nRF52820 PWM Device Tree / API

RE: nRF52820 PWM Device Tree / API

CCL-KH — Wed, 17 May 2023 15:35:01 GMT

Thank you for your support

RE: nRF52820 PWM Device Tree / API

khelmutlord — Wed, 17 May 2023 15:16:20 GMT

Apologies. Upon further investigation, it seems that only one software PWM instance is supported at a time.

https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/pwm/pwm_nrf5_sw.c

There is a possible solution that my require modifying some files within the Zephyr SDK.

https://github.com/zephyrproject-rtos/zephyr/blob/42b121ee9519d5bb96c6e6197733aa204d99486e/dts/bindings/pwm/nordic%2Cnrf-sw-pwm.yaml#L3

In the device tree bindings, it makes clear that the number of PWM channels supported is the number of timer compare registers minus 1. For the nRF52820, that is 3 total for timer[0-2]. However, timer3 has 6 compare registers so would support 5 PWM channels.

...

To make this change, modify the example to use timer3 for the generator, modify the device tree bindings in the Zephyr SDK to support up to 5 PWM cells, and set #pwm-cells to 5.

RE: nRF52820 PWM Device Tree / API

CCL-KH — Wed, 17 May 2023 14:49:21 GMT

Hi,

Thanks for your support

I was able to build the project 'as is' however I think you have a typo

line 25: pwm_dev1 = DEVICE_DT_GET(PWM_NODE_LABEL);

should be

line 25: pwm_dev1 = DEVICE_DT_GET(PWM_NODE_LABEL_1);

which fails build with:

RE: nRF52820 PWM Device Tree / API

khelmutlord — Wed, 17 May 2023 14:41:58 GMT

Hello,

I was able to get two software PWM instances to compile with the following DeviceTree overlay. Key thing is that the overlay file is named "nrf52833dk_nrf52820.overlay"

You will find this in the attached project.

devzone.nordicsemi.com/.../led_5F00_pwm_5F00_5_5F00_17_5F00_2023.zip

Thanks,

Helmut Lord

RE: nRF52820 PWM Device Tree / API

CCL-KH — Tue, 16 May 2023 13:57:06 GMT

Thank you for you help, I have now successfully implemented all 3 pwm channels via the single sw-pwm instance.

I am experimenting adding more sw-pwm instances (I believe each requires 1 generator and X PPI channels). I am hitting compilation errors. In the code below 'sw-pwm' is defined in #include <nordic/nrf52820_qdaa.dtsi> however I am leaving that 'status=disabled' and creating 2 new nodes: 'sw_pwm0: sw-pwm0' & 'sw_pwm1: sw-pwm1' that are compatible with 'nordic,nrf-sw-pwm'

/dts-v1/;
#include <nordic/nrf52820_qdaa.dtsi>

/ {
	sw_pwm1: sw-pwm1 {
		compatible = "nordic,nrf-sw-pwm";
    	status ="okay";
    	channel-gpios = <&gpio0 14 GPIO_ACTIVE_LOW>,
    					<&gpio0 15 GPIO_ACTIVE_LOW>;
    	clock-prescaler = <0>;
    	generator = <&timer2>;
		#pwm-cells = <3>;
	};

	sw_pwm0: sw-pwm0 {
		compatible = "nordic,nrf-sw-pwm";
    	status ="okay";
    	channel-gpios = <&gpio0 16 GPIO_ACTIVE_LOW>;
    	clock-prescaler = <0>;
    	generator = <&timer1>;
		#pwm-cells = <3>;
	};
};

pwm_init()

	const struct device *driver0;
	driver0 = DEVICE_DT_GET(DT_NODELABEL(sw_pwm0));
	pwm_set_cycles(driver0, 0, CONFIG_SYS_CLOCK_TICKS_PER_SEC, CONFIG_SYS_CLOCK_TICKS_PER_SEC / 8, PWM_POLARITY_INVERTED);

	const struct device *driver1;
	driver1 = DEVICE_DT_GET(DT_NODELABEL(sw_pwm1));
    pwm_set_cycles(driver1, 0, CONFIG_SYS_CLOCK_TICKS_PER_SEC, CONFIG_SYS_CLOCK_TICKS_PER_SEC, PWM_POLARITY_INVERTED);

compile error:

RE: nRF52820 PWM Device Tree / API

khelmutlord — Mon, 15 May 2023 17:34:11 GMT

Hello,

I have attached an example project that shows how to use software PWM to blink an LED (directly! not through the LED library). It is set up to be used for an nRF52840-DK because that I don't have a 52833-DK handy but you should be able to just rename the board overlay file that I included.

I included a comment w/ a link to the nRF5 SW-PWM implementation for more information.

https://github.com/zephyrproject-rtos/zephyr/blob/main/drivers/pwm/pwm_nrf5_sw.c

devzone.nordicsemi.com/.../led_5F00_pwm.zip

Thanks,

Helmut Lord