Events

Files associated with events.

Name: events.xml

Document Type Definition: events.dtd

Purpose

This validated XML file provides the list of the latest events for a constituent of Picolo U4 H.264 PCI-104. The corresponding constituent depends of the file's location in the directory structure. The validation is done using the appropriate Document Type Definition (DTD) file, located in the same directory.

Attributes

The events XML file is readable and writable. The DTD file is always read-only.

Event Queue

Each time an event is signaled by the hardware, it is logged by the Virtual File System driver in a ring buffer queue. The queue is made to contain up to a configurable number of events. When the queue is full, the oldest events are automatically overwritten.

Read

When the application opens the XML file, the driver generates its content from the information of the driver-maintained event queue. This ensures that reading the file, even partially, always produces valid data.

Reading the whole file provides the listing of all events from the event log.

Write

The file can be written, to selectively remove events from the event log.

When writing the file, the driver processes the written data, and removes the acknowledged events from the event queue. This happens when the file is closed, to ensure that only valid XML files will be processed.

Writing valid XML content containing only a subset of the events (typically only acknowledged events to be deleted) is allowed.

A flagged event is removed as soon as the XML block corresponding to that event is completely parsed. If a parsing error occurs, only the event causing the error and the subsequent ones are ignored.

The only XML elements required to remove an event are Index and Acknowledge. All other elements are allowed but ignored.

Delete

Deleting an event file is allowed, at any time. It flushes the event queue, removing all logged events. A new file reappears immediately thereafter, with updated content.

The delete operation doesn't modify the QueueSize parameter.

Synchronization

Several applications can access the files simultaneously. When doing so, it is the application's responsibility to synchronize the file accesses.