BFE Engineering
42fb386f60
Replace every em dash with real punctuation (rewrites, not hyphen swaps) in docs, code comments, scripts, configs, and the port records; convert en dashes, curly quotes, ellipsis glyphs, arrows, and section signs to ASCII; drop machine-writing tell phrases from living docs. ADR titles now use a colon. The M2 bring-up DTS model string carried an em dash into the patch series and its record echoes; fixed at both, and the full series re-verified to apply cleanly onto pristine 6.18.46. One comment in freshness.h deliberately names the em dash glyph the UI renders as the unknown mark; that is data, kept as prose naming it. Verified: cargo tests (sim, config-lint, rs485-bridge), shellcheck, both driver MC/DC harnesses, patches-apply.
34 lines
1.7 KiB
Markdown
34 lines
1.7 KiB
Markdown
# ADR 0002: Tiered MC/DC
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**Status:** Accepted (2026-08-25).
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## Context
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The goal "port + harden 100% of drivers to 100% MC/DC" is infeasible as literally
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stated: ~97% of driver LOC is vendor blobs (the AIC8800 wifi driver alone is 88.5K
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lines) that we cannot meaningfully unit-test to MC/DC on the host. Forcing MC/DC on
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that code would be theatre, not assurance.
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## Decision
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A **two-tier** policy, measured against the Hardware Abstraction Seam:
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- **Tier 1, our own hardware-facing code -> real 100% MC/DC.** `modbus_engine.c`,
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`relays.c`, `warden_rga.c` (wrapper), `hpmcu.rs`, `devmem.rs`, `freshness.c`, plus
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the two smallest near-mainline drivers where feasible. Enforced in CI
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(`gcc-14 -fcondition-coverage` + `gcov-14 --conditions`). Rust uses
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`cargo-llvm-cov` line/region coverage for now; true `--mcdc` needs a nightly
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toolchain (`-Z coverage-options=condition`) and is deferred on that tooling skew;
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the C drivers carry the literal MC/DC gate.
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- **Tier 2, ported/vendor drivers -> fault-injection + branch coverage + benchmarks**
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against the simulator, behind a stable seam. Explicitly NOT literal MC/DC.
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## Consequences
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- Matches the user's framing: "as many drivers as possible at 100% MC/DC; for the
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rest, a very serious testing and benchmarking system."
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- The seam is the shared object: the same thing MC/DC is measured against and the
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simulator implements; the two goals reinforce, not duplicate.
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- Every Tier-1 file gets a `drivers/<name>/test/` host harness (a `Makefile` +
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`test_<name>.c`) that calls the one shared `drivers/enforce-mcdc.sh`, which derives
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the driver name from the `.gcov` file, so there is a single gate to maintain, not a
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per-driver copy. The CI `mcdc` job auto-discovers any `drivers/*/test/Makefile` and
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fails below 100%.
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