incompatible period.
00> D: pwm_set_dt = -22

I didn't find anything in the documentation of pwm_set for the error 22.

How can I change period and pulse while the pwm is running?

Best regards,

Christian

Top Replies

Sigurd 2 months ago in reply to ilockit_CFR +1 verified

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

Parents

0 Sigurd 8 months ago

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.
*/

Reply

0 Sigurd 8 months ago

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.
*/

Children

0 ilockit_CFR 8 months ago in reply to Sigurd

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
0 Sigurd 8 months ago in reply to ilockit_CFR

Try using pwm_set_cycles()

https://docs.nordicsemi.com/bundle/zephyr-apis-latest/page/group_pwm_interface.html#gaff280789f7b45fdefc354b3f841fe3ef
0 ilockit_CFR 8 months ago in reply to Sigurd

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
0 Sigurd 8 months ago in reply to ilockit_CFR

Hi!

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

Here is the project I used for testing:

pwm_test.zip

Tested with NCS 2.8.0 and nRF52832DK(build target nrf52dk/nrf52832)
0 ilockit_CFR 4 months ago in reply to Sigurd

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