Experimental Physics and
Industrial Control System

Michael Davidsaver <[email protected]> · Thu, 13 Nov 2014 17:57:09 -0500

On 11/13/2014 04:18 PM, J. Lewis Muir wrote:
> Without monotonic time, the closest I can get to this in a simple way
> is to use epicsTimeGetCurrent and epicsTimeDiffInSeconds.  This is
> suboptimal because I have to deal with time that can advance backward
> or forward in an unpredictable way, and it's not possible to correctly
> compensate for that.

Strictly speaking epicsTimeGetCurrent() does try to prevent backwards
jumps.  Subsequent calls should never return later values.  Of course in
some cases this means that time stops...

The root problem I see is that generalTime tries to provide at once the
properties of a real (wall clock) time source, and a monotonic time
source.  It only partially succeeds in this as epicsTimeGetCurrent() has
some properties of a real time clock (absolute reference, global
meaning), and some of a monotonic clock (not jumping backwards).

I think it wouldn't be difficult to add a real monotonic time source
which defaults to epicsTimeGetCurrent() for platforms without such a
time source.  POSIX has clock_gettime w/ CLOCK_MONOTONIC and similar
(RTEMS implements this).  Windows has something as well.  Not sure about
vxWorks.

https://bugs.launchpad.net/epics-base/+bug/1392516

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System