STAR Trigger Architecture

Paper: 416
Session: B (talk)
Speaker: Lindenstruth, Volker, Company UC-Berkeley Space Sciences Laboraztory, Berkeley
Keywords: networking, parallelization, SCI, massive parallel systems, trigger systems

STAR Trigger Architecture
V. Lindenstruth(1), H. Crawford(1), E. Judd(1), K. Marks(1), J. Whitfield(2)
UC-Space Sciences Lab, Carnegy Melon University


The Solenoidal Tracker at RHIC (STAR) is a funded large scale high-energy
physics detector scheduled to run in 1999. Its trigger system implements an
FPGA tree for the L0 trigger decision, which is based on the 15GB/sec of
Trigger raw data. The L0 trigger rate of 10**5 events/sec is reduced by two
orders of magnitude by a hierarchical multiprocessor farm. The STAR Trigger
Architecture, discussed here, implements a new concept allowing to completely
eliminate dead time- and abort/clear signals of subdetector systems. The
Trigger system itself is dead-time free. All important functional elements of
this sytem are built as prototypes and are operational since January 1996.
The over all performance is thoroughly simulated using ModSim.

STAR Trigger uses a method allowing to globally synchronize all subdetectors
upon a trigger. For the example of the STAR TOF system it is discussed how
Trigger and TOF are communicating triggers and aborts without the need of
dead time signals.

Upon a Trigger each event is analyzed further in a twin multi processor farm
capable of handling 10**5 events/sec (100 bytes large) in layer I and 10**4
events/sec (1kB large) in layer II. Within these design parameters (trigger
rate averaging time 2000 events) this MP system is dead time free. This is
accomplished by implementation of a new buffer resource management method,
allowing to eliminate resource locks and allowing to implement a write-only
inter processor communication scheme.
The physical Trigger implementation is based on commercially available VME
processors. The Trigger FPGA tree, however, is custom built. There are about
8 VME crates required. The communication between the crates and between the
detector and the counting house is based on the Scalable Coherent Interface
(SCI). The Trigger SCI link is currently running at 200MB/sec raw throughput.