Hello Richard, We implemented this correction in our driver using a private IOCTL and it would have been nice to have used some standardised interface instead. However, I think timestamp correction belongs in the PHY’s driver (or whatever is doing the times-tamping). Data sheets report expected delays so defaults can be automatic and the corrections can be changed automatically according to link-speed for instance. There should also be a standardised mechanism to update correction offsets at runtime as a fallback mechanism when defaults are not good enough.
Having said that, having TX/RX timestamps correction also in linuxptp is a good idea! My comments: (1) In some cases is not acceptable to restart linuxptp, so being able to change the correction at runtime would be useful. This could be added later. (2) For some reason I would prefer (but not strongly) adding a signed correction offset in both the egress and ingress directions instead of adding in one direction and subtracting in the other. Thanks -- Delio On 06 Dec 2014, at 22:59, Richard Cochran <richardcoch...@gmail.com> wrote: > 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. > > In theory one could place the sum of the correction factors into the > delayAsymmetry field. However, the standard specifies that the slave > applies this correction field, and never the master. Having these two > new correction fields allows each node to compensate for its own part > of the offset error. > > 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
