4. Application switching.

One major feature of this software is the ability to change between focal stations on-line. There are several related actions which have to be taken into account when changing focal station. Firstly the serial port which the CCD controller is controlled via has to be selected. This is done by having one task per serial port, and simply selecting which one runs the serial port handling code. Secondly the header code which accompanies the image data on the Fibre optic link uniquely identifies which CCD controller is sending the data. In order to initialise the DICI card to receive the correct data, this header number has to be selected. Thirdly, each CCD controller can have up to two CCD's attached to it. The correct Virtual head has to be selected for each CCD controller command. Finally the type of Application has to be selected, to enable the image to be interpreted correctly.

The selection is done hierarchically in the autoguider. There are two network commands:

HED selects the Focal Station, and the corresponding serial port, header code and Virtual head within the CCD controller.

APP selects the Application code to interpret the CCD data. The routines have different actions for different focal stations, for example the guide window tracks at Cassegrain, but the fibres at UES are fixed.

The APP-STATUS command displays the currently selected values of each of these five parameters. Within the software, it is possible to change each of these parameters individually, by forcing variables to selected values in order to set up an unusual configuration for hardware testing. An odd situation will be shown up accordingly. In the example below, the header code has been forced to be that for the Cassegrain CCD controller, which was the only one in the Laboratory.

ok

APP-STATUS

Port Focus Header Application Head

UES UES Cass UES 1

ok

An ICL command procedure will eventually be implemented to change both the head and application together and handle any error status. This has been done in the engineering terminal user interface with the commands CASSEGRAIN UES PRIME and AUTOFIB. Note that the AutoFib instrumnet uses the Prime head, the Prime header code, and the Autofib application.