The ROTSE Daemon: rotsed

The ROTSE Daemon (rotsed) is the central nervous system of the ROTSE daq system, as shown in Figure 1.1. rotsed controls system startup and shutdown and handles interdaemon communication. It also handles emergency responses to bad weather and outputs system status for the web based status monitor (See Section 8.4.2).

The ROTSE IPCS shared memory structure is divided into several structures, one for each daemon. Each daemon has a status structure used to report status to rotsed, and a command structure, to receive commands from rotsed. On each loop, rotsed reads the status of each daemon to ensure that they are all running smoothly. If a daemon has not updated its timestamp recently, rotsed shuts down the system. If a status structure from one daemon contains information for another daemon, rotsed copies the relevant information to the command structure of the destination daemon.

When the weather turns bad, rotsed is responsible for issuing an immediate command to close the clamshell. It must be noted that the weather monitor daemon, weathd, must be turned on in order for this to work.

While shared memory commands are used to communicate between two daemons at a time, Linux system signals are used to communicate with all the daemons at once. There are several signals used by rotsed and the daq system:

• SIG_TERM: The termination signal (15)^1.1 is used to tell a ROTSE daemon to shutdown cleanly. Usual system shutdown is accomplished by issuing a SIG_TERM to rotsed, which passes on the signal to the other daemons.

• SIG_ROTSE: The ROTSE signal (equivalent to interrupt (2)) is used to tell all the ROTSE daemons to stop what they are doing and wait for further commands. The camera will abort an exposure, the mount will stop slewing, and the scheduler will interrupt its current programming for this important announcement. This signal is used when a burst alert is received by alertd, or when the weather turns bad in weathd.

• SIG_HUP: The hangup signal (1) is used to tell the astrod scheduler to re-read its configuration file and reset the schedule, as described in Section 4.1. The other daemons ignore this signal.

• SIG_KILL: When all else fails, a KILL signal (9) can be used to terminate a daemon with extreme prejudice. A daemon killed in this way might not exit cleanly.

When the weather turns bad, weathd signals a weather alarm in the shared memory status, and sends out a SIG_ROTSE to interrupt the other daemons. When rotsed receives a SIG_ROTSE in conjunction with the weather alarm, it directs clamd to close the clamshell.

Figure 1.1: The ROTSE-III Data Aquisition system is made up of a number of interconnected daemons which communicate through the central rotsed. Each daemon interfaces with a different logically distinct aspect of the telescope system. The daemons with asterisks are also able to send Linux signals to interrupt the camera, mount, and scheduler.