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[c-RCP-AUDIT-05] Two genuine TC18 ambiguities surfaced during citation backfill (not force-cite, need real investigation) #184

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@SoundMatt

Surfaced during Phase 2 citation backfill (issue #164, batches 2/6/11). Both are left honestly uncited in .fusa-reqs.json rather than force-cited, per the standing per-batch discipline. Filing separately so they don't get lost in PR descriptions/memory once #164 closes.

1. REQ-ACF-012RCP_ACF_MTV_UNCERTAIN

rcp_acf_gbb_is_timed() returns true only when info.mtv == RCP_ACF_MTV_VALID. There's a third enum value, RCP_ACF_MTV_UNCERTAIN, whose TC18 basis was not found during batch 2 (PR #172) review of §11.2.1 Figure 7/Table 4. Needs someone to read the full mtv-bit definition in TC18 (not just the table cited so far) and determine: is MTV_UNCERTAIN a real third wire state, or an implementation-only convenience value with no wire representation? Either answer resolves the citation; right now it's just unresolved.

Source: src/acf.c / include/rcp/acf.h, rcp_acf_gbb_is_timed().

2. RCP_EP_PWM_IN_NO_SIGNAL sentinel (REQ-PWM-047, REQ-PWM-054, and the equivalent ADC entries)

TC18 Table 27 defines PWM_IN_NO_SIGNAL as a numbered wire error code (§ error-response err field). c-RCP's PWM_IN and ADC endpoints additionally use RCP_EP_PWM_IN_NO_SIGNAL (0xFFFF) as a payload sentinel value inside an otherwise-normal Read Response. TC18 does not appear to define a payload-sentinel convention anywhere — only the Table 27 error-code path. Two ways this could resolve:

  • The sentinel is a c-RCP-only convenience (not a TC18 concept) — in which case these requirements should stay uncited permanently as an implementation detail, not a gap.
  • TC18 has a payload-sentinel convention elsewhere (e.g. in the PWM_IN or ADC chapter's worked examples) that wasn't found during batches 6/11's citation passes — in which case it's a real citation gap.

Needs a full read of §13.7.6 (PWM_IN) and §13.7.9 (ADC) prose, not just the tables already cited, to settle which case applies. Until then these stay uncited, consistent with the standing "don't force-fit" discipline (see REQ-ACF-012 precedent above, which is the same class of open question).

Related: #163 (Table 27 error-code wiring — PWM_IN_NO_SIGNAL is also one of the still-unwired codes there, so these two issues may turn out to share one investigation), #164 (citation backfill, where both were found).

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