Hardware PWM doesn't operate with 100% duty cycle

RE: Hardware PWM doesn't operate with 100% duty cycle

Håkon Alseth — Mon, 16 Mar 2026 09:02:40 GMT

Hi,

Sorry, forgot to mention that you should rename/delete that file for the purpose of this testing.

[quote user="Woo-chan Kim"]

When I fixed using the `sw_pwm` periperal that you recommend by refer the sample,

[/quote]

blinky_pwm defines that specifically for the nrf5340dk_nrf5340_cpuapp.overlay board. You can safely use "normal" pwm with it, by deleting that file.

Check this by searching for "CONFIG_PWM_NRFX" in build/blinky_pwm/zephyr/.config file, and if this is set to 'y'; then "NRF_PWM" hardware peripheral is used.

[quote user="Woo-chan Kim"]

I need to control 3 channel pwm to implement full color led.

[/quote]

sw_pwm is made specifically for 1 channel. Having several will cause issues, as explained here:

RE: How to use two sw_pwm instances with nrf5340 with Zephyr?

Kind regards,

Håkon

RE: Hardware PWM doesn't operate with 100% duty cycle

Woo-chan Kim — Mon, 16 Mar 2026 01:05:21 GMT

Thanks for your reply.

When I fixed using the `sw_pwm` periperal that you recommend by refer the sample,

it makes error like this.

/opt/nordic/ncs/v3.2.1/zephyr/drivers/pwm/pwm_nrf_sw.c:420:9: error: invalid operands to binary & (have 'nrfx_gpiote_t *' and 'nrfx_gpiote_t')
  420 |         &GPIOTE_NRFX_INST_BY_NODE(NRF_DT_GPIOTE_NODE_BY_IDX(_node_id, _prop, _idx))
      |         ^
/Users/woochankim/Project/Firmware-Sense1-Guardian/build_development/Firmware-Sense1-Guardian/zephyr/include/generated/zephyr/devicetree_generated.h:8654:9: note: in expansion of macro 'GPIOTE_AND_COMMA'
 8654 |         fn(DT_N_S_sw_pwm, channel_gpios, 1) \
      |         ^~
/opt/nordic/ncs/v3.2.1/zephyr/include/zephyr/devicetree.h:5499:33: note: in expansion of macro 'DT_N_S_sw_pwm_P_channel_gpios_FOREACH_PROP_ELEM'
 5499 | #define DT_CAT4(a1, a2, a3, a4) a1 ## a2 ## a3 ## a4
      |                                 ^~
/opt/nordic/ncs/v3.2.1/zephyr/include/zephyr/devicetree.h:5271:9: note: in expansion of macro 'DT_FOREACH_PROP_ELEM'
 5271 |         DT_FOREACH_PROP_ELEM(DT_DRV_INST(inst), prop, fn)
      |         ^~~~~~~~~~~~~~~~~~~~
/opt/nordic/ncs/v3.2.1/zephyr/drivers/pwm/pwm_nrf_sw.c:425:17: note: in expansion of macro 'DT_INST_FOREACH_PROP_ELEM'
  425 |                 DT_INST_FOREACH_PROP_ELEM(0, channel_gpios, GPIOTE_AND_COMMA)
      |                 ^~~~~~~~~~~~~~~~~~~~~~~~~
ninja: build stopped: subcommand failed.

I need to control 3 channel pwm to implement full color led.

this is the overlay that i used to.

&pwm0 {
    status = "disabled";
};

&sw_pwm {
    status = "okay";
    channel-gpios = <&gpio1 4 PWM_POLARITY_INVERTED>,
                    <&gpio1 5 PWM_POLARITY_INVERTED>,
                    <&gpio1 6 PWM_POLARITY_INVERTED>;
};

pwmleds {
    compatible = "pwm-leds";
    pwm_green: pwm_led_0 {
        pwms = <&sw_pwm 0 PWM_MSEC(20) PWM_POLARITY_INVERTED>;
    };
    pwm_blue: pwm_led_1 {
        pwms = <&sw_pwm 1 PWM_MSEC(20) PWM_POLARITY_INVERTED>;
    };
    pwm_red: pwm_led_2 {
        pwms = <&sw_pwm 2 PWM_MSEC(20) PWM_POLARITY_INVERTED>;
    };
};

could you help me to solve this problem.

If you can, please tell me why I need to use the `sw_pwm`?

Because, In previous SDK version, the pwm works well.

RE: Hardware PWM doesn't operate with 100% duty cycle

Håkon Alseth — Fri, 13 Mar 2026 09:59:22 GMT

Hi,

As per the code, if you check further down in the same function that you copied code from, it will disable the pwm module, and use nrf_gpio to set it to a high or low level, based on if you input 100% or 0 % duty cycle.

Here is a quick test, based on zephyr/samples/basic/blink_pwm:

/*
 * Copyright (c) 2016 Intel Corporation
 * Copyright (c) 2020 Nordic Semiconductor ASA
 *
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * @file Sample app to demonstrate PWM.
 */

#include <zephyr/kernel.h>
#include <zephyr/sys/printk.h>
#include <zephyr/device.h>
#include <zephyr/drivers/pwm.h>

static const struct pwm_dt_spec pwm_led0 = PWM_DT_SPEC_GET(DT_ALIAS(pwm_led0));

#define MIN_PERIOD PWM_SEC(1U) / 128U
#define MAX_PERIOD PWM_SEC(1U)

int main(void)
{
	uint32_t max_period;
	uint32_t period;
	uint8_t dir = 0U;
	int ret;

	printk("PWM-based blinky\n");

	if (!pwm_is_ready_dt(&pwm_led0)) {
		printk("Error: PWM device %s is not ready\n",
		       pwm_led0.dev->name);
		return 0;
	}

	/*
	 * In case the default MAX_PERIOD value cannot be set for
	 * some PWM hardware, decrease its value until it can.
	 *
	 * Keep its value at least MIN_PERIOD * 4 to make sure
	 * the sample changes frequency at least once.
	 */
	printk("Calibrating for channel %d...\n", pwm_led0.channel);
	max_period = MAX_PERIOD;
	while (pwm_set_dt(&pwm_led0, max_period, max_period / 2U)) {
		max_period /= 2U;
		if (max_period < (4U * MIN_PERIOD)) {
			printk("Error: PWM device "
			       "does not support a period at least %lu\n",
			       4U * MIN_PERIOD);
			return 0;
		}
	}

	printk("Done calibrating; maximum/minimum periods %u/%lu nsec\n",
	       max_period, MIN_PERIOD);

	period = max_period;
	while (1) {
		/* Set 100% for 1 sec */
		ret = pwm_set_dt(&pwm_led0, period, period);
		if (ret) {
			printk("ret: %d\n", ret);
		}
		k_sleep(K_SECONDS(1U));
		/* 50 % for 2 sec */
		ret = pwm_set_dt(&pwm_led0, period, period / 2U);
		if (ret) {
			printk("ret: %d\n", ret);
		}
		k_sleep(K_SECONDS(2U));
		/* 0 % for 4 sec */
		ret = pwm_set_dt(&pwm_led0, period, 0);
		if (ret) {
			printk("ret: %d\n", ret);
		}
		k_sleep(K_SECONDS(4U));
	}
	return 0;
}

Which behaves like this:

Kind regards,

Håkon