Experimental Physics and
Industrial Control System

"Zhang Yuliang" <[email protected]> · Mon, 6 Jul 2015 10:14:06 +0800 (GMT+08:00)

Hi Ralph,

> Why do you want to change the sync interval?
Originally, i want to improve the accuracy of the vxWorks internal clock by shorter the sync interval. 
Now, based on your reply ,it think maybe it will not impove much.

Another question:
 If the vxWorks clock rate is 60 Hz and measured clock rate is 60.7 Hz, and suppose the networks is ok(ntp client can be synced every time per minute). Is the max deviation less than one tick(16.67ms)?

Regards,
Zhang Yuliang 

> -----原始邮件-----
> 发件人: "Ralph Lange" <[email protected]>
> 发送时间: 2015年7月3日 星期五
> 收件人: "EPICS Tech-Talk" <[email protected]>
> 抄送: "Zhang Yuliang" <[email protected]>
> 主题: Re: setting NTP time sync interval on vxWorks
> 
> Hi Yuliang,
> 
> The NTP sync interval is a compile time constant, thus it cannot be 
> changed at run time.
> 
> One question, though.
> Your time report shows that the measured tick rate is 60.007 Hz, which 
> is a difference of about 2 us per tick, 120 us per second, 7.2 ms per 
> minute. Time resolution is in ticks, i.e. 16.67 ms. That means the NTP 
> sync will skip a single tick in the counter every two or three minutes.
> Why do you want to change the sync interval?
> Setting it longer will make the situation worse: more than one tick will 
> be skipped at larger intervals.
> Setting it shorter will increase network traffic without changing the 
> situation much: a deviation of 7.2 ms per minute will always be 
> corrected by skipping one tick after between two and three minutes.
> 
> Cheers,
> ~Ralph
> 
> 
> On 03/07/2015 10:36, Zhang Yuliang wrote:
> > Hi all,
> >
> > I want to know how to set the NTP time sync interval on vxWorks. The output of "NTPTime_Report 1" shows the default interval is 60 seconds:
> >
> > timingMain>NTPTime_Report 1
> > NTP driver is synchronized with server
> > Syncronization interval = 60.0 seconds
> > Last synchronized at 2015-07-03 16:06:19.062927
> > OS tick rate = 60 Hz (nominal)
> > Measured tick rate = 60.007 Hz
> > NTP Server = 10.1.201.31
> > value = 0 = 0x0
> >
> > I can modify the variable "NTPTimeSyncInterval" in file $(EPICS_BASE)\src\libCom\osi\osiNTPTime.c to change the sync interval. Is there a command can be used in ioc shell?
> >
> > Best regards,
> > Zhang Yuliang
> >
> >
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System