Interface config_db: Path-Safe Virtual Interface Handoff

Core Contract

Keep this startup boundary deterministic, observable, and fail-fast.

Treat startup as reusable infrastructure: ownership, ordering, and liveness checks must be explicit.

[UVM][ENV] vif publication contract

set in top:
  type + key + path

get in agent/env:
  same type + key + reachable scope

contract mismatch => null handle

[UVM][ENV] boundary model

boundary A: ownership and lifecycle
boundary B: publication and path scope
boundary C: first-activity liveness proof

fix the first broken boundary first

• Document ownership and ordering assumptions in code, not only slides.

• Make startup diagnostics actionable and low-noise.

• Prefer deterministic startup defaults over convenience shortcuts.

Reference Implementation

initial begin
  uvm_config_db#(virtual axi_if)::set(null, "uvm_test_top.env.axi_agt*", "vif", axi_if0);
  uvm_config_db#(virtual apb_if)::set(null, "uvm_test_top.env.apb_agt*", "vif", apb_if0);
  run_test();
end

class axi_agent extends uvm_agent;
  `uvm_component_utils(axi_agent)
  virtual axi_if vif;

  function void build_phase(uvm_phase phase);
    super.build_phase(phase);
    if (!uvm_config_db#(virtual axi_if)::get(this, "", "vif", vif))
      `uvm_fatal("NOVIF", $sformatf("missing vif at %s", get_full_name()));
  endfunction
endclass

[ENV] implementation audit

- critical startup assumptions validated?
- missing-state paths fail immediately?
- diagnostics include component path and context?
- minimal smoke seed can exercise this boundary?

[UVM][ENV] startup observability

track timestamps/counters for:
  reset release
  first sequence launch
  first monitor publish
  first checker compare

these markers reduce triage latency dramatically

• Keep startup code simple enough to audit in code review.

• Use fatal failures for non-recoverable startup contract violations.

• Expose startup metrics in report_phase for CI artifacts.

Debug Workflow

Triage order

1. Reproduce with one seed and startup tracing enabled.

2. Verify startup boundary counters and first-activity markers.

3. Classify failure by boundary before deep waveform analysis.

4. Fix root boundary and rerun identical seed to confirm.

simv +UVM_TESTNAME=smoke_test        +UVM_VERBOSITY=UVM_LOW        +UVM_CONFIG_DB_TRACE        +UVM_OBJECTION_TRACE

[UVM][ENV] quick diagnosis

fails before build:
  run_test/factory/config publish issue

build passes, no traffic:
  reset/sequence launch gating issue

monitor active, checker idle:
  connect/subscriber pipeline issue

Key takeaways

• Type, key, and path must match exactly between set and get.

• Failing fast on missing vifs saves hours of downstream debug.

• Scoped paths are safer than broad wildcards for large envs.

• A deterministic startup workflow improves regression trust and team velocity.

Common pitfalls

• Ignoring get() return values and debugging null later.

• Over-broad wildcard paths leaking wrong interfaces.

• Renaming hierarchy without updating set scopes.

• Skipping startup smoke and finding setup regressions only in long runs.

Applied Patterns

Use this reusable grid before landing startup-related changes.

[UVM][ENV] startup pattern grid

contract:
  ownership + ordering + liveness documented

implementation:
  fail-fast checks and deterministic defaults

observability:
  milestone counters and concise logs

verification:
  smoke seed + boundary-first triage + closure checklist

function void startup_health_report();
  `uvm_info("STARTUP_SUMMARY",
    $sformatf("rst=%0t seq=%0t mon=%0t cmp=%0t",
      first_reset_release_time,
      first_sequence_start_time,
      first_monitor_publish_time,
      first_scoreboard_compare_time),
    UVM_LOW)
endfunction

• Treat startup updates as infrastructure API changes.

• Keep code and checklist language aligned.

• Require stable startup summaries in regression logs.