Hardware interview practice
Look up time-indexed register history
Store timestamped values for four register keys and answer queries with the value whose stored timestamp is the greatest one less than or equal to the requested time.
Reviewed example
Work through one case
Input
write key=2 (t=10,A), then (t=20,B); query key=2 at t=5,10,17,20Expected output
MISS, A, A, BThe backward search returns the newest timestamp less than or equal to the query and treats an exact timestamp as a hit.
What to cover
Requirements
- Support four keys and at most eight writes per key, with strictly increasing timestamps within each key.
- Serialize accepted commands and make every accepted write visible to every later accepted query.
- Return a miss before the first stored timestamp and use inclusive less-than-or-equal behavior for exact matches.
- Model a one-cycle local-memory read rather than comparing an entire history combinationally.
- A query response must remain stable until accepted; writes do not generate responses.