Re: [chrony-users] Is it possible to smooth out jitter caused by USB interface?

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

That is how chrony already works. It uses linear regression on the last N
readings where N gets adjusted so that the quadratic is small. For PPS
measurements, it averages the last R readingsthrowing out the largest
outliers, over the time between chrony readings.

It is not clear that that would get rid of the problems for usb serial ports.
You might think about getting a real serial port for the machine.

William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
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On Fri, 20 Sep 2024, Sviatoslav Feshchenko wrote:

> [CAUTION: Non-UBC Email]Hello,
>
> I have a Garmin 18x LVC GPS receiver, which produces RS-232 serial output and has 1PPS signal. I am
> contemplating using it on a computer that does not have a serial port. I would connect the GPS
> receiver via a RS-232 to USB adapter, and then to a USB 2.0 port on the computer (higher USB version
> is not available). I know this will introduce a lot of jitter given how USB works. Is it possible to
> adjust the parameters in Chrony such that the software will "smooth out" the jitter caused by the USB
> interface (i.e. by measuring time over a long period of time, and averaging it out)? If so, what would
> be the recommended configuration parameters for maximum accuracy?
>
> Many thanks,
>
> Sviatoslav

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