https://devzone.nordicsemi.com/f/nordic-q-a/10498/why-timer-of-sdk-9-0-needn-t-code-to-trigger-the-clockI read timer example of SDK7.0/6.0, and found that often we write some code to tigger the clock. but the same example of SDK9.0 needn&#39;t. why ? the code of SDK7.0: NRF_CLOCK-&gt;TASKS_HFCLKSTART = 1; to trigger the clock. /** @brief Functionen-USTelligent Community 13Fri, 27 Nov 2015 01:50:50 GMThttps://devzone.nordicsemi.com/thread/39033?ContentTypeID=1Fri, 27 Nov 2015 01:50:50 GMT137ad170-7792-4731-bb38-c0d22fbe4515:42c729ed-91fa-4ccc-9af0-0981af1ea30fhawk<p>thanks a lot.</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/39032?ContentTypeID=1Thu, 26 Nov 2015 11:29:09 GMT137ad170-7792-4731-bb38-c0d22fbe4515:12be5ac3-dbf1-48ce-9386-a4f93efdeb47Einar Thorsrud<p>The HFCLK is always running when the CPU is running or if a peripheral that requires it is active. (It can also be configured to run when it is not used, for constant latency, but it will increase the power consumption). The naming may be a bit confusing, but setting <a href="http://infocenter.nordicsemi.com/topic/nrf52.v1.7/Chunk401120700.html#topic"><code>TASKS_HFCLKSTART</code></a> actually starts the crystal oscillator, which is more accurate than the RC oscillator. If the application or peripheral (e.g. the radio) requires a accurate clock, the crystal oscillator must be used. If not, the RC is probably better as it starts up faster.</p><div style="clear:both;"></div>