https://devzone.nordicsemi.com/f/nordic-q-a/63768/device-lockup-by-serial-write-in-critical-regionHi, In my project, there is a device lock up and I found the problematic point that a debug log using nrf_serial_write() in critical region. I think it is not a good idea to use debug log in critical region and I suspected if the previous criticalen-USTelligent Community 13Wed, 15 Jul 2020 14:42:51 GMThttps://devzone.nordicsemi.com/thread/260185?ContentTypeID=1Wed, 15 Jul 2020 14:42:51 GMT137ad170-7792-4731-bb38-c0d22fbe4515:ae8ecb6a-8c8b-42ee-88d2-3a2788355126J&#248;rgen Holmefjord<p>Hi,</p> <p>When you enter a critical region, all peripheral interrupts will be disabled/masked. Most likely, the&nbsp;<span>nrf_serial_write does a blocking wait for some event (transfer completed, timeout, error, etc). If you call this inside the critical region, the interrupts will never fire and the function will never complete.</span></p> <p><span>If you need to use logging inside the critical region, you may use the&nbsp;<a href="https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.0/lib_nrf_log.html#nrf_log_processing">NRF_LOG library in deferred mode</a>. This will add the logs to a buffer, and you need to process the buffer in the main loop to send the actual logs on UART.</span></p> <p><span>Best regards,<br />Jørgen</span></p><div style="clear:both;"></div>