Re: [Linuxptp-users] linuxptp result doesn't match 1PPS measurement
On Fri, Sep 09, 2022 at 08:45:19AM +0800, Hamilton Alex wrote: > Hi, Richard: > I am not quite understand. I am using Calnex master-->board slave, if the > linuxptp print out is correct, that means local clock > has the same frequency and phase as master clock, then the 1PPS out should > near the reference 1PPS. > > why path asymmetry would affect the 1PPS out? You reported a 40 nanosecond phase offset. One possible cause is path asymmetry. The PTP assumes the Tx and Rx transmission delays are exactly equal. However, this is almost never true. Any real asymmetry results in a phase offset that is uncorrectable by the PTP. Because your 40 ns phase offset is very small, you might very well have path asymmetry somewhere in your system. For example, your PHY might delay frames longer on Tx than on Rx. HTH, Richard ___ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
Re: [Linuxptp-users] linuxptp result doesn't match 1PPS measurement
Hi, Richard: I am not quite understand. I am using Calnex master-->board slave, if the linuxptp print out is correct, that means local clock has the same frequency and phase as master clock, then the 1PPS out should near the reference 1PPS. why path asymmetry would affect the 1PPS out? Thanks Alex Richard Cochran 于2022年9月8日周四 21:40写道： > On Thu, Sep 08, 2022 at 07:41:53PM +0800, Hamilton Alex wrote: > > > however, the 1pps time error is around 40 NS, which means my board is > > ahead of the reference for about 40NS, which doesn't match the result > > dumped by ptp4l. > > > > anyone has met similar issue before? how to debug such issue? > > This is likely due to path asymmetry. > > HTH, > Richard > ___ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
Re: [Linuxptp-users] linuxptp result doesn't match 1PPS measurement
On Thu, Sep 08, 2022 at 06:40:26AM -0700, Richard Cochran wrote: > On Thu, Sep 08, 2022 at 07:41:53PM +0800, Hamilton Alex wrote: > > > however, the 1pps time error is around 40 NS, which means my board is > > ahead of the reference for about 40NS, which doesn't match the result > > dumped by ptp4l. > > > > anyone has met similar issue before? how to debug such issue? > > This is likely due to path asymmetry. Oh, and Miroslav is correct, 9 usec path delay is huge. It should be only 5 ns per meter of cable. Good luck, Richard ___ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
Re: [Linuxptp-users] linuxptp result doesn't match 1PPS measurement
On Thu, Sep 08, 2022 at 07:41:53PM +0800, Hamilton Alex wrote: > however, the 1pps time error is around 40 NS, which means my board is > ahead of the reference for about 40NS, which doesn't match the result > dumped by ptp4l. > > anyone has met similar issue before? how to debug such issue? This is likely due to path asymmetry. HTH, Richard ___ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
