A Small Unix-based Data Acquisition System

The proposed SLAC B Factory detector plans to use Unix-based machines for all aspects of computing, including real-time data acquisition and experimental control[l][2][3]. An R&D program has been established to investigate the use of Unix in the various aspects of experimental computation. Earlier R&D work[4] investigated the basic real-time aspects of the IBM RS/6OOO workstation running AIX. The next step in this R&D is the construction of a prototype data acquisition system which attempts to exercise many of the features needed in the final on-line system in a realistic situation. For this project, we have combined efforts with a team studying the use of novel cell designs and gas mixtures in a new prototype drift chamber[5]. _ .-I. FUNCTIONAL REQUIRkMENTS The prototype drift chamber is a 90 sense wire &vice requiring both time and amplitude measurements. FADC information& a limited number of channels is also required to study pulse shapes. Triggers are generated by the coincidence of a cosmic ray through a pair of scintillators placed on oppo site sides of the chamber. Enabling and resetting of the trigger must be accomplished under computer control. The data aquisition system must be capable of handling an event rate of -1 Hz; be able to sense and report errors; format the data into usable structures; log data to tape/disk; provide real-time data access to an analysis process; and, provide an operator un control interface. This system must be operational by late June 1993. In addition to the requirements imposed by the drift chamber itself, we have imposed a number of requirements speci!lcally to test features of the Unix and data acquisition environments which will be needed for a future on-line system. These extra requirements include: functional separation of pro.cesses; distributing processes across machine boundaries; making use of standard network protocols for data transfer; use of interprocess communication mechanisms both for data and control; ability to play back logged data through the system; use of new external I/O buses; creation of a simple GUI for the control program; and, use of an object-oriented programming language. II. HmWAFtE ARCHITECTURE Hardware components for this system begin with the digitization of analog signals and are shown schematically in Work supported by Department of Energy, contract DE-ACO3-765FOO515 Fig. 1. All 90 sense wires are instrumented with LeCroy 2249 gated ADCs and LeCroy 2228 TDCs resident in two CAMAC crates. This choice was largely governed by economic considerations and the ready availability of this equipment at SLAC. CAMAC is connected via a LeCroy 8901 crate controller to a GPIB bus and finally into an IBM RS/6000-520 workstation via a National Instruments MC-GPIB interface. The CAMAC crates also contain crate verifier and dataway display modules for diagnostics. FADC measurements are made by two STRUCK DL515 VME modules. Each module contains four channels operating at up to 250 MI-Ix with 8-bit resolution. The i’h%E crate is connected to the workstation via a National Instruments VME controller, MXI cable and MC-MXI interface. All of the National Instruments equipment (including the GPIB interface) comes with driver software and configuration utilities. Finally, triggering and trigger control will be done using a custom &sign VKI module based upon a Interface Technology development board with a register-based aughter board. The VXI crate is daisy-chained to the VME crate via the MKI cable and a National Instruments slot 0 controller module.