How to change pwm period on runtime in ncs?

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

Parents Reply
  • 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

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