Passive Sampling: Observe Without Side Effects

Passivity contract

Passivity means zero DUT signal driving and zero active control. The monitor only samples and emits observations.

[MON] legal actions
- sample pins
- decode protocol states
- publish analysis transactions

illegal:
- drive or force signals
- control sequencer/driver flow

function bit can_sample();
  if (!vif.rst_n) return 0;
  if ((^{vif.addr, vif.valid, vif.ready}) === 1'bx) return 0;
  return 1;
endfunction

• Gate sampling during reset and X/Z conditions.

• Track drop reasons for auditability.

• Keep passivity checkable in code review.

Applied Patterns

This appendix consolidates reusable monitor patterns for enterprise-scale UVM environments where multiple teams share protocol VIP.

Use this as a quick implementation checklist before releasing monitor updates into regression branches.

[MON][UVM][AGT] reusable pattern grid

sampling:
  accepted-handshake gating only

reconstruction:
  key-based accumulator with completion predicate

publishing:
  clone policy + counter instrumentation

debug:
  boundary-first triage with deterministic smoke

function void monitor_health_report();
  `uvm_info("MON_HEALTH",
    $sformatf("sampled=%0d published=%0d dropped=%0d pending=%0d",
      sampled_cnt, published_cnt, dropped_cnt, pending_cnt),
    UVM_LOW)
endfunction

[MON] review checklist

- passive contract verified
- reset/flush policy documented
- publish ownership policy documented
- consumer fan-out validated
- counters visible in report_phase

• Design monitor updates as API changes to downstream consumers, not local edits.

• Keep monitor diagnostics always-on and low overhead for regression reliability.

• Revalidate sample-to-publish boundary after every protocol extension.