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

[Poul-Henning Kamp]

--------
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 :-)


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Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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