First PWM pulse stretched when starting nrfx_pwm_complex_playback() on nRF54L15

[Haresh05]

Hi,

My configuration:

• Base clock: 16 MHz

• COUNTERTOP: 20

• Duty ticks: 5 (25%), 10 (50%), 15(75%)

• repeats = 0, end_delay = 0

• Pin configured with default polarity

Expected waveforms:

• 25% → 0.25 µs high

• 50% → 0.625 µs high

• 75% → 0.875 µs high

The very first pulse after starting playback is stretched to ~1.25 µs high
After that, the waveform is correct and stable at 800 kHz with the expected duty cycles

I tried clearing the GPIO before starting playback → issue still occurs.

Questions:

1. Is this a known behavior of PWM startup on nRF54 series (similar to nRF52 anomaly 109, but different chip)?

2. Is there a recommended way to avoid or mask the stretched first pulse?

3. Any best practices when using very small COUNTERTOP values (20 ticks) at high PWM frequencies like 800 kHz?

Thanks in advance!

pwm_seq_update__ind_test.zip

[Susheel Nuguru]

Hi Haresh,

I have run your project and probing pin at P1.10 does not show any issues to me

I tested this on nRF54L15DK using NCSv3.1.0 on VSC

if you are using custom board to test it, I suggest reviewing the external pulls you have on these GPIIOs so that you can configure the software to match it.