[time-nuts] Serial port server .. any interest in a write up on using ?

Bob Camp lists at rtty.us
Wed May 23 16:08:33 UTC 2012


Hi

If the timing involved is NTP, I'm not so sure that a normal home lan with
gigabit switches would be a problem. You can indeed saturate the poor thing.
Unless you have a very unusual system, it is unlikely you will saturate it
for very long or saturate it very often. NTP is pretty tolerant of the
occasional burp of a few ms. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Attila Kinali
Sent: Wednesday, May 23, 2012 11:10 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Serial port server .. any interest in a write up on
using ?

On Wed, 23 May 2012 01:54:20 -0700
Hal Murray <hmurray at megapathdsl.net> wrote:

> > There aren't noticable more jitter for moderate (1-2 MByte/s) traffic.
> > (Probably visible if i would do a statistical analysis...but..) 
> 
> 1-2 megabytes/sec is 8-16 megabits/sec.  You won't get into serious
troubles 
> until you saturate a link.  With modern CPUs, it's trivial to saturate 100

> megabit links and not very hard to saturate 1 gigabit links.

Yes, i know. I deliberately did not saturate the link. I know that it looks
quite differently if i do and that jitter will rise into the ms range even
on a local LAN. But anyone who does work with precision timing in such
an enviroment is lost anyways. If you do timing over ethernet, you are well
advised to use a seperate network that does not carry any other traffic,
use fast, low latency, high bandwidth switches, etc pp...

Ofcourse unless you go the way of IEEE1588, but then you're playing in
a different league and probably have the money to buy a Cs clock or two :-)

As for the problem of serial ports (to come back to the original topic),
i'd probably use just a bunch of USB serial cables (the ones from Exsys
work quite good) if i don't need any timing information. They are cheap,
readily available, and if they have FTDI chip, they also work fine.

For timing.. I don't know. But i guess a small PC with some RS232 cards
in (there are even 4port cards for PCI-E available, and they are not
expensive) would be more than enough for the needs i have.

Anything else seems to me like either overkill, or not fitting to the
problem description.


			Attila Kinali
-- 
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
		-- Tirin, The Dispossessed, U. Le Guin

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