Re: [Linuxptp-users] Building a PTP grandmaster with disciplined oscillator

[Andre P. <and...@sr...>]

Hi Axel,

On 10/3/22 21:23, Axel Simon wrote:
> Your subject has "disciplined oscillator" in it. That sounds like you want ptp4l to carry the time forward while there is no GPS reception. Thus, it seems that you have a setup where your GPS receive does not have a lock to GPS at all times.

Not quite. But perhaps my explanation wasn't sufficient. What I have is 
an external device that is GPS synced and has 10MHz/1PPS output. Even if 
it's not GPS locked, the oscillator is much better and so the 1PPS 
output will be stable.

What I am actually interested in is using the 1 PPS reference and 
discipline the NIC's oscillator.

I am still not quite sure to which extend this would improve the 
timestamp accuracy.


> We found that ptp4l can only synchronize NIC clocks (e.g. i210) to an accuracy of ~2µs due to the latency PCIe transactions. If you want better synchronization, ptp4l with off-the-shelf NICs is not a solution.

Interesting. For my application (telecom) I definitely need accuracy in 
the range of 1.5us.

In your statement, are you referring to off-the-shelf NICs acting as 
slaves or master?
Also, are you referring to unmodified off-the-shelf NICs or modified, 
i.e. disciplined or equipped with higher quality oscillators?

Thanks
Andre

> 
> Cheers,
> Axel
> 
>>
>>> However, making a reliable GM product is quite a bit of work.  The PTP
>>> software stack is only one piece of the puzzle.
>>
>> Yes of course. This effort is just to develop a poor man's GM as a PoC.
>>
>> But nonetheless interesting to observe that there is practically no NIC out there that brings together all the pieces. Should be quite easy to do. Cards like the Intel XXV710-DA2T or E810-XXVDA4T with GPS input are hard to get and $$$.
>>
>> Thanks
>> Andre
>>
>>
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> 


-- 
Andre Puschmann

Software Radio Systems (SRS)
https://www.srs.io
an...@sr...

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