https://devzone.nordicsemi.com/f/nordic-q-a/7275/gazell-callbacks-not-workingI have the following code, it&#39;s pretty bare in terms of its functionality: #include &lt;stdint.h&gt; extern &quot;C&quot; { #include &quot;nrf_delay.h&quot; } #include &quot;gazell.h&quot; #include &quot;tools.h&quot; #include &quot;uart.h&quot; #include &quot;core.h&quot; extern uint8_t nodeMode;en-USTelligent Community 13Wed, 27 May 2015 09:44:37 GMThttps://devzone.nordicsemi.com/thread/25719?ContentTypeID=1Wed, 27 May 2015 09:44:37 GMT137ad170-7792-4731-bb38-c0d22fbe4515:05c29c0c-444a-417e-b2d4-c321def9ce80ImQ009<p>Turns out they are being called just fine, it&#39;s just that I have my UART print functions wait for an interrupt indicating that the transmission is over. Seems like Gazell&#39;s interrupts are higher priority so the UART interrupt isn&#39;t called when I need it to. Is there any way around that? I just need to check whether UART tx fifo is empty.</p><div style="clear:both;"></div>