RE: Reduction in System off mode wake up time

Håkon Alseth — Thu, 14 Nov 2019 13:29:30 GMT

Hi,

[quote user=""]I am using UART read write operation along with the system off mode. So, usually nRF9160 chip goes to sleep and wakes up when it receives something on UART and again goes to sleep(system-off). I have tried to measure the wake up time and found out that it varies. The minimum, it takes around 1sec to wakeup which is alot. Sometimes, it takes more than 1sec. Can you please tell me the reason of different wake up times and suggest me any solution to reduce this wake up time as it is affecting my application operations.[/quote]

Waking up from system off generates a reset condition, meaning that clock sources need to stabilize properly before the rest of the application can fully start up.

A external 32k LFCLK usually takes several hundred milliseconds to start up, and on the nRF9160 the typical time is set at 200 ms:

https://infocenter.nordicsemi.com/topic/ps_nrf9160/pmu_oscillators.html?cp=2_0_0_4_0_3_1#lfclk

If you also print several things on boot-up (spm module prints by default), these will delay the execution to main().

Kind regards,

Håkon