Experimental Physics and
Industrial Control System

Nick Rees <[email protected]> · Tue, 18 Feb 1997 23:01:37 -1000 (HST)

I have a suspicion of a problem with R3.13 alpha 5. It may be related
to the CA infinite loop problem, but probably not. It may be not a
problem at all.

I have a two axis servo system driven at 100 Hz off a sattelite clock
interrupt. It is fed position updates at 20 Hz via CA from a Vax. The
actual demand position is interpolated from successive position updates.
It is our primary telescope mount servo. It worked fine from October 95 to
August 96. 

The problem began when I upgraded to 3.13.0 alpha 5 in August 96 and the
system started oscillating every now and again, with major problems
occuring once every 3 days or so. The problem has always been cured by an
IOC reboot. A related symptom is at around the same time as the
oscillations the telescope drives are often switched off. This comes from
a dead mans handshake between the IOC and the VAX that is transmitted
using channel access. The handshake is sent at 20 Hz and if it isn't
observered for a period of two seconds a state program switches the
telescope drives off.

I suspected a hardware problem, but out of desperation I changed back
to R3.12.1 on the evening of Sept 8th. The problem never recurred under
R3.12.1, and only reappeared when I went back to R3.13 in November.

Thus I seem to have a problem relating to R3.13, and one of the symptoms
is likely to be caused by Channel Access messages not being delivered for
substantial perods of time. The system is on an isolated network (the 20
Hz messages are the major traffic) and the IOC normally runs at 10% CPU
utilization. I very rarely get a chance to look at the system when a
problem occurs since the telescope is in use so it is quicker to reboot
and tell me about it in the morning.

Has anyone seen related problems? Have later versions fixed the problem?
If so, can I just recompile a subset of base, or do I have to start with a
complete new release?

Cheers

Nick Rees

Joint Astronomy Centre                    Ph:       +1 (808) 961-3756
660 N. Aohoku Place                       Fax:      +1 (808) 961-6516
Hilo, HI.  96720                          Internet: [email protected]

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System