DenseChip

AMS Interface · All levels

Link Training: Step-by-Step Walkthrough

Step-by-Step Walkthrough for Link Training.

Step-by-step analysis walkthrough

Use this when you own Link Training during an AMS war room.

  1. Capture failing mode and environmental condition.

  2. Pull synchronized waveform, logs, and report artifacts.

  3. Mark first boundary where legal behavior diverges.

  4. Audit reset/clock/power sequence assumptions.

  5. Check physical coupling contributors (floorplan/power/package) where relevant.

  6. Assign single-thread ownership for the first fix.

  7. Propose bounded change and define success criterion.

  8. Run scenario and safety regressions.

  9. Document findings in closure memo.

  10. Update signoff dashboard and waiver state.

Artifacts to collect

  • training state trace, firmware log, protocol analyzer capture

  • handoff contract

  • firmware/config tag

  • physical signoff snapshot

  • decision memo

Decision memo template

diagram
AMS DECISION MEMO — Link Training
mode/condition:
metric:
hypothesis:
fix:
regression:
owners: firmware owner, PHY owner, system validation lead

Reference visuals

Training state path

diagram
detect -> poll -> config EQ -> align -> active/L0
      ^                                  |
      +------------- retry/fallback -----+

AMS deep dive

SerDes closure requires protocol, training, and SI evidence together.

Concept diagram

diagram
SERDES FLOW

training -> equalization -> lane margin -> protocol stability

Metric graph

diagram
BER VS EQ

BER
 ^
 |  high  low  high
 +-----------------> EQ setting

Reports and artifacts

  • lane BER

  • training state transitions

  • EQ sweep report

  • link retry counters

Mini case study

Link looked protocol-clean but lane margin collapsed under thermal sweep.

Debug branches

  • Correlate LTSSM and lane metrics

  • Check SI margins

  • Review firmware timeout assumptions

Senior review question

Ask: what boundary condition proves this topic is actually closed?

Key takeaways

  • State boundary, mode, and evidence tag with every claim.

  • Always align analog, digital, and physical owners before signoff decisions.

Common pitfalls

  • Fixing averages while tails still fail.

  • Skipping package/supply evidence in jitter or SerDes issues.

  • Shipping with waivers that lack owner and expiration criteria.

Principal AMS review addendum

Training protocols establish lane polarity, timing, equalization, and protocol states; digital state machines must synchronize with PHY indications and timeout policies.

Metric: training pass rate, time-to-L0, fallback mode frequency

Practice this lesson