Primary debug scenario

Symptom: DMA reads hang after 10 seconds of operation. Link is healthy. No AER errors. LTSSM in L0.

Triage steps

1. Check completion credit counters — are they exhausted?

2. Count outstanding non-posted requests vs completion buffer size.

3. Look for completion timeout in config space.

4. Check the failing TLP size against requester MPS, downstream capabilities/configuration and any bridge or switch limits; do not require every function's field to match.

5. Capture TLP log: are completions being returned?

Common pitfalls

• Confusing credits with link width.

• Debugging endpoint logic when credits are the bottleneck.

• Ignoring completion credit pool separate from request credits.