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

DescriptionQ923

Page ↗

Q923DVASIC interview problem

Scoreboard variable-length bitmap ranges

TechniquesDVScoreboardVariable responseFramingBackpressure

DifficultyHard

TopicReference Models

LanguageSystemVerilog

Requirements5 checkpoints

Problem

Verify a bitmap compressor that turns a 32-lane active mask into zero or more maximal inclusive ranges. Check the variable-length output stream, last marker, completion, and stalls.

Example input and output

Use this case to check your interpretation

Input

accepted mask=32'h0000_00E6; stall the first range response once

Output

ranges=[1,2] then [5,7]; last=0 then1; done pulses when [5,7] is accepted

Explanation

Bits 1-2 and 5-7 form two maximal low-to-high runs; backpressure cannot change the held first range.

Requirements (5)

On an accepted idle start, scan low to high and enqueue each maximal run of adjacent set bits.
Compare and pop one expected range only on range_valid and range_ready; an output with an empty queue is an immediate failure.
Mark only the final expected range as last and keep range payload stable while stalled.
For an all-zero mask, require no range transfer and exactly one done pulse.
For nonzero masks, require done on acceptance of the final marked range and flush all state on reset.