Domain Use Cases: Power Islands, Multi-Clock, VIP Timelines

Legitimate use cases

Power-managed islands

A block that powers up mid-simulation needs its own reset→configure→main cycle after power-good. The main fabric may already be in main_phase while the island is still in reset. A separate domain models this naturally.

Independent clock domains with staged bring-up

When two clock domains have unrelated reset release times and separate bring-up sequences, domains let each follow its own schedule without ad-hoc delays in run_phase.

Third-party VIP with internal phasing

Some VIP packages install their own domain. Your env must sync with the VIP domain at handshake phases or risk racing configure against VIP reset.

[PHASE][UVM] use-case fit matrix

power island late bring-up     → STRONG fit
unrelated reset release times  → STRONG fit
VIP-owned domain               → REQUIRED (sync with vendor domain)
staggered sequence start times → WEAK fit (use objections instead)
different test lengths         → WEAK fit (objections handle this)

Anti-patterns (do not use domains for these)

• Delaying one agent's stimulus start — use sequences and objections.

• Isolating passive vs active agents — use agent is_active config.

• Skipping reset for one interface — use reset_phase objections locally.

• Running two tests in one sim — use separate tests, not domains.

// WRONG: domain to delay stimulus (use objection instead)
// RIGHT: main_phase objection until local ready
task main_phase(uvm_phase phase);
  wait(local_ready);
  phase.raise_objection(this);
  run_traffic();
  phase.drop_objection(this);
endtask

Key takeaways

• Domains model independent lifecycle schedules, not simple delays.

• Power islands and VIP-owned domains are the strongest use cases.

• Objections on a single domain solve most staggered-start needs.

Common pitfalls

• Domain per agent proliferation — creates sync nightmare.

• Using domains to paper over broken reset sequencing.

Architect checklist

1. Document which subtrees own which domain.

2. List all cross-domain hardware handoffs.

3. Map each handoff to a sync barrier phase.

4. Confirm VIP domain requirements in integration guide.