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

DescriptionQ296

Q296DesignDVASIC interview problem

Build a reloadable countdown timer

TechniquesCounterPulsePriorityBFM

DifficultyEasy

TopicRTL Design

LanguageSystemVerilog

Requirements4 checkpoints

Problem

Design a parameterized countdown timer with load, load_value, busy, and a one-cycle expired pulse. Add a BFM task that starts a nonzero delay and waits for expiry.

Example input and output

Use this case to check your interpretation

Input

load value 3, observe three countdown edges; later load value 0

Output

busy during the first two countdown edges and expired pulses on the third; zero load pulses expired immediately and remains idle

Explanation

A nonzero N expires after exactly N active edges, while load priority and the zero special case each produce one-cycle pulses.

Requirements (4)

Loading has priority over counting.
A value N expires after N active countdown edges.
expired is a pulse, not a permanent idle indicator.
A zero load expires immediately and leaves the timer idle.