Here we describe the general operation of the SC-10 software on GRB. New users may want to start PSYS, the SC-10 control program on the PC, and the SC-10 programs on GRB, to practice running the system as they read this section. Step-by-step instructions for doing so are contained in Observing Tutorial .
Two programs running under CDE are provided for SC-10 operation: the Data Acquistion Program, SCACQ, and the Display program, SCDISP. These programs communicate with each other through X windows events and shared memory. SCACQ acts as a remote terminal to the PSYS program on the PC, with which it communicates via the ethernet link. The SCACQ-PC connection operates in full-duplex mode. For example, when a command is sent to move the filter wheel, PSYS receives the command, moves the wheel to the desired position, then transmits the new position back to SCACQ. The appropriate indicator in the SCACQ window goes blank while PSYS executes the command, and displays the new value it receives from the PC. Be aware of this time lag effect: If you try to send commands faster than PSYS can execute them, confusing and unpredictable behaviour may be the result.
The current values of all the instrument parameters displayed by SCACQ are stored in a file on the PC which is frequently updated during operation. When PSYS is started, it reads this file and resets all the parameters to their values when the program was last running.
If a scan is underway, SCACQ also receives data from the PC via the ethernet link, typically at intervals of 1 to 20 seconds which constitues one beam. Each beam is usually composed of two frames representing the two chopping positions.
The naming and writing of FITS files to disk is fairly automatic. When SCACQ is first run, a window appears in which the desired data directory for the night is entered. A file with a name like ``SCLOG.01'' is opened for log messages. When a scan is initiated, a FITS file with a name in the form of ``sc000'' is automatically opened and a header is written. The two frames of each beam are added to the file as they appear on the ethernet, so an 8-beam scan will result in a 16 band FITS file. For the next scan SCACQ will open a file named ``sc001'', and so on. The program always checks the current data directory for the presence of a certain FITS or Log file name before opening the file, and increments the file index until it reaches a name with no conflicts, so if the program has to be restarted you can continue to use the same data directory.
SCACQ also writes the incoming data to shared memory, both during a scan and during ``Continuous Acquistion'' mode (for which data is NOT saved to disk). The SCDISP program can manipulate and display the shared memory data in various ways.
It is very important to note that the SCDISP program has no effect on the data saved to disk -- data is always written in the rawest form available from the PC.