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

DescriptionQ430

Q430DVASIC interview problem

Constrain a Gray-adjacent sequence

TechniquesRandomizationGray codeUnique sequence

DifficultyMedium

TopicConstraints

LanguageSystemVerilog

Requirements3 checkpoints

Problem

Randomize 16 unique 4-bit values starting at zero so each adjacent pair differs in exactly one bit.

Example input and output

Use this case to check your interpretation

Input

randomize 16 unique 4-bit values with values[0]=4'b0000

Output

One valid result: [0000,0001,0011,0010,0110,0111,0101,0100,1100,1101,1111,1110,1010,1011,1001,1000]

Explanation

This complete Gray path visits every 4-bit value once and each constrained adjacent pair has Hamming distance one; the last-to-first transition is not constrained.

Requirements (3)

Fix the first value at 4'b0000.
Require a Hamming distance of one between neighbors.
Use every 4-bit value at most once.