Experimental Physics and
Industrial Control System

Andy Foster <[email protected]> · Wed, 21 Feb 1996 18:00:53 +0000 (GMT)

I have some questions/comments on EPICS "Access Security":

(1) I wanted to see the effect of stopping a user from accessing
data values with "dm", by using a suitably set-up access security file.
It did work. However, I was somewhat surprised by the message returned in
the "dm" text box which was "No data available". It was only when I looked
at messages in my command tool that I realised that access was being denied.
I don't see at present, how the user, just from looking at the "dm" screen could
tell that access was being denied? Couldn't "dm" be made clever enough to distinguish
the cases of "No data available" and "Insufficient Access"? At 14,000 ft 
misleading messages will lead to even greater confusion when a system is
being debugged!

(2) In another scenario, I was making a database in IOC1 send a command to
a database in IOC2. By sending a command, I mean writing to a field of a record
in IOC2 which had ASL = 0 and PP = YES in the ascii file. 
I found that when the command 
was blocked by the access security mechanism, the following appeared on the IOC1
shell (sender of the command):

************************************************************************
task: 0Xe7d640 dbCaOutput
dbCa_unknownECA ERROR: queue_ca_put() unrecognizable status returned 376

Bus Error
Program Counter: 0x00f0bc72
Status Register: 0x3000
Access Address : 0xf8609ffc
Special Status : 0x0485
Task: 0xe4f338 "process_asynch_events_task"
************************************************************************** 

When I saw "Bus Error" I was rather shocked. Should blocking out access really
cause such an error to occur in the sending IOC or is this indicative of a
more serious error?

I sort of expected a nice message to appear saying "access denied".

Can anyone with "Access Security" experience please help?

Andy

P.S. Use of EPICS for the Gemini Project.

===================================================================================
Andy Foster
Royal Greenwich Observatory	Tel:       44 (0)1223 374899 (direct)
Madingley Road			Fax:       44 (0)1223 374700
Cambridge			E-mail:    [email protected]
CB3 0HA				Home Page: http://www.ast.cam.ac.uk/~ajf
UK

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System