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<== Date ==> <== Thread ==>
Subject: Re: PyEpics -- full-resolution timestamps?
From: Matt Newville <[email protected]>
To: Eric Norum <[email protected]>
Cc: tech-talk <[email protected]>
Date: Wed, 26 Oct 2016 11:14:16 -0500
Hi Eric,

On Wed, Oct 26, 2016 at 10:14 AM, Eric Norum <[email protected]> wrote:
The pv.timestamp attribute returns the record time stamp as a floating point value.  This provides 53 bits of significand.  The ’seconds' now take about 31 bits leaving around 22 bits for fractional seconds so the resolution is only around 250 ns or so.

How about adding a couple of more atrtributes, say pv.seconds (POSIX) and pv.nanoseconds, to provide access to the full resolution time stamp?


Ah, yes, you are right.   Currently, the pv.timestamp is calculated as
    EPICS2UNIX_EPOCH + stamp.secs + 1.e-6*int(1.e-9*stamp.nsec)
where "EPICS2UNIX_EPICS" is the 1990 to 1970 translation, and "stamp" is the struct of two unsigned integers.   Like you say, that will not retain full  precision. Your idea of separately storing these two integer fields as "seconds" and "nanoseconds" as attributes is a great idea.   Will do.

Thanks,

--Matt

References:
PyEpics -- full-resolution timestamps? Eric Norum
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