[ntp:questions] Radioclock connection via serial to usb adaptor on Linux or BSD?

David Lord snews at lordynet.org
Thu Sep 3 09:40:53 UTC 2009


David Lord wrote:

> I'd now like to try via a serial to usb for use with notebook. My
> Vodafone mobile broadband connection regularly has differential
> latency of maybe +/- 2 seconds and even chrony can't make sense
> of this.
> 

I think I'll have to go back to using chrony restarted from
ppp-up/down scripts to get internet time for mobile use.

MSF+ntp takes much too long to converge for it to be of any use
on netbook.

Not that this matters too much now, but it seems I can't use
PPSAPI with usb serial converter. Ntp.log gives an error that
ioctl is inappropriate but PPSAPI works ok using standard serial
port. With either PL-2303 or FTDI on Ubuntu I could use "iwait"
mode with radioclkd2 and that is claimed to give better than 1ms.

Below is from eeepc running Ubuntu 9.04, ntp source via Vodafone
mobile broadband and MSF connected using the Prolific serial to
usb adapter using radioclkd2 and SHM drivers - this is after
about an hour although was still converging:

Tue Sep  1 09:09:12 BST 2009
      remote           refid      st t when poll reach   delay   offset 
  jitter
==============================================================================
  ntp1.lon.bitfol 212.13.204.4     3 u    1   64  377  1995.33  957.145 
  30.225
*SHM(0)          .MSF.            2 l   17   64  377    0.000   -8.800 
  0.220

After that I gave up as even having a mobile broadband connection
up and using ntpdate before starting ntpd there's a good chance
I'll be more than a second out (in above case about 1500 ms
offset when ntpd switched to MSF). Lowest latency I see at
various times is around 150ms with highest near 10000 ms but
currently 2 seconds seems the norm. Traceroutes show delay is in
the Vodafone network. On wired adsl I've not seen same pool
source as above but currently dnscache-london is second
preferred with delay=18ms, offset=0.616 and poll=2048.


I'm now looking into getting a timestamp from the mobile signal
or if that's not possible maybe use embedded board with enough
resource to run ntpd, serial port for MSF, holdover pps source,
and usb or ethernet for connection to pc.


David




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