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Proceedings Paper

Real-time operation without a real-time operating system for instrument control and data acquisition
Author(s): Randolf Klein; Albrecht Poglitsch; Fabio Fumi; Norbert Geis; Murad Hamidouche; Rainer Hoenle; Leslie Looney; Walfried Raab; Werner Viehhauser
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Paper Abstract

We are building the Field-Imaging Far-Infrared Line Spectrometer (FIFI LS) for the US-German airborne observatory SOFIA. The detector read-out system is driven by a clock signal at a certain frequency. This signal has to be provided and all other sub-systems have to work synchronously to this clock. The data generated by the instrument has to be received by a computer in a timely manner. Usually these requirements are met with a real-time operating system (RTOS). In this presentation we want to show how we meet these demands differently avoiding the stiffness of an RTOS. Digital I/O-cards with a large buffer separate the asynchronous working computers and the synchronous working instrument. The advantage is that the data processing computers do not need to process the data in real-time. It is sufficient that the computer can process the incoming data stream on average. But since the data is read-in synchronously, problems of relating commands and responses (data) have to be solved: The data is arriving at a fixed rate. The receiving I/O-card buffers the data in its buffer until the computer can access it. To relate the data to commands sent previously, the data is tagged by counters in the read-out electronics. These counters count the system's heartbeat and signals derived from that. The heartbeat and control signals synchronous with the heartbeat are sent by an I/O-card working as pattern generator. Its buffer gets continously programmed with a pattern which is clocked out on the control lines. A counter in the I/O-card keeps track of the amount of pattern words clocked out. By reading this counter, the computer knows the state of the instrument or knows the meaning of the data that will arrive with a certain time-tag.

Paper Details

Date Published: 15 September 2004
PDF: 8 pages
Proc. SPIE 5496, Advanced Software, Control, and Communication Systems for Astronomy, (15 September 2004); doi: 10.1117/12.551111
Show Author Affiliations
Randolf Klein, Max-Planck-Institut fur extraterrestrische Physik (Germany)
Albrecht Poglitsch, Max-Planck-Institut fur extraterrestrische Physik (Germany)
Fabio Fumi, Max-Planck-Institut fur extraterrestrische Physik (Germany)
Norbert Geis, Max-Planck-Institut fur extraterrestrische Physik (Germany)
Murad Hamidouche, Univ. of Illinois/Urbana-Champaign (United States)
Rainer Hoenle, Max-Planck-Institut fur extraterrestrische Physik (Germany)
Leslie Looney, Univ. of Illinois/Urbana-Champaign (United States)
Walfried Raab, Max-Planck-Institut fur extraterrestrische Physik (Germany)
Werner Viehhauser, Max-Planck-Institut fur extraterrestrische Physik (Germany)

Published in SPIE Proceedings Vol. 5496:
Advanced Software, Control, and Communication Systems for Astronomy
Hilton Lewis; Gianni Raffi, Editor(s)

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