Use Case:  ATCS Global System State Update

Description:  The current state of each subsystem is continuously monitored to detect any change and to update immediately:

• the global system state (OFF, LOADED, STANDBY, ONLINE)
• the global system substate (COLD-STARTING, STARTING, PRESETTING, IDLE, STOPPING, SHUTTING-DOWN, ERROR).
• the tracking state (PRESETTING, TRACKING, IDLE, ERROR)
• the auto guiding state (IDLE,OPERATING,GUIDING,MANUAL,ERROR)

Role(s)/Actor(s): 
Primary: Any sub-system changing state

Priority: Critical

Performance: 2 seconds

Frequency:  Asynchronous. Up to 10 per second.

Package Assignment:  Mode Switching.

Preconditions: 

• AT Control Software ready to accept commands

Basic Course: 

• Any required and not ignored sub-system changes state
  Alternate Course: ATCS Query Subsystem States of all required and not ignored sub-systems.
  Exception Course: States cannot be retrieved
• ATCS Evaluates Global System State as combination of the states of all required and not ignored sub-systems.
  Exception Course: State cannot be evaluated
• ATCS Evaluates Global System Substate as combination of the states of all required and not ignored sub-systems.
  Exception Course: State cannot be evaluated
• ATCS Evaluates Tracking State as combination of the states of all tracking sub-systems.
  Exception Course: State cannot be evaluated
• ATCS Evaluates Guiding State as combination of the states of all guiding sub-systems.
  Exception Course: State cannot be evaluated

Exception Course: State cannot be retrieved

• ATCS put in lowest state that can be retrieved
• ATCS put in ERROR substate
  Postcondition: ATCS in substate ERROR

Exception Course: State cannot be evaluated

• ATCS put in lowest state that can be evaluated
• ATCS put in ERROR substate
  Postcondition: ATCS in substate ERROR

Postconditions: 

• ATCS global system state, substate, tracking state and auto guiding state are up to date and available for query.

Issues to be Determined or Resolved: 

Notes:

• The VLTI SRS defined requirements for ATCS states in section 3.2 "ATCS States". This definition has prooved not feasible during design and implementation of the UT Control Software and had to be modified.
  In particular indication of tracking and auto guiding/field stabilization states had to be separated from the global system substate.
  For example, the telescope can be TRACKING but at the same time STANDBY if a non-tracking subsystem (i.e. a subsystem not involved in tracking a target) is for any reason in STANDBY state. Even in this condition it can be possible to continue observation under degraded performances. This has been accepted at SRS review. Section 3.2 of VLTI SRS has to be fixed.

Last modified: Thu Jun 28 13:32:55 UTC 2001