Operation Handshake#

Control Nodes#

Track In, Track Out, and Abort use the same three-bit contract.

All three bits are Boolean and are normally false while the operation is idle.

Communication Flows#

Machine-Initiated#

sequenceDiagram
    autonumber
    participant M as Machine / PLC
    participant S as OPC UA Server
    participant I as Connect IoT
    participant E as Critical Manufacturing MES

    M->>S: Write Material
    M->>S: MachineOperationRequest = true
    S->>I: Request and payload change notification
    I->>I: Validate Resource, request, and Material Name
    I->>E: Execute MES operation
    E->>E: Validate and perform within transaction

    alt MES validation and processing succeed
        E-->>I: Operation performed, awaiting machine confirmation
        I->>S: MESOperationPerformed = true
        S-->>M: Performed signal available
        M->>M: Consume result

        alt Confirmation before MachineReplyTimeout
            M->>S: MachineOperationConfirmed = true
            S-->>I: Confirmation change notification
            I-->>E: Machine confirmed
            E->>E: Commit transaction
            E-->>I: Operation succeeded
            I->>S: MESOperationPerformed = false
            M->>S: Request and confirmation = false
        else MachineReplyTimeout expires
            I-->>E: Machine confirmation timeout
            E->>E: Roll back transaction
            I->>S: MESOperationPerformed = false
            I-->>I: Record failure diagnostic
        end
    else MES validation or processing fails
        E-->>I: Failure and rollback
        I-->>I: Record diagnostic, performed remains false
    end

Step by step:

1. The machine writes the operation payload, including Material.Name when available.
2. The machine sets MachineOperationRequest = true once.
3. Connect IoT resolves the applicable Resource and Material.
4. Connect IoT invokes the corresponding MES operation.
5. MES applies its normal preconditions and performs the operation within the current transaction.
6. Connect IoT sets MESOperationPerformed = true and starts waiting for the machine confirmation.
7. The machine consumes the result and sets MachineOperationConfirmed = true.
8. When confirmation arrives before MachineReplyTimeout, MES commits the transaction.
9. Connect IoT resets MESOperationPerformed.
10. The machine resets its request and confirmation bits.
11. If the confirmation does not arrive in time, the command fails and the MES transaction rolls back.

Operator-Initiated and Hybrid#

sequenceDiagram
    autonumber
    actor O as Operator
    participant U as MES UI
    participant E as Critical Manufacturing MES
    participant I as Connect IoT
    participant S as OPC UA Server
    participant M as Machine / PLC

    O->>U: Perform Track In, Track Out, or Abort
    U->>E: Execute standard MES operation
    E->>E: Validate and perform within transaction
    E-->>I: Operation event, awaiting machine confirmation

    I->>S: MESOperationPerformed = true
    S-->>M: Performed signal available
    M->>M: Consume MES-originated result

    alt Confirmation before MachineReplyTimeout
        M->>S: MachineOperationConfirmed = true
        S-->>I: Confirmation change notification
        I-->>E: Machine confirmed
        E->>E: Commit transaction
        E-->>U: Operation succeeded
        U-->>O: Success
        I->>S: MESOperationPerformed = false
        M->>S: MachineOperationConfirmed = false
    else MachineReplyTimeout expires
        I-->>E: Machine confirmation timeout
        E->>E: Roll back transaction
        E-->>U: Operation failed
        U-->>O: Failure
        I->>S: MESOperationPerformed = false
    end

In this path:

• The operator acts through the MES UI.
• MES validates and performs the standard operation within its transaction.
• MachineOperationRequest remains false.
• The affected Material is taken from the MES operation context, not from the OPC UA Material node.
• The machine must monitor MESOperationPerformed even when it did not issue a request.
• MES commits the operation only after the machine confirms within MachineReplyTimeout.

Material Resolution#

For a machine-initiated request, Connect IoT resolves the Material in this order:

1. If Operation.<Operation>.Material.Name is non-empty, resolve that exact MES Material.
2. Otherwise, read IndEqAutomationOperationAllowFIFO from the Resource attribute.
3. If FIFO is disabled, reject the request.
4. If FIFO is enabled, select the first eligible Material for the operation.

FIFO does not mean an arbitrary Material. The selected Material must still satisfy the normal MES operation rules.

Missing Acknowledgement and Recovery#

After setting MESOperationPerformed = true, Connect IoT waits for MachineOperationConfirmed = true for the period configured by /IndEq/Automation/OpcUaServer/MachineReplyTimeout/.

• If confirmation is received in time, the MES operation completes and its transaction commits.
• If the timeout expires first, the command fails, the MES operation is not successful, and its transaction rolls back.
• A rollback restores the MES transaction, but it cannot prove that the physical machine did not already react to the performed signal.
• Recovery must reconcile MES, handshake values, and the physical machine state before resetting or retrying.

See Automation Timeout Settings for configuration guidance.

Reset Contract#

The idle state is:

MachineOperationRequest   = false
MESOperationPerformed     = false
MachineOperationConfirmed = false

The machine must not raise a new request until the previous cycle has returned to idle. Connect IoT must not interpret a bit that remained high from the preceding cycle as a new request.