Dag-Erling Smørgrav wrote:
Chuck <[EMAIL PROTECTED]> writes:
anyone know if i run freebsd with pps turned on in the kernel and the
ntpd set to kernel pps if i also load gpsd not to feed ntpd as it will
never have the server info in it, but to allow telnet and web
interfaces into checking satellite coverage etc, will gpsd interfere
with the kernel processing the time properly?
It won't. All gpsd does is provide a convenient interface to a GPS
receiver; it does not touch the clock.
DES
On the other hand, the ntp driver for the gps receiver will probably not
work when gpsd is running.
When locking on PPS, you need two types of information:
- absolute time, to get the clock set within a second
- PPS pulses, which only provide information about the exact time the
seconds tick, but not the time of day it is.
The GPS drivers in ntpd do read the serial stream from the receiver to
know the time of day, and use the PPS pulses to provide accurate sync.
When such a driver reads the serial stream, it no longer is available
for other programs that e.g. want positioning information, like gpsd.
That is why time suppport was built into gpsd. gpsd reads the serial
stream and can also monitor the pps. It makes it available as two
shared memory areas that ntpd can use: 1 with the info from the serial
stream, and 1 with the PPS information.
When you setup gpsd and use the first clock for acquisition with ntpd
and use the PPS pulses as direct input to the kernel, I think ntpd will
get confused. But maybe not, you could try.
But in any case you should not use gpsd together with one of the gps
drivers in ntpd. That would require some "tee" functionality that
splits the received gps serial stream in two directions.
Rob
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