nRF51822 PWM strange behavior

[Vrabec]

Hi.

I'm using latest version of nrf51-pwm-library to test if PWM works fine, but unfortunately, it's not. I have very simple program which should fade LED from 255 to 0 in infinite loop, but instead fading, I can see LED light on 100% and then turn off (blink instead fade). When I debug, I notice, LED is on (without any fading) when i > 0 and LED is off when i == 0.

Any suggestions? Btw no softdevice is used so far.

This is how my code look like:

#include <stdbool.h>
#include <stdint.h>
#include "nrf.h"
#include "nrf_gpio.h"
#include "nrf_delay.h"
#include "nrf_pwm.h"
#include "boards.h"

int main(void)
{
    nrf_pwm_config_t pwm_config = PWM_DEFAULT_CONFIG;
    
    pwm_config.mode             = PWM_MODE_LED_255;
    pwm_config.num_channels     = 1;
    pwm_config.gpio_num[0]      = 9;   
    
    // Initialize the PWM library
    nrf_pwm_init(&pwm_config);

		for(uint8_t i = 255; i >= 0; i--){
			nrf_pwm_set_value(0, i);
			nrf_delay_ms(100);
		}
}

[Vrabec]

I don't find reason why this happened, but using nrf_pwm_noglitch solves the issue. But anyway it can be useful to know what is wrong in nfr_pwm libraby.

[Stefan Birnir Sverrisson]

Hi Vrabec

Thank you for your question.

I can not reproduce the issue with your code, using nrf_pwm.h, SDK 7.0.1 and nRF51-DK. What SDK version and hardware are you using?

[Vrabec]

I'm using Keil uVision. I started with latest version of PWM example through uVision's Pack Installer. This works fine (I'm not using softdevice for now), however I read using this PWM and Softdevice at once can lead to problems. Therefore I download and import latest version of nrf_pwm. In addition, I'm not using DK but this. Hopefully my answer somehow helps.

[Stefan Birnir Sverrisson]

The latest nrf_pwm library is to use with SDK 7.0.1+. Are you using SDK 7.0.1 or later?

What are the chip laser markings on the nRF51 chip on your module? That should say something about if it is second or third revision nRF51, see the nRF51 compatibility matrix

[Vrabec]

I'm using latest SDK (9.0.0). The marking on chip is: N51822 GFAAG0 1407AV what based on compatibility matrix and forum responses seems to be 2nd revision.