Hardware interview practice
Compact valid cache-line words in place
Compact the valid words in a bounded cache-line register bank toward slot zero while preserving order. Clear every vacated valid bit and data slot.
Reviewed example
Work through one case
Input
valid=5'b10110; data=[dirty,A,B,dirty,C] by slot 0..4Expected output
valid=5'b00111; data=[A,B,C,0,0]Compaction reads only original valid slots in order and clears both data and validity in every vacated suffix slot.
What to cover
Requirements
- Use the valid bitmap, not the data value, to decide which words to retain.
- Preserve the original order of all valid entries.
- Replace the internal line state with the compacted result without overwriting unread values.
- Provide fixed busy/done behavior and support all-valid and all-invalid lines.