Talk at Stanford: Nanosecond-level Clock Synchronization in a Data Center

[Achim Gratz]

Hal Murray via devel writes:
> One is the use the PTP style time-stamping available on many modern Ethernet 
> interfaces.  Does anybody know how that works?  API?  I assume there is a 
> counter in the Ethernet hardware.  How does that counter get converted into a 
> time stamp?

Yes, it's a hardware counter and it runs with the local clock of the
interface (you'll typically find a 25MHz quartz next to the ethernet
chip, although for gigabit ethernet that clock is obviously internally
multiplied with a PLL).  The timestamp can be recorded in a register,
attached to the transmit or receive frame memory or even added to the
outgoing packet.  Highlevel API would be PTP for Linux (ptp4l) or
linuxptl, kernel API:

https://www.kernel.org/doc/Documentation/ptp/ptp.txt

Also, Dan drown is again ahead of you… :-)

https://blog.dan.drown.org/apu2-ntp-server-2/

> Their other approach is to collect much more data.  There are a couple of good 
> slides showing the offset with an empty band in the middle.

I'm not going to look at that stuff on YouTube… any link to oldfashioned
non-multimedia?


Regards,
Achim.
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