Experimental Physics and
Industrial Control System
| 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 <2018> 2019 2020 2021 2022 2023 2024 | Index | 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 <2018> 2019 2020 2021 2022 2023 2024 |
| <== Date ==> | <== Thread ==> |
|---|
| Subject: | RE: Latency between NI LabVIEW RT (cRIO) and EPICS on RT Linux |
| From: | Mark Rivers <[email protected]> |
| To: | "'Mooney, Tim M.'" <[email protected]>, "'Johannes Spinneken (EGI)'" <[email protected]>, "'[email protected]'" <[email protected]> |
| Date: | Fri, 9 Feb 2018 13:14:12 +0000 |
|
Hi Johannes, I was curious about what could be obtained in a test that is more similar to what you are asking, where there is an exchange of messages between an EPICS client and server. I did another test, this time with IOCs running on 2 different Linux machines. Each IOC is both a Channel Access client and a Channel Access server. Machine 1 runs this database: record(calc, "Calc1") { field(INPA, "Calc2 CP") field(CALC, "A+1") } Machine 2 runs this database record(calc, "Calc2") { field(INPA, "Calc1 CP") field(CALC, "A+1") } Note that the INPA field has the CP property, meaning that calc record will process whenever it receives a Channel Access monitor on its input PV. So the way it works is that Calc1 increments its value, Calc2 receives a monitor for that
and increments its value, which in turn causes Calc1 to receive a monitor and increment its value, etc. There is thus an exchange of messages as fast as possible. It will be limited by the overhead in CA writes, CA monitor reception, processing the records,
and network latency. Here is the result of running camonitor in both records over a 10 ms time interval. The Calc1 record incremented from 910732 to 910948 in this time, or a difference of 216. It increments by 2 for each round-trip exchange, so there were
108 round trips. Since this was over a period of 10 ms that means that the round-trip time was about 92 microseconds. So the 10 ms time you are seeing is definitely not limited by EPICS Channel Access, record processing, or network overhead, it is something specific to your system! corvette> camonitor Calc1 Calc2 … Calc1 2018-02-09 06:51:09.779757 910732 Calc2 2018-02-09 06:51:09.780078 910733 Calc1 2018-02-09 06:51:09.779837 910734 Calc2 2018-02-09 06:51:09.780161 910735 Calc1 2018-02-09 06:51:09.779919 910736 Calc2 2018-02-09 06:51:09.780242 910737 Calc1 2018-02-09 06:51:09.780001 910738 Calc2 2018-02-09 06:51:09.780325 910739 Calc1 2018-02-09 06:51:09.780082 910740 Calc2 2018-02-09 06:51:09.780409 910741 Calc1 2018-02-09 06:51:09.780175 910742 Calc2 2018-02-09 06:51:09.780494 910743 Calc1 2018-02-09 06:51:09.780250 910744 Calc2 2018-02-09 06:51:09.780576 910745 Calc1 2018-02-09 06:51:09.780331 910746 Calc1 2018-02-09 06:51:09.780411 910748 Calc2 2018-02-09 06:51:09.780655 910747 Calc1 2018-02-09 06:51:09.780495 910750 Calc2 2018-02-09 06:51:09.780739 910749 Calc2 2018-02-09 06:51:09.780818 910751 Calc1 2018-02-09 06:51:09.780578 910752 Calc2 2018-02-09 06:51:09.780903 910753 Calc1 2018-02-09 06:51:09.780661 910754 Calc2 2018-02-09 06:51:09.780983 910755 Calc1 2018-02-09 06:51:09.780744 910756 Calc2 2018-02-09 06:51:09.781065 910757 Calc1 2018-02-09 06:51:09.780824 910758 Calc2 2018-02-09 06:51:09.781148 910759 Calc1 2018-02-09 06:51:09.780902 910760 Calc2 2018-02-09 06:51:09.781229 910761 Calc1 2018-02-09 06:51:09.780984 910762 Calc2 2018-02-09 06:51:09.781307 910763 Calc1 2018-02-09 06:51:09.781066 910764 Calc2 2018-02-09 06:51:09.781388 910765 Calc1 2018-02-09 06:51:09.781148 910766 Calc2 2018-02-09 06:51:09.781473 910767 Calc1 2018-02-09 06:51:09.781232 910768 Calc2 2018-02-09 06:51:09.781556 910769 Calc1 2018-02-09 06:51:09.781315 910770 Calc2 2018-02-09 06:51:09.781634 910771 Calc1 2018-02-09 06:51:09.781394 910772 Calc2 2018-02-09 06:51:09.781719 910773 Calc1 2018-02-09 06:51:09.781479 910774 Calc2 2018-02-09 06:51:09.781802 910775 Calc1 2018-02-09 06:51:09.781559 910776 Calc2 2018-02-09 06:51:09.781883 910777 Calc1 2018-02-09 06:51:09.781642 910778 Calc2 2018-02-09 06:51:09.781965 910779 Calc1 2018-02-09 06:51:09.781726 910780 Calc2 2018-02-09 06:51:09.782060 910781 Calc1 2018-02-09 06:51:09.781825 910782 Calc2 2018-02-09 06:51:09.782160 910783 Calc1 2018-02-09 06:51:09.781917 910784 Calc2 2018-02-09 06:51:09.782239 910785 Calc1 2018-02-09 06:51:09.781997 910786 Calc2 2018-02-09 06:51:09.782321 910787 Calc1 2018-02-09 06:51:09.782078 910788 Calc2 2018-02-09 06:51:09.782401 910789 Calc1 2018-02-09 06:51:09.782158 910790 Calc2 2018-02-09 06:51:09.782479 910791 Calc1 2018-02-09 06:51:09.782235 910792 Calc2 2018-02-09 06:51:09.782580 910793 Calc1 2018-02-09 06:51:09.782338 910794 Calc2 2018-02-09 06:51:09.782705 910795 Calc1 2018-02-09 06:51:09.782461 910796 Calc2 2018-02-09 06:51:09.782827 910797 Calc1 2018-02-09 06:51:09.782591 910798 Calc2 2018-02-09 06:51:09.782953 910799 Calc1 2018-02-09 06:51:09.782712 910800 Calc2 2018-02-09 06:51:09.783078 910801 Calc1 2018-02-09 06:51:09.782836 910802 Calc2 2018-02-09 06:51:09.783204 910803 Calc1 2018-02-09 06:51:09.782962 910804 Calc2 2018-02-09 06:51:09.783328 910805 Calc1 2018-02-09 06:51:09.783086 910806 Calc2 2018-02-09 06:51:09.783451 910807 Calc1 2018-02-09 06:51:09.783209 910808 Calc2 2018-02-09 06:51:09.783576 910809 Calc1 2018-02-09 06:51:09.783333 910810 Calc2 2018-02-09 06:51:09.783699 910811 Calc1 2018-02-09 06:51:09.783456 910812 Calc2 2018-02-09 06:51:09.783826 910813 Calc1 2018-02-09 06:51:09.783590 910814 Calc2 2018-02-09 06:51:09.783951 910815 Calc1 2018-02-09 06:51:09.783713 910816 Calc2 2018-02-09 06:51:09.784081 910817 Calc1 2018-02-09 06:51:09.783859 910818 Calc2 2018-02-09 06:51:09.784212 910819 Calc1 2018-02-09 06:51:09.783990 910820 Calc2 2018-02-09 06:51:09.784325 910821 Calc1 2018-02-09 06:51:09.784084 910822 Calc2 2018-02-09 06:51:09.784448 910823 Calc1 2018-02-09 06:51:09.784206 910824 Calc2 2018-02-09 06:51:09.784570 910825 Calc1 2018-02-09 06:51:09.784333 910826 Calc2 2018-02-09 06:51:09.784695 910827 Calc1 2018-02-09 06:51:09.784453 910828 Calc2 2018-02-09 06:51:09.784819 910829 Calc1 2018-02-09 06:51:09.784583 910830 Calc2 2018-02-09 06:51:09.784944 910831 Calc1 2018-02-09 06:51:09.784701 910832 Calc2 2018-02-09 06:51:09.785074 910833 Calc1 2018-02-09 06:51:09.784831 910834 Calc2 2018-02-09 06:51:09.785222 910835 Calc1 2018-02-09 06:51:09.785000 910836 Calc2 2018-02-09 06:51:09.785338 910837 Calc1 2018-02-09 06:51:09.785100 910838 Calc2 2018-02-09 06:51:09.785456 910839 Calc1 2018-02-09 06:51:09.785213 910840 Calc2 2018-02-09 06:51:09.785565 910841 Calc1 2018-02-09 06:51:09.785320 910842 Calc2 2018-02-09 06:51:09.785690 910843 Calc1 2018-02-09 06:51:09.785444 910844 Calc2 2018-02-09 06:51:09.785816 910845 Calc1 2018-02-09 06:51:09.785572 910846 Calc2 2018-02-09 06:51:09.785941 910847 Calc1 2018-02-09 06:51:09.785697 910848 Calc2 2018-02-09 06:51:09.786072 910849 Calc1 2018-02-09 06:51:09.785862 910850 Calc2 2018-02-09 06:51:09.786195 910851 Calc1 2018-02-09 06:51:09.785971 910852 Calc2 2018-02-09 06:51:09.786303 910853 Calc1 2018-02-09 06:51:09.786063 910854 Calc2 2018-02-09 06:51:09.786385 910855 Calc1 2018-02-09 06:51:09.786142 910856 Calc2 2018-02-09 06:51:09.786463 910857 Calc1 2018-02-09 06:51:09.786218 910858 Calc2 2018-02-09 06:51:09.786544 910859 Calc1 2018-02-09 06:51:09.786303 910860 Calc2 2018-02-09 06:51:09.786627 910861 Calc1 2018-02-09 06:51:09.786392 910862 Calc2 2018-02-09 06:51:09.786714 910863 Calc1 2018-02-09 06:51:09.786473 910864 Calc2 2018-02-09 06:51:09.786796 910865 Calc1 2018-02-09 06:51:09.786554 910866 Calc2 2018-02-09 06:51:09.786875 910867 Calc1 2018-02-09 06:51:09.786635 910868 Calc2 2018-02-09 06:51:09.786956 910869 Calc1 2018-02-09 06:51:09.786716 910870 Calc2 2018-02-09 06:51:09.787037 910871 Calc1 2018-02-09 06:51:09.786801 910872 Calc2 2018-02-09 06:51:09.787122 910873 Calc1 2018-02-09 06:51:09.786883 910874 Calc2 2018-02-09 06:51:09.787204 910875 Calc1 2018-02-09 06:51:09.786965 910876 Calc2 2018-02-09 06:51:09.787285 910877 Calc1 2018-02-09 06:51:09.787047 910878 Calc2 2018-02-09 06:51:09.787373 910879 Calc1 2018-02-09 06:51:09.787133 910880 Calc2 2018-02-09 06:51:09.787455 910881 Calc1 2018-02-09 06:51:09.787214 910882 Calc2 2018-02-09 06:51:09.787538 910883 Calc1 2018-02-09 06:51:09.787299 910884 Calc2 2018-02-09 06:51:09.787623 910885 Calc1 2018-02-09 06:51:09.787379 910886 Calc2 2018-02-09 06:51:09.787701 910887 Calc1 2018-02-09 06:51:09.787458 910888 Calc2 2018-02-09 06:51:09.787782 910889 Calc1 2018-02-09 06:51:09.787538 910890 Calc2 2018-02-09 06:51:09.787863 910891 Calc1 2018-02-09 06:51:09.787624 910892 Calc2 2018-02-09 06:51:09.787948 910893 Calc1 2018-02-09 06:51:09.787705 910894 Calc2 2018-02-09 06:51:09.788025 910895 Calc1 2018-02-09 06:51:09.787786 910896 Calc2 2018-02-09 06:51:09.788112 910897 Calc1 2018-02-09 06:51:09.787869 910898 Calc2 2018-02-09 06:51:09.788192 910899 Calc1 2018-02-09 06:51:09.787949 910900 Calc2 2018-02-09 06:51:09.788273 910901 Calc1 2018-02-09 06:51:09.788030 910902 Calc2 2018-02-09 06:51:09.788352 910903 Calc1 2018-02-09 06:51:09.788108 910904 Calc2 2018-02-09 06:51:09.788432 910905 Calc1 2018-02-09 06:51:09.788189 910906 Calc2 2018-02-09 06:51:09.788513 910907 Calc1 2018-02-09 06:51:09.788270 910908 Calc2 2018-02-09 06:51:09.788594 910909 Calc1 2018-02-09 06:51:09.788352 910910 Calc2 2018-02-09 06:51:09.788673 910911 Calc1 2018-02-09 06:51:09.788429 910912 Calc2 2018-02-09 06:51:09.788754 910913 Calc1 2018-02-09 06:51:09.788510 910914 Calc2 2018-02-09 06:51:09.788841 910915 Calc1 2018-02-09 06:51:09.788599 910916 Calc2 2018-02-09 06:51:09.788921 910917 Calc1 2018-02-09 06:51:09.788682 910918 Calc2 2018-02-09 06:51:09.789001 910919 Calc1 2018-02-09 06:51:09.788757 910920 Calc2 2018-02-09 06:51:09.789081 910921 Calc1 2018-02-09 06:51:09.788837 910922 Calc2 2018-02-09 06:51:09.789162 910923 Calc1 2018-02-09 06:51:09.788919 910924 Calc2 2018-02-09 06:51:09.789245 910925 Calc1 2018-02-09 06:51:09.789000 910926 Calc2 2018-02-09 06:51:09.789324 910927 Calc1 2018-02-09 06:51:09.789080 910928 Calc2 2018-02-09 06:51:09.789404 910929 Calc1 2018-02-09 06:51:09.789162 910930 Calc2 2018-02-09 06:51:09.789485 910931 Calc1 2018-02-09 06:51:09.789241 910932 Calc2 2018-02-09 06:51:09.789566 910933 Calc1 2018-02-09 06:51:09.789328 910934 Calc2 2018-02-09 06:51:09.789645 910935 Calc1 2018-02-09 06:51:09.789401 910936 Calc2 2018-02-09 06:51:09.789725 910937 Calc1 2018-02-09 06:51:09.789483 910938 Calc2 2018-02-09 06:51:09.789806 910939 Calc1 2018-02-09 06:51:09.789562 910940 Calc2 2018-02-09 06:51:09.789886 910941 Calc1 2018-02-09 06:51:09.789646 910942 Calc2 2018-02-09 06:51:09.789965 910943 Calc1 2018-02-09 06:51:09.789722 910944 Calc2 2018-02-09 06:51:09.790046 910945 Calc1 2018-02-09 06:51:09.789803 910946 Calc2 2018-02-09 06:51:09.790127 910947 Calc1 2018-02-09 06:51:09.789882 910948 Calc2 2018-02-09 06:51:09.790208 910949 Mark From: Mark Rivers
Hi Johannes, Here is one quick measurement. -
I have an areaDetector simDetector running on a Linux machine. It has a small image size (50x50) so it can run very fast. It is doing about 5,500 frames/s. -
There is an image counter PV that updates each time there is a new image, i.e. at 5,500 Hz. -
I ran “camonitor” on a different Linux machine to see how fast it received the monitor updates on that PV. I used –tcs so we see both the CA client timestamps and the CA server timestamps. I sent the camonitor output to a file so the
terminal I/O would not slow it down. -
Both of these machines have 10GB Ethernet connections. This is the result, covering a time period of about 10 ms. Viper:~>camonitor -tcs 13SIM1:cam1:ArrayCounter_RBV > test.out ^C Viper:~>more test.out 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.602116(2018-02-06 14:34:30.602287) 4182302 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.602320(2018-02-06 14:34:30.602489) 4182303 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.602505(2018-02-06 14:34:30.602611) 4182304 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.602696(2018-02-06 14:34:30.602888) 4182305 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.602899(2018-02-06 14:34:30.603005) 4182306 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.603127(2018-02-06 14:34:30.603238) 4182307 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.603344(2018-02-06 14:34:30.603470) 4182308 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.603536(2018-02-06 14:34:30.603642) 4182309 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.603727(2018-02-06 14:34:30.603838) 4182310 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.603899(2018-02-06 14:34:30.604019) 4182311 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.604109(2018-02-06 14:34:30.604228) 4182312 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.604318(2018-02-06 14:34:30.604440) 4182313 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.604506(2018-02-06 14:34:30.604606) 4182314 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.604692(2018-02-06 14:34:30.604842) 4182315 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.604884(2018-02-06 14:34:30.605005) 4182316 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.605076(2018-02-06 14:34:30.605206) 4182317 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.605260(2018-02-06 14:34:30.605363) 4182318 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.605427(2018-02-06 14:34:30.605539) 4182319 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.605613(2018-02-06 14:34:30.605725) 4182320 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.605795(2018-02-06 14:34:30.605919) 4182321 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.605966(2018-02-06 14:34:30.606132) 4182322 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.606149(2018-02-06 14:34:30.606265) 4182323 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.606319(2018-02-06 14:34:30.606431) 4182324 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.606479(2018-02-06 14:34:30.606594) 4182325 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.606611(2018-02-06 14:34:30.606727) 4182326 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.606820(2018-02-06 14:34:30.606917) 4182327 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.607015(2018-02-06 14:34:30.607116) 4182328 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.607186(2018-02-06 14:34:30.607287) 4182329 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.607363(2018-02-06 14:34:30.607459) 4182330 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.607542(2018-02-06 14:34:30.607643) 4182331 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.607732(2018-02-06 14:34:30.607841) 4182332 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.607914(2018-02-06 14:34:30.608016) 4182333 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.608100(2018-02-06 14:34:30.608202) 4182334 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.608252(2018-02-06 14:34:30.608355) 4182335 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.608432(2018-02-06 14:34:30.608532) 4182336 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.608620(2018-02-06 14:34:30.608731) 4182337 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.608801(2018-02-06 14:34:30.608909) 4182338 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.608983(2018-02-06 14:34:30.609098) 4182339 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.609164(2018-02-06 14:34:30.609279) 4182340 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.609341(2018-02-06 14:34:30.609449) 4182341 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.609526(2018-02-06 14:34:30.609625) 4182342 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.609701(2018-02-06 14:34:30.609817) 4182343 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.609877(2018-02-06 14:34:30.609990) 4182344 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.610057(2018-02-06 14:34:30.610185) 4182345 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.610268(2018-02-06 14:34:30.610392) 4182346 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.610454(2018-02-06 14:34:30.610568) 4182347 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.610620(2018-02-06 14:34:30.610739) 4182348 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.610800(2018-02-06 14:34:30.610908) 4182349 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.610988(2018-02-06 14:34:30.611097) 4182350 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.611168(2018-02-06 14:34:30.611289) 4182351 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.611355(2018-02-06 14:34:30.611454) 4182352 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.611536(2018-02-06 14:34:30.611644) 4182353 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.611728(2018-02-06 14:34:30.611834) 4182354 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.611915(2018-02-06 14:34:30.612013) 4182355 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.612084(2018-02-06 14:34:30.612204) 4182356 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.612265(2018-02-06 14:34:30.612388) 4182357 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.612447(2018-02-06 14:34:30.612543) 4182358 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.612619(2018-02-06 14:34:30.612721) 4182359 13SIM1:cam1:ArrayCounter_RBV 2018-02-06 14:34:30.612806(2018-02-06 14:34:30.612915) 4182360 You can see that it does not appear to lose any monitors, and the time between monitors is just under 200 microseconds. So at least in this setup we have not yet hit the EPICS protocol or network speed limits. Mark From:
[email protected] [mailto:[email protected]]
On Behalf Of Mooney, Tim M. Hi Johannes, With an interrupt service routine, vxWorks can read from or write to an IndustryPack FPGA at around 10 kHz, but I would not try to process an EPICS record at that rate - at least not a record that
isn't prepared to throttle the rate at which it posts monitors. I don't usually process general purpose EPICS records faster than around 100 Hz. I think it's pretty common practice to keep stuff faster than around 100 Hz restricted to driver code, which
doesn't really have to know about EPICS. Tim Mooney ([email protected]) (630)252-5417 From:
[email protected] <[email protected]> on behalf of Johannes Spinneken (EGI) <[email protected]> Hi I am fairly new to EPICS and have been testing an application with the following setup:
The setup works in principle, but I am seeing higher latencies than I was expecting. I was hoping to achieve latencies in the low ms order (say 1 – 2ms data round trip
from cRIO to RT Linux back to cRIO). In practice, I observe round-trip timings of order 10ms. Two questions:
(i)
What is the best timing (latency) that can generally be achieved using EPICS? Is there something fundamental in the protocol that prohibits data exchange in the low ms order? I understand that this will of
course depend on target hardware / software, but a ballpark figure would be good as “expectation management”. A typical ping between cRIO and Linux RT takes approx. 0.2ms, so the hardware seems clearly capable of <1ms timings.
(ii)
Does anyone have experience with running EPICS on LabVIEW RT / cRIO? I suspect some (most) of the latency is due to the way in which NI handles TCP traffic. I already discovered that data is normally buffered
for 10ms (or 8 kB). This can be avoided by using the Shared Variable Data Flush VI:
http://zone.ni.com/reference/en-XX/help/371361H-01/lvcomm/flushsharedvar/
which indeed reduced round-trip timings by around 8-10ms. However, I seem to be unable to push timings down further below the 10ms round-trip mark. Any guidance would be much appreciated. Many thanks! Best wishes Johannes Johannes Spinneken PhD FRSA Principal Systems Engineer Evergreen Innovations UK & USA +1 916 266 3709 (US cell) +44 7868 923583 (UK mobile) |
- Replies:
- RE: Latency between NI LabVIEW RT (cRIO) and EPICS on RT Linux Mark Rivers
- References:
- Latency between NI LabVIEW RT (cRIO) and EPICS on RT Linux Johannes Spinneken (EGI)
- Re: Latency between NI LabVIEW RT (cRIO) and EPICS on RT Linux Mooney, Tim M.
- RE: Latency between NI LabVIEW RT (cRIO) and EPICS on RT Linux Mark Rivers
- Navigate by Date:
- Prev: FLNK length limit Hinko Kocevar
- Next: Question about values of historic PVs dislpayed in CSS XY Graph widget lzf neu
- Index: 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 <2018> 2019 2020 2021 2022 2023 2024
- Navigate by Thread:
- Prev: RE: Latency between NI LabVIEW RT (cRIO) and EPICS on RT Linux Mark Rivers
- Next: RE: Latency between NI LabVIEW RT (cRIO) and EPICS on RT Linux Mark Rivers
- Index: 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 <2018> 2019 2020 2021 2022 2023 2024
·
Home
·
News
·
About
·
Base
·
Modules
·
Extensions
·
Distributions
·
Download
·
· Search · EPICS V4 · IRMIS · Talk · Bugs · Documents · Links · Licensing ·