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docs(ab): hw4 evidence fix round 1 - bit-write gap provenance, README/CLI/fixture docs, libplctag-deletion gap

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Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe
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Joseph Doherty
2026-10-09 04:12:53 -04:00
parent 14ec145487
commit 9e894decb0
7 changed files with 37 additions and 31 deletions
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docs/drivers/AbLegacy-Test-Fixture.md
+6 -8
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@@ -11,8 +11,8 @@ for N-file (Int16), F-file (Float32), and L-file (Int32) reads across all
three families when `AB_LEGACY_CIP_PATH=1,0` (the default). The earlier
`BadCommunicationError` was traced to `ab_server` requiring a non-empty CIP
routing path before forwarding to the PCCC dispatcher — the `/1,0` workaround
resolves it (see `Docker/README.md §Known limitations`). Residual gap: bit-file
writes (`B3:0/5`) still surface `0x803D0000` against `ab_server`. Unit tests
resolves it (see `Docker/README.md §Known limitations`). The old bit-file write
gap (`B3:0/5` giving `0x803D0000`) no longer reproduces (2026-10-09, `AbLegacyBitWriteTests`). Unit tests
via `FakeAbLegacyTag` carry full contract coverage for all paths.
## What the fixture is
@@ -105,12 +105,10 @@ cover the common ones but uncommon ones (`R` counters, `S` status files,
## Follow-up candidates
1. **Close residual ab_server bit-file write gap** — N (Int16), F (Float32),
and L (Int32) files round-trip cleanly across SLC500 / MicroLogix / PLC-5
modes with the `/1,0` cip-path workaround in place. Remaining gap: bit-file
writes (`B3:0/5`) surface `0x803D0000` against `ab_server --plc=SLC500`.
Contributing a patch to `libplctag/libplctag` to close this would remove
the last Docker-vs-hardware divergence for bit writes.
1. **(Closed, 2026-10-09) ab_server bit-file write gap** — N, F and L files
round-trip with the `/1,0` workaround, and `B3:0/5` bit writes now pass on
SLC500/MicroLogix (both transports; `AbLegacyBitWriteTests`). The May 2026
`0x803D0000` does not reproduce; its cause is undetermined.
2. **Rockwell RSEmulate 500 golden-box tier** — Rockwell's real emulator
for SLC/MicroLogix/PLC-5. Would close UDT-equivalent (integer-file
indirection), timer/counter decomposition, and real ladder execution