rtl-block-contract-test-policy

Block-Parallel Contract Test Policy

Contract Test Directory Structure

Each block maintains its contract tests under:

sim/{block}/contract/
    {block}_if_contract_tb.sv    # Interface compliance tests
    {block}_timing_check.sv      # Timing assertion checks
    {block}_stub.sv              # Mock for counterpart blocks

Three Contract Test File Types

1. Interface Compliance Test ({block}_if_contract_tb.sv)

Verifies that the block's ports conform to the frozen interface definitions:

• Port names match rtl/intf/*_if.sv signal names
• Port widths match rtl/pkg/codec_if_pkg.sv type definitions
• Valid/ready handshake protocol compliance (no valid drop, data stability)
• Multi-beat transfer length matches interface specification
• All required interface signals are connected (no dangling ports)

2. Timing Assertion Check ({block}_timing_check.sv)

Verifies timing contracts embedded in interface files:

• Handshake latency within specified bounds
• Throughput meets minimum rate (pixels/cycle or coefficients/cycle)
• Backpressure duration does not exceed maximum specified in timing contract
• Pipeline depth matches declared value
• Clock domain crossings use proper synchronization (where applicable)

3. Counterpart Stub ({block}_stub.sv)

Provides a mock implementation of the block for use by other blocks' tests:

• Implements all output interfaces with configurable response patterns
• Accepts all input interfaces and logs received data
• Supports programmable backpressure injection (for stress testing)
• Minimal logic — behavioral model only, NOT synthesizable
• Auto-generated from interface definitions where possible

Merge-Time Verification Procedure

Execution Order

When merging a block into the integrated trunk, execute tests in this order:

1. Target block contract test: Run the merging block's own contract tests

   sim/{block}/contract/{block}_if_contract_tb.sv    → PASS required
   sim/{block}/contract/{block}_timing_check.sv      → PASS required
   

2. Cross-block integration test: Run integration tests with already-merged upstream blocks

   sim/integration/{upstream}_{block}_integration_tb.sv  → PASS required
   

   Uses real upstream block (already merged) + stubs for not-yet-merged downstream blocks.

Upstream-First Merge Sequence

Blocks merge in dependency order — upstream blocks first:

1. entropy   (no upstream dependency — merges first)
2. tq        (depends on: entropy)
3. me        (depends on: dpb for references, but dpb merges later — use dpb_stub)
4. mc        (depends on: me, dpb — use dpb_stub)
5. intra     (depends on: none for merge — reconstruction is downstream)
6. filter    (depends on: reconstruction output)

Rationale: Upstream-first ensures that when a block merges, its upstream dependencies are already real (not stubs), providing higher-fidelity integration tests.

Exception: me and mc depend on dpb for reference frames, but dpb is a downstream consumer of filter. Use dpb_stub.sv for me/mc merge tests, then re-run integration tests after dpb merges.

PASS/FAIL Criteria

Per-Test Verdict

• PASS: Zero assertion failures, all protocol checks clean, timing within bounds
• FAIL: Any assertion failure, protocol violation, or timing contract breach

Retry Policy

On FAIL, the merge-time verification allows up to 3 retry attempts:

Attempt 1: Run contract tests → FAIL
  → Block worker fixes the issue, re-runs
Attempt 2: Run contract tests → FAIL
  → Block worker applies second fix, re-runs
Attempt 3: Run contract tests → FAIL
  → ESCALATE to user via coordinator

After 3 consecutive failures:

1. Coordinator marks the block as MERGE_BLOCKED
2. Coordinator sends SendMessage to leader: MERGE_BLOCKED: {block} — {failure_summary}
3. Leader escalates to user via AskUserQuestion
4. Remaining blocks continue merging independently (skip blocked block's downstream)

Cross-Block Regression

After each successful merge, re-run all previously merged blocks' contract tests to ensure the new block introduction does not break existing integrations.

Stub Generation Rules

When to Generate Stubs

• At Phase 4 start: generate stubs for ALL 6 blocks from interface definitions
• Stubs are placed in sim/{block}/contract/{block}_stub.sv
• Stubs are updated if interface definitions change (requires freeze violation approval)

Stub Content Requirements

Each stub MUST provide:

module {block}_stub (
    // All ports matching the block's interface connections
    // Directly derived from rtl/intf/*_if.sv
);

    // 1. Default output drivers (valid=0, data=0)
    // 2. Programmable response mode:
    //    - IDLE: all outputs deasserted
    //    - ECHO: reflect inputs after N-cycle delay
    //    - PATTERN: output predefined test vectors
    // 3. Backpressure injection:
    //    - ready deassertion probability (0-100%)
    //    - maximum consecutive stall cycles
    // 4. Transaction logging:
    //    - Log all input transactions to file
    //    - Configurable verbosity level

endmodule

Stub Replacement During Merge

As blocks merge in upstream-first order, stubs are progressively replaced:

Before entropy merge:  ALL blocks use stubs
After entropy merge:   entropy is real, others use stubs
After tq merge:        entropy + tq are real, others use stubs
...
After filter merge:    ALL blocks are real, no stubs needed

Each merge step replaces one stub with the real block in integration tests. Previously passing integration tests MUST be re-run with the real block.