The Camera Daemon: camerad and camserverd

The Camera Daemon (camerad) handles communication with the CCD camera computer. Connection is provided by a TCP/IP socket connection over a private LAN network configured on the eth1 secondary ethernet card. The camerad acts as the socket client, and the Camera Server Daemon (camserverd) acts as the server on the camera computer itself. If the socket connection fails and connection cannot quickly be reestablished, camerad assumes the camera computer has crashed, and the daq system will be shut down.

The camera will accept the following commands:

• PICT_EXPOSE: Take an image with the shutter open.
• PICT_DARK: Take an image with the shutter closed.
• PICT_STATUS: Return the status (expose, dark, readout, temperature, etc.)
• PICT_ABORT: Abort the current exposure. [Will this abort during readout?]

camserverd is organized on a ping/pong buffer format. The multi-threaded code can write one image to disk from one buffer (``ping''), while it reads out another image from the camera to the other buffer (``pong''). The image is saved in FITS format, with a custom header describing every relevant statistic from the daq system, including date, time, exposure and weather information, as described in Section C.1. Additionally, the mean and rms deviation of the bias region and the central subframe are calculated. If the mean value of the central subframe is too large, eg, when all the pixels are saturated, then only the image header is written to disk. The bias values are a good indication of the readout noise in the camera. camserverd also creates a symbolic link to the image which is read in by the automated analysis pipeline program, as described in Chapter 8.