KTeV Data Acquistion System and Online Software

Paper: 315
Session: B (talk)
Speaker: Oleynik, Gene, Fermilab, Batavia
Keywords: data acquisition systems, event building

KTeV Data Acquistion System and Online Software

Ed Blucher,Vivian O'Dell,Tsuyoshi Nakaya,Taku Yamanaka
PO Box 500
Batavia, IL 60510

KTeV (FNAL E799/E832), a new fixed target experiment at Fermilab, is designed
to measure the direct CP violation parameter epsilon prime as well as
measure rare decays in the neutral kaon system. In order to achieve a high
precision on the measurement of epsilon prime (O(10-4)) an order of magnitude
increase in statistics over our previous measurement is needed: hence a high
kaon flux and a DAQ that can handle the rate. KTeV uses a multi-level trigger
approach, with Levels 1 and 2 being comprised of specially designed hardware,
and Level 3 being a software filter running on a multi-processing
Challenge L deskside server.

The KTeV DAQ system, which is part of the Fermilab DART project, was designed
to handle a projected rate of 160 MBytes/second into the Level 3.
The KTeV DAQ can be visualized as a matrix in which each element corresponds
to a memory node in VME for event storage. Data from sub-detector systems
flow in six parallel streams into the memory nodes along RS485 cables.
Event collection is done in parallel in four VME crates daisy-chained along
the RS485 cables and the event data are pulled from the crates into
the Challenge L machines via a VME/VME interface. The overall throughput can
be increased by increasing the number of streams or planes
or both. The system is partitionable for detector commissioning and debugging.

Each Level 2 accepted event is sent to a specific plane according to trigger
type, allowing the flexibility to send specific trigger types to specific
tape drives and thus do an online "split" of events.

Once the events arrive in the UNIX workstations, they are further
selected by the on-line Level 3 filtering. The computing power for
this filtering corresponds to about 3600 Mips with three SGI Challenges,
each of which has 8 R4400/200MHz CPUs. The fourth plane
(VME crate + SGI Challenge) is used for processing calibration events and
for online monitoring of a percentage of the physics data. Calibration
constants are calculated online during each run, and each run uses the
calibration constants from the preceeding run.

In each Challenge, a process reads the data from the memory
modules in VME and sends it to one of 8 Level 3 filtering jobs running in
parallel. The Level 3 code does a full reconstruction of the events,
builds the events that pass the filter, and sends them to a separate process
which handles the tape media I/O. The built events are then written to a
specific DLT tape drive depending on trigger type. The data are monitored
across CPUs and planes using a combination of shared memory and NFS mounted
filesystems. HEPDB is used as a database for all constants and
to connect the slow da to the fast da.

The KTeV DAQ is commissioned and started taking data in July 1996.
In this paper we will report on the performance of the KTeV DAQ and online
software for both E799 and E832.