PROMPT
You see BER, link retrain count, throughput under real traffic on High-Speed I/O Debug. Walk through root cause and fix.

STRONG ANSWER
1. Names the layer and transaction identity.
2. Explains debug crosses digital packet counters, PHY adaptation, board SI, firmware sequencing, and workload traffic shape.
3. Requests link monitor log, eye/margin report, packet analyzer capture.
4. Proposes one reduced sequence and one system regression.

WEAK ANSWER
Jumps to widening the interface, increasing FIFO depth, or blaming firmware without evidence.

BIT ERROR RATE vs EQ SETTING

BER (log)
 1e-3 |*                         *
 1e-6 |  *                    *
 1e-9 |     *             *
1e-12 |        *  *  *  *        <- usable window
      +-------------------------> EQ / tap setting
Pick the center of the low-BER window, not the edge.

ROOT-CAUSE TREE — High-Speed I/O Debug

BER, link retrain count, throughput under real traffic looks wrong
        |
   reproducible?
     /        \
   no          yes
   |            |
 flaky env   same first transaction every time?
 / seed         /            \
              yes             no
               |               |
        protocol rule     timing/reset/PVT
        or config bug     or load-dependent

HIGH-SPEED STACK

app -> MAC/framing -> PCS/encoding -> SerDes/PHY -> channel

CRC errors often mean PCS/PHY/channel, not TCP.

BER vs EQ SETTING

BER
1e-3 |*
1e-6 |  *
1e-9 |     **** usable window
1e-12|          *
     +-----------------> EQ tap