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We have built and tested a computational unit for on-line processing of special algorithms to be embedded in the central processing unit VERSAmodule Eurocard (CPU VME)-crate of the CHIMERA data acquisition system. The computational unit consists of a number of VME digital signal processor (DSP)-based commercial boards delivering 720 MFlops/board.

In nuclear physics at intermediate energies, the use of multidetector arrays consisting of thousands of detectors is customary. This paper presents a novel approach to the automatic classification of data collected by the 4/spl pi/ detector CHIMERA, constituted by 1192 telescopes of a thin silicon transparent detector coupled to a thick CsI(Tl) scintillator. The method is based on spatial density data processing and produces frequency distributions of the most significant physical parameters. These one-dimensional spectra can be more easily analyzed than the standard two-dimensional scatter plots. With respect to manual or semiautomatic procedures, presently used for data analysis, our method offers the advantages of drastic time reduction and unbiased criteria for cluster identification. The proposed method can be successfully used in both off-line data analysis and multidetector stability control.

CHIMERA is a second generation 4/spl pi/ detector for high resolution light particle and fragment measurements in the field of intermediate energy nuclear reactions. An enhanced data acquisition, control and trigger system has been developed to manage the almost 5000 electronic channels of the detector. The data acquisition system is based on a Fast Data Link (FDL) connection between 9U VME crates. The FDL is a highly programmable VME device. It performs data readout and transfer to a destination VME CPU, the FIC8243, running the real time OS9 operating system. Data read and transfer is performed by a fast protocol (Sparse Data Scan) whose performances have been improved introducing the Chained Block Transfer mode (CBLT) technique. Data collected by the CPU are broadcast to analysis work-stations for on-line data analysis and storage. All commands from and to the VME CPU are sent by socket-based network protocols. Complete remote control of the electronic front-end is obtained by a system of client-server applications. A first level event selection and control during readout is made by a trigger system based on a new VME 9U board (MUSE), fully integrated with the FDL readout system.

A commercial two-DSP-based board is the basic unit of the on-line computational and control system under development for the multidetector array CHIMERA. The system design includes a small scale parallel and distributed architecture of PCs and DSP boards. The PCs are used both as host computer and interface between user and network. Each PC can host up to three DSP boards. The system is able to accomplish the on-beam control of CHIMERA, by means of the on-line computation of special algorithms, instead of using the usual techniques of special pulses to be sent off-beam. The physical data, collected and organized in UDP packets by the data acquisition system, are read through a 10 Mbit/s Ethernet network. The PC software, running under Windows NT 4.0, is based on threads and assures the communication and program managing as well as the result presentation. The DSP-software is written in C++ and takes care of the communication with the PC and of the computation of algorithms. The preliminary on beam results for the first three wheels (about 100 telescopes), obtained by employing two biprocessor boards located in the PCI bus of a Pentium MMX PC, are also presented.