[ntp:hackers] About time_pps_kcbind()

Venu Gopal neo.venu at gmail.com
Mon Oct 6 09:16:10 UTC 2008

Hi Friends,

    I have been working with the LinuxPPS for Linux 2.6 series kernel 
since a week.
There are patches for few refclock drivers to make them work with LinuxPPS
implementation, which otherwise use PPS Kit written by Ulrich Windl with 
Linux 2.4 kernels.

One such patch was submitted my Udo for NMEA refclock driver. So we are 
towards adding this patch to NTP mainstream(BUG#610). Now this new PPS 
doesn't implement the optional *time_pps_kcbind*() function. This is 
used by the refclock drivers
where in a flag by name *pps_enable* is set true if the function call 
succeeds. This flag is
in turn used in *ntp_loopfilter.c*. I am not aware of the significance 
this flag plays when
enabled or otherwise.

I have an experimental setup with three boxes running
1. FreeBSD-6.2 (recompiled with PPS enabled),
2. Linux-2.4.20-NANO and
3. Linux-2.6.23 (patched with LinuxPPS) respectively.

As per my observations, when the pps_enable flag is not set (when using 
LinuxPPS), the offset
keeps increasing and never comes down. So I set the pps_enable flag to 
true (even though the
function fails), then I see the offset slowly coming down from few 
milliseconds to sub-microseconds
and settles fine.

Only today morning I started running NTPD with pps_enable set to false 
to see if the results repeat.
as observed initially and so far the results are not encouraging.

I need comments on the importance of pps_enable flag from the 
experienced guys.


More information about the hackers mailing list