linux-kernel - Re: [PATCH 0/5] Enable PPS reporting for USB serial devices

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Date:	Tue, 10 Sep 2013 13:02:34 -0700
From:	"Gary E. Miller" <gem@...lim.com>
To:	Rodolfo Giometti <giometti@...eenne.com>
Cc:	Paul Chavent <Paul.Chavent@...ra.fr>, linux-usb@...r.kernel.org,
	gregkh@...uxfoundation.org, jhovold@...il.com,
	fschaefer.oss@...glemail.com, jslaby@...e.cz, max@...e.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] Enable PPS reporting for USB serial devices

Yo Rodolfo!

On Tue, 10 Sep 2013 09:31:05 +0200
Rodolfo Giometti <giometti@...eenne.com> wrote:

> I have nothing against with this solution but consider that reporting
> a PPS signal through USB bus may add unknown delays that may vanish
> clock stability... as far as I know you should not use USB serial port
> with PPS. Have you some statistics about clock stability in a real
> implementation?

gpsd project has been using PPS over USB 1.1 for over a year.  Typical
accuracy and repeatability in the range of +/- 1 milliSec.  This is much
better than you can get using simple ntp over gigabit ethernet to an
adjacent stratum 1 server.

Sure PPS over a local UART is 10 to 100 times better, but often PPS
over USB is your best second choice.  As serial ports become extinct
it may become your best choice.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
	gem@...lim.com  Tel:+1(541)382-8588

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