[ntp:questions] GPS RMC .second

Komka Péter KomkaP at prolan.hu
Fri Dec 9 17:44:07 UTC 2005


In
ntp-stable-4.2.0a-20050816\ntpd\refclock_nmea.c
(about 673rd line):

 From what does the program know, when (in the past) was that time what it holds?
 From the PPS we know the current msec, but not the current second (and hour 
etc.).
Suppose, the stamp holds ".. 23 sec 993 msec". And from the PPS we know that 
now we are at the 011th msec in some second.
The stamp must have "traveled" a certain amount of time. Estimate it: minimum 
300 msec. maximum 1250 msec. (Included the calculation time in the GPS.) The 
moment of which time it holds was sometime (now-300)....(now-1250).
So the second ".. 23 sec 993 msec" has to be in the past, preceeding current 
second by 2.
So the current second must be ".. 25 sec".
(I cannot see adjustation of second in the source.)

Komka Péter



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