Cannot get PWM Blinky to work on an Arduino Due board - created new arduino_due.overlay

[Gerriko]

I am trying to use the on board LED but the LED remains constantly on. I have even tried turning the LED completely off (0 pulse) but no change.

Any ideas as to why it's not working.

Here is my arduino_due.overlay:

#include <zephyr/dt-bindings/pwm/pwm.h>
/ {
    aliases {
        mypwmled = &pwmled_0; /* Point my-led to our defined LED, using hyphenated alias */
    };

    /* Define a custom group for our application's PWM LED */
    app_pwm_leds {
        compatible = "pwm-leds"; /* Standard compatible string for PWM LEDs */

        /* Define our PWM LED on D13 (PB27 - Onboard LED), driven by pwm0 channel 3 (PWML1) */
        pwmled_0: pwmled-0 {
            pwms = <&pwm0 3 1000000000 PWM_POLARITY_NORMAL>; /* Use pwm0, channel 3 for PB27 (D13) */
            label = "User PWM LED D13"; /* Label for our PWM LED */
        };
    };
};

---

and here is my example code:

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

#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(mypwmled));

/* Min/Max period for initial hardware validation, not directly the blinking frequencies */
#define MIN_PWM_PERIOD (PWM_SEC(1U) / 128U)		//PWM_SEC() converts value to nanoseconds
#define MAX_PWM_PERIOD (PWM_SEC(1U))

#define INTERVAL_SECONDS 4U

int main(void)
{
	uint32_t max_period; /* For initial hardware capability check */
	uint32_t current_period;
	uint8_t dir = 0U;

	int ret;

	printk("\n\nPWM-based blinky demo\n");

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

	printk("...using PWM device %s on channel %u\n\n", pwm_led0.dev->name, pwm_led0.channel);
	
	k_sleep(K_SECONDS(INTERVAL_SECONDS / 2U)); // Brief pause to observe demo title
	
	/*
	 * In case the default MAX_PERIOD value cannot be set for
	 * some PWM hardware, decrease its value until it can.
	 *
	 * Keep decreasing MAX_PERIOD through the loop iteration until
	 * period_set() succeeds with a non-zero value.
	 */
	printk("Calibrating for the channel...\n");

	max_period = MAX_PWM_PERIOD;
	printk("Initial Max Period = %u\n", max_period);

	/* Attempt to set period and 50% duty cycle */
	while (pwm_set_dt(&pwm_led0, max_period, max_period / 2U)) {
		max_period /= 2U;
		if (max_period < (4U * MIN_PWM_PERIOD)) {
			printk("Error: PWM device does not support a period of at least %lu\n", 4U * MIN_PWM_PERIOD);
			return 0;
		}
	}

	printk("Done calibrating; max & min periods are %u | %lu usecs\n\n", max_period/1000U, MIN_PWM_PERIOD/1000U);

	/* The pwm_led0.period is now set to a valid period by the hardware.
	 * We will now control the period directly.
	 */

	/* Turn LED ON after calibration and before starting the main pattern */
	printk("Setting LED to ON state initially to observe that it's working.\n");
	ret = pwm_set_dt(&pwm_led0, max_period, max_period); /* 0U for pulse width = 0% duty cycle */
	if (ret) {
		printk("Warning: Failed to set LED to ON state, error %d.\n", ret);
		// Depending on severity, you might choose to return or continue
	}
	k_sleep(K_SECONDS(INTERVAL_SECONDS)); // Brief pause to observe LED OFF state

	/* Turn LED OFF after calibration and before starting the main pattern */
	printk("Setting LED to OFF state initially to observe no LED.\n\n");
	ret = pwm_set_dt(&pwm_led0, max_period, 0U); /* 0U for pulse width = 0% duty cycle */
	if (ret) {
		printk("Warning: Failed to set LED to OFF state, error %d.\n", ret);
		// Depending on severity, you might choose to return or continue
	}
	k_sleep(K_SECONDS(INTERVAL_SECONDS)); // Brief pause to observe LED OFF state

	current_period = max_period;
	
	while (1) {
		ret = pwm_set_dt(&pwm_led0, current_period, current_period / 2U);
		if (ret) {
				printk("Error %d: failed to set pulse width\n", ret);
				return 0;
		}
		if (current_period > 100000000)
			printk("Using period %u msec\n", current_period/1000000);
		else if (current_period > 100000)
			printk("Using period %u usec\n", current_period/1000);
		else
			printk("Using period %u nsec\n", current_period);

		current_period = dir ? (current_period * 2U) : (current_period / 2U);
		if (current_period > max_period) {
			current_period = max_period / 2U;
			dir = 0U;
			printk("...decreasing period\n");
		} else if (current_period < MIN_PWM_PERIOD) {
			current_period = MIN_PWM_PERIOD * 2U;
			dir = 1U;
			printk("...increasing period\n");
		}

		k_sleep(K_SECONDS(INTERVAL_SECONDS));

	}
	return 0;
}

[Gerriko]

I have narrowed my focus to:
compatible = "pwm-leds"; /* Standard compatible string for PWM LEDs */

The bindings for pwm-leds describes the setup.

# Copyright (c) 2018, Linaro Limited
# SPDX-License-Identifier: Apache-2.0

description: |
  Group of PWM-controlled LEDs.

  Each LED is defined in a child node of the pwm-leds node.

compatible: "pwm-leds"

child-binding:
  description: PWM LED child node
  properties:
    pwms:
      required: true
      type: phandle-array
      description: |
        Reference to a PWM instance.

        The period field is used by the set_brightness function of the LED API.
        Its value should at least be greater that 100 nanoseconds (for a full
        brigtness granularity) and lesser than 50 milliseconds (average visual
        persistence time of the human eye). Typical values for the PWM period
        are 10 or 20 milliseconds.

    label:
      type: string
      description: |
        Human readable string describing the LED. It can be used by an
        application to identify this LED or to retrieve its number/index
        (i.e. child node number) on the parent device.

I'm struggling to work out how to define my "group of pwm leds" for the due.

[Gerriko]

It turns out the Arduino docs for the Due is not strictly correct.

There is no PWML1 linked to D13 and hardware PWM is not available for all pins 2 to 13.

Arduino must have a software implementation for some pins.
https://content.arduino.cc/assets/A000056-full-pinout.pdf

Trawling through ATSAM3X8E data confirms this.

Anyway I got it working using D9/PC21 for my test. The secret sauce to learning which pins will work etc and getting the correct detail for pinmux is in: #include <dt-bindings/pinctrl/sam3XXe-pinctrl.h>

Here is the overlay I used:

/*
 * Devicetree overlay for the arduino_due in the pwm_blinky application.
 *
 */

#include <zephyr/dt-bindings/pwm/pwm.h>
#include <dt-bindings/pinctrl/sam3XXe-pinctrl.h>

/ {
	aliases {
		pwm-0 = &pwm0;
		pwm-led0 = &pwml4_gpio9_21;
	};

	pwmleds {
		compatible = "pwm-leds";
		pwml4_gpio9_21: pwml4_gpio9_21 {
			label = "PWM LED0";
			pwms = <&pwm0 4 PWM_MSEC(20) PWM_POLARITY_INVERTED>;
		};
	};
};

&pinctrl {
	/* Override the default pinctrl for pwm0 to use PC21 (PWML4) */
	pwm0_default: pwm0_default {
		group1 {
			pinmux = <PC21B_PWM_PWML4>; /* Configures PC21 as PWML4 with pull-up */
		};
	};
};