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

DescriptionQ774

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Q774DVASIC interview problem

Capture per-iteration values in fork...join_none

TechniquesDVSystemVerilogfork joinAutomatic lifetimeConcurrency

DifficultyMedium

TopicTestbench Concurrency

LanguageSystemVerilog

Requirements4 checkpoints

Problem

A loop spawns three join_none children. Correct the code so each child prints its own iteration value, then state what output ordering is and is not guaranteed.

Starting declarationSystemVerilog

for (int i = 0; i < 3; i++) fork
  // child print
join_none
wait fork;

Example input and output

Use this case to check your interpretation

Input

three iterations spawn three join_none children

Output

one legal print order is 0, 2, 1

Explanation

The captured multiset is deterministic, but sibling scheduling is not, so any permutation of 0, 1, and 2 is legal.

Requirements (4)

Print exactly one occurrence of each value 0, 1, and 2.
Capture i in an automatic variable declared in the fork scope for that iteration.
Wait for every spawned child before the parent finishes.
Do not assert any particular ordering among sibling processes.