The Schier Mount Daemon: schierd

The Schier Mount Daemon (schierd) handles communication with the mount controller computer. Connection is provided by a serial line at 9600 baud, with CRC checksums to ensure every command is understood. The mount controller itself takes simple commands to find its home position, change axis speed, and change target position. All commands are in absolute encoder steps, and it is the responsibility of schierd to make the necessary transformations to point at the sky and track at the correct speed and direction. schierd also uses the outside temperature and the target elevation to apply a simple focus model described in Chapter 6 and move the focus motor. The connection to the focus motor controller is also via a serial line, at 32000 baud.

schierd is controlled by a stack of commands. For example, upon receipt of a ``move'' command, three commands are put on the stack in the following order: track, move, adjust focus. In this way, the focus is adjusted and the telescope slews (this actually happens in parallel for a faster response time), and then the mount begins to track on the sky. Only when the mount starts tracking does schierd signal that the move is complete. schierd is also able to park the mount, find the home position, and move to ``standby'' position towards the zenith, which optimizes the response time to a random location on the sky.