GPS time for NTP configuration

bminish

I have a nice little embedded GPS board that is used to synchronize an oscillator to provide an extremely accurate frequency reference, it's based on this project.

It also outputs time information at 4800 bd using standard NMEA sentences. I believe you can configure NTP to use these to do the clock synchronization but I can't find much in the way of documentation telling me how to do it

I am aware that the NMEA string won't be as accurate as the 1PPS pulse but it seems a shame not to have a go at using it

BTW the NMEA strings look like this and are output every second at 4800 bd

$GPGSA,A,2,31,03,22,,15,,,,,,,,,,*18
$GPZDA,121943.00,25,03,2004,00,00*68
$GPGSV,3,1,10,03,46,129,49,08,12,286,,11,40,249,,14,09,108,*75
$GPGSV,3,2,10,15,27,067,47,18,15,038,,22,42,064,50,27,01,259,*77
$GPGSV,3,3,10,28,17,320,,31,82,207,46*7A
$GPRMC,121944.00,A,5350.4590,N,00922.3766,W,0.1,285.2,250304,,*20
$GPGGA,121944.00,5350.4590,N,00922.3766,W,1,04,2.4,105.9,M,,M,,*62

GPGSA tells us which statelites are in use
GPZDA tells us the time
GPGSV tells us about the signals and sat geometry
GPRMC gives position as does GPGGA


.Brendan

Typedef

Why not have a cron once a minute that runs hwclock --sync ?

bminish

Originally posted by Typedef
Why not have a cron once a minute that runs hwclock --sync ?

It's a bit of a messy hack doing this way though isn't it? What happens if the GPS is offline or outputting bum data
I would also by all accounts get a better accuracy ~ 0.1 sec using the NMEA string with NTP if only I could figure it out :-(

There is also the the TAC Totally Accurate Clock approach if ~0.1 sec isn't good enough

.Brendan