Part 2 · Phases & Lifecycle · Intermediate

Phase Trace Tools: PHASE_TRACE, Topology, Objection Dump

Command-line and in-code debug tools for observing phase traversal, component topology, and live objection state.

Command-line traces

UVM provides built-in command-line switches that log phase and objection activity without modifying testbench code. Use them on every hang investigation.

bash

# Standard debug invocation
simv +UVM_TESTNAME=my_test \
     +UVM_PHASE_TRACE \
     +UVM_OBJECTION_TRACE \
     +UVM_VERBOSITY=UVM_MEDIUM \
     -l sim.log

+UVM_PHASE_TRACE — logs START/END for every phase on every component.
+UVM_OBJECTION_TRACE — logs raise/drop with reason string and running count.
+UVM_VERBOSITY — increase to UVM_HIGH for surrounding context.

In-code inspection

systemverilog

function void end_of_elaboration_phase(uvm_phase phase);
  super.end_of_elaboration_phase(phase);
  `uvm_info("TOPOLOGY", "=== component tree ===", UVM_LOW)
  uvm_top.print_topology();
endfunction

systemverilog

// Dump objection state mid-phase (debug only)
task run_phase(uvm_phase phase);
  super.run_phase(phase);
  phase.raise_objection(this, "work");
  #1us;
  `uvm_info("OBJ_DBG", phase.phase_done.convert2string(), UVM_NONE)
  do_work();
  phase.drop_objection(this, "work done");
endtask

diagram

[PHASE][UVM] what to look for in PHASE_TRACE

expected:
  build (top-down) → connect (bottom-up) → ... → run_phase START

red flags:
  connect_phase before build_phase completes
  run_phase END at time 0
  same phase START twice without END (re-entry bug)

Key takeaways

Run PHASE_TRACE + OBJECTION_TRACE on every hang — non-negotiable.
print_topology in end_of_elaboration catches missing components early.
convert2string() shows who still objects at any snapshot.

Common pitfalls

Filtering sim.log verbosity so PHASE_TRACE lines are lost.
Reading trace without correlating simulation time stamps.

Log grep patterns

bash

# Find last objection raise without drop
grep OBJECTION sim.log | tail -20

# Confirm run_phase duration
grep "run_phase" sim.log | head -5
grep "run_phase" sim.log | tail -5

# Find phase ordering anomalies
grep "PHASE" sim.log | grep -E "START|END"

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