[time-nuts] Re: Silicom PCIe timestamping network cards

[Poul-Henning Kamp]

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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/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)

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
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FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.