Exceptions
Files associated with exceptions:
Name: exceptions.xml
Document Type Definition: exceptions.dtd
Purpose
This validated XML file provides exception information. It contains the list of the latest exceptional events issued by 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 exceptions XML file is readable and writable. The DTD file is always read-only.
Exception Queue
Each time an exception is signaled by the hardware or the Virtual File System driver, it is logged by in a queue. The queue is made to contain up to a configurable number of items. When the queue is full, the oldest items are automatically overwritten.
Read
When the application opens the XML file, the driver generates its content from the information of the driver-maintained exception queue. This ensures that reading the file, even partially, always produces valid data.
Reading the whole file provides the listing of all exception from the exception queue.
Write
The file can be written, to selectively remove exceptions from the queue.
When writing the file, the driver processes the written data, and removes the acknowledged exceptions from the 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 exceptions (typically only acknowledged exceptions to be deleted) is allowed.
An acknowledged exception is removed as soon as the XML block corresponding to that exception is completely parsed. If a parsing error occurs, only the exception causing the error and the subsequent ones are ignored.
The only XML elements required to remove an exception are Index and Acknowledge. All other elements are allowed but ignored.
Delete
Deleting an exceptions file is allowed, at any time. It flushes the exceptions queue, removing all logged exceptions. 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.