Duty cycle and frequency

[Swati kumari]

Hi,

I am trying to test the sample code example of PWM,

I am not able to change duty cycle other than 25% and 75%.

please suggest !!

Thank you.

[Kenneth]

Hello,

Maybe you can share the lines of code you have used to set 25% and 75%, and then I can help you set something else?

Kenneth

[Swati kumari]

Hi @ Kenneth,

below sample code for testing.

http://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.3.2/zephyr/samples/basic/blinky_pwm/README.html

nCS\v1.8.0\zephyr\samples\basic\blinky_pwm

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

#define PWM_LED0_NODE DT_ALIAS(pwm_led0)

#if DT_NODE_HAS_STATUS(PWM_LED0_NODE, okay)
#define PWM_CTLR DT_PWMS_CTLR(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_CTLR DT_INVALID_NODE
#define PWM_CHANNEL 0
#define PWM_FLAGS 0
#endif

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

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

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

pwm = DEVICE_DT_GET(PWM_CTLR);
if (!device_is_ready(pwm)) {
printk("Error: PWM device %s is not ready\n", pwm->name);
return;
}

/*
* In case the default MAX_PERIOD_USEC value cannot be set for
* some PWM hardware, decrease its value until it can.
*
* Keep its value at least MIN_PERIOD_USEC * 4 to make sure
* the sample changes frequency at least once.
*/
printk("Calibrating for channel %d...\n", PWM_CHANNEL);
max_period = MAX_PERIOD_USEC;
while (pwm_pin_set_usec(pwm, PWM_CHANNEL,
max_period, max_period / 2U, PWM_FLAGS)) {
max_period /= 2U;
if (max_period < (4U * MIN_PERIOD_USEC)) {
printk("Error: PWM device "
"does not support a period at least %u\n",
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);
if (ret) {
printk("Error %d: failed to set pulse width\n", ret);
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));
}
}

[Kenneth]

I changed the infinite while loop and it seems to work well here, e.g.:

	max_period = 1000;
	period = 0;

	while(1) {
				ret = pwm_pin_set_usec(pwm, PWM_CHANNEL, max_period, period, PWM_FLAGS);
				if (ret) {
					printk("Error %d: failed to set pulse width\n", ret);					
				}	
				period += 10;
				if(period>max_period)
					period = 0;
				
				k_sleep(K_MSEC(100U));
	}