[ntp:questions] NTP NMEA driver

unruh unruh at invalid.ca
Mon Feb 11 23:56:32 UTC 2013

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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