Layer: L7 Application · Build flags: PC_ENABLE_PACKML

What this example teaches

PackML (OMAC / ISA-88) is the state model packaging and process machines expose so a line controller - usually over OPC UA - can command and observe any machine the same way. It is defined by ISA-TR88.00.02 ("Machine and Unit States: An Implementation Example of ISA-88", ISBN 978-1-64331-224-8). services/packml is a pure, fixed-BSS implementation of it: a state engine plus an owned PackTags service. This sketch runs it as a simulated machine and serves it over HTTP.

The machine lives in one of 17 states. Seven are stable wait states (the machine waits for a command or condition): Stopped(2), Idle(4), Execute(6), Held(11), Suspended(5), Complete(17), Aborted(9). Ten are transient acting states that auto-advance when their action finishes: Resetting, Starting, Holding, Unholding, Suspending, Unsuspending, Completing, Stopping, Aborting, Clearing. The numbers are the ISA-TR88.00.02 StateCurrent wire values, so a PackTags Status.StateCurrent needs no translation.

Commands drive the transitions. Stop and Abort are near-universal (Abort from any state into the fault branch; Stop into the shutdown branch); the rest are state-specific:

Stopped --Reset--> Resetting --SC--> Idle --Start--> Starting --SC--> Execute
Execute --(run done)--> Completing --SC--> Complete --Reset--> Resetting --> Idle
Execute --Hold--> Holding --SC--> Held --Unhold--> Unholding --SC--> Execute
Execute --Suspend--> Suspending --SC--> Suspended --Unsuspend--> Unsuspending --SC--> Execute
any --Abort--> Aborting --SC--> Aborted --Clear--> Clearing --SC--> Stopped
any --Stop--> Stopping --SC--> Stopped

(SC = State-Complete: the machine signals it finished the acting state's action.) The pure engine is three functions plus a couple of predicates:

PackMlState s = PackMlState::STOPPED;
s = pc_packml_command(s, PackMlCommand::RESET);   // -> Resetting  (invalid command -> unchanged)
s = pc_packml_state_complete(s);                  // -> Idle       (acting states auto-advance)
s = pc_packml_command(s, PackMlCommand::START);   // -> Starting
s = pc_packml_state_complete(s);                  // -> Execute
s = pc_packml_execute_complete(s);                // -> Completing (production run finished)
pc_packml_command_valid(s, PackMlCommand::HOLD);  // is a command legal here?
pc_packml_is_acting(s);                           // transient (auto-advancing) vs wait state?

On top, the owned service (pc_packml_svc_*) carries the PackTags a real machine reports: the current state + unit mode, MachSpeedActual, the ProdProcessedCount / ProdDefectiveCount production counters, and the StateCurrentTime / AccTimeSinceReset timers - so the sketch just drives commands and reads a status snapshot.

Run it

No hardware beyond the ESP32 - the "machine" is simulated in loop() (acting states complete after a short dwell; a unit is produced each second while executing). Endpoints:

GET /packml            -> live PackTags JSON
GET /packml/reset      GET /packml/start     GET /packml/stop
GET /packml/hold       GET /packml/unhold    GET /packml/suspend
GET /packml/unsuspend  GET /packml/abort     GET /packml/clear   GET /packml/complete

pio ci --board=esp32dev --project-option="framework=arduino" \
  --project-option="build_flags=-DPC_ENABLE_PACKML=1" \
  --lib="." examples/L7-Application/PackML/PackML.ino

Flash, then drive it:

$ curl http://192.168.1.42/packml
{"stateCurrent":2,"state":"Stopped","unitMode":1,"machSpeedActual":0.0,...}
$ curl http://192.168.1.42/packml/reset      # Stopped -> Resetting -> (dwell) -> Idle
$ curl http://192.168.1.42/packml/start      # Idle -> Starting -> Execute
$ curl http://192.168.1.42/packml            # now Execute, counters climbing
{"stateCurrent":6,"state":"Execute","unitMode":1,"machSpeedActual":120.0,"prodProcessedCount":7,...}
$ curl http://192.168.1.42/packml/complete   # end the run -> Completing -> Complete

An illegal command in the current state answers 409 with "accepted":false and leaves the state put (e.g. start while Stopped).

Annotated source

The complete sketch is PackML.ino. The state engine + service are in src/services/machine_tool/packml/packml.h; the 17-state model, the StateCurrent numbers, the command set, and the transitions follow ISA-TR88.00.02. Pure codec, host-tested (native_packml, 16 cases). The real deployment surfaces the same PackTags over OPC UA; here they ride the library's HTTP server. Pairs with the Umati, HaasMdc, and Fanuc FOCAS machine-tool examples.