[Help] Alveo U50 OpenNIC Shell - 100G Link Down with Spirent Tester, RS-FEC Enabled

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Hi all,

I am using a Xilinx Alveo U50 card with the OpenNIC shell (Vivado 2024.1, QDMA 5.0 driver) and trying to bring up the 100Gbps Ethernet port. The setup is as follows:

FPGA: Xilinx Alveo U50
Bitstream: OpenNIC shell, RS-FEC enabled, CAUI-4 mode, CMAC configured (preset.xml checked)
Driver: QDMA 5.0, no errors in dmesg, CMAC instance detected
Test Instrument: Spirent 100G tester (QSFP28 LR4 module, RS-FEC enabled, 100G speed)
Cable/Module: Fiber and QSFP28 module tested OK (Spirent-to-Spirent link works fine)
Problem:

When connecting the Spirent tester to the U50 card, the link does NOT come up (ethtool enp59s0 shows "Link detected: no").
All RX/TX counters are zero (ethtool -S enp59s0).
The same cable and module work perfectly between two Spirent ports.
The U50 card is recognized by the system, QDMA and CMAC initialize without errors, but the physical link never comes up.
RS-FEC is enabled on both FPGA and Spirent sides.
What I have tried:

Verified fiber and QSFP28 module (no hardware issue).
Checked preset.xml and bitstream parameters (RS-FEC, CAUI-4, CMAC).
Confirmed Spirent tester settings (100G, RS-FEC enabled).
No errors in dmesg or driver logs, but rx status ok: 0 in driver output.
Questions:

Are there any known compatibility issues between OpenNIC shell (U50) and Spirent testers for 100G LR4/RS-FEC?
Is there any additional CMAC or FEC configuration required in the bitstream or driver for U50?
How can I further debug why the link does not come up, even though all hardware and parameters seem correct?
Any advice or checklist for troubleshooting 100G link issues with OpenNIC shell and test instruments?
Any help or suggestions would be greatly appreciated!

Thank you!