Adding additional pins to PWM channel

RE: Adding additional pins to PWM channel

Amanda Hsieh — Fri, 10 Feb 2023 17:41:53 GMT

Hi,

That is an overlay file for nRF52840dongle. The PWM0 pin assigned is here https://github.com/nrfconnect/sdk-zephyr/blob/main/boards/arm/nrf52840dongle_nrf52840/nrf52840dongle_nrf52840-pinctrl.dtsi#L59-L75

-Amanda H.

RE: Adding additional pins to PWM channel

Mike Austin (LPI) — Thu, 09 Feb 2023 21:10:58 GMT

Thanks Amanda.

So, just to clarify my understanding:

With this overlay file you have pwmleds assigned to PWM0, and then red_pwm_led, green_pwm_led and blue_pwm_led are assigned to channels 0, 1 and 2 respectively of PWM0. There is then a second instance, pwmleds1, that is assigned to PWM1, and which has pwm_led1 assigned to channel 0.

I can see that PWM1 has been allocated to Pin 6, and PWM0 has been allocated to the standard PWM0 pin for the nRF52840DK, but what I don't understand is how do you allocate different channels to a pin? Or do all the channels drive the same GPIO? For example, where is the definition that says which pin red_pwm_led, green_pwm_led and blue_pwm_led connect to?

Regards,

Mike

RE: Adding additional pins to PWM channel

Amanda Hsieh — Wed, 01 Feb 2023 17:42:39 GMT

Hi,

[quote user="Mike Austin (LPI)"]If I read the specs for the nRF52832 correctly, there are 3 PWM instances (PWM0, PWM1 and PWM2) available, and then the option for up to 4 channels per instance.[/quote]

That's correct and it's the answer to the first question.

[quote user="Mike Austin (LPI)"]I want to try and understand how to access different channels in the same instance, compared to, say, channel 0 in different instances.[/quote]

It depends on the pwms property of pwmleds. See this overlay and this overlay.

The following are the PWM examples in the NCS:

PWM Blinky

PWM: RGB LED

-Amanda H.

RE: Adding additional pins to PWM channel

Mike Austin (LPI) — Wed, 01 Feb 2023 06:29:44 GMT

Thanks Amanda.

One other thing I can't quite understand, nor find any clear explanation of, is the difference between:

PWM instance
PWM channel

And what you can and can't do with either.

If I read the specs for the nRF52832 correctly, there are 3 PWM instances (PWM0, PWM1 and PWM2) available, and then the option for up to 4 channels per instance.

And then I want to try and understand how to access different channels in the same instance, compared to, say, channel 0 in different instances.

Are there any examples, or explanations, available online that would help me understand how the PWM stuff all works?

Cheers,

Mike

RE: Adding additional pins to PWM channel

Amanda Hsieh — Tue, 31 Jan 2023 17:35:40 GMT

Hi,

Try to add aliases into overlay file for the DT_ALIAS() function:

    aliases {
		pwm-led0 = &pwm_led0;
        pwm-led1 = &pwm_led1;

	};

So the overlay file would look like this:

&pinctrl {
    pwm0_custom: pwm0_custom {
        group1 {
            psels = <NRF_PSEL(PWM_OUT0, 0, 22)>,
                    <NRF_PSEL(PWM_OUT1, 0, 23)>;
            nordic,invert;
        };
    };

    pwm0_csleep: pwm0_csleep {
        group1 {
            psels = <NRF_PSEL(PWM_OUT0, 0, 22)>,
                    <NRF_PSEL(PWM_OUT1, 0, 23)>;
            low-power-enable;
        };
    }; 
};

&pwm0 {
    status = "okay";
    pinctrl-0 = <&pwm0_custom>;
    pinctrl-1 = <&pwm0_csleep>;
    pinctrl-names = "default", "sleep";
};

/{
    pwmleds {
        compatible = "pwm-leds";
        pwm_led0: pwm_led_0 {
            pwms = <&pwm0 0 PWM_MSEC(1) PWM_POLARITY_NORMAL>;
        };
        pwm_led1: pwm_led_1 {
            pwms = <&pwm0 1 PWM_USEC(100) PWM_POLARITY_NORMAL>;
        };
    };

    aliases {
		pwm-led0 = &pwm_led0;
        pwm-led1 = &pwm_led1;

	};
};

Regards,
Amanda H.