GREAT Data Acquisition
Event Builder - Data Input Stage
The primary input data stream within GREAT will be via the DSP-DSP links into the Data Collector VME crate. This stream will carry all data from the VXI modules which handle the segmented clover Ge detectors.
Other input data streams could be ,for example, via VME ADC modules used for ancillary detector systems.
Each input data stream would have an associated input module which handles data from that data source.
The Input Module function includes the following tasks:
Data checking appropiate to the hardware interface
ensuring all data items include the essential global timestamp information.
Basic consistency checks on the data items.
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.
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.
Generate singles histograms at this point. Unlike previous VXI based systems which use a bus readout mechanism this will be the first point at which singles histograms will be available. Note however that since GREAT is a TDR system histograms created here will be "true" singles since we are collecting all data generated within the detectors.
For the GREAT system the Data Input Stage will be a component of the Data Collector VME crate.