Experimental Physics and
Industrial Control System

Steven M Beard <[email protected]> · Fri, 3 May 1996 09:33:03 +0100 (BST)

On Thu, 2 May 1996, William Lupton wrote:

>   We are discussing how to handle simulation both when IOCs are present and
> when they are absent. For simulation at other sites we are writing a Unix
> CA server which emulates part of our VME database. For simulation at the
> telescope we are toying with the idea that we might run the Unix CA server
> all the time but that connections to it would only be used when the vxWorks
> CA server was not running.
> 
>   This raised the question of whether anyone has ever discussed implementing
> "fallback" CA servers which would automatically be used (perhaps only for
> gets?) if the "master" server failed. At the CA server level it would imply
> that the server had an associated priority level. At the CA client level,
> multiple responses to ca_search() would have to make use of the priority
> level to decide which server to connect to, and connection state change
> could cause server rollover.

One word of warning. If you automatically fall back into a simulation mode
it is possible that an operator might run part of your system in
simulation mode without realising it, because the system responds in the
way the operator expects. This is more likely if the operator is working
at high altitude. I would prefer to make a switch-over to simulation mode
a manual operation, so the operator actually has to do something.

Steven

==============================================================================
Steven Beard
Royal Observatory                  Tel.   : +44 (0)131 668 8253 (direct)
Blackford Hill                              +44 (0)131 668 8100 (switchboard)
Edinburgh EH9 3HJ                  Fax.   : +44 (0)131 668 1130
UK                                 E-mail : [email protected]       (Internet) 
                                   WWW    : http://www.roe.ac.uk/smbwww/

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System