epics/pcas
0
0
Fork 0
Code Issues Pull Requests Projects Wiki Activity

General Time.

Browse Source
This commit is contained in:
Andrew Johnson
2008-09-12 22:56:25 +00:00
parent 6430a49300
commit 70dfa451d2
1 changed files with 45 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

45
documentation/RELEASE_NOTES.html
View File

@@ -12,6 +12,51 @@
<h2 align="center">Changes between 3.14.9 and 3.14.10</h2>
<!-- Insert new items below here ... -->
<h4>General Time subsystem</h4>
<p>The way in which EPICS gets the time has been significantly revised since
R3.14.9 with the introduction of the General Time subsystem. Two kinds of
pluggable time providers are now supported, which return either the current time
or the latest timestamp of a numbered Time Event from a hardware event system.
All IOCs must have at least one Current Time provider, but Event Time providers
are optional. The General Time subsystem guarantees that the timestamps
returned never step backwards, even when switching between time providers.</p>
<p>A Current Time Provider reports the current wall-clock time if it is able to
when asked; if it can't it says so, and the time subsystem will then ask the
next provider in its list and so on until someone replies with the time. Event
Time providers are handled similarly, except that they are asked for the
timestamp associated with a particular Time Event number rather than the current
wall-clock time. The registered time providers can be listed using the IOC
command <tt>generalTimeReport(int interest)</tt> and some time providers also
have their own separate report commands.</p>
<p>Different target architectures come with different default Current Time
providers in Base. The Unix-like architectures rely on the underlying operating
system clock, which normally involves running something like ntpd as a separate
process. The real-time operating systems vxWorks and RTEMS install two Current
Time providers; the native OS Clock at the lowest priority (this provider
includes a task to periodically reset the OS Clock from a higher priority time
provider), and an NTP time provider which synchronizes the underlying OS' tick
timer with an NTP server. Microsoft Windows targets using the Win32 API use a
Windows-specific time provider which contains a built-in PLL</p>
<p>There are no Event Time providers included with Base except for an optional
"Last Resort" Event provider which can be installed if a site wants to be sure
that every Time Event number will have a recent timestamp associated with it
even if the hardware event system goes down. The Last Resort Event Time provider
returns the current time for every Time Event number. To install this provider,
run the command <tt>installLastResortEventProvider</tt> from your IOC startup
script.</p>
<p>Additional information about General Time and the time providers included
with Base can be found in the IOC Application Developers Guide for R3.14.10,
sections 9.7 and 20.6. General Time was originally written by David H. Thompson
and Sheng Peng at ORNL, subsequently worked on by Babak Kalantari and Timo
Korhonen of PSI, and merged into Base by Peter Denison from Diamond. Andrew
Johnson provided input into the design at various points and made various code
revisions after the merge.</p>
<h4>New ioc/dllPath.bat file for Win32</h4>
<p>When creating an IOC with one of the win32-x86 target architectures, a file