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

DescriptionQ414

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Q414DVASIC interview problem

Model a round-robin arbiter

TechniquesPythonArbitrationRound robinFairness

DifficultyMedium

TopicReference Models

LanguagePython

Requirements4 checkpoints

Problem

Implement a parameterized round-robin reference model. Given a Boolean request vector, return the next granted index and rotate priority after a grant.

Example input and output

Use this case to check your interpretation

Input

N=4, next_priority=0; request vector ports {1,3}; evaluate twice, then evaluate no requests

Output

grants=1 then 3; next_priority becomes 0; idle returns -1 and leaves priority at 0

Explanation

The circular scan resumes after each winner and an idle cycle does not rotate priority.

Requirements (4)

Search at most one complete wrap around the requester vector.
Return -1 and preserve the priority pointer when no requester is active.
After granting index i, begin the next search at i + 1 modulo N.
Validate the request-vector width.