Hi > On Jul 4, 2022, at 10:04 AM, Poul-Henning Kamp via time-nuts > <time-nuts@lists.febo.com> wrote: > > -------- > Poul-Henning Kamp via time-nuts writes: > >> The timestamping counter gets its clock from the ethernet line >> signals, and the counting frequency therefore depends on the ethernet >> speed: >> >> 100 Mb/s 1.5625 MHz >> 1 Gb/s 15.625 MHz >> 10 Gb/s 156.25 MHz >> >> (The 8ns timestamping mentioned must be something outside the 82599) > > I should probably expand on this to prevent misunderstandings: > > The 82599 chip will timestamp with 6.4ns resolution, and since both > the frequency and the timestamp edge is derived from the ethernet > signal when you time packets, there is no noise process involved, > and you do get your full 6.4ns worth. > > I understand the "8ns" number in the datasheet for the card to refer > to the PPS input and assume the extra 1.5ns to be noise in the > analog domain outside the i82599 chip.
Could be. They also mention a 25 MHz clock on the card. That could get you to a 125 MHz time base with a 8 ns resolution. Again, without a deep dive into what they did … who knows. Bob > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > p...@freebsd.org | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by incompetence. > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
