Real-time operation without a real-time operating system for instrument control and data acquisition

Randolf Klein, Albrecht Poglitsch, Fabio Fumi, Norbert Geis, Murad Hamidouch, Rainer Hönle, Leslie Looney, Walfried Raab, Werner Viehhauser

Research output: Contribution to journalConference articlepeer-review


We are building the Field-Imaging Far-Infrared Line Spectrometer (FIFILS) 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 asynchronously, 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.

Original languageEnglish (US)
Article number16
Pages (from-to)138-145
Number of pages8
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - Dec 1 2004
EventAdvanced Software, Control, and Communication Systems for Astronomy - Glasgow, United Kingdom
Duration: Jun 21 2004Jun 22 2004


  • Data acquisition
  • Instrumentation control
  • Real-time control

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering

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