Equalization and training policies trade BER margin against bring-up speed.
+------------------+----------------+----------------+----------------+
| Approach | Strength | Weakness | Best when |
+------------------+----------------+----------------+----------------+
| Conservative | robust | more overhead | new tapeout |
| Balanced | practical | needs rigor | mature flow |
| Aggressive | faster | high regressions | late stage |
| Architectural | durable | slow loop | recurring issue |
+------------------+----------------+----------------+----------------+Choose the smallest change that proves mechanism and preserves system margins.
Treating all AMS problems as analog-only
Skipping package and power evidence
AMS EVIDENCE MATRIX — High-Speed SI Awareness
+-------------------+------------------------+--------------------------+-------------------------+
| Evidence | Tells you | Does not prove | Next action |
+-------------------+------------------------+--------------------------+-------------------------+
| Waveform/log pair | sequence behavior | physical root cause | correlate with signoff |
| Signoff report | metric movement | contract correctness | audit assumptions |
| Floorplan view | physical proximity | dynamic mode behavior | run stress mode |
| Firmware trace | state progression | analog quality | combine with lab data |
| Dashboard summary | closure status | single-failure mechanism | inspect raw artifacts |
+-------------------+------------------------+--------------------------+-------------------------+SerDes closure requires protocol, training, and SI evidence together.
SERDES FLOW
training -> equalization -> lane margin -> protocol stabilityBER VS EQ
BER
^
| high low high
+-----------------> EQ settinglane BER
training state transitions
EQ sweep report
link retry counters
Link looked protocol-clean but lane margin collapsed under thermal sweep.
Correlate LTSSM and lane metrics
Check SI margins
Review firmware timeout assumptions
Ask: what boundary condition proves this topic is actually closed?
State boundary, mode, and evidence tag with every claim.
Always align analog, digital, and physical owners before signoff decisions.
Fixing averages while tails still fail.
Skipping package/supply evidence in jitter or SerDes issues.
Shipping with waivers that lack owner and expiration criteria.
At multi-Gbps speeds, package/channel discontinuities and return-path quality convert into jitter and eye closure that appear as digital protocol instability.
Metric: SI-induced retries, lane margin, intermittent link drop rate
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