Hardware interview practice
Detect duplicate valid cache tags
Design a checker for a small fully associative cache set that reports whether any two valid ways contain the same tag and returns the earliest matching way pair.
Reviewed example
Work through one case
Input
valid=4'b1111; tags by way=[A,B,A,A]Expected output
duplicate=1; way_a=0; way_b=2Way pairs (0,2) and (0,3) match, and the nested lowest-way priority chooses (0,2); invalid ways would not participate.
What to cover
Requirements
- Compare only distinct valid ways and return way_a < way_b.
- Ignore equal tags in invalid ways.
- Use lowest-way lexicographic priority when several duplicate pairs exist.
- Accept check only when check_ready is high, pulse done once per accepted check, and return zero indices when no duplicate exists.