Rasp Pi at +/- 1 us from GPS

[Hal Murray]

devel at ntpsec.org said:
> - pps-client installed as expected. One gets the Stretch source and
> compiles the kernel as part of that. 

It would be interesting to poke around in pps-client to see what it actually 
does.

There are two ways to use PPS.  One is to to capture the data and then feed 
the offset into a normal algorithm like ntpd uses.  The other is to set a 
mode bit so the kernel does all the work.

The latter doesn't work with the NO_HZ scheduling option in the kernel.  Most 
distros ship a kernel with that option enabled to save power.  Rebuilding the 
kernel is a strong hint that they want to use the kernel mode.  If that's the 
case, you can use ntpd to do the same thing.  It's a flag bit to the PPS 
driver.

It would be interesting to compare whatever pps-client does with what ntpd 
does (same kernel) with and without that flag.


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