https://devzone.nordicsemi.com/f/nordic-q-a/53833/freertos-tickless-idle-not-supported-by-systick-port-for-nrf52The SysTick port for NRF52 does not support tickless idle on freeRTOS, what is the reason for this limitation? Are there any known problems behind this limitation?en-USTelligent Community 13Wed, 30 Oct 2019 20:43:26 GMThttps://devzone.nordicsemi.com/thread/217620?ContentTypeID=1Wed, 30 Oct 2019 20:43:26 GMT137ad170-7792-4731-bb38-c0d22fbe4515:f49b142b-13bc-4ce2-88ba-be104187a31ajakbird<p>SysTick runs off the core instruction clock.&nbsp; When entering IDLE mode the clock stops, so SysTick stops as well.</p> <p>FreeRTOS needs to know the elapsed number of ticks while the core sleeps.&nbsp; If SysTick is used as the time base there is no way to determine the elapsed time while the core is asleep.&nbsp; Nor is there a mechanism to wake up after the maximum tick delay for tickless mode.</p> <p>The solution is to use RTC1 for the timebase.&nbsp; Since it uses LFCLK it continues to run, and a compare register can be set to force an interrupt when the maximum tick delay is reached.</p> <p>This works in System On, IDLE mode but not System Off.&nbsp; If you have to track time in System Off mode you&#39;ll need an external RTC.&nbsp; LFCLK is stopped so RTC1 won&#39;t work.</p> <p>&nbsp; Jack Peacock</p><div style="clear:both;"></div>