The ProgramStateMachineType components consist of a set of References to the Object instances of StateTypes, TransitionTypes, EventTypes and the Methods that collectively define the Program FiniteStateMachine.

image008.png

Figure 5 – Program References

Figure 5 illustrates the component References that define the associations between two of the ProgramStateMachineType’s states, Ready and Running. The complementary ReferenceTypes have been omitted to simplify the illustration.

The state Objects are instances of the StateType defined in OPC 10000-16. Each state is assigned a unique StateNumber value defined in Table 6. Subtypes of the ProgramStateMachineType can add references from any state to a subordinate or nested StateMachine Object to extend the FiniteStateMachine.

The Halted state is the idle state for a Program. It can be an initial state or a terminal state. As an initial state, the Program Invocation cannot begin execution due to conditions at the Server. As a terminal state, Halted can indicate either a failed or completed Program. A subordinate state or result can be used to distinguish the nature of the termination. The Halted state references four Transition Objects, which identify the allowed state transitions to the Ready state and from the Ready, Running, and Suspended states.

The Ready state indicates that the Program is prepared to begin execution. Programs that are ready to begin upon their creation may transition immediately to the Ready state. The Ready state references four Transition Objects, which identify the allowed state transitions to the Running and Halted states and from the Halted and Ready states.

The Running state indicates that the Program is actively performing its Function. The Running state references five Transition Objects, which identify the allowed state transitions to the Halted, Ready, and Suspended states and from the Ready and Suspended states.

The Suspended state indicates that the Program has stopped performing its Function, but retains the ability to resume the Function at the point at which it was executing when suspended. The Suspended state references four Transition Objects, which identify the allowed state transitions to the Ready, Running, and Halted state and from the Ready state.

ProgramStateMachineType Transitions are instances of the TransitionType defined in OPC 10000-16 which also includes the definitions of the ToState, FromState, HasCause, and HasEffect references used. Table 7 specifies the transitions defined for the ProgramStateMachineType. Each transition is assigned a unique TransitionNumber defined in Table 6.

Table 7 – ProgramStateMachineType Additional References

SourceBrowsePath

Reference Type

Is Forward

TargetBrowsePath

HaltedToReady

ToState

True

Ready

FromState

True

Halted

HasCause

True

Reset

HasEffect

True

ProgramTransitionEventType

HasEffect

True

AuditProgramTransitionEventType

ReadyToRunning

ToState

True

Running

FromState

True

Ready

HasCause

True

Start

HasEffect

True

ProgramTransitionEventType

HasEffect

True

AuditProgramTransitionEventType

RunningToHalted

ToState

True

Halted

FromState

True

Running

HasCause

True

Halt

HasEffect

True

ProgramTransitionEventType

HasEffect

True

AuditProgramTransitionEventType

RunningToReady

ToState

True

Ready

FromState

True

Running

HasEffect

True

ProgramTransitionEventType

HasEffect

True

AuditProgramTransitionEventType

RunningToSuspended

ToState

True

Running

FromState

True

Suspended

HasCause

True

Suspend

HasEffect

True

ProgramTransitionEventType

HasEffect

True

AuditProgramTransitionEventType

SuspendedToRunning

ToState

True

Running

FromState

True

Suspended

HasCause

True

Resume

HasEffect

True

ProgramTransitionEventType

HasEffect

True

AuditProgramTransitionEventType

SuspendedToHalted

ToState

True

Halted

FromState

True

Suspended

HasCause

True

Halt

HasEffect

True

ProgramTransitionEventType

HasEffect

True

AuditProgramTransitionEventType

SuspendedToReady

ToState

True

Ready

FromState

True

Suspended

HasCause

True

Reset

HasEffect

True

ProgramTransitionEventType

HasEffect

True

AuditProgramTransitionEventType

ReadyToHalted

ToState

True

Halted

FromState

True

Ready

HasCause

True

Halt

HasEffect

True

ProgramTransitionEventType

HasEffect

True

AuditProgramTransitionEventType

The HaltedToReady transition specifies the transition from the Halted to Ready states. It may be caused by the Reset Method.

The ReadyToRunning transition specifies the transition from the Ready to Running states. It is caused by the Start Method.

The RunningToHalted transition specifies the transition from the Running to Halted states. It is caused by the Halt Method.

The RunningToReady transition specifies the transition from the Running to Ready states. The RunningToSuspended transition specifies the Transition from the Running to Suspended states. It is caused by the Suspend Method.

The SuspendedToRunning transition specifies the transition from the Suspended to Running states. It is caused by the Resume Method.

The SuspendedToHalted transition specifies the transition from the Suspended to Halted states. It is caused by the Halt Method.

The SuspendedToReady transition specifies the transition from the Suspended to Ready states. It is caused internally.

The ReadyToHalted transition specifies the transition from the Ready to Halted states. It is caused by the Halt Method.

Two HasEffect References are specified for each Program transition. These effects are Events of ProgramTransitionEventType and AuditProgramTransitionEventType defined in 5.2.5. The ProgramTransitionEventType notifies Clients of the Program transition and conveys result data. The AuditProgramTransitionEventType is used to audit transitions that result from Program Control Methods.

image009.png

Figure 6 – ProgramStateMachineType causes and effects