PHENIX ONLINE DISTRIBUTED COMPUTING SYSTEM ARCHITECTURE

PHENIX is one of the two large experiments at the Relativistic Heavy I on Collider (RHIC) currently under construction at Brookhaven National Laboratory, The detector consists of 11 subdetectors, that are furthe r subdivided into 29 units (''granules'') that can be operated indepen dently, which includes simultaneous data taking with independent data streams and independent triggers. The detector has 250 000 channels an d is read out by front-end modules, where the data is buffered in a pi peline while awaiting the level1 trigger decision. Zero suppression an d calibration is done after the level1 accept in custom built data col lection modules (DCMs) with DSPs before the data is sent to an event b uilder (design throughput of 2 Gb/sec) and higher level triggers. The On-line Computing Systems Group (ONCS) has two responsibilities. First ly, it is responsible for receiving the data from the event builder, r outing it through a network of workstations to consumer processes and archiving it at a data rate of 20 MB/sec. Secondly, it is also respons ible for the overall configuration, control and operation of the detec tor and data acquisition chain, which comprises the software integrati on for several thousand custom built hardware modules. The software mu st furthermore support the independent operation of the above mentione d granules, which includes the coordination of processes that run in 6 0-100 VME processors and workstations. ONCS has adapted the Shlaer-Mel lor Object Oriented Methodology for the design of the top layer softwa re. CORBA is used as communication layer between the distributed objec ts, which are implemented as asynchronous finite state machines. We wi ll give an overview of the PHENIX online system with the main focus on the system architecture, software components and integration tasks of the On-line Computing group ONCS and report on the status of the curr ent prototypes. (C) 1998 Elsevier Science B.V.