[time-nuts] clock-block any need ?

Jim Lux jimlux at earthlink.net
Thu Dec 27 19:30:37 UTC 2012

On 12/27/12 11:17 AM, Chris Albertson wrote:
> On Thu, Dec 27, 2012 at 10:55 AM, Dennis Ferguson
> <dennis.c.ferguson at gmail.com> wrote:

> The reason you can't distribute ns level time over a network to normal
> NTP clients is because of the random queing that happens inside the
> client's ethernet interfaces.  The normal installed base of ethernet
> cards does not do time stamping.  So even uSec level timing is lost in
> the typical client.

I've been playing with Arduinos and Ethernet over the past couple weeks 
(all those home automation kind of chores.. not like I need to time the 
smoker temperature ramps to nanosecond precision), but this brings up an 
interesting issue..

A lot of the uncertainty is because of the "smart" Ethernet interface 
that tries to do stuff to offload the processor (buffering, etc.). This 
is one of the cases where old, less capable interfaces might do better.

So, what about the USB-Ethernet dongles?  (I use them a lot at work to 
add a second interface for a laptop in test equipment setups, talking to 
a Prologix, for instance)

Or, the Wiznet "Ethernet/IP stack" on a chip devices that talk via SPI, 
or basically, a serial port.

https://www.sparkfun.com/products/9473 for a widget
https://www.sparkfun.com/products/9471?  for the part
http://www.saelig.com/product/BRD002.htm  a Ethernet to serial port board

Some of these might have deterministic enough timing that it would be 
useful. They sure are cheap.

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