[time-nuts] ``direct'' RS-232 vs. RS-232 via USB vs. PPS decoding cards

Christopher Hoover ch at murgatroid.com
Thu Feb 16 22:38:31 EST 2017

On Thu, Feb 16, 2017 at 10:42 AM, Christopher Hoover <ch at murgatroid.com>

> Ntp has support to pick up hardware packet timestamps from the Linux
> kernel.   I wrote the patch; it was merged years ago.
I'm wrong about this.

The patch I wrote added support for SO_TIMESTAMPNS (see [1]).    With
SO_TIMESTAMPNS, the kernel puts the timestamp on the packet just after the
driver hands it to the receive path.

There's a newer interface, SO_TIMESTAMPING, for access to NIC hardware
timestamps.    There's no support it on the ntp head for this AFAICT.
 The necessary patch looks straightforward, but I don't think I have the
hardware to test it.

-- Christopher
73 de AI6KG.

[1] https://www.kernel.org/doc/Documentation/networking/timestamping.txt

-c73 de AI6KG
> On Thu, Feb 16, 2017 at 9:59 AM, Denny Page <denny at cococafe.com> wrote:
>> If your Ethernet chipset (mac or phy) has timestamping capabilities, you
>> can use Chrony which has hardware timestamp support. This greatly improves
>> accuracy, and generally eliminates the CPU loading issue.
>> Denny
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