USB GPS receiver as reference clock

[Christopher Sean Hilton]

On Sat, 2006-11-25 at 11:06 +0200, Bo Granlund wrote:

[ snip ]

> 
> I loaded the uplcom module and reattached the gps receiver. And then I
> linked /dev/cuaU0 to /dev/gps1. Cat'ing /dev/gps1 returns NMEA data, but
> when I try start ntpd this comes to the logs:
> 
> Nov 25 10:58:24 battleangel ntpd[798]: refclock_nmea: time_pps_create
> failed: Inappropriate ioctl for device
> 
> Do you have any clue as to why it complains about an inappropriate ioctl?
> 
> Thanks for the uplcom pointer, now I got somewhat forward in my attempts to
> make ntpd work with my usb receiver.
> 

GPS Clocks for ntp synchronization need to do something called "Pulse
Per Second". This involves toggling the state of one of the serial
control lines once every second to indicate the edge of a measured time
period. I'm not sure if ntp can sync to a clock using nmea data alone.
It's possible since the nmea sentences have the full time information
embeded withing them but I don't know how accurate it would be. There
may be an ntp configuration option for gathering time data from within
the nmea sentence itself but I'm not familiar enough with ntd to
actually set that up. 

-- Chris