UVM Coding Practice · Senior

Objection Count & Drain Time

raise/drop pairing and pipeline drain.

Interview prompt

Test hangs at end — walk through objection debug.

diagram

WHITEBOARD CHAIN

1. DECLARE    interfaces / types / ports you need
2. SKELETON   class extends + utils macro + key methods
3. MECHANISM  fill one critical method while narrating
4. PITFALL    name one bug juniors make on this pattern
5. TEST       how you would smoke-test the component

Reference sketch (≤40 lines)

systemverilog

task run_phase(uvm_phase phase);
  phase.raise_objection(this);
  seq.start(env.sqr);
  phase.phase_done.set_drain_time(this, 100);
  phase.drop_objection(this);
endtask

Mechanism to narrate

Draw timeline: raise → stimulus → drain → drop
If hang: print who still has objection (UVM objection trace)
Pipelined DUT needs drain_time before drop

Smoke test (5 minutes)

Normal test ends within timeout.
Remove drop_objection — sim hangs (repro leak).
Zero drain on pipelined DUT — compare with 100ns drain.

Common pitfalls

Missing drop_objection.
No drain on pipelined DUT.
Seq and test both raise without policy.

Practice this lesson