[ntp:questions] A proposal to use NIC launch time support to improve NTP
jwalck at netnod.se
Thu Dec 13 10:00:57 UTC 2012
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On 12/13/2012 03:52 AM, Brian Utterback wrote:
> On 12/12/2012 8:57 PM, Rick Jones wrote:
>> It would seem that at least one NIC has the ability to allow one
>> to "schedule" the time at which a packet will be transmitted.
>> This is called "launch time support." Someone in Linux-land has
>> started asking about the prospect of enabling support of that in
>> the stack, with his stated use case being to improve the jitter
>> of NTP-based timekeeping.
>> The initial posting can be found at:
>> rick jones
> This is going to be very hard to get it to be useful. Looking at
> the specs for the card, the timestamp you give is relative to a
> clock that is internal to the controller, and is only accurate to
> the nearest second. That is, it is like the PPS in that it is
> assumed that the clock is in sync to within .5 seconds to avoid
> aliasing the timestamp.
The internal clock of the network controller is the PHC for IEEE1588,
it has a 1 ns resolution, and can be steered with a 32 bit fractional
of 1 ns. see SYSTIML and TIMINCA in the I210 datasheet.
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