Experimental Physics and
Industrial Control System

"Jeff Hill" <[email protected]> · Tue, 9 Mar 2004 11:18:18 -0700

Hello Timo,

I used a phase locked loop code in libCom/osi/os/win32/osdTime.cpp to
synchronize the fine resolution (but subject to drift problems) windows
performance counter with the coarse resolution windows time of day clock. I
suspect that this technique could be generalized for all systems that have a
high precision counter with drift problems that needs to be synchronized
with some external timing source periodically while not producing
discontinuities in the regular progression of time stamps. This is the
approach that is used by NTP.

There is an interface available in vxWorks systems for a high precision but
drifty source of time that is not currently used. With this interface and a
phase locked loop we might be able to provide uSec level time stamp
precision w/o specialized hardware. 

But, perhaps you are already considering such techniques?

Jeff

> -----Original Message-----
> From: Korhonen Timo [mailto:[email protected]]
> Sent: Tuesday, March 09, 2004 10:13 AM
> To: [email protected]; [email protected]; [email protected]; Chernousko,
> Y (Yuri); Jeff Hill
> Cc: Kalantari Babak; [email protected]
> Subject: Timestamp (drvTS) progress
> 
> Hello all,
> 
> I do not remember who all were interested in this topic in the
> beginning, but please feel free to forward this and also let
> me know who should also be involved.
> 
> More than two years ago in San Jose we had a time stamp meeting where I
> listed a number of problem points in the drvTS code. I also promised
> to start working on them. Finally last autumn we (myself and Babak
> Kalantari who actually has done most of the work) finally were able
> to get started with this work. Since that we have already got quite
> far (although many things still need to be done.)
> 
> The improvements so far include:
> -monitoring of the event receiver status and the link health, fault
> statistics
> -automatic switching to soft timing if there are problems with
> the EVR
> -synchronization of the local (vxWorks) clock with the "hard" time
> continually (this way we can switch from hard to soft time without jumps)
> -Channel Access interface to be able to monitor the status and to switch
> between soft/hard timestamp modes
> -several problems with startup were corrected (if the communication with
> the master timing does not work, etc.)
> -and so on...
> 
> Now the system is really robust (well, at least in lab...) The switching
> happens smoothly (we tested it by pulling the plug - and could not see
> any jumps in timestamps, within the available resolution.) We plan to
> take this new stuff in operation at SLS in one of the next shutdowns.
> 
> 
> The work so far has been done starting from the existing drvTS version.
> Actually, we would like to rewrite the whole thing at some point and
> make a better link to (S)NTP, etc., but to be sure that we understand
> the issues we decided first to rework drvTS.
> 
> This might be something of interest for the next collaboration meeting.
> I would be happy if you have some comments even before that.
> 
> best regards,
> 
> Timo
> --
> Timo Korhonen  PSI (Paul Scherrer Institut)
>                 CH-5232 Villigen PSI
>                 tel + 41- 56 3103262  fax + 41 - 56 310 3383
> e-mail:	       [email protected]

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System