How to flash the leds with a duty cycle that does not equal 50%?

[milor]

Hello,

I use the nrf5340 pdk. I would like to flash the led1 with a duty cycle which is different from 50%, so i tried to open the binky_pwm project, but the segger shows that there is error.

So, I look on the forum and I find that there are people who have encountered the same problem and it has solved it well. So I follow the same steps, but it's still wrong for me. (ps: https://devzone.nordicsemi.com/f/nordic-q-a/71402/i-am-looking-for-simple-example-of-hw-driver-of-qdec-for-nrf5340)

So I would like to ask if you have any ideas on this?

Or can you give me a simpler example to achieve my goal? (for example: time on equals 2ms and time off equals 1ms.)

Thank you in advance!

[Øivind]

Hi,

If you want a simpler example, which works out of the box, try the blinky example.

There you can make a few simple changes to achieve what you are looking for.

At the top make two different times:

/* 1000 msec = 1 sec */
#define ON_TIME_MS      2000
#define OFF_TIME_MS     1000

In the while loop, alternate between the times:

	while (1) {
		gpio_pin_set(dev, PIN, (int)led_is_on);
		led_is_on = false;
		k_msleep(ON_TIME_MS);
		gpio_pin_set(dev, PIN, (int)led_is_on);
		led_is_on = true;
		k_msleep(OFF_TIME_MS);
	}

[milor]

Hello, thank you for the example.

In fact, I successfully ran the example binky_pwm, so I would like to ask if you know how to set a pwm_ledext1 at pin1.00 because I set an external led at PIN1.00 through the file nrf5340pdk_nrf5340_cpuapp.overlay.

 {
	aliases {
		pwm-led0 = &pwm_led0;
                pwm-ledext1 = &pwm_ledext1;
                ledext1 = &ledext1;
	};
};

/ {
pwmleds {
	compatible = "pwm-leds";
	pwm_led0: pwm_led_0 {
		pwms = < &pwm0 0x1c >;
	};
        pwm_ledext1: pwm_led_ext1 {
		pwms = < &pwm0 0x1c >;
	};
};
};

/ {
leds {
      compatible = "gpio-leds";
      ledext1: led_ext1 {
		gpios = <&gpio1 00 GPIO_ACTIVE_LOW>;
		label = "LED EXTERNE 1";
      };
};
};

Thank you in advance!

[Øivind]

You can try something along the lines of:

/ {
	pwmleds {
		compatible = "pwm-leds";
		pwm_led0: pwm_led_0 {
			pwms = <&pwm0 32>;
		};
	};

	aliases {
		pwm-led0 = &pwm_led0;
	};
};

&pwm0 {
	ch0-pin = <32>;
};

pin 32 is P1.00.

[milor]

Sorry to bother you again.

I want to connect led1 and external led with PWM0 to run same frequency.

In this regard, I set the ch0-pin to 28 followed by led1, then I set the ch1-pin to 32 for the external led.

&pwm0 {
          ch0-pin = <28>;
          ch1-pin = <32>;
          };

Then in main.c for example blinky-pwm, I write the same code as led1 for external led.

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

#define PWM_LED0_NODE	DT_ALIAS(pwm_led0)
#define PWM_LEDEXT1_NODE	DT_ALIAS(pwm_ledext1)


#if DT_NODE_HAS_STATUS(PWM_LED0_NODE, okay)
#define PWM_LABEL	DT_PWMS_LABEL(PWM_LED0_NODE)
#define PWM_CHANNEL	DT_PWMS_CHANNEL(PWM_LED0_NODE)
#define PWM_FLAGS	DT_PWMS_FLAGS(PWM_LED0_NODE)
#else
#error "Unsupported board: pwm-led0 devicetree alias is not defined"
#define PWM_LABEL	""
#define PWM_CHANNEL	0
#define PWM_FLAGS	0
#endif


#if DT_NODE_HAS_STATUS(PWM_LEDEXT1_NODE, okay)
#define PWM_LABELEXT1	DT_PWMS_LABEL(PWM_LEDEXT1_NODE)
#define PWM_CHANNELEXT1	DT_PWMS_CHANNEL(PWM_LEDEXT1_NODE)
#define PWM_FLAGSEXT1	DT_PWMS_FLAGS(PWM_LEDEXT1_NODE)
#else
#error "Unsupported board: pwm-ledext1 devicetree alias is not defined"
#define PWM_LABELEXT1	""
#define PWM_CHANNELEXT1	0
#define PWM_FLAGSEXT1	0
#endif


#define MIN_PERIOD_USEC	(USEC_PER_SEC / 64U)
#define MAX_PERIOD_USEC	USEC_PER_SEC

void main(void)
{
	const struct device *pwm,*pwmext1;
	uint32_t max_period;
	uint32_t period;
	uint8_t dir = 0U;
	int ret,retext1;

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

        pwm = device_get_binding(PWM_LABEL);
        pwmext1 = device_get_binding(PWM_LABELEXT1);

        if (!pwm) {
		printk("Error: didn't find %s device\n", PWM_LABEL);
		return;
	}
        if (!pwmext1) {
		printk("Error: didn't find %s device\n", PWM_LABELEXT1);
		return;
	}
        
        printk("Calibrating for device %s channel %d...\n",
	       PWM_LABEL, PWM_CHANNEL);
        printk("Calibrating for device %s channel %d...\n",
	       PWM_LABELEXT1, PWM_CHANNELEXT1);

	max_period = MAX_PERIOD_USEC;

	while (pwm_pin_set_usec(pwm, PWM_CHANNELE,
				max_period, max_period / 2U, PWM_FLAGS)&&
            pwm_pin_set_usec(pwmext1, PWM_CHANNELEXT1,
				max_period, max_period / 2U, PWM_FLAGSEXT1)) {
		max_period /= 2U;
		if (max_period < (4U * MIN_PERIOD_USEC)) {
			printk("Error: PWM device %s "
			       "does not support a period at least %u\n",
			       PWM_LABELEXT1, 4U * MIN_PERIOD_USEC);
			return;
		}
	}

	printk("Done calibrating; maximum/minimum periods %u/%u usec\n",
	       max_period, MIN_PERIOD_USEC);

	period = max_period;

	while (1) {

                ret = pwm_pin_set_usec(pwm, PWM_CHANNEL,
				       period, period / 2U, PWM_FLAGS);

                retext1 = pwm_pin_set_usec(pwmext1, PWM_CHANNELEXT1,
				       period, period*9U/10U, PWM_FLAGSEXT1);
                
                if (ret) {
			printk("Error %d: failed to set pulse width\n", ret);
			return;
		}
                if (retext1) {
			printk("Error %d: failed to set pulse width\n", retext1);
			return;
		}

		period = dir ? (period * 2U) : (period / 2U);
		if (period > max_period) {
			period = max_period / 2U;
			dir = 0U;
		} else if (period < MIN_PERIOD_USEC) {
			period = MIN_PERIOD_USEC * 2U;
			dir = 1U;
		}

		k_sleep(K_SECONDS(4U));
	}
}

But when I run it, the LED does not change the frequency. Then I saw Termite, here showing Error-22: Failed to Set Pulse Width. Do you know how to solve it?

Thanks in advance!

[Øivind]

Hi again,

You can't change the period when you are using two channels on the same PWM like that:

/* If any other channel (other than the one being configured) is set up
 * with a non-zero pulse cycle, the period that is currently set cannot
 * be changed, as this would influence the output for this channel.
 */

Set the pulse to 0 before setting the new period:

	period = max_period;

	uint32_t period_temp = max_period;

	while (1) {

                ret = pwm_pin_set_usec(pwm, PWM_CHANNEL,
				       period, period / 2U, PWM_FLAGS);

                retext1 = pwm_pin_set_usec(pwmext1, PWM_CHANNELEXT1,
				       period, period*9U/10U, PWM_FLAGSEXT1);
                
                if (ret) {
			printk("Error %d: failed to set pulse width for led 0\n", ret);
			return;
		}
                if (retext1) {
			printk("Error %d: failed to set pulse width for led 1\n", retext1);
			return;
		}

		period_temp = period;

		period = dir ? (period * 2U) : (period / 2U);
		if (period > max_period) {
			period = max_period / 2U;
			dir = 0U;
		} else if (period < MIN_PERIOD_USEC) {
			period = MIN_PERIOD_USEC * 2U;
			dir = 1U;
		}

		k_sleep(K_SECONDS(4U));

		ret = pwm_pin_set_usec(pwm, PWM_CHANNEL,
				       period_temp, 0, PWM_FLAGS);

        retext1 = pwm_pin_set_usec(pwmext1, PWM_CHANNELEXT1,
				       period_temp, 0, PWM_FLAGSEXT1);
                
        if (ret) {
			printk("Error %d: failed to set pulse width to 0 for led 0\n", ret);
			return;
		}
        if (retext1) {
			printk("Error %d: failed to set pulse width to 0 for led 1\n", retext1);
			return;
		}

	}
}

Or use a second PWM:

/ {
	pwmleds {
		compatible = "pwm-leds";
		pwm_led0: pwm_led_0 {
			pwms = <&pwm0 28>;
		};
		pwm_ledext1: pwm_led_ext1 {
			pwms = <&pwm1 32>;
		};
	};

	aliases {
		pwm-led0 = &pwm_led0;
		pwm-ledext1 = &pwm_ledext1;
	};
};

&pwm0 {
	ch0-pin = <28>;
};

&pwm1 {
	status = "okay";
	ch0-pin = <32>;
};