Issues keeping system in sleep when using SoftDevice API for entering sleep mode

[hestro92]

Hi! We are currently trying to develop a low power framework for our nRF52840 DK with SoftDevice S140. After disabling various peripherals and interrupts we use the provided API for entering sleep in SoftDevice (sd_app_evt_wait()). However it seems to immediately exit and wake the system up; since we're in the idle task it enters sleep mode again and wakes up repeatedly. This gives a few thousand sleep-and-wake loops in a couple of seconds.

To make sure that there was no pending interrupt we used sd_nvic_ClearPendingIRQ on all defined interrupts but still no difference. We have also added the
fix for the FPU bug:

__set_FPSCR(__get_FPSCR()  & ~(FPU_EXCEPTION_MASK));
(void) __get_FPSCR();
NVIC_ClearPendingIRQ(FPU_IRQn);

We also tried to run sd_evt_get() before and after sd_app_evt_wait() to check wether there was any pending events but it turned up empty. Do you have any suggestions on how to overcome this issue?

Thank you!

[Simonr]

Hi

What SDK version are you using? Have you tried using the idle_state_handle function to go to sleep instead, as seen in many of our examples this function makes sure that no processes are kept running, and calls nrf_pwr_mgmt_run(); which prepares the FPU and CPU for sleep before calling sd_app_evt_wait();.You can check out, for example, the ble_app_beacon example to take a look.

Best regards,

Simon

[hestro92]

We're running 15.3 of the SDK, we managed to make it work by adding a __WFE() after the sd_app_evt_wait()-call, that seems to make it remain in sleep. However adding another sd_app-call instead or placing the WFE before it wouldn't work. Trying to use your suggested functions are a bit complicated as we have implemented our own version of nrf_pwr_mgmt_run.