https://devzone.nordicsemi.com/f/nordic-q-a/19002/usb-transfer-on-nrf528401.specification says that we should trigger EP0STATUS task to initiate the status stage for control transfer(read/write). actually nrf52840 will auto ack the OUT TOKEN i.e. the status stage of control read transfer,but nak the IN TOKEN for the controlen-USTelligent Community 13Tue, 17 Jan 2017 13:50:17 GMThttps://devzone.nordicsemi.com/thread/73446?ContentTypeID=1Tue, 17 Jan 2017 13:50:17 GMT137ad170-7792-4731-bb38-c0d22fbe4515:d655a1ff-8349-4af9-8ab8-2a6591cc05b3Sigurd<p>Hi,</p> <p>Thank you for reporting this.</p> <ol> <li>Yes, this is a bug. The HW team is working on solving this issue.</li> <li>It seems that you have found a working solution for the moment. An underlying problem here is that SIZE.EPOUT[n] is write-only at the moment, but should have been RW. &quot;It seems that ack/nak is controlled by STARTEPOUT[n] task instead of SIZE.EPOUT[n].&quot; Note that the behaviour of STARTEPOUT[n] is correct.</li> </ol><div style="clear:both;"></div>