ExoGam Data Acquisition
Event Builder & Event Processing
The primary data stream within Exogam will be via the DT32 bus into the D2VB module in the Event Builder crate. This stream will carry all data from the VXI modules which handle the segmented Ge detectors and their associated BGO shields.
Multiple data sources require that software within the event builder merge the event fragments to generate complete events.
The Event Builder function includes the following tasks:
Event fragment merging - building complete events
Data received via D2VB module (DT32 bus master; 2 Mbyte fast RAM; buffer list processing).
Data received from other data sources.
Basic consistency checks on the event fragments.
The raw data format contains redundant information for security and this can be checked
for self consistency to detect possible hardware errors during data readout.
Convert from specific raw hardware formats to
a common internal representation.
Using the event number within each fragment complete events are
constructed. Further checks can be performed on the complete event to ensure
correct functioning of the frontend electronics and readout mechanism. For
example the data received can be checked against the hardware setup to
detect readout errors.
The fragment tokens are removed at this stage and the
formatted complete event is now in a more compact format than the raw data.
Statistical information is produced so that a constant check can be
kept on the quality of the raw data and alarms produced if the error rate
exceeds reasonable levels.
All data sources are required to generate an event fragment even if it contains no data. This is important for the event construction since it is possible to detect a missing event fragment or malfunctioning data source which would not be the case if empty fragments were not required.
Data processing and formatting
Optional In-line Doppler correction and In-line gain correction.
Reformat to output data format (compatible with existing Euroball format).
Send to Tape Server via high speed broadcast network (100Tx ethernet).
Produce at each step statistical information for monitoring purposes.
At all stages data buffers accessible to GUI for diagnostics.
Possibly generate singles histograms at this point. This would be of particular use for those data items which are not received via the DT32 bus and for which no other hardware histograms are available.