Re: time drift in camonitor timestamps

[Michael Davidsaver <mdavidsaver@bnl.gov>]

> I mean, the difference between two
> consecutive samples is always higher than the SCAN value, accumulating an
> error.
Just to make certain I understand you.  Do you mean that the difference 
increases with each iteration?  Or that the scan start time is moving 
(precessing) relative to start of the system clock's second?
In case you have not seen it, the code in question is periodicTask().

http://bazaar.launchpad.net/~epics-core/epics-base/3.15/view/head:/src/ioc/db/dbScan.c#L561




On 1/3/2013 4:36 PM, Mark Rivers wrote:
> What is the magnitude of the error?  How long does it take before the error is 1 second, for example?
>
> -----Original Message-----
> From: tech-talk-bounces@aps.anl.gov [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of ibadillo@essbilbao.org
> Sent: Thursday, January 03, 2013 3:09 PM
> To: tech-talk@aps.anl.gov
> Subject: time drift in camonitor timestamps
>
> Hi,
>
> We have realized that when monitoring periodic PVs, provided by soft IOCs in
> standard machines under Windows/Linux/MacOS, it is observed a drift in the
> timestamps (server time) . I mean, the difference between two
> consecutive samples is always higher than the SCAN value, accumulating an
> error.
>
> It seems that  this issue does not occur in RT systems such as VxWorks (as
> expected).
>
> We are wondering if this is a known issue. In our opinion, this fact could
> lead to
> malfunction problems, especially if it is not taken into account.
>
> Does anyone in the list experienced this problem?
>
> thank you