Jake, >-----Original Message----- >From: Keller, Jacob E [mailto:[email protected]] >Sent: Wednesday, December 10, 2014 1:00 AM >To: Richard Cochran; [email protected] >Subject: Re: [Linuxptp-devel] [PATCH RFC V2 0/4] Time stamp asymmetry >correction > >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.
We did a few measurements of egress and ingress timestamping delays (see [1]). We actually measured negative delays for some hardware (see Table III in [1]). Our conclusion was that this hardware must already be (over)compensating PHY delays, however I did not yet manage to ask this question to the manufacturer. But it shows that there are cases where one wants to compensate a negative egress or ingress latency. Regards, Christian [1] http://www.riesch.at/christian/ISPCS2013_Measurement_of_egress_and_ingress_delays_of_PTP_clocks.pdf ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
