The enhanced data acquisition system for the 4π detector CHIMERA

CHIMERA is a second generation 4π detector for high resolution light particles and fragments measurements in the field of intermediate energy nuclear physics. An enhanced data acquisition, control and trigger system has been developed to manage the almost 5000 electronic channels of the detector. Data acquisition is based on fast data link (FDL) connection between 9U VME crates. FDL is a highly programmable VME device. It performs data readout and transfer to a destination board VME CPU, 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 (CELT) technique. Data collected by the CPU are broadcasted to the analysis stations for on-line data analysis and storage. All commands from and to 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 assured by a trigger system based on a new VME 9U board (MUSE), fully integrated with the FDL readout system