Does DFU HCI(serial) requires an ack from bootloader?https://devzone.nordicsemi.com/f/nordic-q-a/3130/does-dfu-hci-serial-requires-an-ack-from-bootloaderHello, I&#39;m stuck in DFU using HCI(serial).. I&#39;m using nrf51822 , softdevice s110 ver 6.0.0 . I used example code in &quot;nrf51_sdk_v6_0_0_43681\nrf51822\Board\nrf6310\device_firmware_updates\bootloader&quot;, and using nRFgo Studio --&gt; nRF51 Bootloader toen-USTelligent Community 13Tue, 14 Feb 2017 08:53:32 GMTRE: Does DFU HCI(serial) requires an ack from bootloader?https://devzone.nordicsemi.com/thread/11591?ContentTypeID=1Tue, 14 Feb 2017 08:53:32 GMT137ad170-7792-4731-bb38-c0d22fbe4515:f563d6bb-0313-49fc-a4f3-cab6d5d676abDonWoo<p>irarykim</p> <p>hi,I&#39;m having the same problem.Have you found out why the ack is missing?Thanks.</p><div style="clear:both;"></div>RE: Does DFU HCI(serial) requires an ack from bootloader?https://devzone.nordicsemi.com/thread/11590?ContentTypeID=1Tue, 15 Jul 2014 12:29:36 GMT137ad170-7792-4731-bb38-c0d22fbe4515:bf0cf4a1-70f8-4397-bce4-0cb106365825irarykim<p>The answer is YES. ack_transmit() is called if receives a start packet. My module returns an ack, then receives data packets. But doesn&#39;t send back ack... nRF6310 + PCA10005 works fine for HCI DFU~ I should compare them and find why.</p><div style="clear:both;"></div>