strange signal / noise on PWM. Noise diaspears when connecting to JLINK! WHY?

[MaxRPEng]

Hi,

i am using a PWM signal to control the brightness of a LED. When the brightness is at zero, i have a random flickering on the LED.

This signal is also present at the pin itself. The strange thing, as soon i connect a JLINK probe the signal is perfect zero. So no noise anymore.

As soon i remove the JLINK the flickering is back.

Annoing magic.

Any idea why the JLINK influnces the behaviour of the nRF52?

thank you

Max

[haakonsh]

One source could be the DCDC regulator or the clocks. The debugger will force the nRF52's regulator into LDO mode and keep the HFCLK running. 

Try disabling the DCDC regulator. If that does not work try to enable Constant Latency (force HFCLK on, see Sub power modes). 

See in the POWER Registers, see DCDCEN register, and the TASKS_CONSTLAT. 

[MaxRPEng]

Hi, thank you for your fast answer: DCDC is disabled.

nrfjprog  --memrd 40000578
0x02625C42: 0000                                      |..|

I turned the CONSTLAT on: NRF_POWER->TASKS_CONSTLAT = 1;

But i still have that strange random signal on my PWM output.

[haakonsh]

Try using nrf_drv_pwm_sequence_values_update() instead of nrf_drv_pwm_simple_playback() to change the duty cycle.

[MaxRPEng]

according some examples i implemented the following:

static nrf_pwm_values_individual_t seq_values[];

 seq_values[0].channel_0 = 50;
  seq_values[0].channel_1 = 50;

  nrf_pwm_values_t new_pwm_values;

  new_pwm_values.p_individual = seq_values;

nrf_drv_pwm_sequence_values_update(&m_pwm0, 0, new_pwm_values);

But now i dont have any PWM output !

[haakonsh]

How do you start the PWM now? I think you need to call nrf_drv_pwm_simple_playback() before you call nrf_drv_pwm_sequence_values_update.

[MaxRPEng]

but you told me to usenrf_drv_pwm_sequence_values_update instead of nrf_drv_pwm_simple_playback()

[MaxRPEng]

i included the playback call to the init. now i have a pwm output. but still the same issue with the random signal