[embassy-nrf]: Unexpected behavior of `SimplePwm` `set_duty`: Higher values result in lower duty cycle

[jmjoy]

When testing embassy-nrf on nrf52840, I found that the set_duty method of SimplePwm seems to behave unexpectedly. Specifically, the higher the value set by set_duty, the lower the actual PWM duty cycle output. Here is a minimal example:

let mut pwm = SimplePwm::new_1ch(p.PWM1, p.P0_13);
pwm.set_prescaler(embassy_nrf::pwm::Prescaler::Div1);
pwm.set_max_duty(32767);
pwm.set_duty(0, 10000);
pwm.enable();

I connected an LED with its anode to P0_13 and cathode to GND. When I increase the value of set_duty, the LED becomes dimmer (i.e., the output duty cycle actually decreases).

I am unsure if this is a misunderstanding on my part, or if it is specific to my board or setup. My expectation is that increasing the value passed to set_duty should increase the duty cycle (i.e., the output should be "on" for a longer portion of each cycle). Is this the intended behavior, or is there something I am missing?

[frenkoes]

Sounds like the hardware output is in active-low configuration:

• 100% duty cycle = always low (off)
• 0% duty cycle = always high (on)

[jmjoy]

Sounds like the hardware output is in active-low configuration:

• 100% duty cycle = always low (off)

• 0% duty cycle = always high (on)
  

Yes, do you have an NRF board? Can you test it?