VERDICT: FAIL

ISSUES:

1. **Unsupported quantitative claim (Sign-Off Criteria).** The document states "≥ 95% cover-point hit, ≥ 90% cross-coverage hit," "≥ 95% statement, ≥ 90% branch," and "≥ 80% of injected mutations detected" while also disclaiming these are "illustrative starting points and not validated targets." A reviewer cannot independently verify that these specific numbers are reasonable industry starting points; they are presented as if they were standard thresholds but no source is cited. Either cite the source for the industry-norm claim or remove the specific numbers entirely. The "every threshold below is restated with this caveat" claim is also factually false — the Functional Coverage, Code Coverage, and Mutation Testing bullets each restate the caveat exactly once; they are not independently verified industry defaults.

2. **Contradictory framing of the "no numeric thresholds" stance.** The Status header says "Concrete sign-off criteria, tool selection, and quantitative thresholds are deferred until the OPEN QUESTION inputs are resolved," yet the Sign-Off Criteria section then provides specific numeric thresholds (95%, 90%, 80%) and presents them as candidates. This is self-contradictory — either the thresholds are deferred (and the numbers should not appear) or they are illustrative starting points (and the Status should not claim deferral). The disclaimer repeated at each threshold does not resolve the contradiction; it merely flags it.

3. **Incorrect/unsupported RISC-V claim regarding `riscv-arch-test` vs `riscv-tests`.** The document claims "`riscv-tests` is the broader collection and `riscv-arch-test` is the architectural conformance subset" and that "the relationship is not 'legacy vs. replacement.'" This is unsupported by citation and the actual repository structure is not asserted with a specific source. The framing in the FACT block makes a load-bearing distinction (sign-off evidence vs. regression input) but provides no citation confirming the relationship. Without a specific commit/version reference, the FACT classification is inappropriate.

4. **Insufficient source specificity for `riscv-dv` license.** The document says "The license should be confirmed against the current repository state at the time of toolchain selection; this document does not assert a specific license version." This is appropriate as a caveat, but then later (in the "Open-source constrained-random generator" section and again in the Sources section) it implies the tool can be used without confirming the license. For a FACT claim that this is a viable XH-1 component, the license must be confirmed or the FACT classification removed.

5. **Unsupported claim about Verilator UVM support.** The Alternative 1 discussion states "open-source SystemVerilog simulation support (Verilator) has limited UVM-class support relative to commercial offerings." This is presented as a near-fact that drives the "open-source viability is medium" rating, but no specific source, version, or measurement is cited. Verilator's UVM support has been evolving; a claim about its current state requires a dated, version-specific citation.

6. **Unsupported / questionable claim about the replication-leverage argument.** The document repeatedly states that "an unfixed defect in the core RTL is replicated 128-fold in silicon, multiplying its downstream cost." This is true only under strict bit-identical replication with no per-core variation, no timing variation, and uniform defect distribution. The document acknowledges this (Assumption: replication homogeneity) but presents the 128× multiplier as a load-bearing argument throughout without flagging the conditions under which it breaks (process variation, voltage/frequency corners, partial-good cores, masked defects). For a 128-core design on a real die, this is an oversimplification presented as fact.

7. **Weak verification reasoning on the "Inconclusive formal ≠ proven" claim.** The document correctly flags that inconclusive formal results are not equivalent to proven properties, but the discussion of how to operationally distinguish inconclusive from a real proof (e.g., bounded vs. unbounded, depth limits, abstraction quality) is shallow. The phrase "operational requirement: every inconclusive formal result must have a documented risk-acceptance disposition" is a recommendation, not a verification argument; it does not explain how to assess whether an inconclusive result is acceptable risk.

8. **Missing alternatives / asymmetric treatment.** The Alternatives section lists 5 strategies but Alternative 5 (Hybrid) is itself the proposed direction; the comparison table then treats Hybrid as a peer of the pure strategies even though it is a composition. The table's Hybrid column is acknowledged as not an independent comparison, but the table format contradicts that acknowledgment. A 4-column comparison would be more accurate.

9. **Unsupported claim about Sail's nature.** The document states Sail is "a first-order imperative language designed for ISA specification, with a RISC-V model generated from the RISC-V ISA formal definition." The "generated from the RISC-V ISA formal definition" portion is a specific technical claim that requires citation to a specific Sail/RISC-V release and version. The current Sail RISC-V model has a specific generation history that is not characterized here.

10. **Incorrect or imprecise terminology: "co-simulation" vs "reference-model checking."** The document makes a careful distinction between the two, which is good, but then later (in the Performance Considerations) refers to "Spike co-simulation overhead per committed instruction" while the proposed direction uses reference-model checking, not strict co-simulation. The terminology slip in the performance section is inconsistent with the carefully drawn distinction in Section D.

11. **Failure to address verification of the verification environment at 128-core scale substantively.** The document acknowledges in the "Testbench verification at 128-instance scale" bullet that "the testbench's own correctness becomes a non-trivial verification problem" but defers it to the multicore layer without specifying what the core-layer testbench must do to make multicore-layer testbench verification tractable. This is a missing requirement, not a deferral.

12. **Unsupported performance claim about FPGA prototyping throughput.** The document says FPGA prototyping runs "at higher throughput than software simulation" and that emulation platforms "provide a middle ground," but explicitly disclaims any specific multiplier. Then it lists FPGA prototype throughput as a performance consideration and again disclaims. The discussion is structurally circular — it identifies throughput as a key dimension but provides no quantitative or even qualitative range, and the "INSUFFICIENT EVIDENCE" disclaimers do not substitute for a reasoned analysis of the order-of-magnitude difference (e.g., 10–100× typical, 1000× for emulation).

13. **The proposed direction's gating is underspecified.** "The specific framework within the hybrid (UVM vs. lightweight) is gated on OPEN QUESTION 3, OPEN QUESTION 4, and OPEN QUESTION 11" — but the document does not specify what the resolution criteria are. A gate that does not state what outcome it produces for each input combination is not a gate; it is a punt. The document should specify, at least in outline, "if open-source only and small team, then lightweight; if commercial EDA and large team, then UVM," etc.

14. **Inconsistency between "fact" classification and open status.** The Sources section lists "RISC-V International, *The RISC-V Instruction Set Manual, Volume I*" with "Version pin: OPEN — to be selected at toolchain selection." Listing a document in Sources when the version pin is OPEN is fine, but combined with the FACT claims that depend on a specific version (e.g., "Spike or Sail validated against the chosen RISC-V compliance tests"), the FACT classification is not supported because the version is not pinned. Several "FACT" claims in Sections I and K are conditional on a version that is OPEN.

15. **Missing discussion of bring-up sequencing for the verification program itself.** The Implementation Considerations section mentions "Block-level → core-level → multicore → system" but does not address the order in which the XH-1 verification *program* itself is built. The hybrid proposal requires significant upfront investment in formal, UVM/co-sim, FPGA prototyping, and reference-model integration; the document does not discuss a build sequence for the verification environment (e.g., bring up reference-model checking first, add formal second, add FPGA third), which is a practical methodology gap.

16. **The "Engineering cost can easily exceed the RTL design cost" claim is presented as a "consideration" without citation.** The Disadvantages section calls this "folkloric" but presents it as a planning input. Either drop it (since "folkloric" is not a basis for planning) or cite a source.

REQUIRED_FIXES:

1. Either cite specific industry sources for the 95% / 90% / 80% illustrative thresholds or remove the specific numbers and replace with "TBD by verification plan."

2. Reconcile the Status header's "thresholds deferred" claim with the Sign-Off Criteria section's provision of specific numbers. Pick one posture and apply it consistently.

3. Provide a specific dated source (commit SHA, release tag) for the `riscv-arch-test` vs `riscv-tests` relationship, or downgrade the FACT claim and remove the "not legacy vs. replacement" assertion.

4. Confirm the `riscv-dv` license at a specific version and either cite it or downgrade the FACT claim.

5. Provide a specific dated source for the Verilator UVM-support claim, including Verilator version and what specifically is limited.

6. Add explicit caveats to the 128× defect-cost argument about process variation, voltage/frequency corners, and partial-good cores; or weaken the argument's load-bearing use.

7. Strengthen the formal-verification reasoning: explain how inconclusive results are distinguished operationally (depth limits, abstraction quality, witness traces) and provide a concrete example of a risk-acceptance criterion.

8. Restructure the Alternatives comparison to either treat Hybrid as the proposed composition (not a peer) or add a separate column for "composition criteria" and explain how the columns compose.

9. Cite a specific Sail/RISC-V release and version for the "generated from the RISC-V ISA formal definition" claim.

10. Fix the terminology slip in the Performance Considerations section to consistently distinguish co-simulation (strict) from reference-model checking.

11. Specify what the core-layer testbench interface must provide to make multicore-layer testbench verification tractable (e.g., determinism contract, instance-indexed outputs, replay capability).

12. Provide a reasoned order-of-magnitude range for FPGA prototyping vs. software simulation throughput with workload-class qualifiers, or remove the "Performance Considerations" subsections that add no information beyond "we don't know."

13. Specify the gating logic for the hybrid composition: for each resolution of OPEN QUESTIONS 3, 4, 11, what is the chosen framework, with at least an outline of the decision rule.

14. Either pin the RISC-V version (and remove the OPEN) or move the version-dependent FACT claims into ASSUMPTION or PROPOSAL classifications.

15. Add a build sequence for the verification program itself (which environment component is brought up first, second, etc.) with rationale.

16. Either cite a source for the "engineering cost can exceed RTL design cost" folkloric claim or remove it.

CONFIDENCE: HIGH
