Joseph Doherty cde018aec1 Phase 3 PR 52 -- Modbus exception-code -> OPC UA StatusCode translation. Before this PR every server-side Modbus exception AND every transport-layer failure collapsed to BadInternalError (0x80020000) in the driver's Read/Write results, making field diagnosis 'is this a tag misconfig or a driver bug?' impossible from the OPC UA client side. PR 52 adds a MapModbusExceptionToStatus helper that translates per spec: 01 Illegal Function -> BadNotSupported (0x803D0000); 02 Illegal Data Address -> BadOutOfRange (0x803C0000); 03 Illegal Data Value -> BadOutOfRange; 04 Server Failure -> BadDeviceFailure (0x80550000); 05/06 Acknowledge/Busy -> BadDeviceFailure; 0A/0B Gateway -> BadCommunicationError (0x80050000); unknown -> BadInternalError fallback. Non-Modbus failures (socket drop, timeout, malformed frame) in ReadAsync are now distinguished from tag-level faults: they map to BadCommunicationError so operators check network/PLC reachability rather than tag definitions. Why per-DL205: docs/v2/dl205.md documents DL205/DL260 returning only codes 01-04 with specific triggers -- exception 04 specifically means 'CPU in PROGRAM mode during a protected write', which is operator-recoverable by switching the CPU to RUN; surfacing it as BadDeviceFailure (not BadInternalError) makes the fix obvious. Changes in ModbusDriver: Read catch-chain now ModbusException first (-> mapper), generic Exception second (-> BadCommunicationError); Write catch-chain same pattern but generic Exception stays BadInternalError because write failures can legitimately come from EncodeRegister (out-of-range value) which is a driver-layer fault. Unit tests: MapModbusExceptionToStatus theory exercising every code in the table including the 0xFF fallback; Read_surface_exception_02_as_BadOutOfRange with an ExceptionRaisingTransport that forces code 02; Write_surface_exception_04_as_BadDeviceFailure for CPU-mode faults; Read_non_modbus_failure_maps_to_BadCommunicationError with a NonModbusFailureTransport that raises EndOfStreamException. 115/115 Modbus.Tests pass. Integration test: DL205ExceptionCodeTests.DL205_FC03_at_unmapped_register_returns_BadOutOfRange reads HR[16383] which is beyond the seeded uint16 cells on the dl205.json profile; pymodbus returns exception 02 and the driver surfaces BadOutOfRange. 11/11 DL205 integration tests pass with MODBUS_SIM_PROFILE=dl205.

2026-04-18 22:28:37 -04:00

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