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<== Date ==> <== Thread ==>

Subject: 3.14.10 on vxWorks and RTEMs
From: "Mark Rivers" <[email protected]>
To: "EPICS tech-talk" <[email protected]>
Date: Wed, 11 Nov 2009 13:41:16 -0600
Folks,

The Known Problems page for EPICS 3.14.10 contains the following:

*****
"RTEMS and vxWorks systems that use the new NTP Time provider may suffer
from poor time synchronization with NTP if their system clock ticks
faster that it is supposed to. The time provider measures the tick rate
but does not automatically correct it; this measurement is displayed on
a level 1 NTPTime_Report. Apply this patch in the base/src/libCom/osi
directory to correct the synchronization."
*****

It is very important to apply this patch.  It does not just lead to IOC
times being incorrect, it can cause major problems in the IOC.  The IOC
time will be set correctly at boot time, but then, if the tick clock is
faster than it should be, the time difference will grow.  

If the time difference has grown to 15 seconds, for example (which was
my case), then the following happens: every 60 seconds the time returned
by epicsTimeGetCurrent() and date() freezes at the same value for 15
seconds!  This means that record time stamps will be identical for 15
seconds even if the record is processing at 10Hz, and that any software
that depends on calculating a delta time will get 0 during that 15
second period each minute.

In my case it meant that the integral term in a PID calculation was not
updating correctly for 15 seconds every minute, causing the
monochromator to lose feedback lock.  It also caused OMS motors to be in
the MOVING state for up to 15 seconds before they actually moved at all.
There are probably lots of other bad things that can happen.

Apply the patch if you are using 3.14.10 on vxWorks or RTEMS!

Mark



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