EUROPEAN SOUTHERN OBSERVATORY
On wt5tcs a number of high level operations processes are running. These provide for the co-ordination of the underlying software and monitor the health of the system.
Each subsystem of the TCS has a state and a sub state. The basic states are: LOADED, STANDBY and ONLINE. The sub states depend on the module but for example the tracking LCUs can have sub states TRACKING, PRESETING, ERROR and others.
Starting and stooping the telescope is done via commands to mode switching, which in turn co-ordinates the activities such that they occur in a safe manner. For example, it is dangerous to switch the building "off" before switching azimuth "off" since the building can then be hit by the telescope. Mode switching ensures the correct sequence.
In addition, prsControl instructs the auto guiding and image analysis software to start automatically (or not) when the preset is completed.
Any commands that should be performed while the telescope is tracking a target should be issued to the trkwsControl module. This module works with direct commands only and not via setup files.
Additional velocity changes, offsetting the rotator and offsetting the telescope are handled by trkwsControl.
From mode switching, agwsControl receives the information about the active focus and therefore can determine which guide camera to instruct and which guide probe to move.
Note, that although in principle it is possible to drive the NTT directly from the LCU level, by doing so and bypassing mode switching certain functions such as auto guiding become extremely complex to configure correctly.
actconControl also provides the interaction with the preseting module to determine whether active optics is to be initiated immediately after the preset is finished and also prohibit a preset of the telescope while a force setting on M1 is taking place.
The force setting parameters can either be calculated by the active optics or by the M1 module which resides within the M1 LCU. This permits then default force set tings without the need for active optics to be functioning.
Note that, image analysis in closed loop is the default mode of operation for the NTT.
Communication between the LCUs and the workstations is done either via messages or via database reads and writes. To this purpose, the database on the LCUs (or parts thereof) is SCANned into the RTAP database on the workstation.
Scans can be triggered on change or by polling at a fixed frequency. On the NTT system we have chosen, as much as possible, to poll the database for information since this provides for a fixed system load. As a result, some values such as the sidereal time on the workstation are not updated at very high frequencies.
On the tracking LCUs you may find two extra processes, the axis task and the trk task. So for example on the azimuth LCU (lt5az) you would find the task azServer and aztrkServer. The azServer actually controls the axis, reads the encoders etc. etc., while the aztrkServer performs all the calculations necessary to deliver an angle to which the azServer needs to position the telescope. The trkServer processes are identical on all tracking LCUs. That is to say that there is no distinction as far as he tracking software on the LCU is concerned whether it is connected to one of the rotators or the azimuth axis.
On the LCUs connected to the CCD cameras application software also runs. The autoguider error vector conversion to RA and Dec is done in the LCU as are certain image analysis calculations. In the M1 LCU force setting calculations are per formed. Invariably the tasks are called m2Server, m1Server etc etc.