In regards to the comment about whether a negative value should be acceptable, I think it should not. The reason is because I can't think of any scenario in which hardware timestamps the packet *before* it arrives... That is, there should never be a hardware which negative latency as that is physically not possible.
Regards, Jake > -----Original Message----- > From: Richard Cochran [mailto:richardcoch...@gmail.com] > Sent: Tuesday, December 09, 2014 12:55 PM > To: linuxptp-devel@lists.sourceforge.net > Subject: [Linuxptp-devel] [PATCH RFC V2 0/4] Time stamp asymmetry > correction > > * ChangeLog > ** V2 > - rename the configuration options to match those in the standards > > Most (or all?) hardware provides time stamps that are offset from the > actual point at the reference plane. The amount of delay is asymmetrical > between ingress and egress, and depending on the particular technology, > MAC or PHY, and link speed, there can be jitter in the delay. > > Sometimes the manufacturer specifies the amount of expected delay. This > patch series provides a way for the user to correct the delays based on > values from the data sheet or based on empirical data. > > This series was tested with an i210 paired with a dp83640 using a short > cable. These devices have their delay values listed in the data sheet. > PPS signals in both directions showed a remaining offset of about 120 > nanoseconds, which matches the sum of uncertainties (40 and 80) given > for the i210 card at the 100 MBit link speed. > > Comments are welcome. > > Thanks, > Richard > > > Richard Cochran (4): > Introduce a helper function to identify valid (non-zero) time stamps. > Invoke the clock check even if the time stamp nanoseconds field is > zero. > config: Introduce options for correcting transmit and receive delays. > port: correct transmit and receive time stamps for their calibrated > delays. > > config.c | 12 ++++++++++++ > default.cfg | 2 ++ > ds.h | 2 ++ > gPTP.cfg | 2 ++ > msg.c | 2 +- > msg.h | 10 ++++++++++ > port.c | 35 ++++++++++++++++++++++++++++++++--- > ptp4l.8 | 12 ++++++++++++ > ptp4l.c | 2 ++ > 9 files changed, 75 insertions(+), 4 deletions(-) > > -- > 1.7.10.4 > > > ------------------------------------------------------------------------------ > Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server > from Actuate! Instantly Supercharge Your Business Reports and Dashboards > with Interactivity, Sharing, Native Excel Exports, App Integration & more > Get technology previously reserved for billion-dollar corporations, FREE > http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg. > clktrk > _______________________________________________ > Linuxptp-devel mailing list > Linuxptp-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/linuxptp-devel ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=164703151&iu=/4140/ostg.clktrk _______________________________________________ Linuxptp-devel mailing list Linuxptp-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
