[LinuxPPS] LinuxPPS comparable to FreeBSD here

[Miroslav Lichvar]

On Fri, Jun 18, 2010 at 11:01:41AM -0700, Hal V. Engel wrote:
> This was running on my machine for about 12 hours starting yesterday 
> afternoon.  I am using the Oncore driver with a UT+.  It took it awhile 
> (perhaps 10 minutes) to not show errors for ntp_adjtime() and ntp_gettime() 
> when running ntptime.    After about 12 hours the clock still had
> offsets of 2 to 3 microseconds and it never got below 2 microseconds
> at any time when running ntpq -p.

> # ntptime
> ntp_gettime() returns code 0 (OK)
>   time cfc61292.26fac5f4  Fri, Jun 18 2010  8:43:14.152, (.152264848),
>   maximum error 3236 us, estimated error 2 us
> ntp_adjtime() returns code 0 (OK)
>   modes 0x0 (),
>   offset 0.000 us, frequency -38.732 ppm, interval 256 s,
>   maximum error 3236 us, estimated error 2 us,
>   status 0x2107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL,NANO),
>   time constant 4, precision 0.001 us, tolerance 500 ppm,
>   pps frequency -38.741 ppm, stability 0.021 ppm, jitter 2.606 us,
>   intervals 272, jitter exceeded 9, stability exceeded 0, errors 1.

> But there appears to be some issues with hardpps.  When I run
> without hardpps this system will have offsets of less than 1
> microsecond most of the time once things have stabilized (IE. after
> about 1 hour) if it is lightly loaded.  

If the PPS signal really has 2.6us jitter, I think it's working as
expected. FLL doesn't filter noise, so the result will be only as good
as is the input signal.

-- 
Miroslav Lichvar