Verification IP & Protocol Compliance · All levels

Error Injection and Negative Testing: Interview Drills

Interview Drills for Error Injection and Negative Testing.

Interview drills

Interview Drills for Error Injection and Negative Testing focuses on negative-test coverage closure and DUT error-response pass rate. The purpose is to turn memory observations into mechanism-backed actions with explicit owners and release-safe validation.

diagram

PROMPT
You observe negative-test coverage closure and DUT error-response pass rate on Error Injection and Negative Testing. Explain root cause and release decision.

STRONG ANSWER
1. Defines failing traffic context and first transition loss.
2. Explains mechanism: Compliance requires proving correct behavior under illegal stimulus, parity/ECC faults, timeout paths, and recovery sequences. Error-injection checkers validate that monitors, scoreboards, and DUT responses remain coherent when the bus enters degraded modes.
3. Requests proving artifact: negative-test matrix, fault-response log, and recovery sequence trace
4. Proposes bounded fix + owner + rollback-safe validation.

WEAK ANSWER
Gives generic VIP tuning ideas without checker evidence, owner accountability, or risk controls.

Interview evidence matrix

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VIP EVIDENCE MATRIX - Error Injection and Negative Testing

+-------------------------------+--------------------------------+--------------------------------+---------------------------+
| Evidence                      | Tells you                      | Does not prove                 | Next action               |
+-------------------------------+--------------------------------+--------------------------------+---------------------------+
| checker hit/miss + ACT/PRE mix    | locality and row-state cost    | lane-level capture integrity   | inspect training margins  |
| queue age + class breakdown   | fairness and starvation risk   | command legality details       | parse command timeline    |
| spec clause legality + bus timeline | timing-window pressure         | root cause by itself           | correlate with traffic map|
| eye / Vref / skew snapshots   | PHY margin and drift behavior  | controller policy quality      | pair with schedule logs   |
| CE/UE + scrub telemetry       | reliability trajectory         | immediate perf bottleneck only | map to hotspot addresses  |
+-------------------------------+--------------------------------+--------------------------------+---------------------------+

VIP deep dive

SVA and procedural checkers, temporal protocol rules, error-injection validation, and debug strategies for high-signal protocol closure.

Concept diagram

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VIP SECTION - Protocol Checkers & Assertion Strategy

testcase -> agents -> checkers -> coverage -> evidence

Metric graph

diagram

checker noise vs real violations trend

Reports and artifacts

checker hit report
coverage closure sheet
compliance trace matrix
regression health snapshot

Mini case study

A profile drift caused false checker storms until configuration hashes were locked in CI.

Debug branches

Reproduce with locked seed and profile
Isolate checker vs scoreboard vs DUT paths
Map failure to spec clause and owner

Senior review question

Ask: which latency, bandwidth, and reliability evidence proves this VIP topic is closed under real traffic?

Key takeaways

Always tie controller and PHY counter shifts to application latency and throughput outcomes.
Lock firmware timing profile, thermal condition, and DIMM state before comparing VIP captures.

Common pitfalls

Chasing peak bandwidth while ignoring p99 latency and fairness tails.
Changing timing guardbands without separating SI noise from scheduling issues.
Declaring closure without reliability gates, fault injection, and regression replay.

VIP atlas notes

Error Injection and Negative Testing should be read as an end-to-end VIP behavior, not as a single block definition. Production compliance closure reflects interactions between agents, checkers, coverage, and customer evidence before tapeout or IP release claims.

Compliance requires proving correct behavior under illegal stimulus, parity/ECC faults, timeout paths, and recovery sequences. Error-injection checkers validate that monitors, scoreboards, and DUT responses remain coherent when the bus enters degraded modes. VIP inefficiency is multiplicative: one weak checker enable, one hollow coverage bin, or one non-reproducible failure repeated across regressions can dominate signoff risk.

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