TagEventQueue

Opens the tag update event queue. The I/O server writes events into this queue as they are processed. These events include tag updates from drivers that support time-stamped data.

To read events from this queue, use the QueRead() or QuePeek() functions. The data put into the queue contains the following fields:

• Driver (the driver used to communicate with the I/O device)
• Port (the name of the port to which the I/O device is connected)
• Unit (the name of the I/O device)
• Tag (the variable tag name)
• Seconds (a UTC timestamp representing the number of seconds since 1970)
• Milliseconds (number of milliseconds since the last second)
• Value (the tag value)
• Quality (OPC component only equivalent to QualityGetPart, mode 7)

To use this function, you need to enable the tag update event queue with the [IOServer]EnableEventQueue parameter. This parameter will tell the I/O Server to start placing events into the queue. The function TagEventFormat() returns a handle to the format of the data placed into the string field.

Enabling this formatting feature can increase CPU loading and reduce performance of the I/O Server as every tag update event is formatted and placed in the queue. You should reconsider using this feature if a decrease in performance is noticeable.

The maximum length of each queue is controlled by the [Code]Queue parameter. You may need to adjust this parameter so as not to miss alarm events. When the queue is full, the I/O Server will discard events.

Syntax

TagEventQueue()

Parameters - None

Return Value

The queue handle of the Tag Update Event queue.

Related Functions

QuePeek, QueRead, TagEventFormat

Example

FUNCTION

ReadEvents()

   INT status;

   INT queue;

   INT format;

   INT eventId;

   STRING event;

   INT sec;

   INT ms;

   TIMESTAMP time;

   queue = TagEventQueue();

   format = TagEventFormat();

	IF (queue <> -1 AND format <> -1) THEN

	WHILE (true) DO

	 status = QueRead(queue, eventId, event, 1);

	 IF status = 0 THEN

		 ErrLog("eventId: " + IntToStr(eventId));

		 StrToFmt(format, event);

		 ErrLog("   driver: " + FmtGetField(format, "Driver"));

		 ErrLog("   port: " + FmtGetField(format, "Port"));

		 ErrLog("   unit: " + FmtGetField(format, "Unit"));

		 ErrLog("   tag: " + FmtGetField(format, "Tag"));

		 sec = FmtGetField(format, "Seconds");

		 ms = FmtGetField(format, "Milliseconds");

		 time = TimeIntToTimestamp(sec, ms, 1);

		 ErrLog("   time: " + TimestampToStr(time,14));

		 ErrLog("   value: " + FmtGetField(format, "Value"));

		 ErrLog("   quality: " + FmtGetField(format, "Quality"));

		END

	 END

	 END

 END

See Also

Tag Functions