Connect-Phase Wiring: Legal Graphs and Fan-Out Hygiene

Wiring discipline

All structural connectivity should be visible in connect_phase. Avoid delayed or conditional runtime wiring that creates hidden modes.

[ENV][UVM][CHECK] connect graph

ctrl_agt.mon.ap ----                     +--> sb.exp_ctrl
data_agt[0].mon.ap --+--> sb.exp_data
data_agt[1].mon.ap --+--> cov.sub_data

v_sqr.ctrl_sqr_h = ctrl_agt.sqr
v_sqr.data_sqr_h = data_agt[0].sqr

all links established in connect_phase

function void connect_phase(uvm_phase phase);
  super.connect_phase(phase);
  ctrl_agt.mon.ap.connect(sb.ctrl_exp);
  foreach (data_agts[i]) begin
    data_agts[i].mon.ap.connect(sb.data_exp[i]);
    data_agts[i].mon.ap.connect(cov.data_imp[i]);
  end
  v_sqr.ctrl_sqr_h = ctrl_agt.sqr;
  v_sqr.data_sqr_h = data_agts[0].sqr;
endfunction

• Connect graph should be searchable and centralized.

• Fan-out is acceptable when ownership and ordering are explicit.

• Avoid runtime reconnect behavior unless protocol mandates it.

Key takeaways

• Deterministic connect_phase logic is the backbone of stable checker pipelines.

• A readable graph cuts integration debug time dramatically.

Common pitfalls

• Conditional connect logic tied to random scenario knobs.

• Invisible reconnects in run_phase that bypass review.

Applied Patterns

Use a graph inventory helper to verify all expected links are present before stimulus starts.

[ENV] graph inventory

required links:
  ctrl monitor -> sb
  each data monitor -> sb
  each data monitor -> cov
  v_sqr handles -> active sequencers

audit:
  count expected links
  count actual links
  print missing endpoints

function void assert_connectivity();
  if (ap_link_count != expected_ap_links)
    `uvm_fatal("WIRING",
      $sformatf("ap links mismatch exp=%0d got=%0d",
        expected_ap_links, ap_link_count))
endfunction

• Connectivity assertions catch silent no-check regressions.

• Graph inventory belongs in env utilities, not tests.

• Treat link count deltas as first-class review items.

Integration Drilldown

Probe each analysis endpoint with a known transaction and confirm all subscribers increment counters.

[CHECK] endpoint probe recipe

inject txn tag=CONNECT_SMOKE
expect:
  sb.ctrl_hits/data_hits updated
  cov bins sampled
  no duplicate counts beyond expected fanout

Key takeaways

• Endpoint probes prove fan-out correctness without full regressions.

Common pitfalls

• Assuming checker paths are live because monitor logs appear.