USB NAK events continuously received


Recently I have a project which needs to interface usbn9603 with MCU. At PC side the XP can recognize the device as a HID device without problem. However, I have traced the MCU program that it continuously receive NAK events at end point 3. The endpoint 3 is enabled to transfer data in initialization stage. However, I have not run any program at the PC side.

Is it normal? Thanks!

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Yes, it sounds like the host is polling according to the rate set in the HID's endpoint descriptor. If the device isn't ready to return any data to the host, it NAKs.


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If the device has no data, does it return NAK?

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sure! if the device isnt ready to receive data or has 0 bytes to return, but is otherwise functioning OK then NAK is proper response. NAK is not an error response. it means - not yet, try again later.

endpoints that are disabled or not existant or not initialized should return nothing endpoints that have faults or beind set to STALL should return STALL all other initialized, enabled and not in error endpoints should return NAK

well this dependant of the implementation and software etc..


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