[ntp:questions] How do I validate my PPS clocks?

ramadog at gmail.com ramadog at gmail.com
Tue Feb 26 22:42:08 UTC 2013

On Tuesday, February 26, 2013 10:57:22 AM UTC+10, unruh wrote:
> handling. And I only saw 1-2 us difference. Why are you getting 12us on
> the ldisc code?

The 11us in my case is how long it takes to get from early in the interrupt 
code in arch/x86/kernel/irq_32.c to where the time stamp is normally taken for 
the pps.

o127.127.22.0    .PPS.            0 l    5   16  377    0.000    0.000   0.001    .SHM.            0 l    4   16  377    0.000    0.011   0.001

That is from a new kernel I have had running for around an hour. The .PPS.
time stamp is unmodified from the ppsapi and the .SHM. time stamp is taken
at the beginning of the interrupt code. Using /proc to export my time stamp
and the shm driver to feed it to ntp. 

Getting the same 11us difference I see with my normal kernel. Normally I use
the earlier time stamp because it has less jitter and is affected less by
cpu load. 

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