Yo Hal! On Mon, 22 Mar 2021 14:24:50 -0700 Hal Murray <hmur...@megapathdsl.net> wrote:
> Gary said: > > You could try PTP. The linuxptp project is active. With ethernet > > cards that support hardware time stamps you can get 1 micro second > > offsets, maybe a lot better. > > Thanks. Could you say a bit more. > > If I start with 4 PCs plugged into a low end 5 port switch, what else > do I need to make a working PTP setup? Linuxptp and ntpd, that is it. linuxptp writes a SHM that ntpd reads. The net will select one of its own as a grandmaster, or you can force that. There web site has instructions to build, install and run: http://linuxptp.sourceforge.net/ Source code: http://sourceforge.net/projects/linuxptp/files/latest/download The people on their email list are helpfulL https://lists.sourceforge.net/lists/listinfo/linuxptp-devel > Do I have to buy a fancy GrandMaster or can one of the PCs serve that > function? Nah. The "best" is slected automagically. Or force your best GPS PPS steered host as "grandmaster". > Low cost switches aren't going to update any packets. Will that > screw things up if the reason I want the clocks in sync is to measure > network queuing delays when there is a lot of network traffic? Well, anything that uses the network to mesaure your network has that probblem. If you are worried, turn it upside down: set every host from GPS PPS, and use PTP to measure their offsets. > Is there a HOWTO for getting started? Many: https://lmgtfy.app/?q=linuxptp+howto > Since you mentioned PTP, can we use the PTP (IEEE 1588) time stamping > stuff to get better time stamps for NTP packets? (without dragging in > any/much PTP stuff) Yes, but not easily. Some ethernic nics that support hardware PTP have a PPS input. So they can sync to PPS in hardwre. An advanced topic best discussed on the linuxptp list. Most consumer nics do not support any hardware stamping. The middle and upper range Intel nics do. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can't measure it, you can't improve it." - Lord Kelvin
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