https://devzone.nordicsemi.com/f/nordic-q-a/3699/setting-lfclk-gives-hardfaultDescription of my system: Hardware:nRF51822, pca10001 Software: SDK5.20, S120 If i first call the function ble_stack_init(); and then i open the LFCLK first by set NRF_CLOCK-&gt;LFCLKSRC = 1; NRF_CLOCK-&gt;TASKS_LFCLKSTART = 1; the programen-USTelligent Community 13Tue, 02 Sep 2014 14:57:51 GMThttps://devzone.nordicsemi.com/thread/13418?ContentTypeID=1Tue, 02 Sep 2014 14:57:51 GMT137ad170-7792-4731-bb38-c0d22fbe4515:07dca4ee-159d-47dd-8916-0845541598adNikita<p>You shouldn&#39;t try to start lfclk manually after calling ble_stack_init() because when you call ble_stack_init() it&#39;ll call SOFTDEVICE_HANDLER_INIT() that will start lfclk and then softdevice will block all access from your application to lfclf settings.</p> <p>Describe your problem with sd_nvic_SetPriority()/sd_nvic_EnableIRQ() in more detail, what are you trying to do and when you getting HardFault.</p><div style="clear:both;"></div>