| RE: [chrony-users] Is it possible to smooth out jitter caused by USB interface? |
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- Subject: RE: [chrony-users] Is it possible to smooth out jitter caused by USB interface?
- From: "Daniel Gearty" <dpgearty@xxxxxxxxxxxx>
- Date: Fri, 20 Sep 2024 17:22:30 -0400
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Would median filtering help? I use it to smooth out Ethernet
server 192.168.50.230 minpoll -7 maxpoll 2 filter 15
-----Original Message-----
From: Bill Unruh <unruh@xxxxxxxxxxxxxx>
Sent: Friday, September 20, 2024 4:24 PM
To: chrony-users@xxxxxxxxxxxxxxxxxxxx
Subject: Re: [chrony-users] Is it possible to smooth out jitter caused by
USB interface?
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 UBC,
Vancouver,BC _|_ Program in Cosmology |____ unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1 ____|____ and Gravity ______|_ theory.physics.ubc.ca/
I cannot reply to emails from outlook or hotmail or other microsoft domains.
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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