From Spec to Shipping is a 14-part series on how a protocol decoder actually gets written — the method GopherTrunk follows to go from an ETSI or TIA PDF to code that decodes real signals on air. From the Issue Tracker taught these lessons as postmortems: the round-trip test that validates its own bug, the placeholder constant that became a fabricated protocol, the RPC opcode nothing ever checked. This series teaches the same discipline forward — reading standards, choosing reference implementations you can trust, pinning parsers with literal byte vectors, building bit-identical conformance harnesses, staying clean-room, letting operator captures referee when references disagree, and gating every claim behind on-air verification.

The recurring villain is the test that passes because both sides share the same assumption; the recurring hero is the independent reference — another implementation, a reference codec, a reporter’s capture. Every part closes with rules that transfer to any wire format, not just radio.

Every post reads three ways: a TL;DR + cheat-sheet for skimmers, bold headers, tables, and diagrams for the medium read, and full prose with real code for the deep read.

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The Testing module covers the fundamentals this series builds on.<ol class="post-list series-list"><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 1: How to Read a Radio Standard</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">How ETSI EN and TIA-102 standards families are organized, the order a decoder author should read them — physical layer up to PDU layouts — and the constants to extract on day one: sync words, CRC definitions, and the exact bit offsets everything else leans on.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 2: Choosing Reference Implementations You Can Trust</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">The reference stable a protocol decoder is built against — OP25, trunk-recorder, SDRTrunk, osmo-tetra, the ETSI reference codec, mbelib — what each is authoritative for, why proven-on-air beats popular, and how to know what a reference does not decide.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 3: Literal Vectors, Not Round-Trips</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">Why round-trip tests let parser bugs live — the P25 SCCB opcode that read channel B one byte early while its test stayed green — and the fix as method: pin every parser with literal byte vectors cross-checked against an independent decoder, kept as bytes in the test, never generated.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 4: The Conformance Harness — Bit-Identical or Bust</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">Building a conformance harness against the ETSI EN 300 395-2 reference codec: one 137-bit bitstream into both decoders, zero PCM mismatches allowed, the LP64 Word32 gotcha that makes the reference itself lie, and why conformance at two layers brackets everything in between.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 5: Clean-Room Rules — Reading Without Copying</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">How a pure-Go, Apache-2.0 decoder uses GPL decoders as validation oracles without copying them: where the line sits between wire-format facts and copyrightable expression, the vocoder patent aisle, and the licensing hygiene that CI enforces on every build.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 6: When References Disagree, the Capture Referees</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">Two trusted decoders gave two different DMO burst geometries, and a single capture could not pin the colour-code bit offset at all. How GopherTrunk designs referee measurements where the right answer wins by a wide margin — and refuses to answer when it doesn’t.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 7: Tests That Can Disagree With You</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">Four ways GopherTrunk engineers the self-consistent trap out of its test suites: fixture transmitters that behave like real radios, independent-path controls, fake servers that enforce the real protocol’s strictness, and synthetic streams laid out on the real slot grid.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 8: Case Study — Rebuilding SmartNet From Proven Decoders</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">The full #1143 arc as a method case study: a Motorola SmartNet decoder green on every synthetic test yet unable to lock any real system, diagnosed as fabricated framing and rebuilt from OP25 and trunk-recorder — 8-bit sync 0xAC, stride-19 deinterleave, inverted data, CRC-10.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 9: Wire Protocols Without Schemas</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">How GopherTrunk shipped a SoapyRemote client that asked for HAS_DC_OFFSET_MODE when it meant SET_ANTENNA — opcode 600 instead of 501 — and the rules that catch schemaless wire drift: pin constants against upstream literals, validate through introspection, read back what you set.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 10: The On-Air Gate — Green Synthetics Prove Nothing</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">Why every decoder claim in GopherTrunk carries a verification status — synthetic-green, capture-verified, or on-air-verified — and how the TETRA DMO “encrypted” misdiagnosis was overturned three times by three successive operator captures before the real causes surfaced.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 11: Capture-Driven Development</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">How GopherTrunk turns operator IQ recordings into first-class test fixtures — the samples/ conventions, .metadata.json sidecars whose bounds turn log lines into pass/fail gates, env-gated replay harnesses that skip in CI and become field instruments, and the discipline of baselining before fixing.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 12: Failing First — The Regression Rule</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">Why every GopherTrunk bug fix is one narrow commit plus a regression test that fails without the fix — with three worked examples where writing the failing test was the diagnosis, from the DMO colour-0 descramble to the SmartNet rebuild to the noise-grant trio.</p></li><li class="post-card"> <h2 class="post-card__title">From Spec to Shipping, Part 13: Instruments, Not Logs</h2> <p class="post-card__meta"> Deep dives </p><p class="post-card__desc">How GopherTrunk designs decoder diagnostics as instruments — counters on every branch including the failing ones, verdict lines written for operators, WARNs gated on persistence instead of one sampled blip, and health checks that never judge a channel by absolute dBFS.</p></li></ol><p class="blog-feed-link"> See all deep dives or subscribe via RSS. </p>