Re: [Linuxptp-users] One PCs with multiple NICs acting as multiple PTP master / PTP chains
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Re: [Linuxptp-users] One PCs with multiple NICs acting as multiple PTP master / PTP chains
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From: Julien H. <ju...@ya...> - 2014-02-21 13:53:14
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You can try to synchronize several PCs with a standard switch. I measured the delay with one master and one slave and then slightly modified ptp4l with the value obtained (hardcoded). I disabled the delay req messages on the slaves (to avoid messages accumulation on the master side). There is no other traffic on the links. I could measure a delta of a few hundred ns between master and slaves with the oscilloscope and i210 with PPS generation enabled. I use the following schema : |------ netgear GS724T ------ slaves master ---- netgear GS108E |------ netgear GS724T ------ slaves |------ netgear GS724T ------ slaves The result is even better when I use less slaves and a single GS108E (a few tens of ns). But on three GS108E, two give very good results and one is very bad... The best is to test. Julien. ________________________________ De : Richard Cochran <ric...@gm...> À : Koehrer Mathias (ETAS/ESW5) <mat...@et...> Cc : "lin...@li..." <lin...@li...> Envoyé le : Vendredi 21 février 2014 14h33 Objet : Re: [Linuxptp-users] One PCs with multiple NICs acting as multiple PTP master / PTP chains On Fri, Feb 21, 2014 at 01:16:09PM +0000, Koehrer Mathias (ETAS/ESW5) wrote: > Hi all, > > to synchronize a couple (6-8) PCs I want to use one PCs PTP master and the others as PTP slaves. > To interconnect the PCs I can use a PTP capable switch. However these switches are fairly expensive. > The first question I have: How does a "standard" Ethernet switch perform? Which accuracy will be possible if no other traffic is running over the switch but PTP packets? The answer is, it depends. It depends on the switch itself and the amount of traffic through the switch. Usually switches add something like 10 microseconds delay and a few microseconds jitter. I would definitely try this first and just see what kind of RMS numbers come out. > As PC 1 ... PC 7 have two PTP clocks running, these clocks have to be synchronized. > Is this done via phc2sys? If yes, do I have to synchronize directly from PTPx to PTPy or does it work via the PCs System clock? You can use phc2sys to synchronize the PHC clock pairs. However, this will be a PITA to set up, and remember, unless you feed signals from one card to the next, you will be using a kind of software time stamping. Chaining those servos together accumulates the errors. I would guess that the normal switch would perform much better. Try the switch idea first. HTH, Richard ------------------------------------------------------------------------------ Managing the Performance of Cloud-Based Applications Take advantage of what the Cloud has to offer - Avoid Common Pitfalls. Read the Whitepaper. http://pubads.g.doubleclick.net/gampad/clk?id=121054471&iu=/4140/ostg.clktrk _______________________________________________ Linuxptp-users mailing list Lin...@li... https://lists.sourceforge.net/lists/listinfo/linuxptp-users |
