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Hello,
I am running unframed PRBS of data-rate 111.81 Gbps from the analyzer over 4 lane @27.9525 Gpbs as shown in the image with serdes loopback at the receiver. We have done the re-timer RX setting to Adaptive Mode 2 for both retimer.
We have the following observation.
1. PRBS is running ok between QSFP-28 to Retimer and from Retimer to QSFP-28
2. PRBS error is detected between ASICS and Retimer
We have the following query
1. Does multiple Retimer in the path can create an issue?
2. Does the CAL_CLK_IN clock have and role in the error?
3. How to calculate and set Pre and post-emphasis to correct the PRBS errors
Regards,
Aman
Hi Aman,
1. Does multiple Retimer in the path can create an issue?
Since retimers reconstruct the high-speed signal, having multiple retimers in the path shouldn't create any issues.
2. Does the CAL_CLK_IN clock have and role in the error?
As long as CAL_CLK_IN meets these datasheet specs, I don't expect it to be a root cause of the errors.
3. How to calculate and set Pre and post-emphasis to correct the PRBS errors
I recommend conducting greenbox testing to determine optimal TX FIR parameters. This app note explains the testing methodology.
If the issue persists after adjusting the TX FIR parameters, can you share full register dumps from both retimers for me to review?
Best,
Lucas
