[ntp:questions] Can the line audio out of HF radio be used to sync ntp. Trying to get a cheap ($) radio method.

Garrett Wollman wollman at bimajority.org
Fri May 1 02:07:53 UTC 2009

In article <K9WdnS4y5pIuymfUnZ2dnUVZ_t2dnZ2d at giganews.com>,
Richard B. Gilbert <rgilbert88 at comcast.net> wrote:

>USB is nearly useless for NTP!  USB has latencies sufficiently large 
>and variable to render it unsuitable for use with NTP.

It doesn't have to be; USB supports isochronous transfers.
Unfortunately for NTP's needs, USB-to-serial adapters use "interrupt"
transfers exclusively, which, as Richard says, gives unbounded latency
and variance.  You could build a timing device that connected via USB
using isochronous transfers, but you'd need a fairly specialized
(kernel) driver to talk to it.  I wouldn't want to try to feed a 1-PPS
signal through it, either.  (IEEE 1394b might be better in that
regard, but requires a much smarter device, at which point you might
as well just get a timecode receiver that speaks NTP.)

>The newest computers may not have serial ports as they come from the
>factory but there is no reason why one or more serial ports can't be

Certainly there is: you might not have any suitable expansion


Garrett A. Wollman   | The real tragedy of human existence is not that we are
wollman at csail.mit.edu| nasty by nature, but that a cruel structural asymmetry
Opinions not those   | grants to rare events of meanness such power to shape
of MIT or CSAIL.     | our history. - S.J. Gould, Ten Thousand Acts of Kindness

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