[ntp:questions] SHM driver as a PPS source

Hal Murray hmurray at megapathdsl.net
Fri Nov 25 12:36:59 UTC 2016


folkert at vanheusden.com said:
> How can I tell NTPd that an SHM time source is actually a PPS and that it
> thus should combine it with some other sources? (an '*' + 'o' combination so
> to say) 

I don't think you can do it the way you have described.

The API for SHM requires that you have already figured out which second 
matches your PPS pulse.

If you have a real PPS pulse, you can connect it to a modem control pin or whatever your kernel supports and use the ATOM driver.  Or maybe use gpsd.

If your PPS signal comes in via some strange hardware, you can hack your kernel to support the normal PPS API or you can hack the ATOM driver to talk to your hardware.

Or you can make your software that is talking to SHM smart enough to provide the right second.  Look at the ATOM driver and see how it decides if a time stamp is good enough.  You can probably just use the system time and set minsane to 3 so it will outvote your clock if the system time is way off.  I'd have to do some testing to verify that worked right, but it might solve your problem.


-- 
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