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Joseph Doherty ab202a1fa1 mxaccesscli: read/write/subscribe System Platform tags via MxAccess

New tool wrapping ArchestrA.MxAccess.LMXProxyServerClass (the same COM
proxy aaObjectViewer / WindowViewer use) as a CliFx CLI for LLM-driven
debugging.

Commands:
- mxa info      — loaded MxAccess assembly identity, supported value
                   types, MxStatusCategory enum.
- mxa read      — fetch one or more tag values; subscribes briefly,
                   captures first OnDataChange per tag, tears down.
- mxa write     — write a value with optional --type coercion; advises
                   first to resolve the attribute type, then waits for
                   OnWriteComplete with a per-call timeout.
- mxa subscribe — stream OnDataChange events for --seconds; JSON Lines
                   under --llm-json for piped agent consumption.
- mxa diag      — minimal smoke test on a private STA thread; bypasses
                   the CliFx pipeline for diagnosing apartment / pump
                   issues.

Implementation notes documented in docs/api-notes.md (reverse-engineered
because AVEVA does not publish a single canonical MxAccess reference):

- Net48 / x86 / [STAThread] are non-negotiable. The CLI runs the entire
  CliFx pipeline on a dedicated STA thread.
- COM events are dispatched as Win32 messages; AutoResetEvent.WaitOne
  alone does not pump them on this configuration. MxSession.WaitForUpdate
  loops Application.DoEvents() + drain + Sleep(20ms) instead.
- Write requires the target attribute's type to be resolved first.
  WriteCommand advises and waits for the initial OnDataChange before
  calling LMXProxyServerClass.Write to avoid ArgumentException
  "Value does not fall within the expected range".
- Errors carry the full MXSTATUS_PROXY[] from MxAccess (Success,
  Category, DetectedBy, Detail) so an agent can tell exactly which
  layer rejected a request.

Verified against the live ZB galaxy with a writeable tag identified
via grdb (TestChildObject.TestInt, mx_attribute_category=10):
  read:      99 (q=192, MxCategoryOk)
  write 7:   round-tripped — read returned 7 — written back to 99
  write str: TestChildObject.TestString round-tripped a timestamp
  subscribe: captured initial value plus subsequent change from a
             separate process

The vendored ArchestrA.MxAccess.dll is gitignored — it is copied from
C:\Program Files (x86)\ArchestrA\Framework\Bin\ on any System Platform
install per the README.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-05-03 20:02:51 -04:00

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mxaccesscli

A .NET Framework 4.8 / x86 CliFx-based CLI for reading, writing, and subscribing to AVEVA System Platform tags via MxAccess (ArchestrA.MxAccess.LMXProxyServerClass). Output as scannable text or as a stable JSON envelope for LLM consumption. Built-in per-tag and per-call timeouts; structured surface of MxStatus categories on every error.

Hard constraints

MxAccess is a 32-bit COM proxy. The CLI must stay on net48 / x86 / [STAThread]. Do not retarget to .NET 10 or x64 — LMXProxyServerClass is registered for the WoW64 server only.
System Platform must be installed locally so that ArchestrA.MxAccess is registered with COM and the LMX runtime is reachable. Without it Register() fails with a COM error.
MxAccess events fire on the registering apartment. Calls must originate from an STA thread, which is why Program.Main is [STAThread]. If you call from a non-STA thread, events queue but never get pumped and your timeouts will always fire.
Reads are not synchronous in MxAccess. "Read" is implemented as a brief subscribe → wait for first OnDataChange → tear down. If a tag never delivers a DataChange (offscan, wrong reference, security denied), the read times out — that's the correct semantic, not a CLI bug.
Writes need user identity for secured attributes. Default --user-id 0 is "unauthenticated"; secured attributes will reject. Use --user-id <id> after calling AuthenticateUser() from another path (or, for a CLI smoke test, target a non-secured Writeable_USC_* attribute).

Layout

mxaccesscli/
  README.md                this file
  AGENTS.md                agent rules for working in this folder
  MxAccess.Cli.slnx
  lib/
    ArchestrA.MxAccess.dll (copied from System Platform's Framework\Bin)
  src/MxAccess.Cli/
    MxAccess.Cli.csproj
    Program.cs              [STAThread] entry point
    IsExternalInit.cs       net48 polyfill for C# 9 init accessors
    Commands/               read, write, subscribe, info
    Mx/                     MxSession, MxItem, MxUpdate, ValueCoercion
    Output/                 LLM-JSON envelope writer
  docs/
    usage.md                command surface, examples, JSON envelope contract
    api-notes.md            reverse-engineered MxAccess API reference (since AVEVA's
                            online docs are sparse): types, events, threading, status semantics

Resource index — by task

Task	Go to
Agent rules for editing this CLI	`AGENTS.md`
Run the CLI / option reference / examples	`docs/usage.md`
MxAccess API surface, threading model, MxStatus semantics	`docs/api-notes.md`
Find a writeable tag in the live galaxy (so smoke tests have a target)	`../grdb/README.md`
Read tag values via SQL retrieval (an alternative path)	`../histdb/README.md`

External documentation

AVEVA does not publish a single canonical MxAccess reference online. The closest official sources:

https://docs.aveva.com/ — search "MxAccess", "LMXProxyServer", "Object Viewer". Coverage is partial and depends on which product portal you land on.
AVEVA Knowledge Base (subscriber-only): TID-based articles on LMX registration, secured writes, and WriteSecured2.
The shipped MXAccess32.tlb type library at C:\Program Files (x86)\ArchestrA\Framework\Bin\ is the most authoritative source for method signatures. docs/api-notes.md summarizes what it exposes.

Build & run

dotnet build src/MxAccess.Cli/MxAccess.Cli.csproj -p:Platform=x86 -c Release

# Read two tags with a 3-second timeout, JSON envelope:
dotnet run --project src/MxAccess.Cli/MxAccess.Cli.csproj -- read TestMachine_001.Speed Reactor1.Level -t 3 --llm-json

# Write a value with explicit type:
dotnet run --project src/MxAccess.Cli/MxAccess.Cli.csproj -- write TestMachine_001.Setpoint 42.5 --type double

# Subscribe to a tag for 30 seconds, JSON Lines for streaming:
dotnet run --project src/MxAccess.Cli/MxAccess.Cli.csproj -- subscribe TestMachine_001.Speed -s 30 --llm-json

The built executable is bin\x86\Release\net48\mxa.exe. Drop on PATH and use mxa read ....

Maintenance

This README follows the doctrine in ../DOCS-GUIDE.md. When you add a command, an option, or a new field on the JSON envelope, update docs/usage.md in the same change. Update docs/api-notes.md only if the underlying MxAccess assembly changes (different System Platform version, etc.). The root ../CLAUDE.md carries one row pointing at this README — it should not need to change unless the tool's task surface changes.

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