Understanding conformance

Introduced in: rtd-acquire 0.1.0a1

rtd-acquire is intended to have independent Python and portable C implementations of shared behavior. Conformance data provides a language-neutral contract between them.

The important idea is that conformance describes observable behavior, not one language's internal code structure.

For the current MAX31865 work, vectors can describe operations such as:

• native measurement/register decoding; and
• resistance-threshold encoding.

Python and C now consume both current MAX31865 vector families and are compared against the same expected observable results.

Portable C threshold conformance

Introduced in: rtd-acquire 0.2.0

The threshold vector family is the first active cross-language conformance gate. It covers directional rounding, zero-ohm low thresholds, the highest representable high threshold, and rejection of the unrepresentable top band. Because the observable outputs are exact 16-bit register values, this family remains exact and does not use the floating-point resistance tolerance.

Portable C measurement-decode conformance

Introduced in: rtd-acquire 0.2.0

The MAX31865 measurement-decode vectors also execute against the independent C decoder. They compare derived status, resistance presence/value, normalized diagnostic code and severity, and preserved native evidence.

Binary64/binary32 numeric profile

Introduced in: rtd-acquire 0.2.0

The frozen python-binary64-c-binary32 profile applies a relative tolerance of 2^-22 (2.384185791015625e-7) to nonzero resistance values and requires expected zero to remain exactly zero. Status, resistance presence/absence, diagnostics, native evidence, integer fields, and threshold-register outputs remain exact.

The tolerance is deliberately computational rather than metrological: it accounts for binary32 representation/arithmetic differences and does not add sensor accuracy, reference-resistor tolerance, or measurement uncertainty. The vector set includes a non-binary32-exact reference resistance so this path is actually exercised.

Cross-language vector configurations must also remain valid or invalid after conversion to binary32. The profile does not make configuration comparisons fuzzy merely to preserve distinctions that a binary32 C target cannot represent.

High-scale MAX31865 coverage

Introduced in: rtd-acquire 0.3.0

The shared MAX31865 vectors also exercise a 4.3 kΩ reference network. One measurement-decode case sits at the nearest representable resistance below the Pt1000 full-characteristic upper envelope, while one threshold case encodes the Pt1000 low/high envelope endpoints using the existing directional-rounding contract. Both cases execute against Python and portable C.

This is software conformance evidence for the high-scale configuration. It does not by itself establish electrical compatibility or physical validation; those claims are tracked separately.

What conformance does not prove

Passing deterministic vectors does not by itself prove that physical hardware has been wired correctly, that a host transport works on real hardware, or that the analog acquisition circuit meets an accuracy claim. Those require separate hardware validation.