DescriptionQ455
Q455DVASIC interview problem
Scoreboard a maximum-interval accelerator
TechniquesDVScoreboardSigned arithmeticReady/validReset
DifficultyHard
TopicReference Models
LanguageSystemVerilog
Requirements5 checkpoints
01
Problem
Verify a bounded accelerator that accepts up to 16 signed samples and returns the greatest-sum contiguous interval. Build the reference prediction and in-order scoreboard around the request and response handshakes.
Example input and output
Use this case to check your interpretationInput
accepted signed samples=[-2,3,4,-1]; response is stalled for two cyclesOutput
result_valid=1; max_sum=7; start=1; end=2; payload remains stable during stallExplanation
Exhaustive nonempty intervals select [3,4]; the queued prediction is consumed only when the response handshake occurs.
02
Requirements (5)
- Snapshot inputs only when req_valid and req_ready are both high, and evaluate every nonempty interval using signed arithmetic at least 16 bits wide.
- Break equal-sum ties by the lowest start index and then the lowest end index; count zero predicts result_valid low and zero result fields.
- Queue one expectation per accepted request and compare exactly once per accepted response.
- Require rsp_valid and its payload to remain stable while the response is stalled.
- Flush canceled expectations on reset and reject any orphan response before the first post-reset request.