it seems that Figure 2 on this page https://infocenter.nordicsemi.com/index.jsp?topic=%2Fps_nrf52840%2Fpwm.html is incorrect, or at a minimum the figure does not do what the text on the page describes. the caption describes a falling-edge PWM but the figure seems to show a rising-edge PWM. my team spent a lot of time debugging PWM driver issues due to confusion around this issue.