[ntp:questions] Trying to use Dimension 4 time keeper

Charles Elliott elliott.ch at verizon.net
Sun Sep 22 13:57:14 UTC 2013


> Run the usb port
> >> as fast as possible (high baud rate), and after some observation
> with
> >> the machine connected to the internet as well, determine what the
> usb
> >> data time offset is and subtract it out using the time2 option to
> the
> >> driver.

Also, suppress all the nmea messages except RMC, ZDA, etc., whichever 
ONE message you choose from which to extract the time.  Make that one
message be output every second.  You may want
to do this because it makes sense that the NTPD clock driver would
have lower jitter if it did not have to wade through all the GSV, etc.
messages to get to the one message it uses to access the time.  However, 
there is a paucity of empirical evidence to support this view.  You 
can find the format of the nmea suppression (output rate) messages 
for the SURE board by Searching for "MTK NMEA Packet User Manual"
and for SiRF-based GPS devices by searching for "NMEA Reference
Manual" or for "SiRF NMEA Reference Manual" or by looking for it
on the usglobalsat.com website.  You can also completely control
SiRF-based GPS devices by using the "SiRF Demo, ver. 3.87," which
can also be searched for.  This is a very fine program.
Even better, post a request for
enhancement on the www.ntp.org website that ntp.conf be given
A GPS initialization section, such as 

[begin gps init]
"$PSRF103,02,00,01,01*";  # Last 01 enables checksum 
"$PSRFTXT, WAAS Enable*";
"$PSRFTXT, POS: 1256058 -4729245 4077408*";
"$PSRFTXT CHNL: 20*";
***
[end gps init]

Then in its initialization code NTPD could compute the checksum
and add it and "\n\r" to every message and output it to the GPS
device.

There is already such a request for enhancement (Bug # 2280),
to which you could add your name and prestige. 

Charles Elliott

> -----Original Message-----
> From: questions-bounces+elliott.ch=verizon.net at lists.ntp.org
> [mailto:questions-bounces+elliott.ch=verizon.net at lists.ntp.org] On
> Behalf Of Richard B. Gilbert
> Sent: Saturday, September 21, 2013 11:54 AM
> To: questions at lists.ntp.org
> Subject: Re: [ntp:questions] Trying to use Dimension 4 time keeper
> 
> On 9/10/2013 9:47 PM, W. eWatson wrote:
> > ...
> >>>>
> >>>>>
> >>>>> I tried Meinberg for quite some time, but it flops fairly often.
> As I
> >>>>
> >>>> flops? What are the symptoms? Also, if time is important why not
> invest
> >>>> in a GPS (35 dolalrs or so) with PPS.
> >>>
> >>> It moves many seconds in a short time, say a day or two. How is GPS
> >>> going to help? Does it provide access via a USB port.
> >>
> >> It-- which noun does that "it" point to?
> >> Sure, you can have gps provide access via a usb port. The Sure GPS
> even
> >> has a usb port on board that you can directly connect to. It is not
> >> great timekeeping but you can probably get it to within .1 sec or
> so.
> >> The main problem is that you cannot use the PPS via a usb
> connection, so
> >> you have to rely on the timing from the nmea sentences. Run the usb
> port
> >> as fast as possible (high baud rate), and after some observation
> with
> >> the machine connected to the internet as well, determine what the
> usb
> >> data time offset is and subtract it out using the time2 option to
> the
> >> driver.
> > It = GPS. What is PPS?
> > ...
> 
> Pulse per second ???
> 
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