Experimental Physics and
Industrial Control System

Peregrine McGehee <[email protected]> · Mon, 1 Apr 1996 09:26:37 -1000

At the last collaboration meeting (during ICALEPCS) there was a
lengthly discussion during Jeff's talk on the "Portable CA Server
status" that dealt with the relationship between CA, PCAS, and cdev.

I recall a statement being made that the functionality of the CA
client API may be reduced in future releases (4.0+?) under the
assumption that most client applications will be using a cdev layer to
reach CA.

Does this still reflect current thinking? I'm interested since I may
have to interface an existing system with one under development that
uses CA (and possibly cdev).

Also during the discussion, the following table of implementation cases
was drawn up - although this only covers the generalities.

Case/Implementation:	New Service/PCAS		
Server I/F:		PCAS + I/F to PCAS (database-like)
Client I/F:		CA
Notes:			only needs server I/F to PCAS.   

Case/Implementation:	New Service/cdev
Server I/F:		new connection management layer (CA-like)
Client I/F:		cdev + cdev service layer
Notes:			coding required for both client and server

Case/Implementation:	Old Service/PCAS
Server I/F:		old service + new I/F to PCAS (database-like)
Client I/F:		CA
Notes:			subject to constraints of CA API

Case/Implementation:	Old Service/cdev
Server I/F:		old service
Client I/F:		cdev + cdev service layer
Notes:			only needs cdev service layer

The conclusions drawn from the above discussion seemed to be that
1) it's simpler to interface a new service to PCAS (and use the CA +
cdev? on the client side), but
2) it's simpler to interface an old service to cdev.

Aloha,
	Peregrine

-------------------------------------------------------------------------------
Peregrine M. McGehee			http://www.cfht.hawaii.edu/~mcgehee
Telescope Control Systems Group 	Canada-France-Hawaii Telescope
(808) 885-3178				P.O. Box 1597, Kamuela, Hawaii 96743	

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System