1,000+ ASIC Interview Questions: SystemVerilog, UVM & RTL

DescriptionQ669

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Q669FWGoogleASIC interview problem

Localize an intermittent HBM lane failure

TechniquesSiliconHBMReliabilityCharacterization

DifficultyHard

TopicPost-Silicon Validation

LanguagePython

Requirements4 checkpoints

Problem

HBM traffic shows rare CRC failures that may correlate with a physical lane, address region, traffic pattern, or temperature. Implement the complete balanced experiment, numerical failure threshold, first-run classification precedence, and separate power-cycle repeat report.

Starting declarationPython

lanes 0..7
regions A,B,C,D
patterns 0x00,0xFF,0xAA,0x55
temperatures 25 C,100 C
run 10^6 transfers per tuple

Example input and output

Use this case to check your interpretation

Input

Lane 3 has at least 10 errors in all four regions and all four patterns at both temperatures; every other tuple passes

Output

classification=LANE; all 32 lane-3 tuples appear in the repeat plan

Explanation

Lane 3 contains every required 3-region by 3-pattern Cartesian subset at both temperatures, so the highest-precedence LANE rule matches.

Requirements (4)

Execute every lane-region-pattern-temperature tuple with equal transfer count and retain raw error records plus total transfers.
Mark a tuple failing when it has at least 10 errors per 10^6 transfers.
Apply this precedence with complete Cartesian subsets: LANE means one lane across any three regions, any three patterns, and both temperatures; REGION means one region across any six lanes, any three patterns, and both temperatures; PATTERN means one pattern across any six lanes, any three regions, and both temperatures; THERMAL means no failures at 25 C plus a complete 100 C subset spanning any four lanes, any two regions, and any two patterns; otherwise return MIXED.
Repeat every first-run failing tuple after a power cycle and report repeat results separately without changing the first-run classification.