rtl-p5s-uvm-policy

UVM Verification Policy

UVM Naming Conventions

UVM environment code MUST follow the project coding conventions (CLAUDE.md):

• DUT port connections in driver/monitor: i_ prefix for inputs, o_ prefix for outputs
• Clock: clk (single domain) or {domain}_clk (multiple domains, e.g., sys_clk) — NOT clk_i
• Reset: rst_n (single domain) or {domain}_rst_n (multiple domains, e.g., sys_rst_n) — NOT rst_ni
• DUT instance in top-level wrapper: u_dut with u_ prefix
• UVM class member handles: m_ prefix (e.g., m_agent, m_scoreboard, m_driver, m_monitor)
• Use logic in all SV declarations (NOT reg/wire)
• Interface signal names must match RTL ports exactly (e.g., i_data, o_valid)

Coverage Targets (Enforced at Regression Report)

Coverage Type	Target	Tool Flag (VCS)	Notes
Line	≥ 90%	-cm line	Every executable line exercised
Toggle	≥ 80%	-cm tgl	Signal 0→1 and 1→0 transitions
FSM	≥ 70%	-cm fsm	State and transition coverage
Branch	≥ 80%	-cm cond	if/case branch coverage
Functional	≥ 95%	UVM covergroups	Architect-defined coverpoints

Code coverage is always enabled during regression (-cm line+cond+fsm+tgl+branch for VCS, -coverage all for Xcelium, -coverage for Questa). Merged from all seeds before evaluation.

Functional coverage is collected via uvm_subscriber-based coverage collectors in the testbench. Covergroups must be mapped to requirements (REQ-U-*).

Coverage-Driven Verification (CDV) Feedback Loop

When merged coverage falls below targets after regression, run a structured 3-round loop:

Round N: coverage-analyst → CDTG feedback table (gap analysis)
         test-plan-writer  → systematic test plan (ECP/BVA for config-dependent gaps)
         testbench-dev    → directed UVM sequences per gap row + test plan
         eda-runner       → regression with new tests → re-merge coverage
Round N+1: coverage-analyst re-analyzes → new guidance for remaining gaps

1. coverage-analyst identifies uncovered bins, states, branches. Produces CDTG feedback table:

   | Gap ID | Uncovered Bin | REQ | Constraint | Sequence | Expected |
   

2. test-plan-writer applies ECP/BVA methodology for config-dependent gaps (parameter combinations)
3. testbench-dev writes directed UVM sequences per gap row using the systematic test plan
4. Re-run regression with new tests → re-merge → re-analyze
5. Maximum 3 iterations. Convergence detection: 2 consecutive rounds with < 0.5% improvement
6. On convergence: apply Coverage Exclusion Protocol per rtl-p5s-coverage-policy (classify remaining bins as STIMULUS_GAP/STRUCTURAL_DEAD/INFRA_CODE, generate exclusion artifacts)
7. If post-exclusion targets still not met after 3 rounds → escalate to user

UVM Stimulus-to-DUT Connectivity Verification

Before running regression, verify stimulus actually reaches the DUT:

1. Randomization check: All rand fields in test class must be randomized
   • Required: this.randomize() called in build_phase or run_phase
   • Anti-pattern: rand logic field declared but never randomize()-d
2. DUT connectivity check: Every test knob must have a path to DUT port
   • Required: config variable → config_db / virtual_if / backdoor → DUT signal
   • Anti-pattern: rand cfg_xxx in test class but DUT port hardcoded in TB top
3. Effectiveness gate (after first iteration): verify coverage CHANGED across seeds
   • If coverage delta < 0.1% across all seeds → stimulus is NOT reaching DUT
   • Root cause: missing randomization or disconnected config path
   • Action: HALT regression, debug stimulus connectivity before proceeding

Enforcement in Orchestrator

p5s-uvm-orchestrator checks coverage delta after first regression iteration (Step 4). If delta < 0.1% across seeds → invoke uvm-reviewer to diagnose stimulus connectivity before running additional iterations.

Regression Runner

Use skills/rtl-p5s-uvm-verify/scripts/run_regression_uvm.sh for multi-seed regression:

bash run_regression_uvm.sh --sim vcs --seeds "42 123 456 789 1337" --test base_test --module {module}

• Compiles once, runs seeds in parallel with failure halt logic
• Per-seed result JSON + merged coverage + regression report
• Coverage merge: VCS urg, Xcelium imc, Questa vcover

Escalation & Stop Conditions

• No commercial simulator found → HALT immediately, report which simulators are supported
• UVM compilation errors → report exact errors to user, do not attempt workarounds
• Scoreboard mismatch → capture waveform, invoke waveform-analyzer for root cause
• UVM env uses wrong naming convention → testbench-dev must rewrite before compilation

Final Checklist

• Commercial simulator availability verified via Bash CLI before any work
• UVM environment uses correct naming (i_/o_ prefix, sys_clk/sys_rst_n, m_ UVM member prefix, u_ RTL instance prefix)
• UVM environment compiles without errors
• All tests run to completion (no crashes)
• sim/uvm/results/run_summary.log written
• sim/uvm/coverage/uvm_coverage.xml generated
• Pass/fail reported per test

UVM Component Naming and Simulator-Specific Flags

UVM component naming conventions (aligned with project style):

• Agent member handles: m_agent, m_axi_agent, m_apb_agent (m_ prefix for UVM class members)
• Driver/monitor inside agent: m_driver, m_monitor (m_ prefix for UVM class members)
• DUT wrapper instance: u_dut (u_ prefix for RTL instances only)
• All SV code uses logic (never reg/wire)

Simulator-specific coverage flags — both compile and run must enable coverage:

# VCS — compile + run
vcs -full64 -sverilog -ntb_opts uvm-1.2 \
    -cm line+cond+fsm+tgl+branch \
    -cm_hier sim/uvm/coverage/hier.cfg \
    -timescale=1ns/1ps -f rtl/filelist_top.f \
    sim/uvm/agents/*/*.sv sim/uvm/env/*.sv sim/uvm/seq/*.sv \
    sim/uvm/tests/*.sv sim/uvm/tb/*.sv -o simv
./simv +UVM_TESTNAME={test} +ntb_random_seed={seed} \
    -cm line+cond+fsm+tgl+branch -cm_dir sim/uvm/coverage/seed_{seed}.vdb

# VCS — merge (text + XML for coverage-analyst parsing)
urg -dir sim/uvm/coverage/seed_*.vdb -report sim/uvm/coverage/merged \
    -elfile sim/uvm/coverage/exclusion.el -format both

# Questa — compile (MUST include +cover) + run
vlog -sv +cover=bcestf +incdir+sim/uvm \
    -f rtl/filelist_top.f sim/uvm/agents/*/*.sv sim/uvm/env/*.sv \
    sim/uvm/seq/*.sv sim/uvm/tests/*.sv sim/uvm/tb/*.sv
vsim -c -coverage tb_top +UVM_TESTNAME={test} -sv_seed {seed} \
    -do "coverage save -onexit sim/uvm/coverage/seed_{seed}.ucdb; run -all; quit -f"

# Questa — merge
vcover merge sim/uvm/coverage/merged.ucdb sim/uvm/coverage/seed_*.ucdb
vcover report -details sim/uvm/coverage/merged.ucdb

# Xcelium — compile + run (separate phases)
xrun -sv -uvm -compile -coverage all -timescale 1ns/1ps \
    -f rtl/filelist_top.f sim/uvm/agents/*/*.sv sim/uvm/env/*.sv \
    sim/uvm/seq/*.sv sim/uvm/tests/*.sv sim/uvm/tb/*.sv \
    -xmlibdirpath build/xcelium
xrun -R +UVM_TESTNAME={test} -seed {seed} \
    -coverage all -covworkdir sim/uvm/coverage/seed_{seed}/cov_work -covscope tb_top \
    -xmlibdirpath build/xcelium

# Xcelium — merge (via imc TCL script)
imc -exec merge_script.tcl   # merge -run seed_*/cov_work → report

Common mistakes to avoid:

• Questa: omitting +cover=bcestf at vlog compile → runtime -coverage collects nothing
• VCS: omitting -cm at runtime → compile instrumentation wasted
• Xcelium: using -R without matching -xmlibdirpath → snapshot not found
• All tools: merging before all seeds complete → partial coverage report

See references/uvm-architecture.md for complete UVM class hierarchy, phase order, and common UVM mistakes to avoid.