[time-nuts] Re: Silicom PCIe timestamping network cards
Bob kb8tq writes: > 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. That is the clock-supply to the 82599 chip, but there is a boatload of PLL'ery going on such an ethernet chip. I can't remember the details, but I /think/ a 10GB ethernet runs as two independent simplex lines. If so, that 25MHz will only go to the TX side, the RX side will run at whatever frequency the other end supplies. Unless the other end is a PTP-aware switch which does clock slaving from the upstream port and ... To be honest the entire PTP and White Rabbit thing has gone ... ehh ... time-nuttery :-) -- 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] Re: Silicom PCIe timestamping network cards
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/s1.5625 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. -- 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] Re: Silicom PCIe timestamping network cards
John Miller via time-nuts writes: > I'm curious if anyone here knows much about these silicom timestamping > network interfaces? I used the i82599 ethernet chip ten years ago, to measure time in the first Adaptive Optics Real-Time Computer prototype we built for ESO's ELT telescope. I have revision 2.73 of the datasheet (930 pages), but that is probably publically available theses days in a newer revision. The timestamping counter gets its clock from the ethernet line signals, and the counting frequency therefore depends on the ethernet speed: 100 Mb/s1.5625 MHz 1 Gb/s 15.625 MHz 10 Gb/s 156.25 MHz (The 8ns timestamping mentioned must be something outside the 82599) The basic idea is that you can measure the line frequency with the PPS and timestamp PTP ethernet packets TX and RX relative to the PPS. The card is quite picky about which packets it will timestamp, in particular some of the message bytes must look "enough" like a PTP packet to be timestamped. I figured it out eventually, and Intel promised to update the data-sheet. I have not tried to use the 1PPS signal input, it was not available on the cards we used back then and we only needed relative packet timestamps. I am not sure what it would take to produce a 10G ethernet signal from a "house standard", it may not be trivial. So if you want to build a really good PTP server, yes, go for it, but it is not much use for more advanced time-nuttery. -- 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
Re: [time-nuts] Resampling/decimating (was: Frequency standards for different tau in Allen Dev measurement)
In message <20200224172030.8fe69e686dfb1c2f08b7a...@kinali.ch>, Attila Kinali via time-nuts writes: >On Fri, 21 Feb 2020 12:09:53 -0800 >"Gary E. Miller via time-nuts" wrote: > >> Anyone have any references to how to decimate properly? > >(Disclaimer: This is not my forte and I only know the basics, >so take with a grain of salt) I can highly recommend this free book: http://www.dspguide.com/ -- 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, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
