Back to Volume
Paper: Distributing Functionality in the Drift Scan Camera System
Volume: 61, Astronomical Data Analysis Software and Systems III
Page: 473
Authors: Nicinski, T.; Constanta-Fanourakis, P.; MacKinnon, B.; Petravick, D.; Pluquet, C.; Rechenmacher, R.; Sergey, G.
Abstract: Although Fermilab is a High Energy Physics (HEP) laboratory, its experience in producing high speed data acquisition systems was essential in the development of the Drift Scan Camera System (DSC). It integrates high speed CCD (2048 2048 pixels) readout over fiber optics into an embedded VMEbus single board computer with a backend UNIX analysis system. Functionality is distributed across heterogeneous platforms through tight and loose coupling of machines client/server protocols a common interpretive command language Besides being a prototype for the Sloan Digital Sky Survey, the DSC System will be used for independent scientific objectives. It will be installed on the ARC 3.5m telescope at Apache Point Observatory, New Mexico in late 1993. The DSC core consists of two machines: the Instrument Control Computer (ICC) and the Online Analysis Computer (OAC). The ICC, a VMEbus-based Motorola MVME167b, and the OAC, a Silicon Graphics 4D/35, are tightly coupled through a VMEbus repeater. The ICC acquires image data from a 2048 2048 pixels CCD at rates up to 922 KBytes/second and stores this data, packaged into Frames up to 8 MBytes in size, in a local Frame Pool (on disk) in real-time. Frames in the Pool are served by the ICC to the Archiver (tape logger) and/or various OAC clients in near-real-time. As a Frame Pool client, the OAC requests Frames from the ICC via backplane-based RPCs (Remote Procedure Calls) and shared memory. Tight backplane coupling is necessary to provide the OAC with Frames as fast as they become available. This allows quick analysis, during the acquisition of the next Frame, to determine whether the current Frame should be retained, logged, etc. With observation time being precious, it also permits the observer to quickly discover problems (non-visually) and to correct them. The ICC is usually controlled by the OAC. But, as the ICC uses servers that interpret a common command language (Tcl), any machine (including the ICC) can issue commands to it. Thus, if the OAC fails, the ICC is quite capable of continuing its operations. The DSC System also communicates with existing Apache Point machines over a local area network.
Back to Volume