VCU108 evaluation board external loopback with QSFP28+fiber

[elidrissi]

Hello,

I have a problem with VCU108 evaluation board, I cant make an external loopback with QSFP28+fiber but when I use the loopback without fiber (the connector coming with the board) it works very good, I cant figure out what s the problem.

Please I need your help.

Thank you in advance.

Driss.

[saradapr]

Hi @elidrissi,

Can you confirm the the Far end PCS loopback working.

Also please replace the Fiber cable . 

Thanks,

Sarada

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[yenigal]

Hi

Can you give more details on what exactly is not working when you do a external cable loopback?

Are you seeing data errors or no data being looped back?

how are you sending the data?

[elidrissi]

Hi

The far PCS loop-back doesn't work.

Thanks.

[elidrissi]

For more details, I use the IP core IBERT, I configure it to work in this mode 4x25.78125G using the Quad 127 and the appropriate clock 156.25 MHz as mentioned in the documentation then I generate the example design. In this case Vivado generate automatically the XDC file. The bistream is successfully generated and the VCU108 evaluation board is correctly programed. everything works very good with the loop-back without fiber (the loop-back connector given with vcu108 Evaluation board) and each link transmit and receive 25.78125G but when I use my QSFP28 + fiber I can see in Serial I/O Analyzer that there is no-link  and I didn't see any data errors.

Thank you for any help.