[ntp:questions] NTP NMEA driver

Charles Elliott elliott.ch at verizon.net
Tue Feb 12 12:28:04 UTC 2013


> None, not even ZDA put out current time. They all put out time in the
> past. It takes a long time for any of the messages to be composed in
> the
> receiver, to be queued, to be sent at 300-9000 bits per second, and to
> be interpreted.
> 



It is easy to change most GPS receivers to send NMEA messages at a faster
rate than 300-9000 bps.  A rate of  57,600 works better and is easily
achievable.  For SiRF receivers there are two ways:

1. Search for SiRFDemo.exe.  It will control most SiRF GPS receivers.  The
interface is intuitive, but as I recall, click on "Action/Switch Message
Rate."

2. While most GPS boards have similar, you can search for 'SiRF NMEA
Reference Manual.'  This manual lists all the input/output NMEA messages
that SiRF supports.  Then write a small program to output the messages you
need.  It is trivial if you have a copy of Visual Studio (Express); just
copy NTPD's GPS initialization code, but send out your own messages.  I have
this manual; if you can't find it on the Internet, send me an email and I
will send you a copy.

Please stop ragging us about carriage returns in email messages.

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 unruh
> Sent: Monday, February 11, 2013 6:57 PM
> To: questions at lists.ntp.org
> Subject: Re: [ntp:questions] NTP NMEA driver
> 
> On 2013-02-11, Rob <nomail at example.com> wrote:
> > unruh <unruh at invalid.ca> wrote:
> >> Please put carriage returns into your posts. These run on sentences
> can
> >> be very hard to read.
> >
> > Please get a decent newsreader instead of picking on posting format.
> 
> I thought the OP was trying to communicate with us, not doing us a
> favour
> by writing down his least burps to send out into the world. If the
> former is true, then it is up to him to try to make it as easy on the
> listener/reader , not expect them to go out of their way to
> conform to his peculiarities.
> 
> Again, Please put carriage returns into  posts.
> 
> >
> >> Secondly, many messages provide time informations. Why do you pick
> out
> >> one of the bunch? And No other messages do not provide the time of a
> >> position fix, they mark the time of the nearest second that has
> already
> >> occured.  None of the NMEA sentences mark the time of PPS pulse
> because
> >> they all occur long long after that pulse ( on the microsecond
> scale).
> >
> > You are obviously wrong here.  The messages that provide position
> data
> > do not include the current time, they include the "time of fix".
> 
> None, not even ZDA put out current time. They all put out time in the
> past. It takes a long time for any of the messages to be composed in
> the
> receiver, to be queued, to be sent at 300-9000 bits per second, and to
> be intrpreted.
> 
> > You are at the mercy of the receiver outputting the message shortly
> > after the calculation of the fix.  The OP was right.
> 
> You are always at the mercy of the receiver.
> And it is not the fix time. ZDA puts out only to the nearest 10 ms. the
> others to the nearest second or 10ths of a second.  Fix
> times are in the nanosecond realm. They put out times which are the
> time
> label of the latest second (or they should if they are not
> incompetently
> designed as the Garmin 18x was.)
> 
> 
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