[Pool] External device sync / PPS / USB

Michael R. Overholser mikeo at colorbroadband.com
Wed Mar 2 20:06:37 UTC 2011

Hence why I said this (as long as it is a desktop/server and not a laptop):




Michael R. Overholser

Color Broadband Inc.

Phone:562 983 7880 Support Press 1

Fax: 562 983 7881                     

 <mailto:support at colorbroadband.com> support at colorbroadband.com


From: pool-bounces+mikeo=colorbroadband.com at lists.ntp.org
[mailto:pool-bounces+mikeo=colorbroadband.com at lists.ntp.org] On Behalf Of
Daniel Norton
Sent: Wednesday, March 02, 2011 11:11 AM
To: Anssi Johansson
Cc: NTP Pool List
Subject: Re: [Pool] External device sync / PPS / USB


On 3/2/2011 11:00 AM, Anssi Johansson wrote: 

Hi, using USB (either via serial port adapters or otherwise) for time
synchronization is most probably just a waste of your time and money. So, in
short, don't do it. 

A longer answer to this question can be found from
http://gpsd.berlios.de/faq.html#time , for example. 

Thought so. The hidden point not mentioned at that link is that for many
systems (most notably, laptops), serial/RS232 ports are implemented over the
USB bus, so it's not safe to say that a serial/RS232 port is sufficient. It
must be one that is implemented over an appropriate underlying bus.

On 3/2/2011 11:32 AM, David J Taylor wrote: 

Using a Sitecom USB hub which includes a serial port, I made a comparison
here, Daniel: 


Yes, it does increase the jitter.  Whilst certainly not as good as a direct
connection, it's considerably better than a LAN-only connection. 

Well, in your setup that might be true (and with the shorter polling
interval), but it's probably dependent on the other USB traffic on that same
hub (and on up to the main bus).

So I guess it's possible, but probably inadvisable.


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