I am usning USB3 connection only. Do I need connect D+ and D- line? If yes what is functionality of these lines in USB3 protocol.
You need D+ and D- lines if you want to operate your device in USB2.0 speeds (High, Full and low speed).
And if not? I want only superspeed. Somebody told me that USB agents need it for autonegotiation...
If you want only superspeed then you can leave D+ and D- open. There should not be any problem with the functionality of device under superspeed but it is not expected to pass USB certifications.
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I tried to mask the D+/D- pins, to simulate this issue, and did _not_ see the Cypress on the PC.
Please note that in our system configuration the boot is via USB, so the booter should loat the code on the USB3.
Does the booter support USB3 operation?
That is the problem in your case. FX3 bootloader works in USB2.0 mode; not in USB3.0.
So it is not possible to leave out the D+ and D- lines if you are opting for USB boot.