13.3. RING ITEMS PRODUCED

The fribdaq-readout program produces normal FRIB/NSCLDAQ ring items. The format of the ring items, depends on the version of the DAQ the program is linked to. If a timestamp extractor is specified, the ring items will have non-empty body headers. If not, they will have empty body headers.

Prior to all state change items, a format item is emitted. This format item will reflect the format of the underlying version of FRIB/NSCLDAQ. Normally, this will be 12.0 or higher.

For each event, a PYSICS_EVENT item is emitted. As you have seen in the previous section, events can be segmented. The data from each segment are concatenated to form the body of the physics event.

Scaler items are produced whenever the periodic stack produces data. As with the VMUSBReadout, elapsed run time data are produced from an internal timer. In general, this timer will have a finer granularity than a second, so you must take into account the divisor field of these items, if you are accessing the items directly. The unified format library is the recommnded way to access data, this will compute the elapsed times from the time elements and divisors transparently.

The MVLC Scaler readout is purely time based and, therefore, there is not a final scaler item at the end of the run.

The current version does not produce PHYSICS_EVENT_COUNT items. This is planned for a later release of the software.