Redfish Events

UniStream PLCs support Redfish Events, enabling the system to generate, log, distribute, and monitor Redfish-compliant alerts according to the Redfish Event Service standard.

Redfish Events provide a standardized mechanism for communicating system conditions or changes to Redfish clients.

Events are generated from Ladder Logic, logged locally, and delivered to subscribed destinations.

Notes

Redfish Events require an SD card.
Max 50 subscriptions and 1000 logged events.
Up to 16 events can be processed simultaneously.

Redfish Event Service Struct

Automatically created when Redfish is enabled.

Parameter Name	Type	Purpose
Service Enabled	BIT	Is event service enabled or not
Delivery Retry Attempts	UINT32	The number of event retry attempts
Delivery Retry Interval (Seconds)	UINT32	The interval between retries in seconds

Event Subscription Management

The Redfish Event Service maintains a list of active subscribers, each defining where and how event notifications are sent.
While subscriptions are created and deleted through the Redfish interface, UniLogic provides Ladder access for monitoring and diagnostics.

Use the Get All Subscriptions Ladder element to retrieve details for all configured subscribers and store them in a Data Table.
This allows you to inspect each subscriber’s destination URI, filters, and retry configuration directly from the PLC application.

Event Service Behavior

The Event Service defines how the PLC communicates events to subscribed Redfish clients.
When enabled, it monitors all Redfish Event triggers from Ladder Logic, applies filters, and delivers notifications to each destination according to its configuration.

Supported Subscriber Settings

Each subscriber (destination) can define the following parameters, as specified by the Redfish standard:

Parameter	Description
Destination	The target URI to which events are sent (HTTP/HTTPS)
MessageIds	Optional list of Redfish Message IDs. Only matching events are sent
OriginResources	Identifies the Redfish resource that generated the event
ResourceTypes	Filters events by resource type (for example, Chassis, Power, Thermal)
Severity	Optional filter: OK, Warning, Critical
DeliveryRetryPolicy	Defines behavior on failure: - RetryForever - Server retries based on the subscription's retry policy - TerminateAfterRetries - After max attempts, it either disables the subscription (Suspend) or stops trying (Terminate) - SuspendRetries - If successful, the event is removed from the retry queue
Note: UniStream supports filtering by MessageIds, Severity, OriginOfCondition, and ResourceTypes. Filters not supported by the subscriber are ignored by the PLC during event delivery.

Event Delivery Sequence

Configure the Redfish Event Struct with the required arguments (Object / Resource ID, and Message Arguments).
Trigger a Redfish Event from the Ladder application.
The Event Service builds the event payload in JSON format.
The payload is logged locally to /mnt/sd/Redfish/RedfishLog.json.
The Event Service sends the event to all active subscribers whose filters match the payload.
If a delivery fails, it is retried according to the subscriber's retry policy and the Delivery Rate Interval defined in the Event Service Struct.

Note that to modify retry parameters dynamically, use the Set Service Property Ladder element.