Zephyr PWM: pwm_nrfx err - Invalid channel

Question

Hoping to get pointed in the right direction to resolve an error using Zephyr and PWM on an nRF52833DK (SDK 2.2).

The error is: <err> pwm_nrfx: Invalid channel: #.

The specific pins I'm using are P0.28 and P0.29, but this seems to be pin agnostic outside of the pre-defined LED pins on the DK.

My prj.conf file contains:

CONFIG_PWM=y

CONFIG_PINCTRL=y

Devicetree Overlay (relevant sections):

/ {

    pwm_mtr {
		compatible = "pwm-leds";
		in1: in_1 {
			pwms = < &pwm0 28 PWM_MSEC(20) PWM_POLARITY_NORMAL>;
			label = "MTR IN 1";
		};

		in2: in_2 {
			pwms = < &pwm0 29 PWM_MSEC(20) PWM_POLARITY_NORMAL>;
			label = "MTR IN 2";
		};
    };
};

&pinctrl {
    pwm0_default: pwm0_default {
            group1 {
                    psels = <NRF_PSEL(PWM_OUT0, 0, 28)>,
                            <NRF_PSEL(PWM_OUT0, 0, 29)>;
                    nordic,invert;
            };

    };

    pwm0_sleep: pwm0_sleep {
            group1 {
                    psels = <NRF_PSEL(PWM_OUT0, 0, 28)>,
                            <NRF_PSEL(PWM_OUT0, 0, 29)>;
                    low-power-enable;
            };

    };
};

&pwm0 {
    compatible = "nordic,nrf-pwm";
    reg = <0x4001c000 0x1000>;
    interrupts = <28 NRF_DEFAULT_IRQ_PRIORITY>;
    status = "okay";
    #pwm-cells = <3>;
    pinctrl-0 = <&pwm0_default>;
	pinctrl-1 = <&pwm0_sleep>;
	pinctrl-names = "default", "sleep";
};


Relevant parts of main.c:

static const struct pwm_dt_spec mtr_drv1 = PWM_DT_SPEC_GET(DT_ALIAS(mtrdrv1));

...
[within main()]

if (!device_is_ready(mtr_drv1.dev) {
    LOG_ERR("PWM device is not ready.");
    return -1;
}


pwm_set_pulse_dt(in2, in2->period/period_div);


Are there any other things that need to be done to activate GPIO pins to be used for PWM?  I don't have the equivalent of a gpio_configure_pin_dt() call.  

Are there some GPIO pins that cannot be used for PWM?

Any guidance would be appreciated!

Hieu · Accepted Answer

I was able to modify the PWM Blinky sample to work with two LEDs. The application code is nothing special, just getting the newly defined pwm_led1. Most of the work is in the DTS.

Below is my overlay code, where I added some comments to highlight the parts which seem wrong in your DTS.

Perhaps this would help you?

/ {
    // This overlay setup pwm_led0 on pin 13, and pwm_led1 on pin 15
    aliases {
            pwm-led0 = &pwm_led0;
            pwm-led1 = &pwm_led1;
    };

    pwmleds {
        compatible = "pwm-leds";
        pwm_led0: pwm_led_0 {
                //            |- This is PWM channel, not pin
                //            v
                pwms = <&pwm0 0 PWM_MSEC(20) PWM_POLARITY_INVERTED>;
        };
        pwm_led1: pwm_led_1 {
                //            |- This is PWM channel, not pin
                //            v
                pwms = <&pwm0 1 PWM_MSEC(20) PWM_POLARITY_INVERTED>;
        };

    };

    pinctrl: pin-controller {
        compatible = "nordic,nrf-pinctrl";
        

        pwm0_default: pwm0_default {
                group1 {
                        psels = <NRF_PSEL(PWM_OUT0, 0, 13)>,
                                //            |- The second pin should be selected for output 1, not 0
                                //        vvvvvvvv
                                <NRF_PSEL(PWM_OUT1, 0, 15)>;
                        nordic,invert;
                };

        };

        pwm0_sleep: pwm0_sleep {
                group1 {
                        psels = <NRF_PSEL(PWM_OUT0, 0, 13)>,
                                //            |- The second pin should be selected for output 1, not 0
                                //        vvvvvvvv
                                <NRF_PSEL(PWM_OUT1, 0, 15)>;
                        low-power-enable;
                };

        };

    };

};

Zephyr PWM: pwm_nrfx err -> Invalid channel

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