6 STANDARD STATES

[7] and [9] contain a description of the general states of LCU subsystems and the corresponding commands to switch from one state to another (standard mode switching functions). A subset of these LCU states and their transitions will be quite common for all instrument and detector subsystems, and are therefore available as higher level INS commands, allowing to switch ICS, DCS and OS between different operational states.

An attempt has been made to keep as much as possible compatibility with the states and state transitions defined for TCS in [15].

6.2 LCU states

The different LCU subsystem states are defined in [7]. Generally speaking, the state of an LCU is the least common denominator of the states of its components, i.e. the LCU common software (LCC) and the so-called software devices¹. The states that instrument and detector LCUs can frequently be in or go through are the following:

· OFF: when the corresponding LCU(s) is not operational; consequently an LCU can never reply it is in the OFF state.

· LOADED: all application software is loaded in the LCU, the DB is configured, no access to the hardware interfaces yet.

· STANDBY: the software and the hardware interfaces are initialized; the hardware is not initialized yet, or some components are in a "safe" standby position (partially switched off or brakes engaged).

· ON-LINE: all software and hardware is loaded, initialized and active. This is the normal state during operations.

Remark that simulation is not considered a state, but instead an operational mode; simulation mode can be entered from the states LOADED, STAND-BY or ON-LINE, and for obvious reasons not from the state OFF. So the LCU can be in simulation mode while it is LOADED, in STAND-BY or ON-LINE, without having to get out of these states. When entering or exiting simulation mode the LCU hardware has to be placed in the state LOADED (e.g. if a lamp is switched to simulation, the real lamp should be switched off). After this step, if entering simulation mode, the device should be brought back to the original state.

Also handset, for those devices, such as motors, which foresee it, is not a state, but an operational mode. As for simulation, it can be entered from the states LOADED, STAND-BY or ON-LINE, and exiting from handset will take the LCU into state LOADED.

6.3 Instrument and Detector States

The instrument and detector can each consist of or control several LCU subsystems. The general rule to determine the state of a set of subsystems as a whole is that this state equals the lowest state of any of its subsystems, with the order as listed above in 6.2. In analogy with the LCU states, it should be emphasized that simulation is here not considered as a state. However, one should not forget that exiting the simulation mode on a subsystem will take the LCU to a state where initialization is required.

Although simulation at the LCU level of an LCU in the OFF state is not possible (as it cannot receive commands), ICS and DCS must accept to enter simulation mode even when they are in the OFF state. This means they will simulate the LCU at the WS level. Otherwise one could never arrive to an ON-LINE state with (part of) the hardware absent.

6.4 State transition

There are a number of standard OS/ICS/DCS procedures and commands available that allow to change states:

This is a UNIX script, which takes the specified process (or the whole instrument if no process is specified) from OFF to STAND-BY.

This command switches the destination sub-system from STAND-BY to ON-LINE. This means that subsystems involved are switched from "stand-by" to on-line.

This command switches the destination sub-system from LOADED to STAND-BY or, possibly after moving some functions to predefined secure positions, from ON-LINE to STAND-BY.

This command takes the destination sub-system from STAND-BY to the LOADED state.

This is a UNIX script, which terminates the specified process (or the whole instrument if no process is specified) and therefore takes it to state OFF.

defined as a Message System based LCU application. either controlling some hardware functional unit, or coordinating other software devices (in which case it is sometimes referred to as a pure software device)