https://devzone.nordicsemi.com/f/nordic-q-a/74412/nrf52-esb-rf-enhanced-shockburst-sdkhi, After the TX interrupt event occurs, on_radio_disabled_tx() is executed. There is a timeout event for receiving an ACK. I noticed that the timer timeout was set using TIMER2, but I didn&#39;t see where the timer interrupt was generated. Buten-USTelligent Community 13Mon, 26 Apr 2021 14:52:53 GMThttps://devzone.nordicsemi.com/thread/306856?ContentTypeID=1Mon, 26 Apr 2021 14:52:53 GMT137ad170-7792-4731-bb38-c0d22fbe4515:8091ca14-9ffe-4cf8-89e4-b39dcf82bc5bHung Bui<p>Hi Ellison,&nbsp;</p> <p>The ESB protocol use the TIMER2 in a little bit smart way. So there is no interrupt handler code, but instead the process is automated with PPI. You can find in ppi_init() the automation task-event is connected. So when&nbsp;NRF_ESB_SYS_TIMER-&gt;EVENTS_COMPARE occurs the TASK_DISABLE will be triggered. It automatically stop the PTX from waiting for ACK if it&#39;s timed out.</p> <p>The CC[1] will start TX automatically if there is a retransmission needed.&nbsp;</p><div style="clear:both;"></div>