Re: [chrony-users] Chrony not taking SOCKET data from Application

[sarveshwar k <sarveshwar.kt@xxxxxxxxx>]

Hi Miroslav Lichvar,

Can I use pps directive to a PPS refclock?

refclock PPS /dev/pps1 poll 0 pps lock GPS refid PPS trust prefer

Will this increase the accuracy?

I am using below refclocks:

refclock PPS /dev/pps1 poll 0 lock GPS refid PPS trust prefer

refclock SOCK /var/run/chrony/udssocket.sock poll 0 refid GPS noselect

As we are using GPS and 1PPS, our assumption is chrony synchronizes system clock with nanosecond level accuracy. Am I right on this? But we see microsecond level accuracy even after using makestep directive..

Thanks & Regards

Sarveshwar.K

On Mon, Feb 20, 2023 at 3:56 PM sarveshwar k <sarveshwar.kt@xxxxxxxxx> wrote:

Hi Miroslav,

Thanks for the information.

>My question would be, why do you need the system clock to be so
>accurate? The CPU is connected to the outside world over PCIe, which
>has latency and possibly also asymmetry in hundreds of nanoseconds.
>What do you do on that computer that this accuracy would make a
>difference?

This system clock is being used by other applications like IMU sensor data timestamping. 

We are having this chrony running in an ECU (Electronic Control Unit) along with PTP stack to send PTP packets to other ECUs in the network to get synced to Master ECU.

Thanks & Regards

Sarveshwar.K

On Thu, Feb 16, 2023 at 1:59 PM Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:

On Thu, Feb 16, 2023 at 10:04:02AM +0530, sarveshwar k wrote:
> Is it not possible to achieve synchronization accuracy less than 100ns with
> chrony (with GPS and 1PPS).

With HW timestamping of the PPS signal (e.g. on the I210) it is
possible, but difficult to verify.

My question would be, why do you need the system clock to be so
accurate? The CPU is connected to the outside world over PCIe, which
has latency and possibly also asymmetry in hundreds of nanoseconds.
What do you do on that computer that this accuracy would make a
difference?

> Can we configure chrony behaving as a measurement tool (not to make any
> corrections)?

There is the chronyd -x option or the refclock noselect option for
that.

--
Miroslav Lichvar


--
To unsubscribe email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
with "unsubscribe" in the subject.
For help email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
with "help" in the subject.
Trouble?  Email listmaster@xxxxxxxxxxxxxxxxxxxx.