# `otopcua-twincat-cli` — Beckhoff TwinCAT test client

Ad-hoc probe / read / write / subscribe tool for Beckhoff TwinCAT 2 / TwinCAT 3
runtimes via ADS. Uses the **same** `TwinCATDriver` the OtOpcUa server does
(`Beckhoff.TwinCAT.Ads` package). Native ADS notifications by default;
`--poll-only` falls back to the shared `PollGroupEngine`.

Fifth (final) of the driver test-client CLIs.

## Build + run

```powershell
dotnet run --project src/ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.Cli -- --help
```

## Prerequisite: AMS router

The `Beckhoff.TwinCAT.Ads` library needs a reachable AMS router to open ADS
sessions. Pick one:

1. **Local TwinCAT XAR** — install the free TwinCAT 3 XAR Engineering install
   on the machine running the CLI; it ships the router.
2. **Beckhoff.TwinCAT.Ads.TcpRouter** — standalone NuGet router. Run in a
   sidecar process when no XAR is installed.
3. **Remote AMS route** — any Windows box with TwinCAT installed, with an AMS
   route authorised to the CLI host.

The CLI compiles + runs without a router, but every wire call fails with a
transport error until one is reachable.

## Common flags

| Flag | Default | Purpose |
|---|---|---|
| `-n` / `--ams-net-id` | **required** | AMS Net ID (e.g. `192.168.1.40.1.1`) |
| `-p` / `--ams-port` | `851` | AMS port (TwinCAT 3 PLC = 851, TwinCAT 2 = 801) |
| `--timeout-ms` | `5000` | Per-operation timeout |
| `--poll-only` | off | Disable native ADS notifications, use `PollGroupEngine` instead |
| `--verbose` | off | Serilog debug output |

## Data types

TwinCAT exposes the IEC 61131-3 atomic set: `Bool`, `SInt`, `USInt`, `Int`,
`UInt`, `DInt`, `UDInt`, `LInt`, `ULInt`, `Real`, `LReal`, `String`, `WString`,
`Time`, `Date`, `DateTime`, `TimeOfDay`. The four IEC time/date variants
marshal as `UDINT` on the wire — CLI takes a numeric raw value and lets the
caller interpret semantics.

## Commands

### `probe`

```powershell
# Local TwinCAT 3, probe a canonical global
otopcua-twincat-cli probe -n 127.0.0.1.1.1 -s "TwinCAT_SystemInfoVarList._AppInfo.OnlineChangeCnt"

# Remote, probe a project variable
otopcua-twincat-cli probe -n 192.168.1.40.1.1 -s MAIN.bRunning --type Bool
```

#### Health probe

The OtOpcUa server's TwinCAT driver runs an internal probe loop (PR 3.2, issue #314)
that — alongside the cheap `ReadStateAsync` reachability check — samples four
well-known system symbols once per probe interval and surfaces the result through
the cross-driver `driver-diagnostics` RPC (added for Modbus, task #154). The same
symbols can be probed directly via the CLI for ad-hoc troubleshooting:

```powershell
# Cycle time (UDINT, 100 ns ticks → ÷10000 for ms)
otopcua-twincat-cli probe -n 192.168.1.40.1.1 -s "TwinCAT_SystemInfoVarList._TaskInfo[1].CycleTime" --type UDInt

# Last task execution wall-clock (UDINT, 100 ns ticks → ÷10000 for ms)
otopcua-twincat-cli probe -n 192.168.1.40.1.1 -s "TwinCAT_SystemInfoVarList._TaskInfo[1].LastExecTime" --type UDInt

# Online-change count — increments on every accepted online change
otopcua-twincat-cli probe -n 192.168.1.40.1.1 -s "TwinCAT_SystemInfoVarList._AppInfo.OnlineChangeCnt" --type UDInt

# Loaded PLC project name (STRING(80))
otopcua-twincat-cli probe -n 192.168.1.40.1.1 -s "TwinCAT_SystemInfoVarList._AppInfo.AppName" --type String
```

Within the running OtOpcUa server these four signals land on
`DeviceState.LastDiagnostics` as a `TwinCATDeviceDiagnostics` record + are folded
into `DriverHealth.Diagnostics` keyed `TwinCAT.CycleTimeMs`, `TwinCAT.LastExecTimeMs`,
`TwinCAT.JitterMs` (computed `LastExecTimeMs - CycleTimeMs`),
`TwinCAT.OnlineChangeCnt`, and `TwinCAT.OnlineChangeIncrements`. See
`docs/drivers/TwinCAT-Test-Fixture.md §Diagnostics` for the full mapping.

### `read`

```powershell
# Bool symbol
otopcua-twincat-cli read -n 192.168.1.40.1.1 -s MAIN.bStart -t Bool

# Counter
otopcua-twincat-cli read -n 192.168.1.40.1.1 -s GVL.Counter -t DInt

# Nested UDT member
otopcua-twincat-cli read -n 192.168.1.40.1.1 -s Motor1.Status.Running -t Bool

# Array element
otopcua-twincat-cli read -n 192.168.1.40.1.1 -s "Recipe[3]" -t Real

# WString
otopcua-twincat-cli read -n 192.168.1.40.1.1 -s GVL.sMessage -t WString
```

ADS variable handles for `read` / `write` symbols are cached transparently
inside the CLI's underlying `AdsTwinCATClient`. The first read of a symbol
resolves a handle; repeats reuse the cached handle for smaller AMS payloads
and skipped name resolution. The cache wipes on reconnect, on
`DeviceSymbolVersionInvalid` (with a one-shot retry), and on CLI exit. See
`docs/drivers/TwinCAT-Test-Fixture.md §Handle caching` for the full story
including the staleness caveat after an online change.

### `write`

```powershell
otopcua-twincat-cli write -n 192.168.1.40.1.1 -s MAIN.bStart -t Bool -v true
otopcua-twincat-cli write -n 192.168.1.40.1.1 -s GVL.Counter -t DInt -v 42
otopcua-twincat-cli write -n 192.168.1.40.1.1 -s GVL.sMessage -t WString -v "running"
```

Structure writes refused — drop to driver config JSON for those.

### `subscribe`

```powershell
# Native ADS notifications (default) — PLC pushes on its own cycle
otopcua-twincat-cli subscribe -n 192.168.1.40.1.1 -s GVL.Counter -t DInt -i 500

# Fall back to polling for runtimes where native notifications are constrained
otopcua-twincat-cli subscribe -n 192.168.1.40.1.1 -s GVL.Counter -t DInt -i 500 --poll-only

# Coalesce bursty changes — runtime buffers up to 500 ms before dispatch
otopcua-twincat-cli subscribe -n 192.168.1.40.1.1 -s GVL.Counter -t DInt -i 50 --max-delay-ms 500
```

| Flag | Default | Purpose |
|---|---|---|
| `-s` / `--symbol` | **required** | Symbol path — same format as `read` |
| `-t` / `--type` | `DInt` | IEC type (see Data types section) |
| `-i` / `--interval-ms` | `1000` | **Cycle time** — minimum interval between change checks the PLC runtime applies |
| `--max-delay-ms` | `0` | **Max coalescing window** — upper bound on how long the runtime buffers change events before dispatch. `0` = fire ASAP, no coalescing |
| `--poll-only` | off | Disable native notifications, use `PollGroupEngine` instead |

`-i` / `--interval-ms` and `--max-delay-ms` are different things and both flow
into the Beckhoff `NotificationSettings` ctor:

- **`--interval-ms`** is the *cycle*: the runtime checks for value changes at
  most this often. Smaller = lower latency, higher CPU.
- **`--max-delay-ms`** is the *coalescing ceiling*: once a change is detected,
  the runtime can hold it for up to this long before dispatching, which lets
  it batch a burst of changes into a single callback. Default `0` means
  every detected change fires immediately — same as the pre-PR-3.1 behaviour.

For high-frequency signals (a counter incrementing every 10 ms PLC cycle),
pair a small `-i` (so latency stays bounded) with a non-zero `--max-delay-ms`
(so the OPC UA queue downstream doesn't flood). For slow signals just leave
`--max-delay-ms` at `0`.

The subscribe banner announces which mechanism is in play — "ADS notification"
or "polling" — and includes the `max-delay` value when set, so it's obvious
in screen-recorded bug reports.

`--poll-only` polls go through the same cached-handle path as `read`, so
repeated polls of the same symbol carry only a 4-byte handle on the wire
rather than the full symbolic path.