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<== Date ==> <== Thread ==>

Subject: ca_pend_event question (VAX/VMS only)
From: SAA@slc.slac.stanford.edu
To: tech-talk@aps.anl.gov
Cc: SAA@slc.slac.stanford.edu
Date: Tue, 8 Aug 1995 10:36:55 -0700 (PDT)
Hello -

In the description of ca_pend_event in the Channel Access Reference Manual, 
it says that a very short timeout such as 0.0001 seconds will result in a
"poll".  It appears that on my VAX/VMS system, this "poll" really takes 
around 10 milliseconds since the VAX time resolution is only to the
nearest 10 msecs.  Has anybody ever looked into changing ca_pend_event
so that it truly does a poll (at least on the VAX)?

We are using the EZCA routines on the VAX.  When not in a group, the first
thing every EZCA routine does is a ca_pend_event with a 0.00001 sec timeout.
I'm trying to understand why it does a ca_pend_event with a short timeout
instead of a ca_flush_io - can anybody explain?  

We have a few applications that do not use EZCA groups (ie, one application
posts many monitors (ezcaSetMonitor) and then periodically gets current 
values using non-grouped ezcaGets at different time intervals - ezcaDelay
is periodically called as suggested in the EZCA primer).  I thought 
we could stand the overhead of the extra polling, but obviously not with the 
10 msec wait.  In this particular application, it's tough to group the 
ezcaGet calls.  (OK, Bob Dalesio - you can tell me "I told you so" - go ahead, 
make my day!).

-- Stephanie Allison   saa@slac.stanford.edu


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