Part 7 · Environment & Tests · Intermediate

Virtual Sequence Start Patterns: Objection and Profile Discipline

Start virtual sequences with stable objection handling, profile-driven knobs, and explicit startup diagnostics.

Canonical Start Template

Keep test run_phase concise: raise objection, build/configure vseq, validate requirements, start on env.v_sqr, drop objection after closure.

systemverilog

task run_phase(uvm_phase phase);
  stream_profile_vseq vseq;
  phase.raise_objection(this, "stream_profile");

  vseq = stream_profile_vseq::type_id::create("vseq");
  vseq.need_apb = 1;
  vseq.need_axi = 1;
  vseq.need_irq = 0;
  vseq.profile_name = cfg.profile_name;
  vseq.max_packets = cfg.max_packets;

  if (env.v_sqr == null)
    `uvm_fatal("NO_VSQR", "env.v_sqr null before vseq.start")

  vseq.start(env.v_sqr);
  phase.drop_objection(this, "stream_profile_done");
endtask

diagram

[TEST][UVM] objection ownership

raise:
  immediately before vseq lifecycle

drop:
  after vseq completes and closure checks pass

avoid:
  hidden objection ownership inside random helper components

Key takeaways

A short canonical template prevents objection and startup regressions.
Profile knobs should be visible before start() call.
Fast fatal checks for env.v_sqr existence reduce opaque hangs.

Common pitfalls

Starting virtual sequences without explicit objection envelope.
Passing raw plusargs everywhere instead of typed config values.
Hiding profile choice in deep helper code paths.

Profile-Driven Launch

diagram

[TEST][UVM][VSEQ] profile map

profile      need_apb  need_axi  need_irq  max_packets
-------------------------------------------------------
smoke         1         1         0         32
nightly       1         1         1         512
stress        1         1         1         4000
irq_focus     1         0         1         64

systemverilog

function void apply_profile(string profile);
  if (profile == "smoke") begin
    need_apb = 1; need_axi = 1; need_irq = 0; max_packets = 32;
  end
  else if (profile == "nightly") begin
    need_apb = 1; need_axi = 1; need_irq = 1; max_packets = 512;
  end
  else if (profile == "stress") begin
    need_apb = 1; need_axi = 1; need_irq = 1; max_packets = 4000;
  end
  else if (profile == "irq_focus") begin
    need_apb = 1; need_axi = 0; need_irq = 1; max_packets = 64;
  end
  else begin
    `uvm_fatal("BAD_PROFILE", $sformatf("unknown profile=%s", profile))
  end
endfunction

diagram

[TEST][UVM] profile logging contract

startup log must include:
  profile name
  required handles
  key numeric knobs
  seed
  selected test

this turns launcher issues into immediate visibility

Treat profile names as API and keep them versioned/documented.
Unknown profile should fail loudly, never silently fallback.
Log profile resolution before any traffic starts.

Applied Patterns

diagram

[TEST][UVM][VSEQ] launch checklist

before start():
  verify env.v_sqr exists
  apply profile -> typed config
  validate required handles
  emit startup summary

during start():
  use barrier-based sequencing
  timeout every wait

after completion:
  verify quiet window
  drop objection
  report key counters

systemverilog

function void print_launch_banner(string profile);
  `uvm_info("VSEQ_LAUNCH",
    $sformatf("profile=%s need_apb=%0d need_axi=%0d need_irq=%0d max_packets=%0d",
      profile, need_apb, need_axi, need_irq, max_packets),
    UVM_LOW)
endfunction

Launch discipline dramatically reduces startup-flake noise.
Consistent banners simplify CI triage for failed seeds.
Profiles make scenario intent inspectable and reproducible.

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