One PWM output pin initializes high while the other 2 initialize low

[Dave Littell]

Greetings,

Using SDK v3.1.1 I've configured 3 PWM outputs using the pwm0-2 modules via a DTS overlay.  After reset or power cycle (and prior to making any PWM driver calls), the pwm0 output at P1.15 starts off high while the remaining two outputs are low (P1.14 and P1.07).  My hardware requires that all the outputs start off low.  I've tried changing the polarity of pwm0 with no effect - P1.15 still starts off high.  How do I ensure that all the PWM outputs start off low after a reset or power cycle?

Here's the PWM portions of my DTS overlay:

/ {

	pwmheaters {
		compatible = "pwm-leds";

		pwm0_channel0: pwm0_channel0 {
			pwms = <&pwm0 0 PWM_MSEC(100) 0>;
		};

		pwm1_channel0: pwm1_channel0 {
			pwms = <&pwm1 0 PWM_MSEC(100) 0>;
		};

		pwm2_channel0: pwm2_channel0 {
			pwms = <&pwm2 0 PWM_MSEC(100) 0>;
		};
	};
	
};


&pwm0 {
	status = "okay";
	pinctrl-0 = <&pwm0_default>;
	/delete-property/ pinctrl-1;
	pinctrl-names = "default";
};


&pwm1 {
	status = "okay";
	pinctrl-0 = <&pwm1_default>;
	/delete-property/ pinctrl-1;
	pinctrl-names = "default";
};


&pwm2 {
	status = "okay";
	pinctrl-0 = <&pwm2_default>;
	/delete-property/ pinctrl-1;
	pinctrl-names = "default";
};


&pinctrl {

	pwm0_default: pwm0_default {
		group1 {
			psels = <NRF_PSEL(PWM_OUT0, 1, 15)>;
		};
	};


	pwm1_default: pwm1_default {
		group1 {
			psels = <NRF_PSEL(PWM_OUT0, 1, 14)>;
		};
	};


	pwm2_default: pwm2_default {
		group1 {
			psels = <NRF_PSEL(PWM_OUT0, 1, 7)>;
		};
	};

};

Thanks,

Dave

[Dave Littell]

Resolution: somehow a "nordic,invert" crept into pwm0_default and required a "/delete-property/".  This highlights the need for starting with a CLEAN DTS when creating an overlay for a custom board.  Where can I get a clean DTS for the nRF52840?

[Kazi Afroza Sultana]

you can add this ''PWM_POLARITY_NORMAL'' for each of your pwm instances in the overlay file.

pwmheaters {
	compatible = "pwm-leds";

	pwm0_channel0: pwm0_channel0 {
		pwms = <&pwm0 0 PWM_MSEC(100) PWM_POLARITY_NORMAL>;
	};

	pwm1_channel0: pwm1_channel0 {
		pwms = <&pwm1 0 PWM_MSEC(100) PWM_POLARITY_NORMAL>;
	};

	pwm2_channel0: pwm2_channel0 {
		pwms = <&pwm2 0 PWM_MSEC(100) PWM_POLARITY_NORMAL>;
	};
};  

To get a clean DTS for the nRF52840 you have to create your own out‑of‑tree board based on nRF52840 and customize its BOARD.dts and pinctrl files. You can read this here https://academy.nordicsemi.com/courses/nrf-connect-sdk-intermediate/lessons/lesson-3-adding-custom-board-support/.