- Compare the problem across several devices or PCBs to ensure that the problem is not a one-off case.
- Try using an alternative link partner or test equipment and then compare results.
- Try putting the core into loopback (both by placing the core into internal loopback, and by looping back the optical cable) and compare the behavior. The core should always be capable of Auto-Negotiating with itself and looping back with itself from transmitter to receiver so direct comparisons can be made. If the core exhibits correct operation when placed into internal loopback, but not when loopback is performed through an optical cable, this can indicate a faulty optical module or a PCB problem.
- Try swapping the optical module on a misperforming device and repeat the tests.
Perform these additional checks when using a device-specific
transceiver:
- Directly monitor the following ports of the device-specific transceiver by
attaching error counters to them, or by triggering on them using the debug
feature or an external logic analyzer.
rxdisperrrxnotintableThese signals should not be asserted over the duration of a few seconds, minutes or even hours. If they are frequently asserted, it might indicate a problem with the device-specific transceiver. Consult Answer record 19699 for debugging device-specific transceiver issues.
- Place the device-specific transceiver into parallel or
serial loopback.
- If the core exhibits correct operation in device-specific transceiver serial loopback, but not when loopback is performed by an optical cable, it might indicate a faulty optical module.
- If the core exhibits correct operation in device-specific transceiver parallel loopback but not in serial loopback, this can indicate a device-specific transceiver problem. See Answer Record 19699 for details.
- A mild form of bit error rate might be solved by adjusting the transmitter TX_PREEMPHASIS, TX_DIFF_CTRL and TERMINATION_IMP attributes of the device-specific transceiver.