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