[time-nuts] Raspberry Pi tweaks and custom kernel, was RE: PPS for NTP Server - How Close Is "Good Enough"?

Cube Central cubecentral at gmail.com
Fri Jun 12 09:55:41 EDT 2015

Hi Max!  Thanks for the information, I was wondering if you had documented what you did to your Raspberry Pi so that it might be reproducible to someone like me (a newcomer time-nut and intermediate Linux user) ... you had said:

>>"Here is what I have been able to do with a Motorola Oncore UT+ that I got from Bob Stewart awhile back.  This is with a Raspberry PI 2 with a number of tweaks and a custom compiled kernel.  Nothing too drastic... plus the current Dev version of NTP compile on the Raspberry PI."

What tweaks?  What options have you compiled?  What are the gritty details of your setup?

>> "I'm getting better results letting ntpd discipline the clock over doing kernel discipline...
not surprising because the algorithms in the ntpd code are much more sophisticated than the Linux kernel pps code... ntpd discipline provides much lower jitter in my experience."

what setting is this and how might I go about experimenting with it?  Is that the "flag3" option in the "Generic NMEA GPS Receiver" documented here?  https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html


>>"Not too shabby for a killer deal on an Oncore UT+ for $5 from Bob!  I'm running the PPS out of the UT+ through a level converter to get the ~3.3v PPS output... the serial output on the UT+ is also going through a level converter direct into the Pi 2.  Using the oncore ntpd driver and again, i'm not using hardpps kernel discipline."

I see word HARDPPS in the driver you mentioned (https://www.eecis.udel.edu/~mills/ntp/html/drivers/driver30.html ) but that documentation is a bit scarce... Could you fill me in on how you have it set up?  Is the PPSAPI also used for the "Generic NMEA GPS Receiver" (driver 20) or the PPS driver (driver 22)?

Thanks so much for your assistance!  Sorry if these questions have been posted before, but I am very curious about your setup as it nearly matches mine!

    -Randal "r3" of CubeCentral

More information about the time-nuts mailing list