Re: Timestamp test questions on Linux

[Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov>]

On 3/17/22 19:01, gjzhai at mail.ustc.edu.cn wrote:
> The R&S®SMB100A microwave signal generator outputs 1Hz pulses to the EVG. I select the source of event 125 from front panel input 0.

What you describe is exactly what I would expect if the ~1Hz signal originates
from a free running oscillator which is different to that used for the system
clock.

Unless your signal generator and system clock are ultimately derived from, or
synchronized to, the same reference oscillator (eg. GPS or similar) one will
always drift with respect to the other.


What is usually done is to have a GPS receiver with both an electrical 1Hz
output (often called Pulse Per Second), and a logical connection to an NTP
server.  Devices like this are available from multiple vendors.  Some
examples (which I don't specifically endorse):

https://www.meinbergglobal.com/english/productinfo/gps-time-server.htm

https://www.microsemi.com/product-directory/synchronization-systems/3818-enterprise-network-time-servers

https://endruntechnologies.com/products/ntp-time-servers/ntp-server


> epics> dbpf("TST{evg:1-TrigEvt:0}TrigSrc-Sel","Front0")
> DBR_STRING:          "Front0"
> epics> dbpf("TST{evg:1}1ppsInp-Sel","1")
> DBR_STRING:          "Front0"
> epics> dbpf("TST{evg:1}1ppsInp-MbbiDir_.TPRO","1")
> DBR_UCHAR:          1         0x1
>
>
> > -----原始邮件-----
> > 发件人: "Michael Davidsaver" <mdavidsaver at gmail.com>
> > 发送时间: 2022-03-09 15:05:05 (星期三)
> > 收件人: gjzhai at mail.ustc.edu.cn
> > 抄送: tech-talk at aps.anl.gov
> > 主题: Re: Timestamp test questions on Linux
> >
> > On 3/7/22 00:47, gjzhai--- via Tech-talk wrote:
> > > Hello！
> > >
> > > I installed mrfioc2 2.3.0 on MTCA platform. According to EVR Usage Guide, when I do the timestamp test, there are two problems：
> >
> > Could you describe your setup in more detail?
> >
> > Where does the 1Hz (aka. 1 pulse per second) signal to the EVG
> > originate?  The same GPS receiver as the NTP server in question?
> >
> > https://github.com/epics-modules/mrfioc2/blob/a8cb48d549b7aae13206cf2d168c6f1cfec2e1c4/evgMrmApp/Db/evgMrm.db#L93
> >
> > > a. The system is configured with NTP, but the current time provider does not have NTP
> > >
> > > [opi@localhost ~]$ ntpstat
> > > synchronised to NTP server (202.38.64.7) at stratum 3
> > >      time correct to within 11 ms
> > >      polling server every 512 s
> > >
> > > b. The time interval between the system clock and the EVR time is large.
> > >
> > > epics> generalTimeReport(2) Backwards time errors prevented 446106 times. Current Time Providers: "EVR", priority = 50 Current Time is 2022-03-07 16:34:25.575015. "OS Clock", priority = 999 Current Time is 2022-03-07 16:36:55.978638. Event Time Providers: "EVR", priority = 50
> > >
> > >
> > > Thank you for your time. I am looking forward to your reply.