Low power mode and RTC, Timer and PPI

[JeanMBoones]

SDK15.3

nRF52840

S140 v6.1.1

Q1. I have an RTC compare event connected to a Timer count task over PPI. The Timer is configured in low power counter mode. My question is when I go into low power mode using sd_app_evt_wait(), will the RTC events go off and trigger the Timer's count task over PPI? Or will these peripherals be shutoff during low power mode?

Q2. When a timer's count task is triggered, does it request the HFCLK to increment the timer's counter? If so, how is this handled in low power mode? Will the HFCLK be requested every time the task is triggered in low power mode?

Thanks.

[haakonsh]

Q1)
sd_app_evt_wait() will put the MCU into SystemON Idle, where the CPU is at sleep but the peripheral sub-system is awake. This means that all peripherals are available, with PPI and EasyDMA. Anything running before you call sd_app_evt_wait() will continue to do so. If a peripheral requires the CPU to run a driver the CPU will be woken up. 

Q2)
Yes, because the PPI system requires the 16MHz clock tree, who's a division of the HFCLK clock. 'Low power mode' means that the HFCLK is turned off/on on-demand, vs 'constant latency' where the HFCLK is always on to force a constant latency of the wake-up times of peripherals and CPU.