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fix(driver-modbus-addressing): resolve High code-review finding (Driver.Modbus.Addressing-001)

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The DL205 family-native branch routed every V-prefixed address through
DirectLogicAddress.UserVMemoryToPdu, a plain octal-to-decimal decode.
DL205/DL260 system V-memory (V40400 and up) is not a simple octal decode:
the CPU relocates the system bank to Modbus PDU 0x2100. Octal-decoding
V40400 produced 16640 (0x4100), the wrong register, so any tag addressing
a system register through the grammar string silently read/wrote the
wrong PLC memory.

- Add DirectLogicAddress.VMemoryToPdu, which decodes the octal V-address,
  detects the system bank (octal >= V40400 == SystemVMemoryOctalBase) and
  relocates it through SystemVMemoryToPdu to PDU 0x2100; user-bank
  addresses keep the plain octal decode.
- ModbusAddressParser's DL205 V branch now calls VMemoryToPdu instead of
  UserVMemoryToPdu. UserVMemoryToPdu is retained for user-bank-only callers.
- Correct the ModbusFamilyParserTests V40400 assertion (16640 -> 0x2100)
  and add system-bank regression cases plus direct helper coverage.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Joseph Doherty
2026-05-22 06:53:59 -04:00
parent 532b961cf2
commit 1837b5a828
4 changed files with 88 additions and 7 deletions
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9
code-reviews/Driver.Modbus.Addressing/findings.md
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@@ -7,7 +7,7 @@
| Review date | 2026-05-22 |
| Commit reviewed | `76d35d1` |
| Status | Reviewed |
| Open findings | 9 |
| Open findings | 8 |
## Checklist coverage
@@ -36,7 +36,7 @@ a category produced nothing rather than leaving it blank.
| Severity | High |
| Category | Correctness & logic bugs |
| Location | `ModbusAddressParser.cs:230-235`, `DirectLogicAddress.cs:66-73` |
| Status | Open |
| Status | Resolved |
**Description:** The DL205 family-native branch routes every V-prefixed address through
`DirectLogicAddress.UserVMemoryToPdu`, which is a plain octal-to-decimal conversion. DL205/DL260
@@ -54,7 +54,10 @@ route it through `SystemVMemoryToPdu`, or explicitly reject system V-memory in t
with a diagnostic pointing at the structured tag form. Either way, fix the V40400 test to assert
the corrected mapping.
**Resolution:** _(open)_
**Resolution:** Resolved 2026-05-22 — added `DirectLogicAddress.VMemoryToPdu`, which detects the
system bank (octal >= V40400) and relocates it through `SystemVMemoryToPdu` to PDU 0x2100; the
DL205 V branch in `ModbusAddressParser` now calls it, and the `ModbusFamilyParserTests` V40400
assertion was corrected from 16640 to 0x2100 with system-bank regression cases added.
### Driver.Modbus.Addressing-002