[ntp:questions] Befuddled and confused, again...

Rob nomail at example.com
Mon Feb 15 09:47:02 UTC 2010

unruh <unruh at wormhole.physics.ubc.ca> wrote:
>> That might be a Linux specific feature of gpsd.
>> Man page mentions Linux version of gpsd detecting PPS on
>> serial DCD line otherwise best accuracy around 10ms.
> There is also the shmpps program, which detects pps either on the serial
> or the parallel port and uses the shm driver to deliver the time offset.
> Something else is needed to determine the "seconds" while shmpps
> determines the usec using the serial or parallel port interrupt drivers. 
> I do not know if shmpps works out the box on Freebsd, but it should not
> be hard to adapt, assuming bsd supports the shm refclock driver.

Both the PPS feature of gpsd and shmpps require the availability of
the TIOCMIWAIT ioctl for serial ports (wait for change of status line).

When your OS does not support it, these programs are not going to work.

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